Multimeter

Multimeters/Multi ohmmeters/Multitesters are versatile tools measuring (AC and DC) voltage (the voltmeter), current, and resistance.

Ports

• Ports are jacks/holes to plug test leads/probes into multimeters to measure. Most have 2 ports, some 4.

  • • lead/probe: 

  • Common/Grounding port (black) 

  • V Omega MA port is (red) tests most measurement.

  • 400 mA port (Fig 1; red) is used less often.

  • 300 mA port (red) measures 300 mA.

  • 10 A port (Fig 1; red) is used less often.

It's the same for a analog meters.

Measuring

To measure AC voltage, like an outlet, put the common plug into the big/left prong and the hot wire for the right/small prong--It should say ~120 V.

Ensure to disconnect the wires in the same order theyre pluggged.

To measure DC voltage, like a battery, put the common wire to the negative and hot wire to the positive pole.

Measuring ohms

• The ohms scale (often top) goes from right (0 Ω) to left (infinity value), the opposite of voltage and ampere scales.

  • To measure ohms accurately, first calibrate the meter

(since the meter has a battery, which changes value it reads as it weakens): Set it on DC value (left knob). 

Negative/positive doesn't matter here. 

Set the range selector/selector (middle) switch highest range

10k Ω (middle knob) and touch the leads together.

We must zero it out by set the right knob to zero for the needle

to be at the right. 

Eg. 1# The selector switch is at the 25 V full scale position. How much voltage is read? 

Method 1#

• needle is at ~46V.

• 50 V is voltage's scale max value

• Divide the range by the scale's max value: 25 ÷ 50 = 0.5

• Multiply the the previous answer by 46: 0.5x46 = 23.1 V

So voltmeter reads 23.1 V.

Method 2#

• We can also use the ohm scale: needle is at ~231.25 Ω.

• 250 Ω is the ohm scale's max value.

• needle's value divide max value: 231.25/250 = 0.925

• The range multiplies the previous answer: 0.925x25 = 23.1 V

Measure ohms: By what we think the ohm value will be with the multipliers (Rx1, Rx100. Rx10k) around the middle knob, turn the knob to a multipler. 

E.g. 1# If the needle is on on the 50 Ω and the range selector is on the Rx1k, , the voltmeter reads is 50x1k = 50k Ω

E.g. 2# If the needle is on on the 467 Ω and the range selector is on the Rx100, the voltmeter reads 467x100 = 46700 Ω