Pressure sensor 4-20mA
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Posts: 46,084
Hi guys & girls,
I am working on a HVAC project. I have to read in an 4-20mA pressure
sensor (between -0,5 and 7 BAR brand DIXELL). I've searched a lot on
internet and didn't find a proper solution to connect this sensor to
my BS2P-24. I've already made an easy circuit wich contains an 12BIT
ADC and a resistor (150ohms) so I can get max 3V over my adc inputs.
When I read the ADC in, I get VERY different values. My power supply
is extremly stable (checked with an oscilloscope). Is there
somebody who has created a simular project and could give me a
better way to connect the pressure sensor with my stamp?
Kindly regards
Tim
Belgium
Student ICT
I am working on a HVAC project. I have to read in an 4-20mA pressure
sensor (between -0,5 and 7 BAR brand DIXELL). I've searched a lot on
internet and didn't find a proper solution to connect this sensor to
my BS2P-24. I've already made an easy circuit wich contains an 12BIT
ADC and a resistor (150ohms) so I can get max 3V over my adc inputs.
When I read the ADC in, I get VERY different values. My power supply
is extremly stable (checked with an oscilloscope). Is there
somebody who has created a simular project and could give me a
better way to connect the pressure sensor with my stamp?
Kindly regards
Tim
Belgium
Student ICT
Comments
measurement.
But, since the stamp likes things in 5V, you might want to just throw a
resistor across that guy there. I know I've heard someone say as much
before.
You might actually want to do a search through the archives.
Just take 5volts and divide by 20mA and you should get a resistor value.
That's the best I can remember!
Original Message
From: "ikenniemandanders" <tld-nv@s...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, July 08, 2004 1:50 AM
Subject: [noparse][[/noparse]basicstamps] Pressure sensor 4-20mA
> Hi guys & girls,
>
> I am working on a HVAC project. I have to read in an 4-20mA pressure
> sensor (between -0,5 and 7 BAR brand DIXELL). I've searched a lot on
> internet and didn't find a proper solution to connect this sensor to
> my BS2P-24. I've already made an easy circuit wich contains an 12BIT
> ADC and a resistor (150ohms) so I can get max 3V over my adc inputs.
> When I read the ADC in, I get VERY different values. My power supply
> is extremly stable (checked with an oscilloscope). Is there
> somebody who has created a simular project and could give me a
> better way to connect the pressure sensor with my stamp?
>
> Kindly regards
> Tim
> Belgium
> Student ICT
>
>
>
>
> 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.
>
> Yahoo! Groups Links
>
>
>
>
>
volt is easy.....
Typically, you would use a precision 250 ohm resistor for that conversion.
You convert the 4-20 ma to voltage 1 - 5vdc be inserting a resistor from the
sensor output signal back to ground (single ended inputs on the adc).
Why does it start at 4 ma or 1 volt? Sensor error / Wiring detection.
Here is an ASCII schematic.... Hope it comes out well.
Sensor Power source ----> Sensor --- Sensor Output
> 250
ohm|
> ADC + Input
|
|
Ground
>ADC - Input
Hard to tell, but the resistor is mounted "between" sensor output and
ground.
Remember to subtract 1 volt when you do your scaling for zero since you
start at 4ma / 1 volt for a zero reading or whatever the lower scale point
is of the sensor.
One other note, 250 ohm resisters can be hard to find or expensive. Use 249
ohms and compensate in software or use a couple of 120 ohms with a 10ohm in
series, or a couple of 500 ohms in parallel. it's your preference.
"If" anyone has a good source for reasonably priced 250 ohm resistors let me
know please. $2.00 a peice is not reasonable for me.
Richard
Original Message
From: "SB" <steve.brady@r...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, July 08, 2004 5:50 AM
Subject: Re: [noparse][[/noparse]basicstamps] Pressure sensor 4-20mA
> I'm unsure of hte coding sequence of these guys unless they're an analog
> measurement.
>
> But, since the stamp likes things in 5V, you might want to just throw a
> resistor across that guy there. I know I've heard someone say as much
> before.
> You might actually want to do a search through the archives.
>
> Just take 5volts and divide by 20mA and you should get a resistor value.
> That's the best I can remember!
