Practical Measurements - Philips PM 6670 Operating Manual

18
Hold-Off
PM 6671 is equipped with trigger hold-off, which
avoids false stop triggering on spurious or unwanted
signals. A typical example is the pulses from relay
contact bounce, as illustrated in Fig. 3.15.
Spurious signal posses
through trigger window
Trigger hold-off time
Correct measurement
Afeosurement obtained
without trigger hold-off
Practical
Measurements
Preliminary settings
1.Before connecting the counter to the line, check
that the line voltage selector is correctly set.
2.Set the slide switches on the rear panel to INT SID
and EXT RESET (or ARMING).
3.Release all pushbuttons, as necessary.
4.Press POWER ON.
5.Set HOLD OFF to 0 (PM 6671).
6.Set MEASURING TIME to approx 0.1 s.
7.Set the SENSITIVITY controls fully clockwise
and pulled (AC mode).
Fig. 3.15. Hoid-off avoids false triggering.
Gate monitor
PM 6671 and PM 6672 are equipped with a gate
monitor output. By connecting an oscilloscope to
this output, it is possible to look at the gate open
signal. Figure 3.16 is an illustration of the gate
monitor function. Note that the gate open signal is
longer than the set measuring time due to the
synchronization time.
GATC MONITOR
Set meos. Iirr\e
25 ms
Input A signol
Penod A selected
Disployed value 9rns
GAT € MON! TOR
with Hold- Off
set to JOrnS
Measured Signal
Displayed value Jdrns
n
I I
I I
I 1
r T
I i
I t
Frequency measurements
1 .Make the preliminary settings.
2.Select FREQ.
3.Connect the signal to be measured to Input A
if the frequency is between 10Hz...120MHz.
4.Decrease the sensitivity until no triggering at all
occurs. Push ATT xlO, as necessary.
5.Increase the sensitivity again, until the GATE LED
is flashing and a stable reading is obtained.
6.For improved triggering on noisy LF-signals, use
the low-pass filter.
7.Set the measuring time to give optimum resolution
and measurement speed.
8.PM 6672 only:
If the frequency of the signal to be measured is
higher than 1 20MHz, input C must be used. The
frequency range for input C is 70MHz...1 GHz.
Press pushbutton C (1GHz) to select input C.
The sensitivity is automatically adjusted for input C,
thus facilitating perfect triggering under most
conditions. Maximum allowed voltage at input C
is 1 2Vrivis.
Fig. 3.16. An illustration of the gate monitor function,
with and without hoid-off.
Period measurements
1 .Make the preliminary settings.
2.Select PERIOD A.
3.Connect the signal to be measured to Input A.
4.Decrease the sensitivity until no triggering at all
occurs. Push ATT x 10, as necessary.
5.Increase the sensitivity again, until the GATE LED
flashes and a stable reading is obtained.
6.For improved triggering on noisy LF-signals, use
the low-pass filter.
7.Set the measuring time to give optimum reso
lution and measurement speed.