for a 20V DVM indication, and verifying that the panel
meter is accurate within 4%.
Tracking
d. Connect the DVM to the +20V output, set the ±20V
VOLTAGE control for a DVM indication of 20 volts, and
reconnect the DVM to the -20V output without disturbing
the voltage control. The voltage at the -20V output should
be within 1% of the +20Voutput.
Variable Tracking Ratio
e. Leave the ±20V VOLTAGE control set as in step (d),
and use a DVM to monitor the voltage of the -20V supply
while adjusting the TRACKING RATIO control over its
VARIABLE range. The -20V supply should be capable of
being adjusted from less than 0.5 volts to between 18
and 22 volts. Return the TRACKING RATIO control to the
FIXED position.
NOTE
Leave the TRACKING RATIO control in the
FIXED position throughout the remainder of the
performance test.
Rated Output and Ammeter Accuracy
f. Connect 40Ω 10W load resistors across both of the 20V
outputs of the supply and set the ±20V VOLTAGE control for a
±20V output. (All three supplies must be fully loaded while
checking the rated output voltage and current of each supply.)
g. Connect the test setup shown in Figure 5-3 to the +6V
(or +18V) output. Make the total resistance of R
L
and the
current sampling resistor 2.4 ohms for the Model 6236B (or
18 ohms for the 6237B) to permit operating the output at full
load. R
L
should have a power rating of at least 20 watts.
h. Close the switch and set the +6V (+18V) VOLTAGE
control so that the DVM indicates a voltage drop across the
current sampling resistor that corresponds to a current of 2.5
amps (6236B) or 1.0 amp (6237B).
i. Set the METE R switch to the +6V (+18V) range and
verify that the front panel ammeter indication is within 4% of
2.5 amps (6236B) or 1.0 amp (6237B).
j. Connect the DVM directly across the output terminals of
the +6V (+18V) supply, record the DVM reading, and then
open the switch in the 6V (18V) load circuit without disturbing
the supply's output terminals. The DVM indication should not
change by more than 2.6mV (6236B) or 3.8mV (6237B).
k. Check the rated output and ammeter accuracy of the
+20V and -20V supplies similarly by connecting the test setup
of Figure 5-3 to each output in turn. For each 20V supply:
make the total resistance of R
L
and the current sampling
resistor 40
ohms, set the ±20V VOLTAGE control for a current
indication, on the DVM of 0.5A, check that panel meter
indication is within 4% of 0.5A, connect the DVM to
the fully loaded output terminals, and compare the
output voltage before and after the load circuit is
opened. The voltage should not change by more than
4mV. While checking each supply, the other two must
be fully loaded.
Current Limit
l. Disconnect all loads from the supply.
m. Connect the test setup shown in Figure 5-3 to the
+20 volt output. Substitute a short for R
L
and leave the
load circuit switch open.
n. Set the voltage of the ±20V supplies to 20-volts.
o. Close the load switch and determine the current
flow through the current sampling resistor (meter shunt)
by measuring its voltage drop with the DVM. The current
should be 0.55A ±5%.
p. Check the current limit of the -20V supply in the
same way. Its short-circuit current should also be 0.55A
±5%.
q. (Model 6237B only). Check the current limit of the
+18V supply similarly by setting its output for 18 volts
and using a DVM to measure the current which flows
through a low- resistance current sampling resistor. The
short-circuit current of the +18V supply should be 1.1 A
±5%.
r. (Steps (r) through (t) apply to the 6236B only.)
Connect the test setup shown in Figure 5-3 to the +6V
output. Close the switch, set the total resistance of R
L
and
the current sampling resistor to an initial value of 2.4 ohms
or greater, and set the output voltage to 6 volts.
s. Reduce the value of R
L
gradually while observing the
output current indicated by the DVM. The current should
increase to a maximum of 2.75A ±5% before it begins to
decrease.
t. Connect a short across R
L
and then recheck the
current
5-17 Load Effect (Load Regulation)
Definition: The change
∆
E
OUT
in the static value of dc
output voltage resulting from a change in load
resistance from open circuit to the value that yields
maximum rated output current (or vice versa).
5-18 To check the load effect:
a. Connect a full load resistance and a digital voltmeter
across the output of the +20V supply.
b. Turn on the supply and adjust its voltage to its
maximum rated value.
c. Record the voltage indicated on the DVM.
d. Disconnect the load resistance and recheck the DVM
indication. It should be within .01% plus 2mV of the read-
ing in step (c).
e. Repeat steps (a) through (d) for each of the remain-
ing supply outputs.
5-3
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