>
>
>
Original Message
> From: "ikenniemandanders" <tld-nv@s...>
> To: <basicstamps@yahoogroups.com>
> Sent: Thursday, July 08, 2004 1:50 AM
> Subject: [noparse][[/noparse]basicstamps] Pressure sensor 4-20mA
>
>
> > Hi guys & girls,
> >
> > I am working on a HVAC project. I have to read in an 4-20mA pressure
> > sensor (between -0,5 and 7 BAR brand DIXELL). I've searched a lot on
> > internet and didn't find a proper solution to connect this sensor to
> > my BS2P-24. I've already made an easy circuit wich contains an 12BIT
> > ADC and a resistor (150ohms) so I can get max 3V over my adc inputs.
> > When I read the ADC in, I get VERY different values. My power supply
> > is extremly stable (checked with an oscilloscope). Is there
> > somebody who has created a simular project and could give me a
> > better way to connect the pressure sensor with my stamp?
> >
> > Kindly regards
> > Tim
> > Belgium
> > Student ICT
> >
> >
> >
> >
> > 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.
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
>
>
>
> 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.
>
> Yahoo! Groups Links
>
>
>
>
>
>
> [noparse][[/noparse]Scanned by AwesomeNet Anti-Virus]
>
>
should see 0.6 v for your low end and 3v for you high end. You have to
subtract the initial .6v from your readings.
4ma * 150 = 0.6 v 20ma * 150 = 3 v then 3v - 0.6v = 2.4 volts total
range
Original Message
From: "SB" <steve.brady@r...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, July 08, 2004 5:50 AM
Subject: Re: [noparse][[/noparse]basicstamps] Pressure sensor 4-20mA
> I'm unsure of hte coding sequence of these guys unless they're an analog
> measurement.
>
> But, since the stamp likes things in 5V, you might want to just throw a
> resistor across that guy there. I know I've heard someone say as much
> before.
> You might actually want to do a search through the archives.
>
> Just take 5volts and divide by 20mA and you should get a resistor value.
> That's the best I can remember!
>
>
>
Original Message
> From: "ikenniemandanders" <tld-nv@s...>
> To: <basicstamps@yahoogroups.com>
> Sent: Thursday, July 08, 2004 1:50 AM
> Subject: [noparse][[/noparse]basicstamps] Pressure sensor 4-20mA
>
>
> > Hi guys & girls,
> >
> > I am working on a HVAC project. I have to read in an 4-20mA pressure
> > sensor (between -0,5 and 7 BAR brand DIXELL). I've searched a lot on
> > internet and didn't find a proper solution to connect this sensor to
> > my BS2P-24. I've already made an easy circuit wich contains an 12BIT
> > ADC and a resistor (150ohms) so I can get max 3V over my adc inputs.
> > When I read the ADC in, I get VERY different values. My power supply
> > is extremly stable (checked with an oscilloscope). Is there
> > somebody who has created a simular project and could give me a
> > better way to connect the pressure sensor with my stamp?
> >
> > Kindly regards
> > Tim
> > Belgium
> > Student ICT
> >
> >
> >
> >
> > 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.
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
>
>
>
> 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.
>
> Yahoo! Groups Links
>
>
>
>
>
>
> [noparse][[/noparse]Scanned by AwesomeNet Anti-Virus]
>
>
4-20 MA IS A FAIL-SAFE FEATURE. IF YOU HAVE A BROKEN CONNECTION YOU GET
O WHICH IS A FAULT CONDITION.
YOU SCALE YOUR READING TO 4 MA = O AND 20 MA = FULL SCALL SO IF A DEVICE
WAS 4-20 MA AND 150 VDC, THEN 4 MA WOULD BE 0 VDC AND 20 MA WOULD BE 150VDC.
73
SPENCE
K4KEP
essage: 24
Date: Thu, 8 Jul 2004 06:45:34 -0500
From: "Richard" <rwskinner@a...>
Subject: Re: Pressure sensor 4-20mA
I did "not" look at the particular sensor you mention, but 4-20 ma to 1-5
volt is easy.....
Typically, you would use a precision 250 ohm resistor for that conversion.
You convert the 4-20 ma to voltage 1 - 5vdc be inserting a resistor from the
sensor output signal back to ground (single ended inputs on the adc).
