Frequency and Period Measurement Errors
The multimeter uses a reciprocal counting technique to measure
frequency and period. This method generates constant measurement
resolution for any input frequency. The multimeter’s ac voltage
measurement section performs input signal conditioning. 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 will also occur
if you attempt to measure the frequency (or period) of an input following
a dc offset voltage change. You must allow the multimeter’s input dc
blocking capacitor to fully settle before making frequency measurements.
Making High-Speed DC and Resistance Measurements
The multimeter incorporates an automatic zero measurement procedure
(autozero) to eliminate internal thermal
EMF and bias current errors.
Each measurement actually consists of a measurement of the input
terminals followed by a measurement of the internal offset voltage.
The internal offset voltage error is subtracted from the input for improved
accuracy. This compensates for offset voltage changes due to temperature.
For maximum reading speed, turn autozero off. This will more than double
your reading speeds for dc voltage, resistance, and dc current functions.
Autozero does not apply to other measurement functions.
7
Chapter 7 Measurement Tutorial
Frequency and Period Measurement Errors
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