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3
Measurement Tutorial
Other Primary Measurement Functions
Frequency Measurement Errors
DC Current Measurements
58
The U2741A uses a reciprocal counting technique to measure
frequency. This method generates a constant measurement
resolution for any input frequency. All frequency counters
are susceptible to errors when measuring low- voltage,
low- frequency signals. The effects of both internal noise and
external noise pickup are critical when measuring "slow"
signals. The error is inversely proportional to frequency.
Measurement errors also occur if you attempt to measure
the frequency of an input following a DC offset voltage
change and therefore, you must allow the digital
multimeter's input to fully settle before making frequency
measurements.
When you connect the digital multimeter in series with a
test circuit to measure current, a measurement error is
introduced. The error is caused by the digital multimeter's
series burden voltage. A voltage is developed across the
wiring resistance and current shunt resistance of the digital
multimeter, as shown below.
U2741A User's Guide
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