Calibrating a temperature data logger

Discussion in 'General Electronics Chat' started by drbenne, Jan 5, 2014.

  1. drbenne

    Thread Starter Member

    Jul 30, 2013
    I have some temperature data loggers that may need some calibration and received a response from the manufacturer on calibration procedures. Basically, I need a little help in understanding the procedures and results of calibration.

    The procedure is as follows:
    Here is part of the spreadsheet of a sample logger that was calibrated:
    (not shown: ambient lab temperature was logged at 23.1 °C in cell b11)


    I guess my first questions are:

    1) If the ref voltage is 4096 mV, why are the calibration values represented as negative uV?

    2) When checking the ref voltage what does it mean by 'the analog circuits will be switched on permanently'?

    These are Eltek 1000 series squirrel loggers if anyone is familiar with them.


  2. wayneh


    Sep 9, 2010
    To make it extra confusing? My opinion is that changing the sign or the units - both of which are arbitrary choices - has no effect. Except to make one worry if they understand. Oh wait, maybe the unit change is as simple as the spreadsheet author or text author not knowing how to get the µ symbol into the sheet. Like how microfarads are usually given as mF on capacitors.

    Can't help you there. What's a squirrel logger? Sounds more fun than a temp logger! :p
  3. drbenne

    Thread Starter Member

    Jul 30, 2013
    haha, it's just the name of this particular series of loggers. They're manufactured in England... maybe they have fondness for squirrels or something?? :confused:

    I guess I should've worded that differently. I can understand the units.

    This is what I'm thinking:
    The ambient was recorded at 23.1 C which would correspond to 0 mV being fed into channels 1-16. The negative μV values are referenced to the initial ambient temp reading.

    I don't have the board in front of me right now, but I believe the 16 channels are divided into 4 separate multiplexers all being fed into a 12-bit ADC.

    2^12 = 4096 (hence the ref of 4096 mV)

    Does this sound about right and would 23 °C be a normal temperature to be calibrating most ADCs?
  4. eeabe


    Nov 30, 2013
    1) It sounds like the reference voltage is used for an analog to digital converter, and the calibration values are what you would measure on the SK1 header. If you adjust the pot to fine tune the 4.096V reference, you should see the output on SK1 change.

    2) I'm guessing it just means it will turn on the analog circuit power for you to do the calibration and troubleshooting, and then it will go back to normal operation when you cycle power. It's pretty normal for sensors to turn on and off during normal operation to take samples and save power, but in that normal mode it would be impossible to troubleshoot with a DC meter -- you'd need an oscilloscope.