Ldvdt???
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Posts: 46,084
Has anyone out there ever interfaced a LDVDT to a basic stamp?
If so, could someone explain (or refer me to a site) that could explain
how these things work, where they are used, how to interface it, and
where to buy one?
We have a customer at work who wants us to put one on a machine we are
building for him, but nobody at our (very small) shop knows anything
about them. Basically, they want us to provide a way to sense the
position of an air cylinder so we can tell where in its stroke it is. Is
this a suitable application? Are there better solutions?
Regards,
Aaron
If so, could someone explain (or refer me to a site) that could explain
how these things work, where they are used, how to interface it, and
where to buy one?
We have a customer at work who wants us to put one on a machine we are
building for him, but nobody at our (very small) shop knows anything
about them. Basically, they want us to provide a way to sense the
position of an air cylinder so we can tell where in its stroke it is. Is
this a suitable application? Are there better solutions?
Regards,
Aaron
Comments
can sense distances in the tenths of one thousand of an inch. Some
perspective here. A human hair is usually somewhere around 3 thousands
(.003) This device could measure them like you would use a tape measure
on a room. They would be very difficult, with out some pretty
sophisticated electronics, to interface with the stamp. What I would
suggest is Proximity switch for your stated application. They are often
used they and are much cheaper. Easier to interface too, as they
usually provide a logic 24 VDC or 120 VAC output signal that would be
easy to interface to the stamp.
BTW air cylinders are not usually sensed as to position. Air is
compressible and sensing position on this type of device would be very
difficult. Depending on resolution required, several prox switches
might be used. Air cylinders typically are sensed at either end of
their stroke.
Kind regards,
Leroy
agarb@j... wrote:
>
> Has anyone out there ever interfaced a LDVDT to a basic stamp?
>
> If so, could someone explain (or refer me to a site) that could explain
> how these things work, where they are used, how to interface it, and
> where to buy one?
>
> We have a customer at work who wants us to put one on a machine we are
> building for him, but nobody at our (very small) shop knows anything
> about them. Basically, they want us to provide a way to sense the
> position of an air cylinder so we can tell where in its stroke it is. Is
> this a suitable application? Are there better solutions?
>
> Regards,
> Aaron
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
>
>
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--
*******************************************************
* Leroy Hall *
* 317 Cherokee Drive *
* Loveland, Ohio - USA 45140-2404 *
*******************************************************
* Phone: (513) 697-7539 *
* Cell : (513) 300-8632 *
* Email: leroy@f... *
* Home page URL: http://home.fuse.net/leroy/ *
* Resume URL: http://home.fuse.net/leroy/resume.htm *
*******************************************************
* Leroy Hall *
* 317 Cherokee Drive *
* Loveland, Ohio - USA 45140-2404 *
*******************************************************
digital calipers with the data output, or getting one of the digital readout
units from Grizzly. They are like digital calipers without jaws. They have a
display on them as well as some sort of interface for a larger readout head.
I did not find them in their online catalog, but the last flyer I got listed
them. They are about $110 for a 12" travel unit.
Original Message
> An LVDT is used to measure very small distances on machine tools. They
> can sense distances in the tenths of one thousand of an inch. Some
> perspective here. A human hair is usually somewhere around 3 thousands
> (.003) This device could measure them like you would use a tape measure
> on a room. They would be very difficult, with out some pretty
> sophisticated electronics, to interface with the stamp. What I would
> suggest is Proximity switch for your stated application. They are often
> used they and are much cheaper. Easier to interface too, as they
> usually provide a logic 24 VDC or 120 VAC output signal that would be
> easy to interface to the stamp.
>
> BTW air cylinders are not usually sensed as to position. Air is
> compressible and sensing position on this type of device would be very
> difficult. Depending on resolution required, several prox switches
> might be used. Air cylinders typically are sensed at either end of
> their stroke.
> > If so, could someone explain (or refer me to a site) that could explain
> > how these things work, where they are used, how to interface it, and
> > where to buy one?
> >
> > We have a customer at work who wants us to put one on a machine we are
> > building for him, but nobody at our (very small) shop knows anything
> > about them. Basically, they want us to provide a way to sense the
> > position of an air cylinder so we can tell where in its stroke it is.
Is
> > this a suitable application? Are there better solutions?
> compressible and sensing position on this type of device would be very
> difficult. Depending on resolution required, several prox switches
> might be used. Air cylinders typically are sensed at either end of
> their stroke.
I believe that the "Bimba" line of air cylinders has a cylinder that has
a positioning sensor built into it along with the electronic interface.
Pretty pricey but may be something you could use. I don't know if this
type of cylinder will work for you but it's worth a shot. It may not be
very Stamp compatible, I don't know.
Just FYI
--
Doyle Whisenant
mechanic@s...
http://mechanic.webjump.com
stainless hose clamps to attach hall effect sensors to the outside of the
cylinder. Mostly used to confirm extended or retracted status. Very
important thing when dies and saws share the same work space!
Robert
>
> I believe that the "Bimba" line of air cylinders has a cylinder that has
> a positioning sensor built into it along with the electronic interface.
> Pretty pricey but may be something you could use. I don't know if this
> type of cylinder will work for you but it's worth a shot. It may not be
> very Stamp compatible, I don't know.
>
> Just FYI
>
> --
> Doyle Whisenant
> mechanic@s...
> http://mechanic.webjump.com
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the
> Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
>
> We use these where I work. They have a magnet in the piston and we use
> stainless hose clamps to attach hall effect sensors to the outside of the
> cylinder. Mostly used to confirm extended or retracted status. Very
> important thing when dies and saws share the same work space!
I have used the type you are talking about with the hall effect sensors
but the type I am talking about has some kind of linear resistance
sensor. I remember the flyer mentioning something about it being very
precise.
The OP can have a look this pdf file:
http://www.bimba.com/pdf/control.pdf
I believe this is where I saw this info.
--
Doyle Whisenant
mechanic@s...
http://mechanic.webjump.com
is not all that difficult. It is basically a transformer with a movable
coil. The relative motion of the coil to the core changes how well the
primary coil gets linked up with the secondary coil. The clever part of the
design is that the measured motion has a very linear output over its
operating range. Though you still may need too condition its output signal.
Wheather or not it is appropriate to go on what ever type of machine you are
making is another matter. A little more detail about what it is you are
doing might be helpful.
richard
Original Message
From: "Leroy Hall, Senior" <leroy@f...>
To: <basicstamps@yahoogroups.com>
Sent: Saturday, August 11, 2001 2:24 PM
Subject: Re: [noparse][[/noparse]basicstamps] LDVDT???
> An LVDT is used to measure very small distances on machine tools. They
> can sense distances in the tenths of one thousand of an inch. Some
> perspective here. A human hair is usually somewhere around 3 thousands
> (.003) This device could measure them like you would use a tape measure
> on a room. They would be very difficult, with out some pretty
> sophisticated electronics, to interface with the stamp. What I would
> suggest is Proximity switch for your stated application. They are often
> used they and are much cheaper. Easier to interface too, as they
> usually provide a logic 24 VDC or 120 VAC output signal that would be
> easy to interface to the stamp.
>
> BTW air cylinders are not usually sensed as to position. Air is
> compressible and sensing position on this type of device would be very
> difficult. Depending on resolution required, several prox switches
> might be used. Air cylinders typically are sensed at either end of
> their stroke.
>
>
> Kind regards,
>
> Leroy
>
> agarb@j... wrote:
> >
> > Has anyone out there ever interfaced a LDVDT to a basic stamp?
> >
> > If so, could someone explain (or refer me to a site) that could explain
> > how these things work, where they are used, how to interface it, and
> > where to buy one?
> >
> > We have a customer at work who wants us to put one on a machine we are
> > building for him, but nobody at our (very small) shop knows anything
> > about them. Basically, they want us to provide a way to sense the
> > position of an air cylinder so we can tell where in its stroke it is.
Is
> > this a suitable application? Are there better solutions?
> >
> > Regards,
> > Aaron
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the Subject
and Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
>
> --
>
> *******************************************************
> * Leroy Hall *
> * 317 Cherokee Drive *
> * Loveland, Ohio - USA 45140-2404 *
> *******************************************************
> * Phone: (513) 697-7539 *
> * Cell : (513) 300-8632 *
> * Email: leroy@f... *
> * Home page URL: http://home.fuse.net/leroy/ *
> * Resume URL: http://home.fuse.net/leroy/resume.htm *
> *******************************************************
> * Leroy Hall *
> * 317 Cherokee Drive *
> * Loveland, Ohio - USA 45140-2404 *
> *******************************************************
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
measured. Displacement of the LVDT core of less than 1mm will yeild a
usable reading. Using the LVDT is fairly straightforward, however,
quite a few components are required to get the thing working.
The primary winding must be excited by either AC, or pulsed DC. What
you'll probably end up doing is taking the output of a square wave
oscillator, beefing it up with a buffer, smoothing it out through a
cap, then driving it through the primary winding. This pulsetrain
should also be rectified and used as a reference voltage.
