DMM Reading

Northampton Community College

Jack Schreiber

1 – 3 ½ Digit display

2 – Back light

3 – Rotary switch

4 – Hold button

5 – 10A jack

6 – Common jack “black probe” (negative)

7 – VmA jack “red” probe (positive)

Symbols used on digital meters

Never change the range setting with the meter connected to a live circuit.

Always select a higher range than you expect to measure, if you are unsure select the highest range.

The most accurate readings are taken with the range set to the lowest possible setting for the value under test.

Meter Safety

Never hold the meter in your hand when taking a reading under power.

For current readings above 200mA its best to use a clamp-on meter.

Always wear you personal safety protective equipment.

For low voltage that means safety glass are the minimum

Meter Safety

When the “H” is lit on the display the hold function is selected

The “–” in the display shows a negative voltage or current is applied the red probe – switch polarity to take the reading

The battery symbol denotes the battery needs to be replaced

Never measure more than 240V on the 600V range due to the fuse protection of the meter

It’s best to connect the black probe to the neutral side when measuring AC but it’s not required

The 200V range will display up to 199.9V max

Reading shown is 238 V AC on the 600V AC range

Measure current up to 0.2A starting with the 200mA range

Above 0.2A a clamp-on ammeter is recommended as the 10A range is not fused

Always remove the probe from the mA jack immediately after taking the reading

Always switch the meter off after taking a current reading on any range

The reading shown is 199.9mA DC on the 200mA range

Ohm’s range - always make sure the power is off to the circuit under test

Always make sure the item is isolated when measuring ohm’s

For accurate resistance readings short the probes first then subtract this amount from you final reading

Always use the lowest possible range for the most accurate reading

Reading shown is 96.5 ohms on the 200 ohm scale.

DC voltage – use proper polarity if the “-” sign shows switch the probes

Again the lower the range the more accurate the reading

Example use the 20 V range to read a 9 V battery not the 200 V range

Reading shown is 8.73V on the 20V DC range

Example of a typical camp-on ammeter

Proper use requires clamping around only one current carrying conductor at a time

Not designed for high voltage (over 600V) applications

Looping the conductor will increase the reading by 100% for each loop.

Looping allows for reading low values. Just remember to divide the reading by the number of loops.

Example: 10 loops with a reading of 12 A is actually 1.2 A