Fluke PM6669 Operator's Manual page 20

FUNCTION AND RANGE
For frequency-, period-, and ratio measurements:
Select AC coupling and set the sensitivity so that the
hysteresis band of the Frequency Counter is about
half the amplitude of the signal.
For time measurements:
Select DC coupling and set the trigger level to the de-
sired level using the 1 V/divistion scale on the front
panel.
The filter works on Input-A where it suppresses sig-
nals with higher frequencies than 50 kHz.
Filter suppression: 40 dB at 1 MHz
The Frequency Counter automatically detects if a suit-
able signal is connected to the EXT- REF Input-con-
nector.
Suitable signal:
10 ± 0.1 MHz, 0.5 to 15 V
OPERATING INSTRUCTIONS
Sine wave.
RMS
HINTS AND COMMENTS
1. Set the sensitivity knob fully counter clockwise.
2. Turn it until the input triggers.
3. Continue turning to the 20 mV
position where the display turns unstable due to noise.
4. Set the knob to the position inbetween these two
points.
You will have a stable reading.
If the sensitivity is too high, the Frequency Counter
will be triggered by noise and interference instead of
by the signal.
The filter can also be used to suppress HF-
interference on signals with higher frequencies than
50 kHz, but then the sensitivity of the input will be
reduced.
NOTE: Never use the filter when measuring TIME A-B
since the filter delays the signal on Input-A.
Use external reference when the measurement
requires ultra-high stability.
The Frequency Counter must still have the internal
time base even if an external reference frequency is
used.
If single is selected, the EXT REF indicator on the
display is not switched on until after the first
measurement.
PM 6669 - OPERATORS MANUAL
Page: 19
position, or to the
RMS