5-49 +6V Supply (Model 6236B). To adjust the
current limit circuit in the +6V supply, proceed as follows;
a. Check the setting of the current limit by performing
steps (r) and (s) of paragraph 5-16. (Be sure to set the
output voltage to 6 volts.) If reducing the load resistance
permits the current to exceed 2.9A, stop, turn R46 slightly
clockwise, and repeat the test. If, instead, the current
begins to fall before it reaches 2.6A, turn R46 slightly
counterclockwise and repeat the test.
b. Recheck the setting and readjust R46 until the test
shows that the current limit circuit begins to reduce the
current when a decreasing load resistance increases it to
2.75A ±5%.
5-50 +18V Supply (Model 6237B). To adjust the
current limit circuit in the +18V supply, proceed as follows:
a. Turn current limit adjustment pot (R46) fully clock
wise to its minimum setting.
b. Connect the test circuit of Figure 5-3 to the output
of the +18V supply. Use an 18Ω 20W resistor for R
L
.
c. Turn on the supply and set the +18V VOLTAGE
control for maximum output (fully clockwise).
d. Turn current limit pot (R46) slowly counterclockwise
until the DVM indicates a voltage drop across the shunt
corresponding to a current of 1.1 A ±5%.
5-51 Meter Calibration
5-52 Panel Voltmeters. Check the accuracy of the
panel voltmeter by performing steps (a), (b), and (c) of the
procedure in paragraph 5-16. Since the same range
resistors are used in both 20-volt ranges, their accuracy
will be the same. Adjust R58 so that the percentage error
in the +6V range (or +18V range) is equal to the error in
the 20-volt ranges. Turn R58 clockwise to increase the
indications or counterclockwise to decrease them. If R58
cannot calibrate all voltmeter ranges to within the ±4%
specification, check the values of the resistors in the
voltmeter circuit.
5-53 Panel Ammeter. Check and calibrate the panel
ammeter by following the steps below.
a. 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 (Model 6236B)
or 18 ohms (6237B) to permit operating the supply at its
full rated output. R
L
should have a power rating of at least
20 watts.
b. Close the switch and set the +6V (+18V) VOLTAGE
control so that the DVM indicates an output of 2.5A
(6236B) or 1.0A (6237B).
c. Check and record the panel ammeter accuracy on the
+6V or +18V range.
d. Check each of the 20-volt ammeter ranges similarly,
using the same test setup but making R
L
a 40Ω 10W
resistor and setting the voltage control for a 0.5A output
current. Record the panel ammeter accuracy on each 20-volt
range.
e. Turn R59 clockwise to increase the indications on all
three ranges or counterclockwise to decrease them.
f. If R59 cannot calibrate all three ammeter ranges to
within the ±4% specification, check the values of the resis-
tors in the circuit, including current monitoring resistors R8,
R28, and R48.
5-12
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