Dear Joulescope Team!
Do the relative accuracy specifications of 0.25% of JS220 refer to the current range or to the measured current value?
best Anna
Hi @anna - Yes, the first number is the percentage of relative accuracy given the actual value.
The second number is the offset error, which is independent of the measured value. Some other instruments specify offset error relative to full scale, usually as ppm or %. You then need to multiply to determine the spec and full scale range to give the offset error we specify. Another way of looking at this is that the JS220 has ±150e-6 / 180e-3 * 100 = ±0.083% = ±833 ppm full-scale error in the 180 mA range.
If you are measuring 100 mA in the 180 mA range, the error is then:
error for 100 mA = 100e-3 * 0.0025 + 150e-6 = 400 µA.
thanks a lot! I understood it now 
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