There are usually two secondary windings. The LVDT core, when at
rest, is centered between these windings. Both windings are
individually rectified 180 degrees out of phase, then combined. What
this does is allows the LVDT output to go high or low depending on
the position of the core. This is important for zero, and to assure
that the core is at rest in the proper position. Anyway, the
secondary windings get rectified, go through a summing ammplifier
(allows for display zero) and finally goes to one input of a
differential amplifier. The other input (reference voltage) comes
from the pulses that drive the primary winding. In addition to
driving the primary these pulses also get rectified and sent to a
reference amplifier (another op amp) Scaling and isolation happen
here. The output odf this reference amplifier then goes to the second
input of the differential amplifier. The output of this differential
amplifier would then be input into a 12 bit ADC, which converts the
voltage into it into a binary number the stamp understands.
One other thing
If you do decide to go forward with the LVDT it is VERY important
that the diodes you use are all mounted close together, on a thermal
pad. Failure do so will result in readings that can not be trusted.
Personally, I do not think the LVDT is best suited to your
application. I have little experience doing what you attempt so I
will not offer any alternate ideas. I have had some experience with
the LVDT and can tell you first hand, it can be an ornery little
devil. There has got to be an easier way do do what you want to do.
Regards
Rich
AA2DN
--- In basicstamps@y..., agarb@j... wrote:
> Has anyone out there ever interfaced a LDVDT to a basic stamp?
>
> If so, could someone explain (or refer me to a site) that could
explain
> how these things work, where they are used, how to interface it, and
> where to buy one?
>
> We have a customer at work who wants us to put one on a machine we
are
> building for him, but nobody at our (very small) shop knows anything
> about them. Basically, they want us to provide a way to sense the
> position of an air cylinder so we can tell where in its stroke it
is. Is
> this a suitable application? Are there better solutions?
>
> Regards,
> Aaron
>The LVDT is typically applied where fairly small changes are
>measured. Displacement of the LVDT core of less than 1mm will yeild a
>usable reading. Using the LVDT is fairly straightforward, however,
>quite a few components are required to get the thing working.
>
>The primary winding must be excited by either AC, or pulsed DC. What
>you'll probably end up doing is taking the output of a square wave
>oscillator, beefing it up with a buffer, smoothing it out through a
>cap, then driving it through the primary winding. This pulsetrain
>should also be rectified and used as a reference voltage.
>
>There are usually two secondary windings. The LVDT core, when at
>rest, is centered between these windings. Both windings are
>individually rectified 180 degrees out of phase, then combined. What
>this does is allows the LVDT output to go high or low depending on
>the position of the core. This is important for zero, and to assure
>that the core is at rest in the proper position. Anyway, the
>secondary windings get rectified, go through a summing ammplifier
>(allows for display zero) and finally goes to one input of a
>differential amplifier. The other input (reference voltage) comes
>from the pulses that drive the primary winding. In addition to
>driving the primary these pulses also get rectified and sent to a
>reference amplifier (another op amp) Scaling and isolation happen
>here. The output odf this reference amplifier then goes to the second
>input of the differential amplifier. The output of this differential
>amplifier would then be input into a 12 bit ADC, which converts the
>voltage into it into a binary number the stamp understands.
>
>One other thing
>
>If you do decide to go forward with the LVDT it is VERY important
>that the diodes you use are all mounted close together, on a thermal
>pad. Failure do so will result in readings that can not be trusted.
>
>Personally, I do not think the LVDT is best suited to your
>application. I have little experience doing what you attempt so I
>will not offer any alternate ideas. I have had some experience with
>the LVDT and can tell you first hand, it can be an ornery little
>devil. There has got to be an easier way do do what you want to do.
>
>Regards
>
>Rich
>AA2DN
>--- In basicstamps@y..., agarb@j... wrote:
> > Has anyone out there ever interfaced a LDVDT to a basic stamp?
> >
> > If so, could someone explain (or refer me to a site) that could
>explain
> > how these things work, where they are used, how to interface it, and
> > where to buy one?
> >
> > We have a customer at work who wants us to put one on a machine we
>are
> > building for him, but nobody at our (very small) shop knows anything
> > about them. Basically, they want us to provide a way to sense the
> > position of an air cylinder so we can tell where in its stroke it
>is. Is
> > this a suitable application? Are there better solutions?
> >
> > Regards,
> > Aaron
I did a search at "www.google.com" for "LVDT" and "bschwabe" and found
an article I wrote on September 12th 1996. This method uses a single
COIL and works well, but does not compensate for temperature variances.
Compensation could easily be achieved with a secondary identical coil
in a fixed position used as a reference before the actual coil of
interest was read.
OLD article begins below this line
You can make a very simple "sensitive" LVDT with a resolution greater than
1/2000th of an inch using a BS1 or BS2, 74HC14 or 74HCT14, and 4040B. For
more than one, in addition you can use a 4051B for up to eight LVDT's
LVDT- #40 AGW enamled copper wire wound around a "Coffie-Straw(single tube)",
closely wound with at least 1 inch coil width. (width = travel length)
Vcc(+5V reg) o
o->Vcc(+5V reg)
o---> LVDT <---o | | |
| | 14| |16 ---
| | | o
o
o --- .1uF
| 1|\ 2 | 3|\| 4 10| | |
o
| \o----o----| \o
| 4040 B |--o-> GND
| |/| |/ | |8,11
--- 7| o
o
o
--- .01uF | |Output *
| ZTR* | |
| | o--->Stamp Pin#
o
o---->GND
ZTR* - Zero Temperature Response
4040B - "Pin Outs"
Output* : pin 9 - divide by 2
pin 7 - divide by 4
pin 6 - divide by 8
pin 5 - divide by 16
pin 3 - divide by 32
pin 2 - divide by 64
pin 4 - divide by 128
pin 13 - divide by 256
pin 12 - divide by 512
pin 14 - divide by 1024
pin 15 - divide by 2048
pin 1 - divide by 4096
This position can "Vary" depending on the sensitivity that
you desire. The greater the division, the greater the
sensitivity, however the "sample time" increases also with
greater division factors when using the PULSIN function.
You can use the COUNT function with the BS2 instead for
an even better resolution, but you loose the compatability
between the BS1 and BS2.
EXAMPLE CODE:
LVDT var word
Start:
PULSIN Pin#,0,LVDT 'or COUNT Pin#,Duration,LVDT
debug home,? LVDT
goto Start
DIRECTIONS:
Use a piece of "Coat-Hanger-Wire" to slide in and out of the STRAW.
Beau Schwabe
bschwabe@i...
OLD article stops above this line
After reading this, I would ignore the references to the COUNT
command, and just stick with the PULSIN command.
Beau Schwabe IC Mask Designer
National Semiconductor Wired Communications Division
500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
Would the caliper need to be hacked, or do the inexpensive ones not have
output to a connector? I am sure the name brands (Mitutoyo, etc) do...
Also, is the output in real time, or is there a delay,. They seem to display
instantly to the eye, but....well, you get the point....
Chris
>
Original Message
> From: Rodent [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=d6A7dTE527dWKDAeFFEL1nhDDxfduIZCLpz_jFcigJRmTVKXEbt4UxAAvOxcqMnx5FX_Fisq1qKaRT7-c-o]daweasel@s...[/url
> Sent: Saturday, August 11, 2001 5:34 PM
> To: basicstamps@yahoogroups.com
> Subject: Re: [noparse][[/noparse]basicstamps] LDVDT???
>
>
> If you absolutely have to measure it, you might consider
> hacking a set of
> digital calipers with the data output, or getting one of the
> digital readout
> units from Grizzly. They are like digital calipers without
> jaws. They have a
> display on them as well as some sort of interface for a
> larger readout head.
> I did not find them in their online catalog, but the last
> flyer I got listed
> them. They are about $110 for a 12" travel unit.
>
could get the ones with the output and figure out how to port it to another
device.. You can get them as cheap as $150 -- you just have to shop around.
I've not played with one, but it appears the output is for some sort of QC
logging. At any rate, I believe they are serial output. Here are a couple of
examples -- www.grizzly.com -- product #'s H1021, H1024, and H1025.
Starrett may have additional info on their site.
The readouts Grizzly sells are cheaper. I'll have to see if I still have
their flyer at the house -- the search function on their web page does not
find them.
Original Message
> Great idea, Rodent! "Applause in background"
> Would the caliper need to be hacked, or do the inexpensive ones not have
> output to a connector? I am sure the name brands (Mitutoyo, etc) do...
> Also, is the output in real time, or is there a delay,. They seem to
display
> instantly to the eye, but....well, you get the point....
> > If you absolutely have to measure it, you might consider
> > hacking a set of
> > digital calipers with the data output, or getting one of the
> > digital readout
> > units from Grizzly. They are like digital calipers without
> > jaws. They have a
> > display on them as well as some sort of interface for a
> > larger readout head.
> > I did not find them in their online catalog, but the last
> > flyer I got listed
> > them. They are about $110 for a 12" travel unit.