Why does it start at 4 ma or 1 volt? Sensor error / Wiring detection.
Here is an ASCII schematic.... Hope it comes out well.
Sensor Power source ----> Sensor --- Sensor Output
> 250
ohm|
> ADC + Input
|
|
Ground
>ADC - Input
Hard to tell, but the resistor is mounted "between" sensor output and
ground.
Remember to subtract 1 volt when you do your scaling for zero since you
start at 4ma / 1 volt for a zero reading or whatever the lower scale point
is of the sensor.
One other note, 250 ohm resisters can be hard to find or expensive. Use 249
ohms and compensate in software or use a couple of 120 ohms with a 10ohm in
series, or a couple of 500 ohms in parallel. it's your preference.
"If" anyone has a good source for reasonably priced 250 ohm resistors let me
know please. $2.00 a peice is not reasonable for me.
Richard
Original Message
From: "SB" <steve.brady@r...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, July 08, 2004 5:50 AM
Subject: Re: [noparse][[/noparse]basicstamps] Pressure sensor 4-20mA
>> I'm unsure of hte coding sequence of these guys unless they're an analog
>> measurement.
>>
>> But, since the stamp likes things in 5V, you might want to just throw a
>> resistor across that guy there. I know I've heard someone say as much
>> before.
>> You might actually want to do a search through the archives.
>>
>> Just take 5volts and divide by 20mA and you should get a resistor value.
>> That's the best I can remember!
>>
>>
>>
Original Message
>> From: "ikenniemandanders" <tld-nv@s...>
>> To: <basicstamps@yahoogroups.com>
>> Sent: Thursday, July 08, 2004 1:50 AM
>> Subject: [noparse][[/noparse]basicstamps] Pressure sensor 4-20mA
>>
>>
>
>>> > Hi guys & girls,
>>> >
>>> > I am working on a HVAC project. I have to read in an 4-20mA pressure
>>> > sensor (between -0,5 and 7 BAR brand DIXELL). I've searched a lot on
>>> > internet and didn't find a proper solution to connect this sensor to
>>> > my BS2P-24. I've already made an easy circuit wich contains an 12BIT
>>> > ADC and a resistor (150ohms) so I can get max 3V over my adc inputs.
>>> > When I read the ADC in, I get VERY different values. My power supply
>>> > is extremly stable (checked with an oscilloscope). Is there
>>> > somebody who has created a simular project and could give me a
>>> > better way to connect the pressure sensor with my stamp?
>>> >
>>> > Kindly regards
>>> > Tim
>>> > Belgium
>>> > Student ICT
>>> >
>>> >
>>> >
>>> >
>>> > 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.
>
>>> >
>>> > Yahoo! Groups Links
>>> >
>>> >
>>> >
>>> >
>>> >
>
>>
>>
>>
>> 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.
>>
>> Yahoo! Groups Links
>>
>>
>>
>>
>>
>>
>> [noparse][[/noparse]Scanned by AwesomeNet Anti-Virus]
>>
>>
wrote:
> Hi guys & girls,
>
> I am working on a HVAC project. I have to read in an 4-20mA
pressure
> sensor (between -0,5 and 7 BAR brand DIXELL). I've searched a lot
on
> internet and didn't find a proper solution to connect this sensor
to
> my BS2P-24. I've already made an easy circuit wich contains an
12BIT
> ADC and a resistor (150ohms) so I can get max 3V over my adc
inputs.
> When I read the ADC in, I get VERY different values. My power
supply
> is extremly stable (checked with an oscilloscope). Is there
> somebody who has created a simular project and could give me a
> better way to connect the pressure sensor with my stamp?
>
> Kindly regards
> Tim
> Belgium
> Student ICT
Hi Tim,
with a high pressure, (75 to 100 psi) I assume you might be using
this on a refrigeration compressor ?
In that event, the compressor will generate pulsations that would
make the needle shake on a meter. I have a collection of meters
needles that have fallen off.
A Bourdon Tube meter will have a small capacity and mechanical
resistances so will not reveal the high speed noise that electronics
will. Think mA meter vs. O-Scope.
Determine the time domain you need for a reading and add some filter
that will keep your reading accurate in that time.
