Could you clarify the details of this problem?
Sure. I mentioned it a 2-3 pages back, but here is the setup and pics below. This occurs on the 100V range when the circuit is setup to perform simultaneous V/I measurement. The larger the current in the circuit, the greater the effect. I chose 9V as the source to make it easy to switch between the 10V and 100V ranges. I use a 10R power resistor so the current is high, but not high enough to force me to use the 3A range (although the effect in the 3A/10A ranges are the same).
Basic Setup:
-Manually select DCA Range of 1A
-Manually select DCV Range of 10V
-Auto Impedance or 10M impedance is fine
Simple Circuit:
DMM6500 on 10V/1A Ranges:
DMM6500 on 100V/1A Ranges (Notice the large unexplained voltage drop):
For comparison:
DMM7510 on 10V/1A Ranges:
DMM7510 on 100V/1A Ranges (No large voltage drop):
You don't have to use the exact values I did for the test circuit, but the more current through the circuit the better, since at very small currents you will not see much of a difference. Try it with even larger voltages/current and see larger drops that can't be explained solely by burden voltage.
Keithley originally tried to blame my power supply as the problem. But then I showed them the results using a battery. They have been silent ever since. I even asked if I should send my DMM6550 in for warranty work, and they wouldn't even respond to that. I technically don't even know if it is just my specific DMM6550 that is the problem, but Keithley complete silence is not reassuring.
Edit: All I do is swap the test leads between the DMM6500 and DMM7510, no other changes are made.