There are several DRO (digital read out) units with serial out, used to
be adapted in lathes an milling machines.
I have tried to use an inexpensive digital caliper in my Sherline Lathe
but it not work reliable because interference from AC motor.
ACJacques
Chris Loiacono (E-mail) wrote:
>
> Great idea, Rodent! "Applause in background"
> Would the caliper need to be hacked, or do the inexpensive ones not have
> output to a connector? I am sure the name brands (Mitutoyo, etc) do...
> Also, is the output in real time, or is there a delay,. They seem to display
> instantly to the eye, but....well, you get the point....
>
> Chris
>
> >
Original Message
> > From: Rodent [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=Pu7Y_VZx9b08ljAyjVg0PaqhWHOvCkc_hbUUSufkolc_OcjbtP0qO_OT29xwy-Dr-iQ8fogOT4c-pg]daweasel@s...[/url
> > Sent: Saturday, August 11, 2001 5:34 PM
> > To: basicstamps@yahoogroups.com
> > Subject: Re: [noparse][[/noparse]basicstamps] LDVDT???
> >
> >
> > If you absolutely have to measure it, you might consider
> > hacking a set of
> > digital calipers with the data output, or getting one of the
> > digital readout
> > units from Grizzly. They are like digital calipers without
> > jaws. They have a
> > display on them as well as some sort of interface for a
> > larger readout head.
> > I did not find them in their online catalog, but the last
> > flyer I got listed
> > them. They are about $110 for a 12" travel unit.
> >
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
things slightly. Placing a second coil in a feedback wont do much to
keep things stable. The coil is not nearly as cranky about ambient
temp as a semiconductor junction. Is is for that reason that I
suggested placing all rectifiers over a common thermal pad.
Instability comes from these diodes being at different temps.
Small voltage changes in what goes into the primary result in similar
canges in the secondary. It is necessary to either very tightly
control the primary drive pulsetrain, or to use part of what drives
the primary as a reference voltage which secondary voltages are
compared to. This is the second major source of LVDT instability.
Creating a primary/secondary differential voltage is the best way to
deal with voltage fluctuations around the circuit. (The
primary/secondary ratio does not change)
An LVDT can be made to function without doing as I suggest, but only
as an educational excersize. Because the changes in secondary winding
voltages are so slight absolute circuit stability (electrical and
thermal) is essential.
Regards
Rich
--- In basicstamps@y..., "Beau Schwabe" <bschwabe@a...> wrote:
> At 09:25 PM 8/12/01 +0000, you wrote:
> >The LVDT is typically applied where fairly small changes are
> >measured. Displacement of the LVDT core of less than 1mm will
yeild a
> >usable reading. Using the LVDT is fairly straightforward, however,
> >quite a few components are required to get the thing working.
> >
> >The primary winding must be excited by either AC, or pulsed DC.
What
> >you'll probably end up doing is taking the output of a square wave
> >oscillator, beefing it up with a buffer, smoothing it out through a
> >cap, then driving it through the primary winding. This pulsetrain
> >should also be rectified and used as a reference voltage.
> >
> >There are usually two secondary windings. The LVDT core, when at
> >rest, is centered between these windings. Both windings are
> >individually rectified 180 degrees out of phase, then combined.
What
> >this does is allows the LVDT output to go high or low depending on
> >the position of the core. This is important for zero, and to assure
> >that the core is at rest in the proper position. Anyway, the
> >secondary windings get rectified, go through a summing ammplifier
> >(allows for display zero) and finally goes to one input of a
> >differential amplifier. The other input (reference voltage) comes
> >from the pulses that drive the primary winding. In addition to
> >driving the primary these pulses also get rectified and sent to a
> >reference amplifier (another op amp) Scaling and isolation happen
> >here. The output odf this reference amplifier then goes to the
second
> >input of the differential amplifier. The output of this
differential
> >amplifier would then be input into a 12 bit ADC, which converts the
> >voltage into it into a binary number the stamp understands.
> >
> >One other thing
> >
> >If you do decide to go forward with the LVDT it is VERY important
> >that the diodes you use are all mounted close together, on a
thermal
> >pad. Failure do so will result in readings that can not be trusted.
> >
> >Personally, I do not think the LVDT is best suited to your
> >application. I have little experience doing what you attempt so I
> >will not offer any alternate ideas. I have had some experience with
> >the LVDT and can tell you first hand, it can be an ornery little
> >devil. There has got to be an easier way do do what you want to do.
> >
> >Regards
> >
> >Rich
> >AA2DN
> >--- In basicstamps@y..., agarb@j... wrote:
> > > Has anyone out there ever interfaced a LDVDT to a basic stamp?
> > >
> > > If so, could someone explain (or refer me to a site) that could
> >explain
> > > how these things work, where they are used, how to interface
it, and
> > > where to buy one?
> > >
> > > We have a customer at work who wants us to put one on a machine
we
> >are
> > > building for him, but nobody at our (very small) shop knows
anything
> > > about them. Basically, they want us to provide a way to sense
the
> > > position of an air cylinder so we can tell where in its stroke
it
> >is. Is
> > > this a suitable application? Are there better solutions?
> > >
> > > Regards,
> > > Aaron
>
> I did a search at "www.google.com" for "LVDT" and "bschwabe" and
found
> an article I wrote on September 12th 1996. This method uses a
single
> COIL and works well, but does not compensate for temperature
variances.
> Compensation could easily be achieved with a secondary identical
coil
> in a fixed position used as a reference before the actual coil of
> interest was read.
>
>
>
OLD article begins below this line
>
> You can make a very simple "sensitive" LVDT with a resolution
greater than
> 1/2000th of an inch using a BS1 or BS2, 74HC14 or 74HCT14, and
4040B. For
> more than one, in addition you can use a 4051B for up to eight
LVDT's
>
> LVDT- #40 AGW enamled copper wire wound around a "Coffie-Straw
(single tube)",
> closely wound with at least 1 inch coil width. (width =
travel length)
>
> Vcc(+5V reg) o
o->Vcc
(+5V reg)
> o---> LVDT <---o | | |
> | | 14| |16 ---
> | | | o
o
o --- .1uF
> | 1|\ 2 | 3|\| 4 10| | |
> o
| \o----o----| \o
| 4040 B |--o-> GND
> | |/| |/ | |8,11
> --- 7| o
o
o
> --- .01uF | |Output *
> | ZTR* | |
> | | o--->Stamp Pin#
> o
o---->GND
>
> ZTR* - Zero Temperature Response
>
>
> 4040B - "Pin Outs"
>
> Output* : pin 9 - divide by 2
> pin 7 - divide by 4
> pin 6 - divide by 8
> pin 5 - divide by 16
> pin 3 - divide by 32
> pin 2 - divide by 64
> pin 4 - divide by 128
> pin 13 - divide by 256
> pin 12 - divide by 512
> pin 14 - divide by 1024
> pin 15 - divide by 2048
> pin 1 - divide by 4096
>
> This position can "Vary" depending on the sensitivity
that
> you desire. The greater the division, the greater the
> sensitivity, however the "sample time" increases also
with
> greater division factors when using the PULSIN function.
> You can use the COUNT function with the BS2 instead for
> an even better resolution, but you loose the
compatability
> between the BS1 and BS2.
>
>
>
> EXAMPLE CODE:
>
> LVDT var word
>
> Start:
> PULSIN Pin#,0,LVDT 'or COUNT Pin#,Duration,LVDT
> debug home,? LVDT
> goto Start
>
>
>
> DIRECTIONS:
>
> Use a piece of "Coat-Hanger-Wire" to slide in and out of the STRAW.
>
> Beau Schwabe
> bschwabe@i...
>
>
OLD article stops above this line
>
>
> After reading this, I would ignore the references to the COUNT
> command, and just stick with the PULSIN command.
>
>
>
>
>
>
>
>
> Beau Schwabe IC Mask Designer
> National Semiconductor Wired Communications Division
> 500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
>
things slightly. Placing a second coil in a feedback wont do much to
keep things stable. The coil is not nearly as cranky about ambient
temp as a semiconductor junction. Is is for that reason that I
suggested placing all rectifiers over a common thermal pad.
Instability comes from these diodes being at different temps.
Small voltage changes in what goes into the primary result in similar
canges in the secondary. It is necessary to either very tightly
control the primary drive pulsetrain, or to use part of what drives
the primary as a reference voltage which secondary voltages are
compared to. This is the second major source of LVDT instability.
Creating a primary/secondary differential voltage is the best way to
deal with voltage fluctuations around the circuit. (The
primary/secondary ratio does not change)
An LVDT can be made to function without doing as I suggest, but only
as an educational excersize. Because the changes in secondary winding
voltages are so slight absolute circuit stability (electrical and
thermal) is essential.
I think Rodents' caliper idea is brilliant. Way better than going
this way.
