LTC1298 Quirky Numbers - Successfully Resolved
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Hi Everyone:
Just a short note to let everyone know that I did solve the problem and to
thank you for your input on this matter. What we found was:
a. There was noise on the incoming pins to the A/D converter. We solved the
problem by using three tantalum capacitors: one between both leads, and one
between each lead and the 0V bus on our PC board
b. Found a cold solder joint on the incoming terminal strip. What can I say?
Prototyping has its moments.
Just for other information, the circuit was designed, prototyped, tested and
troubleshot at an electrical shop with a main 600V, three phase incoming
service so we have o'plenty of noise to deal with in the facility. The
circuit is going to be used in a similar environment with respect to
electrical noise and there is some 120VAC control inside the box so we spent
an extra week just noise proofing the circuit. I think for the final test
we'll actually run the box near a welder and if it can stand up to that kind
of localized EMI/RFI, then we know we have something here.
We also found the judicious use of shielded wiring and tantalum bypass
capacitors a must when working in this kind of environment. Kind of
interesting to see a 8 pin A/D converter surrounded by four tantalum caps.
We did a lot of scope work and interestingly enough we did not see a lot of
noise on the inputs. We used good quality digital scopes but I suspect that
if we really wanted to see the noise, then we should have also used an
analog scope as it may have shedded a brighter light on the problem. If so,
there is still a place for analog driven CRT equipment in this day and age.
Once again thank you all for your assistance and suggestions.
> Also note that unfiltered light dimmers, even from a house down the street
> on the same power line transformer, can cause these noise spikes at 120
> times a second. I used to have a noise problem that started every day in
the
> early evening, just as the sun was going down. My neighbor two houses away
> would turn on her lights in the dining room to about 50% dim, which I
could
> actually see on my o'scope. When she turned them to 100% there was no
noise,
> and on the weekends she didn't go in the dining room. Talk about some
> detective work to find the noise source.
>
> > Look at the intput to the LTC with an oscope. I would suspect that
there
> is
> > a motor in the building that is turning on and you are getting noise
from
> > it. Happens here. Also, we get the local AM radio station
sometimes<G>.
> > What is the timing between the bursts of noise? May be an indication.
Just a short note to let everyone know that I did solve the problem and to
thank you for your input on this matter. What we found was:
a. There was noise on the incoming pins to the A/D converter. We solved the
problem by using three tantalum capacitors: one between both leads, and one
between each lead and the 0V bus on our PC board
b. Found a cold solder joint on the incoming terminal strip. What can I say?
Prototyping has its moments.
Just for other information, the circuit was designed, prototyped, tested and
troubleshot at an electrical shop with a main 600V, three phase incoming
service so we have o'plenty of noise to deal with in the facility. The
circuit is going to be used in a similar environment with respect to
electrical noise and there is some 120VAC control inside the box so we spent
an extra week just noise proofing the circuit. I think for the final test
we'll actually run the box near a welder and if it can stand up to that kind
of localized EMI/RFI, then we know we have something here.
We also found the judicious use of shielded wiring and tantalum bypass
capacitors a must when working in this kind of environment. Kind of
interesting to see a 8 pin A/D converter surrounded by four tantalum caps.
We did a lot of scope work and interestingly enough we did not see a lot of
noise on the inputs. We used good quality digital scopes but I suspect that
if we really wanted to see the noise, then we should have also used an
analog scope as it may have shedded a brighter light on the problem. If so,
there is still a place for analog driven CRT equipment in this day and age.
Once again thank you all for your assistance and suggestions.
> Also note that unfiltered light dimmers, even from a house down the street
> on the same power line transformer, can cause these noise spikes at 120
> times a second. I used to have a noise problem that started every day in
the
> early evening, just as the sun was going down. My neighbor two houses away
> would turn on her lights in the dining room to about 50% dim, which I
could
> actually see on my o'scope. When she turned them to 100% there was no
noise,
> and on the weekends she didn't go in the dining room. Talk about some
> detective work to find the noise source.
>
> > Look at the intput to the LTC with an oscope. I would suspect that
there
> is
> > a motor in the building that is turning on and you are getting noise
from
> > it. Happens here. Also, we get the local AM radio station
sometimes<G>.
> > What is the timing between the bursts of noise? May be an indication.
Comments
1. Check the power supply Voltages.
2. Check every step along the circuit.
3. Verify with data sheets that the circuit was laid out correctly<G>.
Excellent!!
We use both digital and analog. The good thing about the digital is that it
will (ours anyway) save the last image on the screen. So if you have low
rep rate happenings, or it happens only once in a blue moon, you can capture
the event and see it bright as day.
Then again, digital scopes will like like a rug if you don't have them set
to the correct period.
Original Message
From: Gerry Shand/Corrinne Bergen [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=3iKBA3WTuNUN-pm80R_NdqNuMo0yPjpKb2Oa41jDr-E6DxD6SjnSgN0BVYWQ0nvD8hj-JKJQDCy0hw]res@i...[/url
Sent: Tuesday, May 25, 2004 10:49 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: LTC1298 Quirky Numbers - Successfully Resolved
Hi Everyone:
Just a short note to let everyone know that I did solve the problem and to
thank you for your input on this matter. What we found was:
a. There was noise on the incoming pins to the A/D converter. We solved the
problem by using three tantalum capacitors: one between both leads, and one
between each lead and the 0V bus on our PC board b. Found a cold solder
joint on the incoming terminal strip. What can I say? Prototyping has its
moments.
Just for other information, the circuit was designed, prototyped, tested and
troubleshot at an electrical shop with a main 600V, three phase incoming
service so we have o'plenty of noise to deal with in the facility. The
circuit is going to be used in a similar environment with respect to
electrical noise and there is some 120VAC control inside the box so we spent
an extra week just noise proofing the circuit. I think for the final test
we'll actually run the box near a welder and if it can stand up to that kind
of localized EMI/RFI, then we know we have something here.
We also found the judicious use of shielded wiring and tantalum bypass
capacitors a must when working in this kind of environment. Kind of
interesting to see a 8 pin A/D converter surrounded by four tantalum caps.
We did a lot of scope work and interestingly enough we did not see a lot of
noise on the inputs. We used good quality digital scopes but I suspect that
if we really wanted to see the noise, then we should have also used an
analog scope as it may have shedded a brighter light on the problem. If so,
there is still a place for analog driven CRT equipment in this day and age.
Once again thank you all for your assistance and suggestions.
> Also note that unfiltered light dimmers, even from a house down the
> street on the same power line transformer, can cause these noise
> spikes at 120 times a second. I used to have a noise problem that
> started every day in
the
> early evening, just as the sun was going down. My neighbor two houses
> away would turn on her lights in the dining room to about 50% dim,
> which I
could
> actually see on my o'scope. When she turned them to 100% there was no
noise,
> and on the weekends she didn't go in the dining room. Talk about some
> detective work to find the noise source.
>
> > Look at the intput to the LTC with an oscope. I would suspect that
there
> is
> > a motor in the building that is turning on and you are getting noise
from
> > it. Happens here. Also, we get the local AM radio station
sometimes<G>.
> > What is the timing between the bursts of noise? May be an
> > indication.
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