Arming; Front Panel Arming; External Arming - Keithley 776 Instruction Manual

2. To return to normal measurement rate. press. in se-
quence.
the
[2ndlEXE]
push-button and then the
[HOLD]
push-button. The HOLD light turns off: indi-
cating that the instrument is now ready to accept and
process readings at its normal rate.
NOTE
Measurement rate is gate time de-
pendent. Model 176 can process 3
readings in one second when its gate
time is set to below 300 ms.
3-14 Arming
Capturing the required sequence of input signals may.
at times. create a major problem for the design engineer.
Imagine a single source that repeatedly generates bursts
of signals having various repetition rates. pulse widths.
and number of pulses. It would be next to impossible to
measure such parameters along the time axis unless the
counter is prepared for this task. Model 776 has arming
capabilities which permits such complex measure-
ments. Do not confuse arming with Trigger. Model 776
may not be triggered. Model 776. unless armed. will not
perform the task of signal processing. Model 776 may
be armed (prepared) for the next measurement in four
ways:
1. Continuously armed by an input signal. when Model
776 is set to its normal mode of operation.
2. With front panel
[CLR]
push-button. when the instru-
ment is set to HOLD mode.
3. With an arming pulse applied to the rear panel EXT.
INPUT connector. when the instrument is in the HOLD
mode.
1. With commands given over the IEEE-488 bus as
described in Section 4. This section covers front panel
and external arming in details.
3-14-1 Continuous Arming With the
Input Signal
When no special arming mode was selected. Model 776
is armed by its input signal. This means that with no
legal input signal, the counter idles. The Gate indicator
is off until the first transition. at the input connector. is
sensed. An input signal. within the dynamic range.
initiates a measurement cycle. The gate light blinks
every time that the internal gate opens. There is no
special procedure to set the Model 776 up for continu-
ous arming. This mode is especially useful in analyzing
the contents of a burst.
3-14-2 Front Panel Arming
Front panel arming is performed with the
[CLR]
push-
button. To use front panel arming proceed with the
following steps:
1. Using the procedure described in paragraph 3-13.
select the hold mode. Obsewe that the HOLD light turns
on and that the gate light ceases from flashing: indicat-
ing that the instrument is in its one-shot measurement
mode. The display zeroes and no reading is processed
until an arming stimulus is applied.
2. To arm the instrument for a single reading. press and
release the
[CLR]
push-button. The nest transition at
the input connector will cause the gate to open. The
instrument then checks for the legality of the input
signal. processes the reading and displays the result on
the display. The display will retain the last processed
reading until cleared, re-armed. or until another func-
tion is selected.
3. To arm the instmment for a new measurement. press
the
[CLR]
push-button. Obsewe that the display zeroes
sod that a new measurement cycle is initiated.
4. To remove the instnunent from its one-shot arming
mode. turn the hold fuoctionoff by pressing in sequence
the [2nd] and
[HOLD]
push-buttons.
3-143 External Arming
External arming operates much like front panel arming
except for the arming stimulus itself. In this case the
arming stimulant is applied to the rear panel EXT. IN-
PUT connector. The arming pulse must conform to TTL
levels. To use the external arming feature. proceed as
folloas:
1.
Using the procedure described in paragraph 3-13.
select the hold mode. Observe that the HOLD light turns
on and that the gate light ceases from flashing: indicat-
ing that the instrument is in its one-shot measurement
mode. The display zeroes and no reading is processed
until an arming stimulus is applied.
2. Connect the external arming source to the rear panel
EXT INPUT connector. The first positive going transi-
tion at the EXT INPUT connector arms the Model 776
for taking and processing the nest available signal.
Note that after each positive going transition of the
arming signal. the numeric display is set IO read zero
until the next data is processed and displayed. Model
776 ignores any transitions at the EXT INPUT
connec-
tar
when the gate is open.
3-l I