Fluke 45 - Manual (Page 36)

Operating the Meter From the Front Panel
Measuring Frequency
3
3-9
Frequency Measurement Rates
The rate at which frequency measurements are taken is a factor of the frequency being
measured (see Table 3-6).
When the frequency function has been selected, pressing
R has no effect on the
frequency update rate.
Table 3-6. Frequency Measurement Rates
Frequency Reading Rate
@ > 150 Hz 1.8/sec
@ 100 Hz 1.6/sec
@ 60 Hz 1.3/sec
@ 15 Hz 1/1.2sec
@10Hz 1/1.7sec
@5Hz 1/3.2 sec
Measuring Frequency of Current (100 mA and 10A) Inputs
Frequency measurements are always taken using the ac input circuitry of the meter.
Normally, measurements are taken on the
Xinput terminal. However, frequency
measurements can also be taken on current inputs. If frequency is to be measured using a
current input, ac current must be selected in the primary display and frequency must be
selected in the secondary display.
When the ac current function in a mA range is selected in the primary display and
frequency is selected as the secondary display function, the frequency of the current at
the 100 mA terminal will be measured. Similarly, when the ac current function in the 10
A range is selected for the primary display and frequency is selected in the secondary
display, the frequency of the current at the 10 A input terminal is measured.
Frequency Sensitivity Selection
Before a frequency measurement is started, the amplitude of the input signal is sampled
and the optimum ac range is selected automatically. For most applications, therefore, the
user need not be concerned with setting the measurement sensitivity for stable frequency
readings.
However, if necessary, measurement sensitivity can be selected manually. To do so, use
the dual display as described in the following procedure:
1. Power-up the meter and press
Zor D to select an ac voltage or current function
in the primary display.
2. Press
E ,U, or T to manually select an ac measurement range.
3. Press
S then press F to select the frequency function in the secondary display.
All frequency measurements on the secondary display will be taken on the selected
ac range.
The maximum input voltage that may be applied on any ac measurement range for
reliable frequency measurements is listed in Table 3-7.
The minimum signal for a stable frequency measurement varies depending on the
frequency and waveform being measured.