Keithley 2701 User Manual page 221

7-8 Scanning Model 2701 User's Manual
Immediate control source
With immediate triggering, event detection is immediate allowing channels to be scanned.
Timer control source
With the timer source enabled (selected), event detection is immediately satisfied. On the
initial pass through the loop, the Timer Bypass is enabled allowing operation to bypass the
Timer and continue to the Delay block.
On each subsequent pass through the loop, the Timer Bypass is disabled. Operation is then
delayed by the Timer or the Delay. If the user-set Timer interval is greater than the user-set
Delay, the Timer will control the length of the delay. Otherwise, the length of the delay is
controlled by the user-set Delay period.
The Timer interval can be set from 0 to 999999.999 seconds. The timer resets to its initial
state when the scan is completed.
STEP operation — As shown in Figure 7-1, the timer control source affects the timing
between scanned channels.
SCAN operation — As shown in Figure 7-2, the timer control source affects the timing
between scans. It has no effect on the timing between scanned channels.
External trigger control source
Pressing the EX TRIG key places the instrument in the external trigger mode (TRIG
annunciator on). When the STEP or SCAN key is then pressed, that scan is enabled.
However, the scan does not start until an external trigger is received or the TRIG key is
pressed. The external trigger or TRIG keypress satisfies event detection.
STEP operation — Each time an external trigger is received (or TRIG key is pressed), one
channel is scanned.
SCAN operation — Each time an external trigger is received (or TRIG key is pressed),
one complete scan is performed.