How to Use a GDT-11 Multimeter

By John Papiewski
Use a multimeter to test your car battery.

Gardner Bender’s GDT-11 is a handheld digital multimeter with a 3 1/2-digit liquid crystal numeric display. The meter measures volts for direct and alternating currents, resistance and DC current. In addition, the unit has a diode check feature.

Preparing Meter and Battery

Snap the battery clip onto one of the batteries; set the battery aside for measuring voltage and current.

Plug the red test probe into the meter socket marked VΩmA.

Plug the black test probe into the meter socket marked COM.

Rotate the function selector knob to any setting other than OFF. If the display does not turn on, or if you see the BAT indicator on the display, replace the meter’s internal 9-volt battery with a fresh one.

Tip

Measurements of a 9-volt battery are safe as the voltage is too low to pose a shock hazard.

DC Voltage

Rotate the function selector knob until it points to the 20 range in the DC voltage scale, indicating a maximum of 20 volts. The DC voltage scale is indicated by the V-- symbol on the meter.

Touch the metal tip of the red meter probe to the positive wire of the battery clip; usually this is the red wire. Touch the tip of the black probe to the negative wire, which is black.

Read the voltage indicated on the meter’s LCD display. The meter should measure roughly 9 volts.

Tip

You can measure voltage or current with the probe polarity reversed; however, the meter will display a negative number. This does not adversely affect the meter or the components you’re testing.

Warning

Avoid touching the metal probe tips when measuring voltages greater that 50V; high voltages pose a shock hazard.

Resistance

Rotate the function selector knob until it points to the 200 range on the meter’s resistance scale, indicated by the symbol.

Touch the red meter probe tip to one of the resistor’s leads. Touch the black probe to the remaining resistor lead.

Read the resistance on the meter’s display. You should see a reading of about 100 ohms; a few percent higher or lower is normal.

Warning

  • Do not touch the metal probe tips when measuring resistance; the resistance of your skin will affect the meter’s accuracy.
  • Do not attempt to measure resistance for circuits or components that are powered on or have currents running through them; you might blow the meter’s fuse or damage the unit.

DC Current

Wrap the positive battery clip wire around one of the leads of the resistor.

Rotate the function selector knob until it points to the 200 range in the meter’s DC current scale, indicated by the A-- symbol.

Touch the tip of the red meter probe to the free lead of the resistor. Touch the tip of the black meter probe to the negative battery clip wire.

Read the current value on the meter’s display. You should see a reading of about 90 milliamps or .09 amps.

Warning

Do not attempt to measure currents in excess of 200 milliamps unless the red meter probe is plugged into the 10A DC socket and the selector knob points to the 10A-- range.

Always measure current with a resistance connected in series with a battery or other power source; the resistance limits the current and avoids a potentially damaging short circuit.

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."