Section 5: Basic Digital Multimeter (DMM) Operation
Series 3700 System Switch/Multimeter User's Manual
5-70
3700S-900-01 Rev. C / July 2008
Trigger level
Frequency and period use a zero-crossing trigger, meaning that a count is taken
when the frequency crosses the zero level. The Series 3700 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. If the input
signal voltage exceeds the selected voltage range, a 000.0000mHz
(0.000000 s) will be returned.
Gate time
The gate time is the amount of time the Series 3700 uses to sample frequency
or period readings. Use the
RATE
key to set the gate time; SLOW sets the gate
time to 0.25 sec, MED sets it to 0.1 sec, and FAST sets it to 0.01 sec. For
remote programming, the gate time can be set from 0.01 to 0.273 sec by setting
the
dmm.aperture
attribute.
The Series 3700 completes a reading when it receives its first positive zero-
crossing after the gate time expires. For example, for any arbitrary frequency,
you may wait up to the gate time plus two times the period of the input waveform
before the Series 3700 returns a reading.
Frequency connections
Frequency connections for the Series 3700 as well as a switching module are
shown below.
Figure 5-41: FREQ and PERIOD input connections