Regards
Rich
--- In basicstamps@y..., "Beau Schwabe" <bschwabe@a...> wrote:
> At 09:25 PM 8/12/01 +0000, you wrote:
> >The LVDT is typically applied where fairly small changes are
> >measured. Displacement of the LVDT core of less than 1mm will
yeild a
> >usable reading. Using the LVDT is fairly straightforward, however,
> >quite a few components are required to get the thing working.
> >
> >The primary winding must be excited by either AC, or pulsed DC.
What
> >you'll probably end up doing is taking the output of a square wave
> >oscillator, beefing it up with a buffer, smoothing it out through a
> >cap, then driving it through the primary winding. This pulsetrain
> >should also be rectified and used as a reference voltage.
> >
> >There are usually two secondary windings. The LVDT core, when at
> >rest, is centered between these windings. Both windings are
> >individually rectified 180 degrees out of phase, then combined.
What
> >this does is allows the LVDT output to go high or low depending on
> >the position of the core. This is important for zero, and to assure
> >that the core is at rest in the proper position. Anyway, the
> >secondary windings get rectified, go through a summing ammplifier
> >(allows for display zero) and finally goes to one input of a
> >differential amplifier. The other input (reference voltage) comes
> >from the pulses that drive the primary winding. In addition to
> >driving the primary these pulses also get rectified and sent to a
> >reference amplifier (another op amp) Scaling and isolation happen
> >here. The output odf this reference amplifier then goes to the
second
> >input of the differential amplifier. The output of this
differential
> >amplifier would then be input into a 12 bit ADC, which converts the
> >voltage into it into a binary number the stamp understands.
> >
> >One other thing
> >
> >If you do decide to go forward with the LVDT it is VERY important
> >that the diodes you use are all mounted close together, on a
thermal
> >pad. Failure do so will result in readings that can not be trusted.
> >
> >Personally, I do not think the LVDT is best suited to your
> >application. I have little experience doing what you attempt so I
> >will not offer any alternate ideas. I have had some experience with
> >the LVDT and can tell you first hand, it can be an ornery little
> >devil. There has got to be an easier way do do what you want to do.
> >
> >Regards
> >
> >Rich
> >AA2DN
> >--- In basicstamps@y..., agarb@j... wrote:
> > > Has anyone out there ever interfaced a LDVDT to a basic stamp?
> > >
> > > If so, could someone explain (or refer me to a site) that could
> >explain
> > > how these things work, where they are used, how to interface
it, and
> > > where to buy one?
> > >
> > > We have a customer at work who wants us to put one on a machine
we
> >are
> > > building for him, but nobody at our (very small) shop knows
anything
> > > about them. Basically, they want us to provide a way to sense
the
> > > position of an air cylinder so we can tell where in its stroke
it
> >is. Is
> > > this a suitable application? Are there better solutions?
> > >
> > > Regards,
> > > Aaron
>
> I did a search at "www.google.com" for "LVDT" and "bschwabe" and
found
> an article I wrote on September 12th 1996. This method uses a
single
> COIL and works well, but does not compensate for temperature
variances.
> Compensation could easily be achieved with a secondary identical
coil
> in a fixed position used as a reference before the actual coil of
> interest was read.
>
>
>
OLD article begins below this line
>
> You can make a very simple "sensitive" LVDT with a resolution
greater than
> 1/2000th of an inch using a BS1 or BS2, 74HC14 or 74HCT14, and
4040B. For
> more than one, in addition you can use a 4051B for up to eight
LVDT's
>
> LVDT- #40 AGW enamled copper wire wound around a "Coffie-Straw
(single tube)",
> closely wound with at least 1 inch coil width. (width =
travel length)
>
> Vcc(+5V reg) o
o->Vcc
(+5V reg)
> o---> LVDT <---o | | |
> | | 14| |16 ---
> | | | o
o
o --- .1uF
> | 1|\ 2 | 3|\| 4 10| | |
> o
| \o----o----| \o
| 4040 B |--o-> GND
> | |/| |/ | |8,11
> --- 7| o
o
o
> --- .01uF | |Output *
> | ZTR* | |
> | | o--->Stamp Pin#
> o
o---->GND
>
> ZTR* - Zero Temperature Response
>
>
> 4040B - "Pin Outs"
>
> Output* : pin 9 - divide by 2
> pin 7 - divide by 4
> pin 6 - divide by 8
> pin 5 - divide by 16
> pin 3 - divide by 32
> pin 2 - divide by 64
> pin 4 - divide by 128
> pin 13 - divide by 256
> pin 12 - divide by 512
> pin 14 - divide by 1024
> pin 15 - divide by 2048
> pin 1 - divide by 4096
>
> This position can "Vary" depending on the sensitivity
that
> you desire. The greater the division, the greater the
> sensitivity, however the "sample time" increases also
with
> greater division factors when using the PULSIN function.
> You can use the COUNT function with the BS2 instead for
> an even better resolution, but you loose the
compatability
> between the BS1 and BS2.
>
>
>
> EXAMPLE CODE:
>
> LVDT var word
>
> Start:
> PULSIN Pin#,0,LVDT 'or COUNT Pin#,Duration,LVDT
> debug home,? LVDT
> goto Start
>
>
>
> DIRECTIONS:
>
> Use a piece of "Coat-Hanger-Wire" to slide in and out of the STRAW.
>
> Beau Schwabe
> bschwabe@i...
>
>
OLD article stops above this line
>
>
> After reading this, I would ignore the references to the COUNT
> command, and just stick with the PULSIN command.
>
>
>
>
>
>
>
>
> Beau Schwabe IC Mask Designer
> National Semiconductor Wired Communications Division
> 500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
>
things slightly. Placing a second coil in a feedback wont do much to
keep things stable. The coil is not nearly as cranky about ambient
temp as a semiconductor junction. Is is for that reason that I
suggested placing all rectifiers over a common thermal pad.
Instability comes from these diodes being at different temps.
Small voltage changes in what goes into the primary result in similar
canges in the secondary. It is necessary to either very tightly
control the primary drive pulsetrain, or to use part of what drives
the primary as a reference voltage which secondary voltages are
compared to. This is the second major source of LVDT instability.
Creating a primary/secondary differential voltage is the best way to
deal with voltage fluctuations around the circuit. (The
primary/secondary ratio does not change)
An LVDT can be made to function without doing as I suggest, but only
as an educational excersize. Because the changes in secondary winding
voltages are so slight absolute circuit stability (electrical and
thermal) is essential.
I think Rodents' caliper idea is brilliant. Way better than going
this way.
Regards
Rich
--- In basicstamps@y..., "Beau Schwabe" <bschwabe@a...> wrote:
> At 09:25 PM 8/12/01 +0000, you wrote:
> >The LVDT is typically applied where fairly small changes are
> >measured. Displacement of the LVDT core of less than 1mm will
yeild a
> >usable reading. Using the LVDT is fairly straightforward, however,
> >quite a few components are required to get the thing working.
> >
> >The primary winding must be excited by either AC, or pulsed DC.
What
> >you'll probably end up doing is taking the output of a square wave
> >oscillator, beefing it up with a buffer, smoothing it out through a
> >cap, then driving it through the primary winding. This pulsetrain
> >should also be rectified and used as a reference voltage.
> >
> >There are usually two secondary windings. The LVDT core, when at
> >rest, is centered between these windings. Both windings are
> >individually rectified 180 degrees out of phase, then combined.
What
> >this does is allows the LVDT output to go high or low depending on
> >the position of the core. This is important for zero, and to assure
> >that the core is at rest in the proper position. Anyway, the
> >secondary windings get rectified, go through a summing ammplifier
> >(allows for display zero) and finally goes to one input of a
> >differential amplifier. The other input (reference voltage) comes
> >from the pulses that drive the primary winding. In addition to
> >driving the primary these pulses also get rectified and sent to a
> >reference amplifier (another op amp) Scaling and isolation happen
> >here. The output odf this reference amplifier then goes to the
second
> >input of the differential amplifier. The output of this
differential
> >amplifier would then be input into a 12 bit ADC, which converts the
> >voltage into it into a binary number the stamp understands.
> >
> >One other thing
> >
> >If you do decide to go forward with the LVDT it is VERY important
> >that the diodes you use are all mounted close together, on a
thermal
> >pad. Failure do so will result in readings that can not be trusted.
> >
> >Personally, I do not think the LVDT is best suited to your
> >application. I have little experience doing what you attempt so I
> >will not offer any alternate ideas. I have had some experience with
> >the LVDT and can tell you first hand, it can be an ornery little
> >devil. There has got to be an easier way do do what you want to do.
> >
> >Regards
> >
> >Rich
> >AA2DN
> >--- In basicstamps@y..., agarb@j... wrote:
> > > Has anyone out there ever interfaced a LDVDT to a basic stamp?
> > >
> > > If so, could someone explain (or refer me to a site) that could
> >explain
> > > how these things work, where they are used, how to interface
it, and
> > > where to buy one?
> > >
> > > We have a customer at work who wants us to put one on a machine
we
> >are
> > > building for him, but nobody at our (very small) shop knows
anything
> > > about them. Basically, they want us to provide a way to sense
the
> > > position of an air cylinder so we can tell where in its stroke
it
> >is. Is
> > > this a suitable application? Are there better solutions?
