Why do IR readings fluctuate @ 500V?
The IR specification covers the voltage range 100 V to 7 Kv, however every test has an associated accuracy specification and this is where at very low currents IR accuracy is degraded.
The accuracy specification is in section 8 of the user manual is shown in the attachment ‘IR Accuracy calculation”
For example, with a voltage of 500 V @ 20 GOhms the following applies:
AI (correction for current level) = 3.2%+(0.000002%/25E-9) = 3.2% + 80% = 83.2%. This is clearly the dominant factor by far in the total accuracy calculation.
Increasing the voltage by a factor of 10 to 5000 V (a current of 250 nA) yields and AI of 8.32%, 10 times less.
Unfortunately at this very low current measurements become dominated by noise and hence the accuracy degrades.
From the attached accuracy calculation it can therefore be seen that a higher test voltage (and hence higher test current) will yield a more accurate result.