Calibration expectations / zero offset

Is the Tra-Cal certified calibration expected to improve accuracy over the Factory calibration, and if so, is there some typical accuracy information for both the Factory and Tra-Cal accuracy? I’d be interested in this for both the JS220 and JS110 if such information is available.
I currently have 3 Joulescopes in use, and sometimes need to measure very small currents into the nA. All of these Joulescopes are well within the stated accuracy in the user manual (and one is more than 4 years old), but if I could get improved offset around 0 current, it would simplify some of my uses.
Before I pay for calibration I want to check if I should even expect improved accuracy from calibration, or is the calibration more likely to be a certification if the unit is already within spec?

Perhaps a different approach to the zero offset concern would be a feature to zero, or “tare” the current and/or voltage (say based on a measurement of a second or so for averaging).

Thank you for your time,

Hi @Jeremy, and welcome to the Joulescope forum! Great to hear that you want to use your existing Joulescopes for even higher precision measurements!

The Tra-Cal calibrations and recalibrations do not improve the accuracy of your Joulescopes. If they test the instrument and find it in spec, they leave it alone. They have never seen a JS110 or JS220 out of spec. We have had broken JS110’s that have been out of spec, but the failure modes are such that they are very easily observed to be out of spec in everyday use.

So, if you want better JS110 offset accuracy in the nA range, sending the instrument to Tra-Cal will not help.

The problem is that the zero readings are different for each current range. If you use only a single, fixed current range, you could create a custom test process in python. The test process could:

  1. capture the zero reading in the current range
  2. performs the measurement
  3. subtracts the zero reading from the measurement

Would this work for you?

The new JS220 was designed to have a “trim” feature to self-trim the zero offsets for each current range. This feature is not yet implemented, and we do not yet have a timeline for when it will be available. We do not plan to add a feature like this to the JS110.

Hi Matt,
Thanks for the reply on the weekend!
That’s very useful to know about the calibration and avoids some down time for shipping & waiting.

Noting the zero current is roughly what I’m doing now, so I’ll continue that.
The zero for the range used is important, though for the measurements where this matters, it’s deeply into the lowest range.

The trim feature sounds like what I’m looking for. I’ll check it out when it’s available.

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