> > >
> > > Regards,
> > > Aaron
>
> I did a search at "www.google.com" for "LVDT" and "bschwabe" and
found
> an article I wrote on September 12th 1996. This method uses a
single
> COIL and works well, but does not compensate for temperature
variances.
> Compensation could easily be achieved with a secondary identical
coil
> in a fixed position used as a reference before the actual coil of
> interest was read.
>
>
>
OLD article begins below this line
>
> You can make a very simple "sensitive" LVDT with a resolution
greater than
> 1/2000th of an inch using a BS1 or BS2, 74HC14 or 74HCT14, and
4040B. For
> more than one, in addition you can use a 4051B for up to eight
LVDT's
>
> LVDT- #40 AGW enamled copper wire wound around a "Coffie-Straw
(single tube)",
> closely wound with at least 1 inch coil width. (width =
travel length)
>
> Vcc(+5V reg) o
o->Vcc
(+5V reg)
> o---> LVDT <---o | | |
> | | 14| |16 ---
> | | | o
o
o --- .1uF
> | 1|\ 2 | 3|\| 4 10| | |
> o
| \o----o----| \o
| 4040 B |--o-> GND
> | |/| |/ | |8,11
> --- 7| o
o
o
> --- .01uF | |Output *
> | ZTR* | |
> | | o--->Stamp Pin#
> o
o---->GND
>
> ZTR* - Zero Temperature Response
>
>
> 4040B - "Pin Outs"
>
> Output* : pin 9 - divide by 2
> pin 7 - divide by 4
> pin 6 - divide by 8
> pin 5 - divide by 16
> pin 3 - divide by 32
> pin 2 - divide by 64
> pin 4 - divide by 128
> pin 13 - divide by 256
> pin 12 - divide by 512
> pin 14 - divide by 1024
> pin 15 - divide by 2048
> pin 1 - divide by 4096
>
> This position can "Vary" depending on the sensitivity
that
> you desire. The greater the division, the greater the
> sensitivity, however the "sample time" increases also
with
> greater division factors when using the PULSIN function.
> You can use the COUNT function with the BS2 instead for
> an even better resolution, but you loose the
compatability
> between the BS1 and BS2.
>
>
>
> EXAMPLE CODE:
>
> LVDT var word
>
> Start:
> PULSIN Pin#,0,LVDT 'or COUNT Pin#,Duration,LVDT
> debug home,? LVDT
> goto Start
>
>
>
> DIRECTIONS:
>
> Use a piece of "Coat-Hanger-Wire" to slide in and out of the STRAW.
>
> Beau Schwabe
> bschwabe@i...
>
>
OLD article stops above this line
>
>
> After reading this, I would ignore the references to the COUNT
> command, and just stick with the PULSIN command.
>
>
>
>
>
>
>
>
> Beau Schwabe IC Mask Designer
> National Semiconductor Wired Communications Division
> 500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
>
things slightly. Placing a second coil in a feedback wont do much to
keep things stable. The coil is not nearly as cranky about ambient
temp as a semiconductor junction. Is is for that reason that I
suggested placing all rectifiers over a common thermal pad.
Instability comes from these diodes being at different temps.
Small voltage changes in what goes into the primary result in similar
canges in the secondary. It is necessary to either very tightly
control the primary drive pulsetrain, or to use part of what drives
the primary as a reference voltage which secondary voltages are
compared to. This is the second major source of LVDT instability.
Creating a primary/secondary differential voltage is the best way to
deal with voltage fluctuations around the circuit. (The
primary/secondary ratio does not change)
An LVDT can be made to function without doing as I suggest, but only
as an educational excersize. Because the changes in secondary winding
voltages are so slight absolute circuit stability (electrical and
thermal) is essential.
I think Rodents' caliper idea is brilliant. Way better than going
this way.
Regards
Rich
--- In basicstamps@y..., "Beau Schwabe" <bschwabe@a...> wrote:
> At 09:25 PM 8/12/01 +0000, you wrote:
> >The LVDT is typically applied where fairly small changes are
> >measured. Displacement of the LVDT core of less than 1mm will
yeild a
> >usable reading. Using the LVDT is fairly straightforward, however,
> >quite a few components are required to get the thing working.
> >
> >The primary winding must be excited by either AC, or pulsed DC.
What
> >you'll probably end up doing is taking the output of a square wave
> >oscillator, beefing it up with a buffer, smoothing it out through a
> >cap, then driving it through the primary winding. This pulsetrain
> >should also be rectified and used as a reference voltage.
> >
> >There are usually two secondary windings. The LVDT core, when at
> >rest, is centered between these windings. Both windings are
> >individually rectified 180 degrees out of phase, then combined.
What
> >this does is allows the LVDT output to go high or low depending on
> >the position of the core. This is important for zero, and to assure
> >that the core is at rest in the proper position. Anyway, the
> >secondary windings get rectified, go through a summing ammplifier
> >(allows for display zero) and finally goes to one input of a
> >differential amplifier. The other input (reference voltage) comes
> >from the pulses that drive the primary winding. In addition to
> >driving the primary these pulses also get rectified and sent to a
> >reference amplifier (another op amp) Scaling and isolation happen
> >here. The output odf this reference amplifier then goes to the
second
> >input of the differential amplifier. The output of this
differential
> >amplifier would then be input into a 12 bit ADC, which converts the
> >voltage into it into a binary number the stamp understands.
> >
> >One other thing
> >
> >If you do decide to go forward with the LVDT it is VERY important
> >that the diodes you use are all mounted close together, on a
thermal
> >pad. Failure do so will result in readings that can not be trusted.
> >
> >Personally, I do not think the LVDT is best suited to your
> >application. I have little experience doing what you attempt so I
> >will not offer any alternate ideas. I have had some experience with
> >the LVDT and can tell you first hand, it can be an ornery little
> >devil. There has got to be an easier way do do what you want to do.
> >
> >Regards
> >
> >Rich
> >AA2DN
> >--- In basicstamps@y..., agarb@j... wrote:
> > > Has anyone out there ever interfaced a LDVDT to a basic stamp?
> > >
> > > If so, could someone explain (or refer me to a site) that could
> >explain
> > > how these things work, where they are used, how to interface
it, and
> > > where to buy one?
> > >
> > > We have a customer at work who wants us to put one on a machine
we
> >are
> > > building for him, but nobody at our (very small) shop knows
anything
> > > about them. Basically, they want us to provide a way to sense
the
> > > position of an air cylinder so we can tell where in its stroke
it
> >is. Is
> > > this a suitable application? Are there better solutions?
> > >
> > > Regards,
> > > Aaron
>
> I did a search at "www.google.com" for "LVDT" and "bschwabe" and
found
> an article I wrote on September 12th 1996. This method uses a
single
> COIL and works well, but does not compensate for temperature
variances.
> Compensation could easily be achieved with a secondary identical
coil
> in a fixed position used as a reference before the actual coil of
> interest was read.
>
>
>
OLD article begins below this line
>
> You can make a very simple "sensitive" LVDT with a resolution
greater than
> 1/2000th of an inch using a BS1 or BS2, 74HC14 or 74HCT14, and
4040B. For
> more than one, in addition you can use a 4051B for up to eight
LVDT's
>
> LVDT- #40 AGW enamled copper wire wound around a "Coffie-Straw
(single tube)",
> closely wound with at least 1 inch coil width. (width =
travel length)
>
> Vcc(+5V reg) o
o->Vcc
(+5V reg)
> o---> LVDT <---o | | |
> | | 14| |16 ---
> | | | o
o
o --- .1uF
> | 1|\ 2 | 3|\| 4 10| | |
> o
| \o----o----| \o
| 4040 B |--o-> GND
> | |/| |/ | |8,11
> --- 7| o
o
o
> --- .01uF | |Output *
> | ZTR* | |
> | | o--->Stamp Pin#
> o
o---->GND
>
> ZTR* - Zero Temperature Response
>
>
> 4040B - "Pin Outs"
>
> Output* : pin 9 - divide by 2
> pin 7 - divide by 4
> pin 6 - divide by 8
> pin 5 - divide by 16
> pin 3 - divide by 32
> pin 2 - divide by 64
> pin 4 - divide by 128
> pin 13 - divide by 256
> pin 12 - divide by 512
> pin 14 - divide by 1024
> pin 15 - divide by 2048
> pin 1 - divide by 4096
>
> This position can "Vary" depending on the sensitivity
that
> you desire. The greater the division, the greater the
> sensitivity, however the "sample time" increases also
with
> greater division factors when using the PULSIN function.
> You can use the COUNT function with the BS2 instead for
> an even better resolution, but you loose the
compatability
> between the BS1 and BS2.
