Hi: I got some troubles while conducting a low-level capacitance measurement using PXI-4072. Our device is a pipe whose length is 40cm, internal diameter is 50cm, and external diameter is 60cm. We enwrap a layer of copperplate outside the pipe to get a pole for our measurement loop. The varnished wire inserting inside the pipe is the other pole. We use a LCR meter in our lab to measure the capacitance of the pipe, and the value is about 10pF but when we use PXI-4072, the value is instable. Sometimes it is UNDRN, and sometimens it is a number. In general, we need to touch the negative to get a number. If we do not, the reading is UNDRN. We think that the ground is not necessary for capacitance measurement, but we do not know why sometimes the negative should be touched to get a reading. At times we connect a wire which is about 3.2m long to the negative, and the reading is normal. Sometimes we smoothly conduct the measurement on the forenoon, but at night the reading returns UNDRN. The above phenomenas is odd. Now we need a solution for our experiment.

Digital Multimeters (DMMs) and Precision DC Sources

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Hi,

I have tried some ranges from pF to uF. The performance in uF range is good, but in pF it is bad.

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