Considder a highest reading or lowest reading, or averaging filter.
And, considder all three. A mechanical pulse eleminator as well as a
hardware filter and software filter.
As far as resistors go, don't worry about expensive precision
resistors as you have already lost the lower 20% of the scale by
converting from 4-20mA. (and as SPENCE poiunted out, gained a broken
wire failure mode)
The resistors will just be for scaling to your 3 volts. Calibraton
can be in software and not hardware. Also, if you add a pot for
adjustment, you just wiped out the benifit of a precision resistor.
Other problems for very noisy ADC input signals are things like a
fluxuatoing power supply on the ADC. Use a Scope and see how steady
the power supply is.
Add a small capacitor on the ADC inputs to ground. This will help to
remove some of the noise. add an R/C filter of larger values to
reduce noise.
Possibly add filter caps on the powr to the devices that are
switching.
And, test a seperate value. create a 12mA signal at the pressure
device and connect that to the wires instead of the pressure device.
if a steady state signal is still noisy, then look for the problem in
the board.
Dave
wrote:
> Dave, how do i determine my capacitor values? Could you be so kind
> to draw the schematic with ADC convertor? I have no idea how to
> connect the capacitor with m
and a bottle of R22 or 404 (it doesn't mather) so a very variable
pressure is not possible. Perhaps i'm not using a very good ADC
(texas instr). I might be able to compensate the fluctuating values
by using a FIFO register with for example ten values, then divide
the sum of the values trough ten so I get an probiately stable value.
I've already changed my DIXELL sensor by an DANFOSS sensor because
the sensor i'm using goes only to -0.5BAR and I must be able to
measure total vacuum for my project.
Greets,
Tim
--- In basicstamps@yahoogroups.com, "Dave Mucha" <davemucha@j...>
wrote:
> --- In basicstamps@yahoogroups.com, "ikenniemandanders" <tld-
nv@s...>
> wrote:
> > Dave, how do i determine my capacitor values? Could you be so
kind
> > to draw the schematic with ADC convertor? I have no idea how to
> > connect the capacitor with m
stable value because the DIXELL and ELIWELL regulators (on doorpanel
mounting modules wich regulates the evaporator fan and reads in the
temperature sensors.
--- In basicstamps@yahoogroups.com, "ikenniemandanders" <tld-
nv@s...> wrote:
> I'm just testing my program with a manometer, the pressure sensor
> and a bottle of R22 or 404 (it doesn't mather) so a very variable
> pressure is not possible. Perhaps i'm not using a very good ADC
> (texas instr). I might be able to compensate the fluctuating
values
> by using a FIFO register with for example ten values, then divide
> the sum of the values trough ten so I get an probiately stable
value.
> I've already changed my DIXELL sensor by an DANFOSS sensor because
> the sensor i'm using goes only to -0.5BAR and I must be able to
> measure total vacuum for my project.
>
> Greets,
>
>
> Tim
>
>
> --- In basicstamps@yahoogroups.com, "Dave Mucha" <davemucha@j...>
> wrote:
> > --- In basicstamps@yahoogroups.com, "ikenniemandanders" <tld-
> nv@s...>
> > wrote:
> > > Dave, how do i determine my capacitor values? Could you be so
> kind
> > > to draw the schematic with ADC convertor? I have no idea how
to
> > > connect the capacitor with m
I often connect 4-20ma instruments to an ADC and Stamp, tensiometers
that monitor soil moisture suction in -90 to +20 kPa range. Here is
a URL:
http://www.emesystems.com/OWL2face.htm#4-20%20ma
Be sure you have the grounds connected properly. Take Dave's
suggestion and look at what you read on a multimeter connected in
parallel with your 150 ohm termination resistor. If that is steady,
with little AC component, then the Stamp reading should be steady too.
-- Tracy
>I am working on a HVAC project. I have to read in an 4-20mA pressure
>sensor (between -0,5 and 7 BAR brand DIXELL). I've searched a lot on
>internet and didn't find a proper solution to connect this sensor to
>my BS2P-24. I've already made an easy circuit wich contains an 12BIT
>ADC and a resistor (150ohms) so I can get max 3V over my adc inputs.