>
>
>
> EXAMPLE CODE:
>
> LVDT var word
>
> Start:
> PULSIN Pin#,0,LVDT 'or COUNT Pin#,Duration,LVDT
> debug home,? LVDT
> goto Start
>
>
>
> DIRECTIONS:
>
> Use a piece of "Coat-Hanger-Wire" to slide in and out of the STRAW.
>
> Beau Schwabe
> bschwabe@i...
>
>
OLD article stops above this line
>
>
> After reading this, I would ignore the references to the COUNT
> command, and just stick with the PULSIN command.
>
>
>
>
>
>
>
>
> Beau Schwabe IC Mask Designer
> National Semiconductor Wired Communications Division
> 500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
>
things slightly. Placing a second coil in a feedback wont do much to
keep things stable. The coil is not nearly as cranky about ambient
temp as a semiconductor junction. Is is for that reason that I
suggested placing all rectifiers over a common thermal pad.
Instability comes from these diodes being at different temps.
Small voltage changes in what goes into the primary result in similar
canges in the secondary. It is necessary to either very tightly
control the primary drive pulsetrain, or to use part of what drives
the primary as a reference voltage which secondary voltages are
compared to. This is the second major source of LVDT instability.
Creating a primary/secondary differential voltage is the best way to
deal with voltage fluctuations around the circuit. (The
primary/secondary ratio does not change)
An LVDT can be made to function without doing as I suggest, but only
as an educational excersize. Because the changes in secondary winding
voltages are so slight absolute circuit stability (electrical and
thermal) is essential.
I think Rodents' caliper idea is brilliant. Way better than going
this way.
Regards
Rich
--- In basicstamps@y..., "Beau Schwabe" <bschwabe@a...> wrote:
> At 09:25 PM 8/12/01 +0000, you wrote:
> >The LVDT is typically applied where fairly small changes are
> >measured. Displacement of the LVDT core of less than 1mm will
yeild a
> >usable reading. Using the LVDT is fairly straightforward, however,
> >quite a few components are required to get the thing working.
> >
> >The primary winding must be excited by either AC, or pulsed DC.
What
> >you'll probably end up doing is taking the output of a square wave
> >oscillator, beefing it up with a buffer, smoothing it out through a
> >cap, then driving it through the primary winding. This pulsetrain
> >should also be rectified and used as a reference voltage.
> >
> >There are usually two secondary windings. The LVDT core, when at
> >rest, is centered between these windings. Both windings are
> >individually rectified 180 degrees out of phase, then combined.
What
> >this does is allows the LVDT output to go high or low depending on
> >the position of the core. This is important for zero, and to assure
> >that the core is at rest in the proper position. Anyway, the
> >secondary windings get rectified, go through a summing ammplifier
> >(allows for display zero) and finally goes to one input of a
> >differential amplifier. The other input (reference voltage) comes
> >from the pulses that drive the primary winding. In addition to
> >driving the primary these pulses also get rectified and sent to a
> >reference amplifier (another op amp) Scaling and isolation happen
> >here. The output odf this reference amplifier then goes to the
second
> >input of the differential amplifier. The output of this
differential
> >amplifier would then be input into a 12 bit ADC, which converts the
> >voltage into it into a binary number the stamp understands.
> >
> >One other thing
> >
> >If you do decide to go forward with the LVDT it is VERY important
> >that the diodes you use are all mounted close together, on a
thermal
> >pad. Failure do so will result in readings that can not be trusted.
> >
> >Personally, I do not think the LVDT is best suited to your
> >application. I have little experience doing what you attempt so I
> >will not offer any alternate ideas. I have had some experience with
> >the LVDT and can tell you first hand, it can be an ornery little
> >devil. There has got to be an easier way do do what you want to do.
> >
> >Regards
> >
> >Rich
> >AA2DN
> >--- In basicstamps@y..., agarb@j... wrote:
> > > Has anyone out there ever interfaced a LDVDT to a basic stamp?
> > >
> > > If so, could someone explain (or refer me to a site) that could
> >explain
> > > how these things work, where they are used, how to interface
it, and
> > > where to buy one?
> > >
> > > We have a customer at work who wants us to put one on a machine
we
> >are
> > > building for him, but nobody at our (very small) shop knows
anything
> > > about them. Basically, they want us to provide a way to sense
the
> > > position of an air cylinder so we can tell where in its stroke
it
> >is. Is
> > > this a suitable application? Are there better solutions?
> > >
> > > Regards,
> > > Aaron
>
> I did a search at "www.google.com" for "LVDT" and "bschwabe" and
found
> an article I wrote on September 12th 1996. This method uses a
single
> COIL and works well, but does not compensate for temperature
variances.
> Compensation could easily be achieved with a secondary identical
coil
> in a fixed position used as a reference before the actual coil of
> interest was read.
>
>
>
OLD article begins below this line
>
> You can make a very simple "sensitive" LVDT with a resolution
greater than
> 1/2000th of an inch using a BS1 or BS2, 74HC14 or 74HCT14, and
4040B. For
> more than one, in addition you can use a 4051B for up to eight
LVDT's
>
> LVDT- #40 AGW enamled copper wire wound around a "Coffie-Straw
(single tube)",
> closely wound with at least 1 inch coil width. (width =
travel length)
>
> Vcc(+5V reg) o
o->Vcc
(+5V reg)
> o---> LVDT <---o | | |
> | | 14| |16 ---
> | | | o
o
o --- .1uF
> | 1|\ 2 | 3|\| 4 10| | |
> o
| \o----o----| \o
| 4040 B |--o-> GND
> | |/| |/ | |8,11
> --- 7| o
o
o
> --- .01uF | |Output *
> | ZTR* | |
> | | o--->Stamp Pin#
> o
o---->GND
>
> ZTR* - Zero Temperature Response
>
>
> 4040B - "Pin Outs"
>
> Output* : pin 9 - divide by 2
> pin 7 - divide by 4
> pin 6 - divide by 8
> pin 5 - divide by 16
> pin 3 - divide by 32
> pin 2 - divide by 64
> pin 4 - divide by 128
> pin 13 - divide by 256
> pin 12 - divide by 512
> pin 14 - divide by 1024
> pin 15 - divide by 2048
> pin 1 - divide by 4096
>
> This position can "Vary" depending on the sensitivity
that
> you desire. The greater the division, the greater the
> sensitivity, however the "sample time" increases also
with
> greater division factors when using the PULSIN function.
> You can use the COUNT function with the BS2 instead for
> an even better resolution, but you loose the
compatability
> between the BS1 and BS2.
>
>
>
> EXAMPLE CODE:
>
> LVDT var word
>
> Start:
> PULSIN Pin#,0,LVDT 'or COUNT Pin#,Duration,LVDT
> debug home,? LVDT
> goto Start
>
>
>
> DIRECTIONS:
>
> Use a piece of "Coat-Hanger-Wire" to slide in and out of the STRAW.
>
> Beau Schwabe
> bschwabe@i...
>
>
OLD article stops above this line
>
>
> After reading this, I would ignore the references to the COUNT
> command, and just stick with the PULSIN command.
>
>
>
>
>
>
>
>
> Beau Schwabe IC Mask Designer
> National Semiconductor Wired Communications Division
> 500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
>
Look for a "drop gauge" with SPC (statistical process control??) output.
These can be found in various lengths. You should also look for a "Mini
recorder" with RS-232 output. You can also goto http://www.Mitutoyo.com if
budget is no concern and purchase a single axis DRO (Digital Read Out).
The "Drop Gauge" mounts to a fixed position on your machine is has a sliding
pin that rests on the moving part of the machine. The distance the part
moves is displayed locally on the gage display and sent to the Mini recorder
through the SPC port. Your device sends a plain ASCII text command to Mini
recorder (using RS-232) which sends back the current reading (again in
ASCII). This is a simple and easy setup. You might be able to leave out
the Mini recorder and interface right to the drop gauge, but I think the
drop gauge communicates in a proprietary format to the mini recorder where
as the mini recorder can be interfaced with RS-232 using ASCII commands.
Good Luck,
BTW. The customer IS always right, but NOT always correct.
Best Regards
Mike Witherspoon
Original Message
From: A.C.Jacques [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=TLz3wVNXxjOCnRIBCDNSOr8nMpSm6ZQjqkXB4VIDZLNUkhulv2W-awHDoWYdtEZKCdaox0vXhEa9iX4nvtgsQj3ePg]acjacques@i...[/url
Sent: Monday, August 13, 2001 10:11 AM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] LDVDT???
Digital calipers are not LVDT. I believe it works using capacitance.(?)
There are several DRO (digital read out) units with serial out, used to
be adapted in lathes an milling machines.
I have tried to use an inexpensive digital caliper in my Sherline Lathe
but it not work reliable because interference from AC motor.
ACJacques
Chris Loiacono (E-mail) wrote:
>
> Great idea, Rodent! "Applause in background"
> Would the caliper need to be hacked, or do the inexpensive ones not have
> output to a connector? I am sure the name brands (Mitutoyo, etc) do...
> Also, is the output in real time, or is there a delay,. They seem to
display
> instantly to the eye, but....well, you get the point....
