User manual

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measure the applied signal. However, auto ranging should not be used when optimum speed is required.
Note that up-ranging and down-ranging occurs at 5% of normal range.
To cancel auto ranging, press or or key. Pressing to cancel auto ranging
leaves the instrument in its present manual range.
The key has no effect on the continuity and diode test functions.
4.1.2 Relative
The relative operation could be used to null offsets or subtract a baseline reading from present and
future readings. When relative function is enabled, the multimeter uses the present reading as a relative
value. Subsequent readings will be the difference between the actual input value and the relative value.
You can define a relative value for each function. Once a relative value is set for a measurement function,
the value is the same for all ranges. For example, if 2 V is set as a relative value on the 20 V range, the
relative is also 2 V on the 1000 V, 100 V, 1 V or 100 mV ranges. For model 5491B, if 2 V is set as
relative value on the 50 V range, the relative is also 2 V on the 1000 V, 500 V, 5 V or 500 mV ranges.
Additionally, when you perform a zero correction for DCV, Ω measurements by enabling REL, the
displayed offset becomes the reference value. Subtracting the offset from the actual input zeroes the
display, as follows:
Displayed reading = Actual Input – Reference
Select a range that cannot accommodate the relative value does not cause an overflow condition, but it
also does not increase the maximum allowable input for that range. For example: on the 2 V range,
model 2831E still overflows for a 2.1 V input. For model 5491B, on the 5 V range it will still overflow for
a 5.1 V input.
To set a REL value, press when the display shows the value you want as the relative value. The
REL annunciator turns on. Press a second time to disable REL.
4.1.3 Rate
The RATE operation sets the integration time of the A/D converter, the period of time the input signal is
measured. The integration time affects the usable digits, the amount of reading noise, as well as the
reading rate of the instrument.
In general, the fastest integration time (FAST set from the front panel or remote interface) results in
increased reading noise and fewer usable digits (resolution), while the slowest integration time provides
the best common-mode and normal-mode rejection and more usable digits. Depending on the selected
rate, user will have to compromise between speed or noise, as well as resolution.
Rel
Rel