Common mode noise can dramatically affect the internal DMM. A typical thermocouple output is a few mil-
livolts and a few millivolts of common mode noise can overload the input to the internal DMM.
Calculation Error
An error is inherent in the way a thermocouple voltage is converted to a temperature. These calculation
errors are typically very small compared to the errors of the thermocouple, wiring connections, and ref-
erence junction.
DC Voltage Measurements
To make a useful DC meter, a “front-end” is required to condition the input before the analog-to-digital
conversion. Signal conditioning increases the input resistance, amplifies small signals, and attenuates
large signals to produce a selection of measuring ranges.
Signal Conditioning for DC Measurements
Input signal conditioning for DC voltage measurements includes both amplification and attenuation. A sim-
plified input to the internal DMM is shown below:
Keysight DAQ970A User's Guide 193
4Measurement Tutorials
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