>
> Chris
>
> >
Original Message
> > From: Rodent [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=8neF1OgHIo6EKjx16Q-e4rKgyW7J3JIOCNn_j0C7vA5aS4sQiMS2ZfTKArEIzKwuCbhO0xj_UKUjLA]daweasel@s...[/url
> > Sent: Saturday, August 11, 2001 5:34 PM
> > To: basicstamps@yahoogroups.com
> > Subject: Re: [noparse][[/noparse]basicstamps] LDVDT???
> >
> >
> > If you absolutely have to measure it, you might consider
> > hacking a set of
> > digital calipers with the data output, or getting one of the
> > digital readout
> > units from Grizzly. They are like digital calipers without
> > jaws. They have a
> > display on them as well as some sort of interface for a
> > larger readout head.
> > I did not find them in their online catalog, but the last
> > flyer I got listed
> > them. They are about $110 for a 12" travel unit.
> >
>
> To UNSUBSCRIBE, just send mail to:
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> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
To UNSUBSCRIBE, just send mail to:
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Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>Using a LVDT with only a single secondary winding only simplifies
>things slightly. Placing a second coil in a feedback wont do much to
>keep things stable. The coil is not nearly as cranky about ambient
>temp as a semiconductor junction. Is is for that reason that I
>suggested placing all rectifiers over a common thermal pad.
>Instability comes from these diodes being at different temps.
Agreed, but the circuit that I provided does have temperature issues
not so much with the coils, but within the 74xx14. To compensate
for this you must have a "dummy coil" that is used to compare against
the LVDT coil. i.e.
( "LVDT coil" * "DeltaTemp" )
Output =
( "dummy coil" * "DeltaTemp")
can be simplified, eliminating any temperature effects to...
"LVDT coil"
Output =
"dummy coil"
(big snip)
> >
> > I did a search at "www.google.com" for "LVDT" and "bschwabe" and
>found
> > an article I wrote on September 12th 1996. This method uses a
>single
> > COIL and works well, but does not compensate for temperature
>variances.
> > Compensation could easily be achieved with a secondary identical
>coil
> > in a fixed position used as a reference before the actual coil of
> > interest was read.
> >
> >
> >
OLD article begins below this line
> >
> > You can make a very simple "sensitive" LVDT with a resolution
>greater than
> > 1/2000th of an inch using a BS1 or BS2, 74HC14 or 74HCT14, and
>4040B. For
> > more than one, in addition you can use a 4051B for up to eight
>LVDT's
> >
> > LVDT- #40 AGW enamled copper wire wound around a "Coffie-Straw
>(single tube)",
> > closely wound with at least 1 inch coil width. (width =
>travel length)
> >
> > Vcc(+5V reg) o
o->Vcc
>(+5V reg)
> > o---> LVDT <---o | | |
> > | | 14| |16 ---
> > | | | o
o
o --- .1uF
> > | 1|\ 2 | 3|\| 4 10| | |
> > o
| \o----o----| \o
| 4040 B |--o-> GND
> > | |/| |/ | |8,11
> > --- 7| o
o
o
> > --- .01uF | |Output *
> > | ZTR* | |
> > | | o--->Stamp Pin#
> > o
o---->GND
> >
> > ZTR* - Zero Temperature Response
> >
> >
> > 4040B - "Pin Outs"
> >
> > Output* : pin 9 - divide by 2
> > pin 7 - divide by 4
> > pin 6 - divide by 8
> > pin 5 - divide by 16
> > pin 3 - divide by 32
> > pin 2 - divide by 64
> > pin 4 - divide by 128
> > pin 13 - divide by 256
> > pin 12 - divide by 512
> > pin 14 - divide by 1024
> > pin 15 - divide by 2048
> > pin 1 - divide by 4096
> >
> > This position can "Vary" depending on the sensitivity
>that
> > you desire. The greater the division, the greater the
> > sensitivity, however the "sample time" increases also
>with
> > greater division factors when using the PULSIN function.
> > You can use the COUNT function with the BS2 instead for
> > an even better resolution, but you loose the
>compatability
> > between the BS1 and BS2.
> >
> >
> >
> > EXAMPLE CODE:
> >
> > LVDT var word
> >
> > Start:
> > PULSIN Pin#,0,LVDT 'or COUNT Pin#,Duration,LVDT
> > debug home,? LVDT
> > goto Start
> >
> >
> >
> > DIRECTIONS:
> >
> > Use a piece of "Coat-Hanger-Wire" to slide in and out of the STRAW.
> >
> > Beau Schwabe
> > bschwabe@i...
> >
> >
OLD article stops above this line
> >
> >
> > After reading this, I would ignore the references to the COUNT
> > command, and just stick with the PULSIN command.
> >
Beau Schwabe IC Mask Designer
National Semiconductor Wired Communications Division
500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
what you suggest. It is difficult for me to accept that the circuit
can be made thermally stable in this fashion. Still, I don't discount
what you say...
What you suggest is much less parts intensive than the only way I
know how to do it. Could you point me somewhere where I may look at
the schematic to which you refer? My curiosity certainly has the best
of me.
Thank You,
Regards
Rich
--- In basicstamps@y..., "Beau Schwabe" <bschwabe@a...> wrote:
> At 05:34 PM 8/13/01 +0000, you wrote:
> >Using a LVDT with only a single secondary winding only simplifies
> >things slightly. Placing a second coil in a feedback wont do much
to
> >keep things stable. The coil is not nearly as cranky about ambient
> >temp as a semiconductor junction. Is is for that reason that I
> >suggested placing all rectifiers over a common thermal pad.
> >Instability comes from these diodes being at different temps.
>
> Agreed, but the circuit that I provided does have temperature issues
> not so much with the coils, but within the 74xx14. To compensate
> for this you must have a "dummy coil" that is used to compare
against
> the LVDT coil. i.e.
>
> ( "LVDT coil" * "DeltaTemp" )
> Output =
> ( "dummy coil" * "DeltaTemp")
>
> can be simplified, eliminating any temperature effects to...
>
> "LVDT coil"
> Output =
> "dummy coil"
>
> (big snip)
>
>
> > >
> > > I did a search at "www.google.com" for "LVDT" and "bschwabe" and
> >found
> > > an article I wrote on September 12th 1996. This method uses a
> >single
> > > COIL and works well, but does not compensate for temperature
> >variances.
> > > Compensation could easily be achieved with a secondary identical
> >coil
> > > in a fixed position used as a reference before the actual coil
of
> > > interest was read.
> > >
> > >
> > >
OLD article begins below this line
--
> > >
> > > You can make a very simple "sensitive" LVDT with a resolution
> >greater than
> > > 1/2000th of an inch using a BS1 or BS2, 74HC14 or 74HCT14, and
> >4040B. For
> > > more than one, in addition you can use a 4051B for up to eight
> >LVDT's
> > >
> > > LVDT- #40 AGW enamled copper wire wound around a "Coffie-Straw
> >(single tube)",
> > > closely wound with at least 1 inch coil width. (width =
> >travel length)
> > >
> > > Vcc(+5V reg) o
o-
>Vcc
> >(+5V reg)
> > > o---> LVDT <---o | | |
> > > | | 14| |16 ---
> > > | | | o
o
o ---
.1uF
> > > | 1|\ 2 | 3|\| 4 10| | |
> > > o
| \o----o----| \o
| 4040 B |--o-
> GND
> > > | |/| |/ | |8,11
> > > --- 7| o
o
o
> > > --- .01uF | |Output *
> > > | ZTR* | |
> > > | | o--->Stamp Pin#
> > > o
o---->GND
> > >
> > > ZTR* - Zero Temperature Response
> > >
> > >
> > > 4040B - "Pin Outs"
> > >
> > > Output* : pin 9 - divide by 2
> > > pin 7 - divide by 4
> > > pin 6 - divide by 8
> > > pin 5 - divide by 16
> > > pin 3 - divide by 32
> > > pin 2 - divide by 64
> > > pin 4 - divide by 128
> > > pin 13 - divide by 256
> > > pin 12 - divide by 512
> > > pin 14 - divide by 1024
> > > pin 15 - divide by 2048
> > > pin 1 - divide by 4096
> > >
> > > This position can "Vary" depending on the sensitivity
> >that
> > > you desire. The greater the division, the greater
the
> > > sensitivity, however the "sample time" increases also
> >with
> > > greater division factors when using the PULSIN
function.
> > > You can use the COUNT function with the BS2 instead
for
> > > an even better resolution, but you loose the
> >compatability
> > > between the BS1 and BS2.
> > >
> > >
> > >
> > > EXAMPLE CODE:
> > >
> > > LVDT var word
> > >
> > > Start:
> > > PULSIN Pin#,0,LVDT 'or COUNT Pin#,Duration,LVDT
> > > debug home,? LVDT
> > > goto Start
> > >
> > >
> > >
> > > DIRECTIONS:
> > >
> > > Use a piece of "Coat-Hanger-Wire" to slide in and out of the
STRAW.
> > >
> > > Beau Schwabe
> > > bschwabe@i...
