ABM-4083
25
Model DMM uses an interactive counting technique to measure frequency and period. This method gener-
ates constant measurement resolution for any input frequency. All frequency counters are subject to errors
when measuring low-voltage, low-frequency signals. Both internal noise and external noise are also critical
when measuring low-voltage, low-frequency signals. 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 dig-
ital multimeter’s DC input blocking capacitor to fully settle before making frequency measurements.
3.5.2 Gate Time
Gate time is the amount of time Model DMM uses to sample frequency or period readings. When the Fast
function is chosen, Model DMM yield a gate time of ten millisecond, the Med function yield a gate time of
one hundred millisecond, thus the settings of the Slow function yield a gate time of one second. The gate
time affects the usable digits, as well as the ultimate reading rate of the instrument.
3.5.3 Connections
Assuming Model DMM is under factory default conditions, the basic procedure is as follows:
1. Connect test leads to INPUT HI and LO terminals.
2. Select frequency or period measurement functions by pressing
Freq
or
Shift
→
Freq
3. Connect test leads to the source as shown in Figure 3-4:
CAUTION: Do not exceed 1000V peak between INPUT HI and INPUT LO or instrument damage may
occur.
4. Taking a reading from the display
Input Impedance
=1MΩ in parallel with <100pF
CAUTION: Maximum Input = 750 RMS, or 1000V Peak
Figure 3-4
Frequency and Period Measurements
