Agilent Technologies E3620A Manual De Funcionamiento Y Servicio página 79

Figure A-4. Front Panel Terminal Connections
volts and 1 amp would require a load resistance of 25 Ω at the
rated output voltage. The wattage rating of this resistor would
have to be at least 25 watts.
Electronic Load. Some of the performance test procedures
require to use an electronic load to test the supply quickly and
accurately. An electronic load is considerably easier to use
than a load resistor. It eliminates the need for connecting
resistors or rheostats in parallel to handle the power, and it is
much more stable than a carbon-pile load. It is easier to
switch between load conditions as required for the load regu-
lation and load transient response tests.
Output Current Measurement. For accurate output current
measurements, a current sampling resistor should be
inserted between the load and the output of the supply. To
simplify grounding problems, one end of this sampling resis-
tor should be connected to the same output terminal of the
supply which will be shorted to ground. An accurate voltmeter
is then placed across the sampling resistor and the output
current is calculated by dividing the voltage across the sam-
pling resistor by its ohmic value. The total resistance of the
series combination should be equal to the full load resistance
as determined in the preceding paragraphs. Of course, if the
value of the sampling resistor is very low when compared to
the full load resistance, the value of the sampling resistor may
be ignored. The meter shunt recommended in Table A-1, for
example, has a resistance of only 100 mΩ and can be
neglected when calculating the load resistance of the supply.
Figure A-5 shows a four terminal meter shunt. The load cur-
rent through a shunt must be fed from the extremes of the
wire leading to the resistor while the sampling connections
are made as close as possible to the resistance portion itself.
Figure A-5. Current Sampling Resistor Connections
Rated Output, Meter Accuracy, and Current Limit
To check that all supplies will furnish their maximum rated output
voltage and current, that the front panel meters are accurate,
and that the current limit circuits function, proceed as follows:
Rated Output Voltage and Voltmeter Accuracy
a. With no loads connected: turn on the supply and push the
V1 METER switch in. Connect a DVM between the V1 +
and - terminals and set V1 VOLTAGE control until front
panel voltmeter indicates 17.00 volts.
b. Check the DVM indication. It should be within ±(0.5% + 2
counts) of the front panel voltmeter indication (16.90 to
17.10 V).
c. Set V1 VOLTAGE control clockwise until front panel volt-
meter indicates 25.0 volts.
d. DVM should indicate 25 volts ±(0.5% + 2 counts) (24.675
V to 25.325 V).
e. Repeat steps (a) through (d) for the V2 supply.
Rated Output Current and Ammeter Accuracy
f. Connect the test setup shown Figure A-6 to the V1 sup-
ply's + and - output terminals.
g. Push the V1 METER switch in to monitor the V1 supply's
output current.
h. Close the load switch and adjust V1 VOLTAGE control
until front panel ammeter indicates 1.000 A.
i. Check that DVM indicates a voltage drop across the cur-
rent sampling resistor that corresponds to a current of 1
amp ±(0.5% + 2 counts) (0.993 A to 1.007 A).
j. Open the load switch and repeat steps (f) through (i) for
the V2 supply.
Figure A-6. Output Current, Test Set Up
k. Disconnect all loads from the supply.
l. Connect the test setup shown in Figure A-6 to the V1
supply's + and - output terminals. Substitute a short for R
and leave the load switch open.
m. Push the V1 METER switch in and adjust the V1 VOLT-
AGE control fully clockwise.
n. Close the load switch and determine the current flow
through the current sampling resistor R
voltage drop with the DVM. The current should be mini-
mum 1 A + 5%.
o. Open the load switch and repeat steps (k) through (n) for
the V2 supply.
A-4
Current Limit
by measuring its
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