Why do I measure a different value between channel 1 and channel 2 on my 2182A?

When measuring the same voltage source, if you notice a difference in reported voltage between channel 1 and channel 2 of your nanovoltmeter, you might be seeing the effects of pumpout current. This effect is significant when measuring voltages <1V and the resistance between Channel 1 LO and Channel 2 LO is >100kΩ. When using using Channel 2 for measurements of <1 V, ensure both channel LOs are connected together. 

If you must use Channel 2 LO to measure <1V, and Channel 2 LO cannot be connected to Channel 1 LO (or the resistance must be >100kΩ) you can use Low Charge Injection Mode to reduce the pumpout current. However, this mode greatly increases measurement noise.

For more information, see the 2182A User's Manual section on pumpout current.