ORTEC 420 - Timing Function Verification

6-2
generator so that the single channel half-triggers. Now set the X2
attenuator switch on the pulse generator. The single channel should
again half-trigger at 500 dial divisions. Next, set the DIFF./INT. switch
to the DIFF. position, and turn the "E" dial to 400 divisions. Turn the
"AE" dial toward zero and observe when the single channel again
begins to half-trigger. This should be approximately 100 dial divisions
on the "AE" dial. We are now certain that the single channel analyzer
is operating as a single channel in the bipolar mode. These same steps
may be repeated for the unipolar mode if desired, and other points
on the pulse height vs dial curves may be observed.
6.1.5 Testing the Timing Function
(1) It is assumed for this test that the steps in 6.1.4 have been performed
and that switch SI is in the BIPOLAR position. Connect the direct output
of the pulse generator to the trigger input to the "B" sweep on the
scope and set the scope for "A" triggered by "B." Obtain such trig
gering of the "A" sweep that the delay control in the "B" sweep
section may be used.
(2) Turn the DELAY control on the Model 420 to 0 and observe the output
pulse either at TP1 or at TP2, then adjust the scope sweep speed and
"B" sweep delay to observe the leading edge of this pulse with a
sweep speed of 20 nanoseconds/cm or less. Set the DIFF./INT. switch
to the INT. position on the Model 420. Set the pulse generator switches
as described in Section 6.1.4, step (4). Place the "E" discriminator at
10 divisions. Attenuate the pulse height by factors of 2, 5, and 10 by
means of the attenuator switches on the pulse generator, and observe
the time shift of the output pulse; the time shift should be less than
4 nanoseconds over this pulse height range. It may be necessary to
trim the time shift by means of the WALK Adj. screwdriver adjustment
(R69) on the front panel. For those users who have critical dynamic
range problems, the single channel may be checked and adjusted to
achieve less than ±10 nanoseconds time shift over a dynamic range
of 50:1, i.e., from 200 mV to 10 volts. Operation with this wide a range
becomes quite critical and R69 may have to be slightly readjusted to
achieve this characteristic. Of course, at very low pulse heights the
amount of jitter observed will be large; this is due to the amplifier
noise modulation of the crossover point.
(3) Set the scope sweep speed at 50 nanoseconds/cm. Observe the out
put signal and turn the DELAY control (R46) through its range. The
output should shift approximately 1000 nanoseconds.