> > >
> > >
OLD article stops above this line
-
> > >
> > >
> > > After reading this, I would ignore the references to the COUNT
> > > command, and just stick with the PULSIN command.
> > >
>
>
> Beau Schwabe IC Mask Designer
> National Semiconductor Wired Communications Division
> 500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
>
http://products.analog.com/products/info.asp?product=AD598
Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
Manufacturer of the famous BOB-II Serial Video Text Display Module!
Thanks for the info, I'll see if I can give it a try.
Regards,
Aaron
>
OLD article begins below this line
>
> You can make a very simple "sensitive" LVDT with a resolution
> greater than
> 1/2000th of an inch using a BS1 or BS2, 74HC14 or 74HCT14, and
> 4040B. For
> more than one, in addition you can use a 4051B for up to eight
> LVDT's
>
> LVDT- #40 AGW enamled copper wire wound around a
> "Coffie-Straw(single tube)",
> closely wound with at least 1 inch coil width. (width =
> travel length)
>
> Vcc(+5V reg)
> o
o->Vcc(+5V reg)
> o---> LVDT <---o | | |
> | | 14| |16 ---
> | | | o
o
o --- .1uF
> | 1|\ 2 | 3|\| 4 10| | |
> o
| \o----o----| \o
| 4040 B |--o-> GND
> | |/| |/ | |8,11
> --- 7| o
o
o
> --- .01uF | |Output *
> | ZTR* | |
> | | o--->Stamp Pin#
> o
o---->GND
>
> ZTR* - Zero Temperature Response
>
>
> 4040B - "Pin Outs"
>
> Output* : pin 9 - divide by 2
> pin 7 - divide by 4
> pin 6 - divide by 8
> pin 5 - divide by 16
> pin 3 - divide by 32
> pin 2 - divide by 64
> pin 4 - divide by 128
> pin 13 - divide by 256
> pin 12 - divide by 512
> pin 14 - divide by 1024
> pin 15 - divide by 2048
> pin 1 - divide by 4096
>
> This position can "Vary" depending on the sensitivity
> that
> you desire. The greater the division, the greater the
> sensitivity, however the "sample time" increases also
> with
> greater division factors when using the PULSIN function.
> You can use the COUNT function with the BS2 instead for
> an even better resolution, but you loose the
> compatability
> between the BS1 and BS2.
>
>
>
> EXAMPLE CODE:
>
> LVDT var word
>
> Start:
> PULSIN Pin#,0,LVDT 'or COUNT Pin#,Duration,LVDT
> debug home,? LVDT
> goto Start
>
>
>
> DIRECTIONS:
>
> Use a piece of "Coat-Hanger-Wire" to slide in and out of the STRAW.
>
> Beau Schwabe
> bschwabe@i...
>
>
OLD article stops above this line
>
>
> After reading this, I would ignore the references to the COUNT
> command, and just stick with the PULSIN command.
>Maybe you are correct, it's just that my "gut" doesn't subscribe to
>what you suggest. It is difficult for me to accept that the circuit
>can be made thermally stable in this fashion. Still, I don't discount
>what you say...
Refer to the attached URL:
Since the same oscillator (U1,U2,and C1, plus the LVDT Coils) is used
for up to 8 LVDT coils then you can bet that all coils will be affected
equally with temperature, and that any differences could be traced to
internal propagation delays within U1.
What the 'LVDT,gif' does require in order to provide compensation
is a LVDT coil dedicated to do nothing as far as movement, but only
for a reference. Typically the "reference coil" or "dummy coil"
would be configured so that the metallic slug would be resting at a
center position. Your software (within a STAMP or PIC) would simply
select the appropriate coil and make a percentage comparison. i.e.
(Pseudo Stamp Code)
Start:
read reference LVDT
read position LVDT
if reference < position then Loop1
if reference > position then Loop2
percent = 0
goto Done
Loop1:
percent = ( reference * 100 ) / position
goto Done
Loop2:
percent = ( position * 100 ) / reference
percent = percent * -1
Done:
debug percent
goto Start
>What you suggest is much less parts intensive than the only way I
>know how to do it. Could you point me somewhere where I may look at
>the schematic to which you refer? My curiosity certainly has the best
>of me.
3 IC's + a Stamp to read 7 LVDT's
http://home.earthlink.net/~y2kbc/Electronics/BasicStamp/LVDT.gif
See also...
http://home.earthlink.net/~y2kbc/Electronics/BasicStamp/Coilread.gif
>Thank You,
>Regards
>
>Rich
>
>--- In basicstamps@y..., "Beau Schwabe" <bschwabe@a...> wrote:
> > At 05:34 PM 8/13/01 +0000, you wrote:
> > >Using a LVDT with only a single secondary winding only simplifies
> > >things slightly. Placing a second coil in a feedback wont do much
>to
> > >keep things stable. The coil is not nearly as cranky about ambient
> > >temp as a semiconductor junction. Is is for that reason that I
> > >suggested placing all rectifiers over a common thermal pad.
> > >Instability comes from these diodes being at different temps.
> >
> > Agreed, but the circuit that I provided does have temperature issues
> > not so much with the coils, but within the 74xx14. To compensate
> > for this you must have a "dummy coil" that is used to compare
>against
> > the LVDT coil. i.e.
> >
> > ( "LVDT coil" * "DeltaTemp" )
> > Output =
> > ( "dummy coil" * "DeltaTemp")
> >
> > can be simplified, eliminating any temperature effects to...
> >
> > "LVDT coil"
> > Output =
> > "dummy coil"
> >
Beau Schwabe IC Mask Designer
National Semiconductor Wired Communications Division
500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
interesting...
I can be SOO00oo stubborn sometimes.
Regards
Rich AA2DN
--- In basicstamps@y..., "Beau Schwabe" <bschwabe@a...> wrote:
> At 07:59 PM 8/13/01 +0000, you wrote:
> >Maybe you are correct, it's just that my "gut" doesn't subscribe to
> >what you suggest. It is difficult for me to accept that the circuit
> >can be made thermally stable in this fashion. Still, I don't
discount
> >what you say...
>
> Refer to the attached URL:
> Since the same oscillator (U1,U2,and C1, plus the LVDT Coils) is
used
> for up to 8 LVDT coils then you can bet that all coils will be
affected
> equally with temperature, and that any differences could be traced
to
> internal propagation delays within U1.
>
> What the 'LVDT,gif' does require in order to provide compensation
> is a LVDT coil dedicated to do nothing as far as movement, but only
> for a reference. Typically the "reference coil" or "dummy coil"
> would be configured so that the metallic slug would be resting at a
> center position. Your software (within a STAMP or PIC) would simply
> select the appropriate coil and make a percentage comparison. i.e.
>
>
> (Pseudo Stamp Code)
> Start:
>
> read reference LVDT
> read position LVDT
>
> if reference < position then Loop1
> if reference > position then Loop2
>
> percent = 0
>
> goto Done
>
> Loop1:
> percent = ( reference * 100 ) / position
> goto Done
>
> Loop2:
> percent = ( position * 100 ) / reference
> percent = percent * -1
>
> Done:
> debug percent
> goto Start
>
>
> >What you suggest is much less parts intensive than the only way I
> >know how to do it. Could you point me somewhere where I may look
at
> >the schematic to which you refer? My curiosity certainly has the
best
> >of me.
>
> 3 IC's + a Stamp to read 7 LVDT's
>
> http://home.earthlink.net/~y2kbc/Electronics/BasicStamp/LVDT.gif
>
> See also...
>
> http://home.earthlink.net/~y2kbc/Electronics/BasicStamp/Coilread.gif
>
>
>
> >Thank You,
> >Regards
> >
> >Rich
> >
> >--- In basicstamps@y..., "Beau Schwabe" <bschwabe@a...> wrote:
> > > At 05:34 PM 8/13/01 +0000, you wrote:
> > > >Using a LVDT with only a single secondary winding only
simplifies
> > > >things slightly. Placing a second coil in a feedback wont do
much
> >to
> > > >keep things stable. The coil is not nearly as cranky about
ambient
> > > >temp as a semiconductor junction. Is is for that reason that I
> > > >suggested placing all rectifiers over a common thermal pad.
> > > >Instability comes from these diodes being at different temps.
> > >
> > > Agreed, but the circuit that I provided does have temperature
issues
> > > not so much with the coils, but within the 74xx14. To
compensate
> > > for this you must have a "dummy coil" that is used to compare
> >against
> > > the LVDT coil. i.e.
> > >
> > > ( "LVDT coil" * "DeltaTemp" )
> > > Output =
> > > ( "dummy coil" * "DeltaTemp")
> > >
> > > can be simplified, eliminating any temperature effects to...
> > >
> > > "LVDT coil"
> > > Output =
> > > "dummy coil"
> > >
>
>
> Beau Schwabe IC Mask Designer
> National Semiconductor Wired Communications Division
> 500 Pinnacle Court, Suite 525 Mail Stop GA1 Norcross, GA 30071
>