>When I read the ADC in, I get VERY different values. My power supply
>is extremly stabled (checked with an oscilloscope). Is there
>somebody who has created a simular project and could give me a
>better way to connect the pressure sensor with my stamp?
>I'm just testing my program with a manometer, the pressure sensor
>and a bottle of R22 or 404 (it doesn't mather) so a very variable
>pressure is not possible. Perhaps i'm not using a very good ADC
>(texas instr). I might be able to compensate the fluctuating values
>by using a FIFO register with for example ten values, then divide
>the sum of the values trough ten so I get an probiately stable value.
>I've already changed my DIXELL sensor by an DANFOSS sensor because
>the sensor i'm using goes only to -0.5BAR and I must be able to
>measure total vacuum for my project.
>
>Greets,
>
>
>Tim
>
>
>--- In basicstamps@yahoogroups.com, "Dave Mucha" <davemucha@j...>
>wrote:snip
>
> > From your first post, your readings were extreem. If you had a
>> little bouncing it would be easier to pin down a cause.
>>
>> What type of thing are you reading ? are you reading water
>> pressure ? air conditioning pressure ?
>> The process you are reading may offer more clues. Water pressure
>> would remain faily constant while Freon pressure in an air
>> conditioner system would be very noisy.
>>
> > Dave
>
wrote:
> I'm just testing my program with a manometer, the pressure sensor
> and a bottle of R22 or 404 (it doesn't mather) so a very variable
> pressure is not possible. Perhaps i'm not using a very good ADC
> (texas instr). I might be able to compensate the fluctuating values
> by using a FIFO register with for example ten values, then divide
> the sum of the values trough ten so I get an probiately stable
value.
> I've already changed my DIXELL sensor by an DANFOSS sensor because
> the sensor i'm using goes only to -0.5BAR and I must be able to
> measure total vacuum for my project.
>
> Greets,
>
>
> Tim
Hi Tim,
If you expect the pressure to be constant and it varies wildly, it
may be a sensor location. it may be a poor connection or many other
things. It may even be a bad chip.
put a small, 0.1 or 0.01uF cap to ground from your input line. See if
that helps.
try a 10k resistor on the input line and a 0.01uF after that to
ground and see if what that does.
Ther are a few software filters, but they are not always the best way
to handle noise. but are usually very easy.
The one I use is to read the input
add the input to a variable.
divide the variable by some value, say 10. This is the average.
then subtract that result from the variable.
it will keep the average rolling and allow the value to respond to
your inputs.
a second duplicate filter could take the result of the divide by ten
as the input. add that to a second variable, divide that by 10 and
then subtract that average from the variable. that winds up being
second filter that will smooth the readings even more.
If you find that adding the values to a total of 10 will exceed the
memory for a variable, you can subtract a constant from each input,
then add it back to the result to get the number.
Dave
high pressure equipment all the time, however we always install a small
orifice (Pressure Dampner) before the sensor. There are many sensor
manufacturers that already supply these in the sensor if you specify it.
They can be bought for under a buck.
It really smooths out the pulsation spikes. Example, a vacuum gauge on an
engine has a pulse for each time a cylinder makes it thru it's cycle.
Without the dampner installed, the needle or readings would be pretty crazy.
With the dampner, they are nice and steady. In this application, most
gauges you buy off the shelf already have it installed.
Also, I just had the same problem as your mentioning a few weeks ago and it
happened to be my grounding. I missed a wire and had an incomplete STAR
ground. My readings were all over the place. Easy to do when playing with
multiple supplies.
We use Danfoss sensors all the time so I know it probably isn't a sensor
problem.
Good Luck,
Richard
Original Message
From: "Dave Mucha" <davemucha@j...>
To: <basicstamps@yahoogroups.com>
Sent: Friday, July 09, 2004 8:33 AM
Subject: [noparse][[/noparse]basicstamps] Re: Pressure sensor 4-20mA
> --- In basicstamps@yahoogroups.com, "ikenniemandanders" <tld-nv@s...>
> wrote:
> > Hi guys & girls,
> >
> > I am working on a HVAC project. I have to read in an 4-20mA
> pressure
> > sensor (between -0,5 and 7 BAR brand DIXELL). I've searched a lot
> on
> > internet and didn't find a proper solution to connect this sensor
> to
> > my BS2P-24. I've already made an easy circuit wich contains an
> 12BIT
> > ADC and a resistor (150ohms) so I can get max 3V over my adc
> inputs.
