How to Use Sperry DM 350A

By John Papiewski

The Sperry DM 350A digital multimeter measures AC and DC voltage, DC current and resistance. The portable, battery-powered unit has a 3 1/2-digit liquid crystal display and is suitable for general troubleshooting of electrical systems and electronic circuits.

DC Voltage

Turn the function selector knob of the DM 350A counterclockwise to the 20-volt DC range, indicated by a V-- on the meter.

Tip

The LCD display should turn on when you rotate the selector knob. If it doesn’t, replace the meter’s internal 9-volt battery.

Plug the red meter probe into the meter’s V-Ω jack. Plug the black probe into the COM jack.

Touch the metal tip of the red probe to the battery’s positive terminal. Touch the tip of the black probe to the negative terminal.

Observe the meter’s display. It shows the battery’s voltage, which should be approximately 9 volts.

DC Current

Turn the function selector knob of the meter to the 200 m setting in the A-- range, which indicates DC current.

Plug the red meter probe into the meter’s mA jack. Plug the black probe into the COM jack.

Wrap one lead of the 1K-ohm resistor around the negative battery terminal.

Touch the black meter probe to the unconnected lead of the resistor. Touch the red meter probe to the positive terminal on the battery.

Observe the meter’s display. It shows the current flowing through the resistor, which should be approximately 9 milliamps.

Tip

If the reading is zero, replace the meter’s internal fuse. The fuse is a 5 x 20 mm type rated at 1/2 amp and 250V.

Resistance

Turn the meter’s function selector knob to the 20K resistance setting marked by the Ω symbol.

Remove the resistor from the battery if the resistor is connected.

Plug the red meter probe into the meter’s V-Ω jack. Plug the black probe into the COM jack.

Touch the tip of one probe to one of the resistor’s leads. Touch the other probe tip to the opposite resistor lead.

Observe the meter’s display. The meter should read about 1,000 ohms.

Warning

  • Never take readings for voltages over 500V or currents known to be greater than 200 milliamps.
  • Do not take current measurements when the voltage is greater than 250V.
  • Always hold the meter probes by the plastic body, not the metal tip. This reduces the possibility of electrical shock and ensures an accurate reading.

About the Author

Chicago native J.T. Barett has a Bachelor of Science in physics from Northeastern Illinois University and has been writing since 1991. He has contributed to "Foresight Update," a nanotechnology newsletter from the Foresight Institute. He also contributed to the book, "Nanotechnology: Molecular Speculations on Global Abundance."