While troubleshooting a strange voltage reading on a DT85 S3, I narrowed it down to this. When I measured the reading outside of a schedule, it measured the voltage correctly. When the same line of code was used in a schedule, it measured the incorrect value.

• Actual voltage measured with a Fluke multimeter at the DT85 terminals: 44.7 mV
• Voltage manually measured by DT85 in DeTransfer without being in a schedule: 44.6 mV
• Voltage measured by DT85 in a schedule: 21.0 mV

This was the line of code used inside and outside of the schedule:

• 3V("Raw Main Current mV",=100CV)

My coworker had an idea; to add a Gain Lock on the channel when it was reading this channel in the schedule.

• 3V("Raw Main Current mV",GL3V,=100CV)

This fixed the issue right away and I always got the correct reading afterward.

He got the idea from this excerpt in the manual:

By default the appropriate gain range is selected automatically. The first time a channel is measured, the DT80 will select
the highest input range (3V if attenuators are not enabled, 30V if they are). If the reading is close to zero then up to two
additional measurements will be made on progressively lower input ranges.
For subsequent measurements of the same channel, the DT80 will initially use the same input range as was used
previously. If the reading is over range or close to zero then the input range will be adjusted up or down respectively and
the measurement repeated.

To me, the Datataker should have chosen the correct range on its own, just like a multimeter. I would have never thought that this could be an issue. I also tried this on another DT85 S3 with the same result.

Why is this happening?? Any ideas?

Hi marjub,

It is true without defined gain lock, dataTaker will use automatic range when reading the voltage. This could be some fault in the logger or the logger need recalibration (factory calibration).

Logger fault may cause incorrect relay close sequence that affecting range selection. Factory calibration will adjust the slope setting for voltage measurement. Unfortunately I can't really tell what happened with your logger.

Best regards,
Rudy Gunawan

We have seen the same issue here with a DT85-S3 unit, although only on one channel. Try adding a measurement delay MDxx as it may fix the issue. This can be done in dEX as well. You may need to experiment with the time in mS.

3V("Raw Main Current mV",=100CV,MD20)

So we then replaced the relays for the channel that was the issue and it now works okay without the measurement delay. We suspect it was a timing issue with the relays.