> > When I read the ADC in, I get VERY different values. My power
> supply
> > is extremly stable (checked with an oscilloscope). Is there
> > somebody who has created a simular project and could give me a
> > better way to connect the pressure sensor with my stamp?
> >
> > Kindly regards
> > Tim
> > Belgium
> > Student ICT
>
>
> Hi Tim,
>
> with a high pressure, (75 to 100 psi) I assume you might be using
> this on a refrigeration compressor ?
>
> In that event, the compressor will generate pulsations that would
> make the needle shake on a meter. I have a collection of meters
> needles that have fallen off.
>
> A Bourdon Tube meter will have a small capacity and mechanical
> resistances so will not reveal the high speed noise that electronics
> will. Think mA meter vs. O-Scope.
>
> Determine the time domain you need for a reading and add some filter
> that will keep your reading accurate in that time.
>
> Considder a highest reading or lowest reading, or averaging filter.
> And, considder all three. A mechanical pulse eleminator as well as a
> hardware filter and software filter.
>
> As far as resistors go, don't worry about expensive precision
> resistors as you have already lost the lower 20% of the scale by
> converting from 4-20mA. (and as SPENCE poiunted out, gained a broken
> wire failure mode)
>
> The resistors will just be for scaling to your 3 volts. Calibraton
> can be in software and not hardware. Also, if you add a pot for
> adjustment, you just wiped out the benifit of a precision resistor.
>
> Other problems for very noisy ADC input signals are things like a
> fluxuatoing power supply on the ADC. Use a Scope and see how steady
> the power supply is.
>
> Add a small capacitor on the ADC inputs to ground. This will help to
> remove some of the noise. add an R/C filter of larger values to
> reduce noise.
>
> Possibly add filter caps on the powr to the devices that are
> switching.
>
> And, test a seperate value. create a 12mA signal at the pressure
> device and connect that to the wires instead of the pressure device.
> if a steady state signal is still noisy, then look for the problem in
> the board.
>
> Dave
>
>
>
>
> 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.
>
> Yahoo! Groups Links
>
>
>
>
>
>
> [noparse][[/noparse]Scanned by AwesomeNet Anti-Virus]
>
>
<rwskinner@a...> wrote:
> Also, something to mention. We use pressure transmitters /
transducers on
> high pressure equipment all the time, however we always install a
small
> orifice (Pressure Dampner) before the sensor. There are many sensor
> manufacturers that already supply these in the sensor if you
specify it.
> They can be bought for under a buck.
> > And, considder all three.
> > A mechanical pulse eleminator as well as a
> > hardware filter and software filter.
This is what I meant by a mechanical filter. A not here is that the
snubber you mention can be had in a few varieties. one is actually
an isolation diaphram (diaphram seal), another a small hole or
orifice.
The farther away from the transmitter, the greater the capacity in
the tubing between the snubber and the transmitter. This should also
decrease the noise. And, you can use multiple units to get even more
filtering. (anyone here thinking, tiny orfice = resistor and large
capacity = capacitor ?)
Dave
dave and richard). I installed an orifice (i'm in the refrigeration
branche so i have some orifices in my possesion (I used the smallest
hole). My pressure value comes in real stable so it works. I tested
it with an 2x16 lcd display and i'm now able to see de pressure in
bars en millibars on the screen. One important part of my project is
finished. You're wright about the vacuumpump noise because the value
became very unstable buth with an orifice it stabled a lot.
Kindly regards,
Tim
student ICT @ Belgium
--- In basicstamps@yahoogroups.com, "Dave Mucha" <davemucha@j...>
wrote:
> --- In basicstamps@yahoogroups.com, "Richard Skinner"
> <rwskinner@a...> wrote:
> > Also, something to mention. We use pressure transmitters /
> transducers on
> > high pressure equipment all the time, however we always install
a
> small
> > orifice (Pressure Dampner) before the sensor. There are many
sensor
> > manufacturers that already supply these in the sensor if you
> specify it.
> > They can be bought for under a buck.
>
>
> > > And, considder all three.
