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Basic EX1200 DMM Operation 91
The resolution of frequency measurements is set from one of the following options: Slow Mode,
Medium Mode, Fast Mode, and User Mode. Table shows the settings used for each mode.
TABLE 4-6: FREQUENCY RESOLUTION MODES
NOTE Larger aperture/gate times increase the number of input signal cycles averaged for a reading. This
improves reading accuracy, but reduces scan speed. The DMM keeps the gate open for one full
waveform cycle up to the timeout value. So, if the input frequency is 3 Hz, the time needed for the
measurement reading to be returned can be up to 0.67 s. The default timeout is 1 s.
When in User mode, the following limits must be observed when setting the aperture time:
TABLE 4-7: RESOLUTION AND APERTURE LIMITS FOR USER MODE
Frequency and period measurement rates are dictated by the aperture time. The settling time
(trigger delay) is the same as the ACV slow mode setting. Note that the maximum measurement
time is no more than the following:
T2Time ApertureTimet Measuremen
where T = period of input waveform
Also note from Table 4-6 that aperture and resolution have an inverse relationship and can be
interchanged using the following formula:
(Hz) Resolution
1
1024(seconds) Time Aperture
6
Connecting to the DMM
For front panel measurements, the ac signal should be connected to the HI and LO input jacks of
the EX1200 DMM using suitable connectors. Although not preferred in fixed installation,
measurements of this type can be used to quickly make readings and troubleshoot field wiring
issues.
DMM Front Panel
Sense HI
Input HI
Input LO
Sense LO
Frequency Source
TABLE 4-8: DMM CONNECTIONS FOR FREQUENCY MEASUREMENTS
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