Agilent Technologies E3630A Rated Output, Tracking, Meter Accuracy, and Cur- rent Limit

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 resistor 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 calculated by dividing the voltage across the sampling 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 recom- mended in Table A-1, for example, has a resistance of only 100 mW and can be neglected when calculating the load resistance of the supply. Figure A-4 shows a four terminal meter shunt. The load current 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-4. Current Sampling Resistor Connections

Rated Output, Tracking, Meter Accuracy, and Cur- rent Limit

To check that all supplies will furnish their maximum rated output voltage and current, that the ±20V outputs track each other, that the front panel meters are accurate, and that the current limit circuits function, proceed as follows:

Voltmeter Accuracy

a.With no loads connected: turn on the supply, connect a digital voltmeter between the +20V terminal and common (COM), and set the ±20V VOLTAGE control so that the DVM indication is as near as possible to 17 volts.

b.Push the +20V METER switch on and check the front panel voltmeter indication. It should be within ±(0.5% +2 counts) of the DVM indication (16.90V to 17.10V).

c.Set the TRACKING RATIO control to the FIXED position, and check the +20V and -20V ranges of the front panel voltmeter similarly by connecting the DVM to each of these outputs in turn, setting the ±20V VOLTAGE control for a 20 volts DVM indication, and verifying that the panel meter is accurate within ±(0.5%+ 2 counts) (19.7V to 20.3V).

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 +20V output (19.8V to 20.2V).

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 19 to 21 volts. Return the TRACKING RATIO control to the FIXED position.

Leave the TRACKING RATIO control in the FIXED position throughout the reminder of the performance test.

Rated Output and Ammeter Accuracy

f.Connect two 40W 20 W load resistors across both of the 20V outputs of the supply and set the ±20V VOLTAGE control for ±20V outputs. (All supplies must be fully loaded while checking the rated output voltage and cur- rent of each supply.)

g.Connect the test setup shown Figure A-5 to the +6V output. Make the total resistance of RL and the current sampling resistor equal to 2.4W to permit operating the output at full load. RL should have a power rating of at least 20 watts.

h.Close the switch and set the +6V VOLTAGE control so that the DVM indicates a voltage drop across the current sam- pling resistor that corresponds to a current of 2.5 amps.

i.Push the +6V METER switch and verify that the front panel ammeter indication is within ±(0.5%+2 counts) of

2.5amps (2.47A to 2.53A).

j.Check the rated output and ammeter accuracy of the +20V and -20V supplies similarly by connecting the test setup of Figure A-5 to each output in turn. For each 20V supply: make the total resistance of RL and the current sampling resistor 40 W, set the ±20V VOLTAGE control for a current indication on the DVM of 0.5 A, check that the panel meter indication is within ±(0.5%+2 counts) of

0.5A (0.48A to 0.52A).

Figure A-5. Output Current, Test Set UP

A-4