8
b. polarity switch to Pos,
c. Cal set to full clockwise and Pulse Height
control to 1000,
d. all Attenuator switches set to X1 position,
e. Direct Output terminated in 100
Ù
and kept
terminated in 100
Ù
throughout the test.
2. Apply power to the Bin and listen for running of
the mercury relay, which will be characterized by a
low frequency hum (50 or 60 Hz).
3. Set the relay s wit ch to Off. Measure the dc
voltage from the wiper of the Pulse Height switch on
the rear panel to ground. It should be greater than 9
V.
4. Dial the Cal control fully counterclockwise and
again measure the dc voltage from the wiper of the
Pulse Height switch to ground. It should be less than
4 V. Turn the Cal control clockwise until the voltage
is 10 V.
5. Set the relay switch to On.
6. Measure the pulse at the direct output test point
TP1.
The pulse amplitude should be between the limits of
4.0 and 6.0 V. The, pulse rise time (10-90%) should
be less than 10 nsec; the pulse fall time to one-half
of its maximum amplitude should be between 230
and 290
ì
sec. Do not remove the 100
Ù
terminator
from the Direct Output.
7. Terminate attenuated output with 100
Ù
. Measure
the pulse at the attenuated Output test point. The
pulse amplitude should be between the limits of 4.0
and 6.0 V. The pulse rise time (10-90%) should be
less than 10 nsec; the pulse fall time to one-half of
its maximum amplitude should be between 110 and
150
ì
sec.
8. Adjust the Pulse Height dial for a Pulse of 800 mV
at the attenuated output test point. As the Attenuator
switches are switched in, the output pulse should be
between the following limits:
9. Set the Polarity switch to Neg. There should be
no change in amplitude from the Pos pos ition.
Observe the output with a sweep of 5 msec/cm and
look for "skipping" or other erratic behavior of the
relay.
5.2. ADJUSTMENT OF DECAY TIME OF
OUTPUT PULSE
As the 480 is normally supplied, the decay time of
the output pulse is essentially fix ed. The output
Pulse will decay with the time constant of 400
ì
sec
if the Attenuated output only is terminated in 100
Ù
and will decay with a time constant of approximately
200
ì
s ec if both the Direct and Atten Outputs are
terminated. In the event that a time constant shorter
than 200
ì
sec is desired, it is necessary to parallel
a fixed resistor from the normally open contact of the
mercury-wetted relay to ground. The value of this
shunting resistor will depend upon the exponential
time constant desired. The addition of this resis tor
should physically be in close proximity to the actual
relay; that is to say, the resistor should be added
directly onto the etched circuit board. Decay time
constants as short as 10
ì
sec can be accomplished
quite easily.
5.3. TABULATED TEST POINT VOLTAGES
The following voltages are intended to indicate the
t ypical dc voltages measured on the etched circuit
board. In some cases the circuit will perform
satisfactorily even though due to component
variations there may be some voltages that measure
outside the given limits. Therefore the voltages given
should not be taken as absolute values, but rather
are intended to serve as an aid in troubleshooting.
All voltages are measured from ground with dvm
having input impedanc e of 10 M
Ù
or greater.
Polarity switch set to Neg.
Summary of Contents for ORTEC 480
Page 6: ...vi ...
