Other Primary Measurement Functions
Frequency and Period Measurement Errors
The multimeter uses a reciprocal counting technique to measure frequency and period. This method gen-
erates constant measurement resolution for any input frequency. The multimeter's AC voltage meas-
urement 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. Meas-
urement errors 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.
DC Current
When you connect the multimeter in series with a test circuit to measure current, a measurement error is
introduced. The error is caused by the multimeter's series burden voltage. A voltage is developed across
the wiring resistance and current shunt resistance of the multimeter, as shown below.
Avoid applying signals to unused current input terminals
If signal inputs are applied to terminals not needed for the current measurement, measurement errors may
occur. The unused terminals are still protected but the un-needed signals may interfere with current meas-
urement. For example, applying inputs to the 3A terminals while making measurements on the 10A ter-
minals will typically cause errors.
The Hi and Lo sense terminals are not used for many measurements. Applying signals here when not
needed can also cause errors. AC or DC voltages above 15 volts peak on the un-needed sense terminals
are likely to cause measurement errors. If unexpected errors are occurring, signals on the un-needed ter-
minals is an area to check.
Keysight Truevolt Series Operating and Service Guide
171
Measurement Tutorial
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