Keithley 199 Instruction Manual page 42

2.8.2 Trigger Sources
For standard bench operation, there are two trigger sources
available: front panel TRIGGER button, and the EXTER-
NAL TRIGGER INPUT jack. Upon power up both these
trigger sources will be enabled. Additional triggers include
IEEE-488 X, GET, and talk commands, as discussed in
paragraph 3.9.7.
NOTES:
1. TRIGGER is always enabled regardless of the selected
trigger source; however, all front panel buttons will be
locked out when the unit is in remote.
2.~ Triggering the unit while it is still processing a reading
from a previous trigger will generate the "TRIGGER
OVERRUN" message.
2.8.3 Trigger Delay
The trigger delay period is the time from the trigger point
until the unit takes a reading. This delay period is also used
after each channel closure when using the scanner. For the
continuous mode, the delay period affects only the fast
conversion; however, with the one-shot mode, the delay
period affects every conversion, with the instrument
waiting the programmed delay time after each tr&ger
before taking a reading. For example, if you program a
300msec trigger delay, the unit will wait 3i%msec after each
trigger before taking a reading.
The allowable range for the trigger delay peliod is between
0 and 999.999 seconds in one millisecond increments. The
trigger delay can be programmed with the TRIG SETUP
key, as described below.
1. Press SHIFT TRIG SETUP and then NEXTand note the
following message is displayed briefly:
DELAY=
000.000s
Here, we have assumed the factory default delay period
of Osec.
2.
Using the the data entry keys (O-9), key in the d#red
trigger delay period in the range of O-9999YYsec.
3. Once the desired delay value is programmed, press
NEXT to go on to the interval selection (or press NEXT
once more to return to normal display).
2.8.4 Reading Interval
The reading interval parameter determines the time period
between individual readings when the instrument is in the
continuous trigger mode. Interval also affects the rate of
data store operation, as discussed in paragraph 2.10, as well
as the interval between channels (step mode) or scan se-
quences (scan mode) when using the optional Model 1992
Scanner (see paragraph 2.11).
The unit can beprogrammed for either default or selected
interval operation. With default interval ("SELECT OFF'!),
a preset interval of l7Smsec is automatically selected. With
selected interval ("SELECT ON") a user-defined interval
can be programmed. The allowable range for selected in-
terval is l5msec to 999.999sec in lmsec increments.
NOTE
Programming too short an interval for the present
instrument configuratiozi when using the scanner
or data store will result in the "INTERVAL OVER-
RUN" message. The interval cannot be programm-
ed if the unit is in the one-shot trigger mode.
Reading interval can be checked or programmed with the
TRIG SETUP key, as follows.
1. Press SHTn TRIG SETUP and then NEXT repeatedly
until the following is displayed:
INTERVAL
Next, the unit displays:
SELECT OFF
Or;~
SELECT ON
2. Use uprange or downrange to select th-e-desired inter-
val type, select or default, then press NEXT. If default
(SELEa OFF) is selected, the interval will be set to
l75msec, and the unit Will return to normal display.
3. If select interval is chosen, the presently selected inter-
val will then be displayed, as in this example:
INTERVAL =
ooo.l.75 s
Here we have assumed the default interval of l75msec.
4. If desired, key in a new reading interval fin the range
of 15msec to Y99.999seC.
5. Once the desired interval is displayed, press NEXT to
return to normal display. If you progam too small =*
interval, the following will be displayed:
MIN = .OlS S
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