What is the input impedance of the U12 data logger?
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What is the input impedance of the U12 data logger?
faqid:
147
Here is a description of the input impedance characteristics of the HOBO U12 data loggers with external inputs. "Rs" and "VA" in the attached diagram represent your source impedance.
Black Box Equivalent
If an input channel is de-selected or when it is not measuring a voltage, that input nominally looks like 2K resistance in series with a 100pF capacitor. The leakage current may look like a nominal 5M resistance.
When switched into the A-D circuit to be measured, that input looks like a 12K resistor in series with a 25pf capacitor has been added to the network. Some digital filtering is performed during the sampling window.
