Measuring Current

Measuring AC Voltage Riding on a DC Source Bias

To measure AC voltage superim- posed on a DC voltage source bias while ignoring the DC voltage, you must first measure the AC and DC voltages separately, then compute the peak voltage using this formula:

Peak voltage = DC voltage + AC volt- age/0.707

WARNINGS:

•TO AVOID INJURY OR DAM- AGE TO YOUR MULTIMETER, NEVER TRY TO MEASURE AN AC VOLTAGE THAT IS RIDING ON A DC SOURCE BIAS WHERE THE PEAK VOLTAGE

EX-CEEDS 100V WITH

RESPECT TO EARTH GROUND.

•TO AVOID INJURY OR DAM- AGE TO YOUR MULTIMETER, NEVER TRY TO MEASURE ANY VOLTAGE MORE THAN 30V AC ON A DC SOURCE BIAS.

Follow these steps to measure an AC voltage superimposed on a DC volt- age source bias.

1.Set the function selector to one of the DCV positions. Then touch the test leads to the circuit you want to test and note the reading on the upper or lower line of ACVA/DCVA on the multimeter.

2.Disconnect the test leads from the circuit.

3.Remove power from the circuit under test and discharge all capacitors.

4.Set the function selector to one of the ACV positions. Then con- nect a 0.1 microfarad/100V poly- ester film capacitor in series with the positive terminal of the volt- age source and the red test lead.

5.Connect the – (common) test lead to ground and note the read- ing on the upper or lower line of ACVA/DCVA on the multimeter. The multimeter shows the AC voltage.

Warning: To avoid electric shock, never touch the circuit and test terminals while testing.

6.When you finish measuring the AC voltage, disconnect the power from the circuit under test then disconnect the capacitor you connected in Step 4.

Measuring DC Current

WARNING: DO NOT APPLY VOLT- AGE TO THE TEST LEADS WHILE THE FUNCTION SELECTOR IS SET TO 150mA DC mA. THE CONNEC-

TION MUST BE IN SERIES WITH THE CURRENT.

Using the Multimeter