Hi,

I have a DT80 datataker attached to several type T thermocouples. My issue is that at some points the thermocouple temperature "jumps". It jumps, then continues at the new temperature for a while, then there is another jump and so on. This occurs even when I am not interacting with my setup.
I have attached a graph showing two jumps, one at around 61 s the other at around 68 s. For reference the temperature should be 10 dC and doesn't change over time.
The problem with these jumps is that they are very inconsistent - the change is not the same for each thermocouple, sometimes there is an increase in temperature, sometimes a decrease.

A second question, which is related: the datataker clicks everytime it samples, however every now and then it does multiple clicks at once. What does this "multiple clicks at once" represent?
I have noticed that the temperture jumps happen more often at these multiple clicks, although not at every time and also not restricted to.

I am somewhat new to using datatakers so apologies for the non-technical language. I have looked at the manual and couldn't find anything helpful.

Let me know if anything needs clarifying.
Thanks very much

Hi hp60,

Apology for late response.

The jump happens because auto calibration feature in the logger, there are 2 possible solution:

• you can turn of auto calibration (please see SWITCHES section specially K switch in user manual).
• you can reduce the calibration value from 3 to 1 to get a smaller jump value (please see PARAMETERS specially P0 in user manual).

The first will remove the jump completely while the second if you set Po=0 it will force DT to do auto calibration on every reading which in the end will remove the jump as well.

Best regards,
Rudy Gunawan

Hi Rudy,

I recently posted on another thread and mentioned this issue affecting my readings as well. Seems that you have already addressed this. My questions is, if I disable this re-calibration will it not adversely affect the accuracy of my readings?

It seems to me that the re-calibration is the cause of some of my issues and since the temperature during my test should not change significantly then there should not be any need for a re-calibration. Maybe the best way would be if I can tell the DT85G to run a calibration at the beginning of my program, i.e. somewhere between BEGIN and my first schedule, say RA"Strain"1S. What are your thoughts?

Thank you!

Hi GeotechEngg,

The effect to the reading is minimal, you can disable the automatic calibration.

Best regards,
dataTaker Expert

Follow-up. Note for Future Reference

Based on my experience, the fluctuations seen in the chart are likely due to electrical noise and the DT80 calibrating as a result of changes in its environment. This effect may stem from the power supply used for the DT80 or from other sources such as variable speed drives, LED lights, solar inverters, battery chargers, etc. It is most noticeable when using thermocouples or strain gauges.

Recommendations:

Power Source:
Try powering the DT80 from its internal battery.

Placement:
Ensure the DT80 is not located near (within 500 mm of) any earthed metal.

Sampling Interval:
Calibration steps are more likely to appear when sampling at intervals longer than a few minutes—the longer the sampling period, the more pronounced the step changes.

Thermal Stability:
Make sure the DataTaker is thermally stable. If necessary, fully insulate it to slow thermal drift.

Data Averaging:
Use averaging techniques if possible, as this can also help reduce step changes.

We encounter similar issue for multiply device connect to one system, the thermocouple sensors are plugged into a Tank, when other device power on (220Vac power supply), then the datalogger reading "jump". The Tank is floating, once we connect the Tank to ground with the Datalogger, the problem solved.

The thermocouple sensor signal is very tiny, system grounding must be stable if powerup by 220AC main.