Fluke 287 Fluke 287 and 289 Multimeter Users Manual - Page 52

Measuring Frequency, Functions Allowing Frequency, Measurement

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287/289 Users Manual W Caution Placing the probes across (in parallel with) a powered circuit when a lead is plugged into a current terminal can damage the circuit you are testing and blow the Meter's fuse. This can happen because the resistance through the Meter's current terminals is very low, so the Meter acts like a short circuit. The following are tips for current measurements: A current meter drops a small voltage across itself, which might affect circuit operation. You can calculate this burden voltage using the values listed in the specifications under Burden Voltage (A, mA, μA). The Meter's current functions have a number of modes which provide more details about a current signal. Pressing the softkey labeled Menu opens a menu of items that can be used to modify the basic current measurement. Refer to the appropriate section in this manual to learn more about each menu item. To clear all modes and return to the basic ac or dc current measurement, press the softkey labeled Menu. Move the menu selector to the item labeled AC,DC. Press the softkey labeled AC to clear all functions and modes and make basic ac current measurements, or DC for basic dc current measurements. Measuring Frequency Frequency is the number of cycles a signal completes each second. The meter measures the frequency of a voltage or current signal by counting the number of times the signal crosses a threshold level within a specified period of time. 42 Figure 23 highlights the functions that allow frequency measurements. est21.eps Figure 23. Functions Allowing Frequency Measurement The Meter autoranges to one of five frequency ranges: 99.999 Hz, 999.99 Hz, 9.9999 kHz, 99.999 kHz, and 999.99 kHz. Figure 24 shows a typical frequency display. Pressing R controls the input range of the primary function (volts or amps) and not the frequency range. To measure frequency, rotate the switch to one of the primary functions allowing frequency measurements highlighted in Figure 23. Press the softkey labeled Menu and move the menu

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287/289
Users Manual
42
W
Caution
Placing the probes across (in parallel with) a
powered circuit when a lead is plugged into a
current terminal can damage the circuit you are
testing and blow the Meter's fuse. This can happen
because the resistance through the Meter's current
terminals is very low, so the Meter acts like a short
circuit.
The following are tips for current measurements:
A current meter drops a small voltage across itself, which might
affect circuit operation. You can calculate this burden voltage
using the values listed in the specifications under Burden Voltage
(A, mA,
μ
A).
The Meter’s current functions have a number of modes which
provide more details about a current signal. Pressing the softkey
labeled
Menu
opens a menu of items that can be used to modify
the basic current measurement. Refer to the appropriate section
in this manual to learn more about each menu item.
To clear all modes and return to the basic ac or dc current
measurement, press the softkey labeled
Menu
. Move the menu
selector to the item labeled
AC,DC
. Press the softkey labeled
AC
to clear all functions and modes and make basic ac current
measurements, or
DC
for basic dc current measurements.
Measuring Frequency
Frequency is the number of cycles a signal completes each
second. The meter measures the frequency of a voltage or
current signal by counting the number of times the signal crosses
a threshold level within a specified period of time.
Figure 23 highlights the functions that allow frequency
measurements.
est21.eps
Figure 23. Functions Allowing Frequency
Measurement
The Meter autoranges to one of five frequency ranges:
99.999 Hz, 999.99 Hz, 9.9999 kHz, 99.999 kHz, and 999.99 kHz.
Figure 24 shows a typical frequency display. Pressing
R
controls the input range of the primary function (volts or amps)
and not the frequency range.
To measure frequency, rotate the switch to one of the primary
functions allowing frequency measurements highlighted in
Figure 23. Press the softkey labeled
Menu
and move the menu