measuring nanoamps with lots of noise

rote:

state relay.

also an output for a regular relay. If so you could switch to a regular re lay and DC for the heating power. Add an one shot and a and circuit so the temp reading can only occur with the heater either on or off , but not wh en the relay is changing state.

That's a good approach. I'd bet the worst noise is zero-crossings in the solid state relay, and you laid out a nice test for that.

The ultimate noise elimination test would be to power the thing with variable DC, such as a rectifier / filter and a variac. That eliminates both potential PID controller noise, and the SSR.

Once electromagnetic interference is reduced as far as possible, shielding might be considered. This reference suggests 310 stainless as suitable for oxidizing atmospheres up to 1,100C.

IIRC it's available as foil, used to wrap parts when heat-treating steel.

Cheers, James Arthur

id state relay.

d also an output for a regular relay. If so you could switch to a regular relay and DC for the heating power. Add an one shot and a and circuit so t he temp reading can only occur with the heater either on or off , but not when the relay is changing state.

tech_brief.pdf

My mistake, the foil is 309 SS, not 310. Rated to 1,200C by this vendor:

Cheers, James Arthur

On Sunday, October 25, 2015 at 1:46:40 PM UTC-4, snipped-for-privacy@gmail.com wrote :

rote:

if anyone could help. This is a project where I have to measure current g enerated by a sample at high temperature inside a furnace. The current is in the picoamp-nanoamp range depending on temperature and I have been using a Keithley picoammeter. The furnace is controlled by a PID temp controlle r connected to a solid state relay. When the relay is off I can get data w ith no issues but when the relay is on there is lots of noise and I cannot get good data. Unfortunately, the high temperature environment makes it di fficult to shield the sample without going to exotic materials like platinu m foil. Is it possible to measure picoamps-nanoamps in the presence of lot s of noise by using some kind of instrumentation amplifier or something wit h very good common mode rejection ratio?

any traditional materials. Basically I have to use platinum wires to conne ct to the sample. Nobody that I know makes a high temp coax that goes to 1

second would be fine.

nace. All the noise goes away and I can get continuous data with no proble m. But that is not a good long term solution since I will need to record d ata over multiple ramp/dwell/cool cycles which is why I am looking for a be tter solution.

tive and same goes for a DC power supply. My furnace runs off 120 V at 14 amps. However, I did find a line filter at the local surplus electronics s tore but I haven't tried it yet.

IVC102 which does this but I am sure there are other solutions as well. Ha s anyone used this IC? Are there other IC's or solutions that someone coul d recommend? I will be honest, my electronics skills are amateur but I hav e breadboarded a few things in my time.

Can you look at the noise/ interference on a 'scope? (or are the signals too small?) If you knew it was 60 Hz, or a switching transient or something else then that would help.

George H.

te:

ng if anyone could help. This is a project where I have to measure current generated by a sample at high temperature inside a furnace. The current i s in the picoamp-nanoamp range depending on temperature and I have been usi ng a Keithley picoammeter. The furnace is controlled by a PID temp control ler connected to a solid state relay. When the relay is off I can get data with no issues but when the relay is on there is lots of noise and I canno t get good data. Unfortunately, the high temperature environment makes it difficult to shield the sample without going to exotic materials like plati num foil. Is it possible to measure picoamps-nanoamps in the presence of l ots of noise by using some kind of instrumentation amplifier or something w ith very good common mode rejection ratio?

many traditional materials. Basically I have to use platinum wires to con nect to the sample. Nobody that I know makes a high temp coax that goes to 1050 C which is why I have virtually no shielding.

r second would be fine.

urnace. All the noise goes away and I can get continuous data with no prob lem. But that is not a good long term solution since I will need to record data over multiple ramp/dwell/cool cycles which is why I am looking for a better solution.

bitive and same goes for a DC power supply. My furnace runs off 120 V at 1

e IVC102 which does this but I am sure there are other solutions as well. Has anyone used this IC? Are there other IC's or solutions that someone co uld recommend? I will be honest, my electronics skills are amateur but I h ave breadboarded a few things in my time.

