Electrical interference and shields/filters

[dullard]

I have a sensor (thermocouple) within an aluminum case that has some other electrical components (mostly resistive heaters and a DC power supply). Every few months, I can see a large amplitude 60 Hz noise on the thermocouple voltage. The noise lasts for a few hours and then it just instantly goes away.

I would like to reduce that noise as much as possible. But I know nothing about it.
1) Do you know of a good intro to topics like this? I would like to educate myself and answer questions such as these:

2) I assume since there is a 60 Hz noise, that it is related to the 60 Hz AC that we use. Is that a reasonable assumption?

3) Does the aluminum case (1/16" thickness) shield the inside from outside noise?

4) Would an AC filter like this have a chance of helping? Or should I try to further shield the thermocouple?

 

[Safeway]

Post in Highly Technical please. :beer:😀

 

[kranky]

Does this help?

 

[So]

Originally posted by: dullard
I have a sensor (thermocouple) within an aluminum case that has some other electrical components (mostly resistive heaters and a DC power supply). Every few months, I can see a large amplitude 60 Hz noise on the thermocouple voltage. The noise lasts for a few hours and then it just instantly goes away.

I would like to reduce that noise as much as possible. But I know nothing about it.
1) Do you know of a good intro to topics like this? I would like to educate myself and answer questions such as these:

2) I assume since there is a 60 Hz noise, that it is related to the 60 Hz AC that we use. Is that a reasonable assumption?

3) Does the aluminum case (1/16" thickness) shield the inside from outside noise?

4) Would an AC filter like this have a chance of helping? Or should I try to further shield the thermocouple?

1) This was the book I used
2) It is reasonable that it's coming somehow from the line, but you have to ask yourself how it's getting there.

3) The case should provide some shielding but any wires going in and out can become "antennas" for the interference. You need those cables to be properly grounded and filtered if you're really worried.

4) Having not done much practical stuff, just having taken a class, I can't say which is the "best" choice. It all depends on the layout of the box.

 

[dullard]

Originally posted by: kranky
Does this help?

That was pretty much the knowledge that I had. Yes, noise is getting in and yes, you can try to reduce it with shields. I just need more detail. Thanks though.

Originally posted by: So
1) This was the book I used
2) It is reasonable that it's coming somehow from the line, but you have to ask yourself how it's getting there.

3) The case should provide some shielding but any wires going in and out can become "antennas" for the interference. You need those cables to be properly grounded and filtered if you're really worried.

4) Having not done much practical stuff, just having taken a class, I can't say which is the "best" choice. It all depends on the layout of the box.

I'll look into that book. Thanks.

 

[hanoverphist]

wheres the power coming from? a lighting panel? is the AC on the same circuit as the sensor? if so, you need to separate those. control wiring should not share space with power wiring, too much noise brought in. isolate your ground, circuit and get a good, shielded cable for your sensor. there are many different Belden cables made for signal and sensors, using unshielded will give you headaches everytime. if it is a shielded cable, check the rating on it. we always use 600v rated shielded cable for our 4-20 and sensor wiring, just so we dont ahve to worry about it. mebbe this will help, mebbe it wont. pretty vague, but your info was also vague.

edit:

oh, and if youre seeing this the same time period every couple months, look what else is on that circuit and check whether it has a cycle it runs every so often. you may be getting feedback from a process that is supposed to be there.