4

Latetly we recognized a parasitic signal in our voltage measurements. It is a perfect sine wave with a period of a few hours (f = uHz). What could be the origin of such a signals?

Ok, a few more details:

We do Hall-Effect measurements in a cryostat. The temperature is held constant at a few hundred mili Kelvin. We use a standart six terminal measurement to obtain the hall resistance and the magnetoresistance. We use standart lock-in amplifiers at a detection frequency of ca 22 Hz to measure the voltage along and transverse the current path through the sample.

P3trus
  • 397
  • 1
  • 3
  • 11
  • 1
    How about you tell us the signal size and actual frequency. Also how you are measuring it. – Andy aka Dec 02 '13 at 11:28
  • 1
    Also, what is your measurement frequency? If it is very close to 50 or 60 Hz there is potential for aliasing, though aliasing with AC mains is unlikely to resemble a pure frequency! –  Dec 02 '13 at 11:50
  • Temperature is the usual culprit. Even though you are using a cryostat, do you have any wires connected from the outside? It could also be from light/windows or perhaps tidal forces if you are measuring something extremely sensitive (http://oceanservice.noaa.gov/education/kits/tides/media/supp_tide07a.html). – Justin Dec 02 '13 at 16:14
  • @justin No we are in a air conditioned lab. Temperature is quite stable, especially in the cryostat(< mK).. Also we don't see this behaviour in other cryostats in this lab measuring similar stuff. – P3trus Dec 02 '13 at 16:36
  • Is your temperature stable to less than a millikelvin (like you say in comments) or less than a few hundred millikelvin (like you say in the question)? Seeing effects from 100's of mK is not too suprising. – The Photon Dec 02 '13 at 17:04
  • @ThePhoton No the temperature is e.g. 100mK and oscillates around this value with less than a mK – P3trus Dec 02 '13 at 17:26
  • OK, then maybe look at all the parts of your system that aren't inside the cryostat. Probably your metering equipment, power supplies, etc., are not all in there being held at 100 mK. – The Photon Dec 02 '13 at 17:29
  • Plot the temperature of the parts outside the cryostat, and see how it correlates to the parasitic signal. – James Cameron Dec 03 '13 at 09:31

1 Answers1

6

Speculation: a temperature dependency of the voltage measurement instrument, the circuit, or the voltage source. Disprove the speculation by placing the system in a temperature controlled enclosure.

James Cameron
  • 1,286
  • 6
  • 12