> > > A mechanical pulse eleminator as well as a
> > > hardware filter and software filter.
>
>
> This is what I meant by a mechanical filter. A not here is that
the
> snubber you mention can be had in a few varieties. one is
actually
> an isolation diaphram (diaphram seal), another a small hole or
> orifice.
>
> The farther away from the transmitter, the greater the capacity in
> the tubing between the snubber and the transmitter. This should
also
> decrease the noise. And, you can use multiple units to get even
more
> filtering. (anyone here thinking, tiny orfice = resistor and
large
> capacity = capacitor ?)
>
> Dave
I guess AC Orifices come that small but smallest ac orifice I had laying
around was a 0.025.
Glad you got it going.
Richard
Original Message
From: "ikenniemandanders" <tld-nv@s...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, July 12, 2004 1:11 PM
Subject: [noparse][[/noparse]basicstamps] Re: Pressure sensor 4-20mA
> Thanks to anyone who has provided me usefull information (allen,
> dave and richard). I installed an orifice (i'm in the refrigeration
> branche so i have some orifices in my possesion (I used the smallest
> hole). My pressure value comes in real stable so it works. I tested
> it with an 2x16 lcd display and i'm now able to see de pressure in
> bars en millibars on the screen. One important part of my project is
> finished. You're wright about the vacuumpump noise because the value
> became very unstable buth with an orifice it stabled a lot.
>
>
> Kindly regards,
>
>
> Tim
> student ICT @ Belgium
>
>
>
>
>
> --- In basicstamps@yahoogroups.com, "Dave Mucha" <davemucha@j...>
> wrote:
> > --- In basicstamps@yahoogroups.com, "Richard Skinner"
> > <rwskinner@a...> wrote:
> > > Also, something to mention. We use pressure transmitters /
> > transducers on
> > > high pressure equipment all the time, however we always install
> a
> > small
> > > orifice (Pressure Dampner) before the sensor. There are many
> sensor
> > > manufacturers that already supply these in the sensor if you
> > specify it.
> > > They can be bought for under a buck.
> >
> >
> > > > And, considder all three.
> > > > A mechanical pulse eleminator as well as a
> > > > hardware filter and software filter.
> >
> >
> > This is what I meant by a mechanical filter. A not here is that
> the
> > snubber you mention can be had in a few varieties. one is
> actually
> > an isolation diaphram (diaphram seal), another a small hole or
> > orifice.
> >
> > The farther away from the transmitter, the greater the capacity in
> > the tubing between the snubber and the transmitter. This should
> also
> > decrease the noise. And, you can use multiple units to get even
> more
> > filtering. (anyone here thinking, tiny orfice = resistor and
> large
> > capacity = capacitor ?)
> >
> > Dave
>
>
>
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I got in on this thread kind of late, so please excuse me if this has
already been covered. If you are measuring pressure from a pump or
something which is a pulsating device, I would say you should buffer the
pulses by running the pressure output into an integrating vessel of some
sort. For high pressure (few hundred PSI) you could use a length of pipe.
This would smooth out the pulsations. If this isn't enough, go to a larger
buffer volume, and/or add a simple RC electronic filter to the input of
your ADC.
steve
wrote:
>
> >But, you do need to figure out why the value swings.
>
> I got in on this thread kind of late, so please excuse me if this
has
> already been covered. If you are measuring pressure from a pump or
> something which is a pulsating device, I would say you should
buffer the
> pulses by running the pressure output into an integrating vessel of
some
> sort. For high pressure (few hundred PSI) you could use a length of
pipe.
> This would smooth out the pulsations. If this isn't enough, go to a
larger
> buffer volume, and/or add a simple RC electronic filter to the
input of
> your ADC.
> steve
Since pressure travels at the speed of sound, there are certain
mechanical problems to be aware of.
One is the capacitance of the sensor. if there is little or no
capacitance, it will respond with little delay to the to signal.
Also if there is no mechanical resistance aka hysteresis or sticktion
then the reading will closely follow the actual pressure.
In refrigeration, they have capillary tubing and a foot or so of that
will dampen quite a lot of the pulsing. having a capacity tank after
that tubing and before the sensor will do even more.
But, having a stabile input is MUCH better than trying to filter the
noise once it is in the electronics.
Dave