The information provided is for help with Commtest Instruments products:
QUESTION
My T4 or T6V4 temperature channels all exhibit simultaneous temperature drifts of 1-2 degrees Celcius. Is the cold junction temperature compensation working?
ANSWER
The T4 and T6V4 cold junction compensation uses a calibrated LM35 temperature sensor, which is mounted inside the module between the thermocouple connectors. The compenstion is normally very good, but the MMS must be in thermal equilibrium to obtain optimum accuracy.
See the Owner's Manual appendix Optimising Temperature Accuracy for several suggestions.
In particular, if the MMS instrument is being used with the battery charger continuously plugged in you may experience temperature drift. As the battery voltage drops the charger will automatically begin operating. It typically turns on for an hour every four hours (approximately). The heat from this process can affect the internal temp sensor at a slightly different rate from the thermocouple connectors, hence slightly affecting readings on all channels.
If your measurement requirements cannot be satisfied by one charge of the battery without re-charging (e.g. making a 24 hr recording with temperature samples, say, every 15 minutes) we suggest that you program the MMS to perform timer-based recordings in which it powers down between samples, thereby extending the charge life of the battery.
To do this you must have firmware version 2.50 or later Proflashed into your MMS. The latest version can be downloaded for free from our website.
Note: You will also need to download and install the latest version of MMS MAS software. We recommend downloading the updated Owner's Manual as well.
FAQ ID: 11660 Last Reviewed: 27/09/2005