3
\$\begingroup\$

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.

\$\endgroup\$
8
  • 1
    \$\begingroup\$ How about you tell us the signal size and actual frequency. Also how you are measuring it. \$\endgroup\$
    – Andy aka
    Dec 2, 2013 at 11:28
  • \$\begingroup\$ 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! \$\endgroup\$
    – user_1818839
    Dec 2, 2013 at 11:50
  • \$\begingroup\$ 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 (oceanservice.noaa.gov/education/kits/tides/media/…). \$\endgroup\$
    – Justin
    Dec 2, 2013 at 16:14
  • \$\begingroup\$ @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. \$\endgroup\$
    – P3trus
    Dec 2, 2013 at 16:36
  • \$\begingroup\$ 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. \$\endgroup\$
    – The Photon
    Dec 2, 2013 at 17:04

1 Answer 1

Reset to default
6
\$\begingroup\$

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.

\$\endgroup\$
1
  • 3
    \$\begingroup\$ Or by deliberately manipulating the environment at a known rate. \$\endgroup\$
    – user_1818839
    Dec 2, 2013 at 11:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.