VTI Instruments Metek EX1202 User Manual page 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.
Mode
Slow
Medium
Fast
User
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:
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:
Measuremen
Also note from Table 4-6 that aperture and resolution have an inverse relationship and can be
interchanged using the following formula:
Aperture
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.
Basic EX1200 DMM Operation
Digits
6½
5½
4½
4½, 5½, or 6½
T 4-6: F
ABLE
User Mode
Min
Max
T 4-7: R
ABLE ESOLUTION AND

t Time Aperture Time
where T = period of input waveform

 
6
Time (seconds) 24 10
Sense HI
Input HI
Input LO
Sense LO
DMM Front Panel
T 4-8: DMM C
ABLE ONNECTIONS FOR
Aperture/Gate Time
140 ms
14 ms
1.4 ms
See Table 4-7
R
REQUENCY ESOLUTION
Resolution (Hz)
0.0025
4.167e-8
A L
PERTURE IMITS FOR

T 2

1

Resolution (Hz)
F
REQUENCY
www.vtiinstruments.com
M
ODES
Aperture Time
(s)
33.33e-6 s
1 s
U M
SER ODE
Frequency Source
M
EASUREMENTS
91