Multimeter: the essential tool for measurement and diagnosis. 

The multimeter is an instrument used by many people involved in electronics, circuit enthusiasts, appliance repair technicians, mechanics, and electricians.

There are many varieties, and their price depends on the integrated functions. Today, we're going to tell you a bit about its history and review its basic functions.

What is a multimeter?

The multimeter, also known as a polymeter or tester, is a fundamental electronic tool used to measure different electrical magnitudes in circuits and devices.

Its basic functions include measuring voltage (V), current (A), and resistance (Ω), although more advanced models can measure capacitance, frequency, temperature, and continuity, among other features.

How was the multimeter invented?

In an office of the  British Post Office, an engineer, Donald Macadie, tired of having to carry three pieces of equipment: the ammeter, the voltmeter, and the ohmmeter, every time he made repairs and maintenance to telecommunications circuits, came up with a way to combine the three pieces of equipment into one, resulting in the first multimeter.

Known as AVO (Ampere, Volt, Ohm) and first commercialized by the company  Automatic Coil Winder and Electrical Equipment Company in 1923, the first model was only for DC circuits. Later, the AC circuit part was implemented.

Digital and analog multimeters.

The first multimeter models were analog, and it wasn't until 1982 when the  Fluke brand launched the first digital models. The series was known as 8060 and marked a development that has not stopped to this day.

Figure 1 shows an analog multimeter and a digital multimeter, where differences in size, measurement readout, and function buttons/knobs can be observed. Modern multimeters can measure temperature, capacitance, duty cycle, transistor gain, and circuit continuity.

 

There are other multimeters called "clamp" or clamp meters, which have a clamp that can measure the electric current flowing through a cable more easily. Figure 2 shows a multimeter of this type from the  Pro'sKit brand, which is also auto-ranging.

This means that the multimeter will automatically know the ranges for voltage, current, resistance, etc.

 

All multimeters have a fuse that protects them from incorrect measurements. However, we could permanently damage our instrument if the range, the measurement leads, or the measuring method are wrong. Below, we present how basic measurements should be performed. It is important that if the multimeter is not auto-ranging, we must select the range.

Advanced functions in modern multimeters

Voltage measurement

The range selector should be in the V῀/VCA/ACV section for AC voltage measurements or V-/VCD/DCV for DC voltage measurements. If it's not auto-ranging, we should set an approximate range based on the expected measurement value.

The probes should be placed in  parallel to the element or circuit being measured.

 

Resistance measurement

The range selector should be in the section marked with the Ω symbol. If the multimeter is not auto-ranging, we must select the approximate range to obtain an easier-to-interpret measurement.  The power supply must be off if we are measuring an electrical or electronic circuit. Additionally, if there are capacitors in the circuit, they must be discharged.

The measurement leads are placed in parallel with the resistor. Figure 4 illustrates this measurement.

 

Current measurement

For measuring current in a circuit, the process is similar to starting a voltage measurement. We must position the range selector, but now in the A-/DCA/ACC section for direct current or in the A῀/ACA section for alternating current. We must select the approximate or maximum range and reduce it until we reach the appropriate one if it is not auto-ranging.

The circuit must be turned off, and the probes should be placed in series with the circuit element being measured; then the circuit should be turned on again. Figure 5 illustrates how this measurement should be performed.

 

It is important to note that the red lead should be placed in the mA or 10 A terminal depending on the current range to be measured.

Measurement Solutions at Incom.

At INCOM, you can find different multimeter models that suit your needs. Remember to always be cautious when taking measurements on active circuits, check that the power supply is off when required, discharge any capacitors that may affect the measurement, and connect the measurement probes correctly.