If it were a zero-crossing SSR, integrating over an integer number of line cycles would help a lot, theoretically. (Avoids the problem of the PID switching asynchronously to the integration interval.)

Cheers, James

To invoke filtering of any sort, you'd have to know that the current source is constant or linear on voltage. If it is a semiconductor sort of thing, it will rectify the noise and mess up the average current measurement.

rote:

ring if anyone could help. This is a project where I have to measure curre nt generated by a sample at high temperature inside a furnace. The current is in the picoamp-nanoamp range depending on temperature and I have been u sing a Keithley picoammeter. The furnace is controlled by a PID temp contr oller connected to a solid state relay. When the relay is off I can get da ta with no issues but when the relay is on there is lots of noise and I can not get good data. Unfortunately, the high temperature environment makes i t difficult to shield the sample without going to exotic materials like pla tinum foil. Is it possible to measure picoamps-nanoamps in the presence of lots of noise by using some kind of instrumentation amplifier or something with very good common mode rejection ratio?

ut many traditional materials. Basically I have to use platinum wires to c onnect to the sample. Nobody that I know makes a high temp coax that goes to 1050 C which is why I have virtually no shielding.

per second would be fine.

furnace. All the noise goes away and I can get continuous data with no pr oblem. But that is not a good long term solution since I will need to reco rd data over multiple ramp/dwell/cool cycles which is why I am looking for a better solution.

hibitive and same goes for a DC power supply. My furnace runs off 120 V at 14 amps. However, I did find a line filter at the local surplus electroni cs store but I haven't tried it yet.

the IVC102 which does this but I am sure there are other solutions as well. Has anyone used this IC? Are there other IC's or solutions that someone could recommend? I will be honest, my electronics skills are amateur but I have breadboarded a few things in my time.

Yup, It's hard to know. Noise/interference (as you know) is like an onion, you can think about all these sources. But practically you need to know which is on the outside layer.

George H.

Another candidate is Inconel (600, 601, 625...); chrome-nickel 'superalloys' that stays intact to 1900C

ering if anyone could help. This is a project where I have to measure curr ent generated by a sample at high temperature inside a furnace. The curren t is in the picoamp-nanoamp range depending on temperature and I have been using a Keithley picoammeter. The furnace is controlled by a PID temp cont roller connected to a solid state relay. When the relay is off I can get d ata with no issues but when the relay is on there is lots of noise and I ca nnot get good data. Unfortunately, the high temperature environment makes it difficult to shield the sample without going to exotic materials like pl atinum foil. Is it possible to measure picoamps-nanoamps in the presence o f lots of noise by using some kind of instrumentation amplifier or somethin g with very good common mode rejection ratio?

s:

out many traditional materials. Basically I have to use platinum wires to connect to the sample. Nobody that I know makes a high temp coax that goes to 1050 C which is why I have virtually no shielding.

per second would be fine.

e furnace. All the noise goes away and I can get continuous data with no p roblem. But that is not a good long term solution since I will need to rec ord data over multiple ramp/dwell/cool cycles which is why I am looking for a better solution.

ohibitive and same goes for a DC power supply. My furnace runs off 120 V a t 14 amps. However, I did find a line filter at the local surplus electron ics store but I haven't tried it yet.

the IVC102 which does this but I am sure there are other solutions as well . Has anyone used this IC? Are there other IC's or solutions that someone could recommend? I will be honest, my electronics skills are amateur but I have breadboarded a few things in my time.

You're right, I'd assumed the EMI wasn't interacting with the signal source .

The furnace itself is typically a brick-lined steel box, which you'd think would be pretty good first-order shielding from the outside world.

With these high impedances, capacitive-coupling from the heating element co uld be serious; an electrostatic shield could fix that.

The easy solution is just to turn the thing off for the one-second measurem ent interval. The thermal time constant is so much longer that 1s shouldn't ma ke a nit's difference to temperature control.

Cheers, James

Online Metals has some for only $120/ft^2 (!)

(Earlier this year I passed on what must have been 150lbs of Inconel for $5/lb--I had no way to melt it!)

Cheers, James Arthur

No, no, that's too easy.