Types Of Multimeter
Last Updated on July 14, 2021 by Gabriel Goddy
The importance of multimeters is not something many people talk about often, but multimeters are highly important. They can be used on various occasions. Read through this guide, as we show you all you need to know about multimeters.
What is a multimeter?
A multimeter or a multitester also called a VOM (volt-ohm-milliammeter), is an electronic measuring instrument that performs several measurement functions in one unit. A typical multimeter can be used to measure voltage, current, and resistance and even to check for conductivity.
Analog multimeters use a microammeter with a moving pointer to show the readings. Digital multimeters (DMM, DVOM), meanwhile, have a numeric display, and can also display a graphical bar indicating the measured value. Digital multimeters are now more common due to their lower cost and higher precision, although analog multimeters continue to be preferred in some instances, especially when one has to track a rapidly changing value.
A multimeter can be a hand-held device useful for basic fault finding and field service work, or a bench instrument that can calculate to a high degree of accuracy. Multimeters come with an array of features and at different price points. Some cost less than $10, while laboratory-grade models with certified calibration can cost upwards of US$5,000.
How to use a Multimeter?
The basic functions and operations of a multimeter are similar for both digital and analog testers. The tester has two leads—red and black—and three ports. The black lead plugs into the “common” port. The red lead plugs into either of the other ports, depending on the desired function.
After plugging in the leads, you turn the knob in the center of the tester to select the function and appropriate range for the specific test. For example, when the knob is set to “20V DC,” the tester will detect DC (direct current) voltage up to 20 volts. To measure smaller voltages, you would set the knob to the 2V or 200mV range.
To take a reading, you touch the bare metal pointed end of each lead to one of the terminals or wires to be tested. The voltage (or other value) will readout on the tester. Multimeters are safe to use on energized circuits and equipment, provided the voltage or current does not exceed the maximum rating of the tester. Also, you must be careful never to touch the bare metal ends of the tester leads during an energized test because you can receive an electrical shock.
Functions of Multimeters
These instruments are capable of different readings based on the model. So basic types of multimeter are mainly used to measure amperage, resistance, voltage, checks continuity and a complete circuit can be tested like the following.
- Resistance in Ohms
- Capacity in Farads
- The temperature in Fahrenheit/ Celsius
- AC Voltage & Amperage
- Inductance Henrys
- DC Voltage & Amperage
- Frequency in Hz
- Conductance in Siemens
- Duty Cycle
To some types of multimeters, special sensors or accessories can be attached for extra readings like acidity, light level, alkalinity, wind speed & relative humidity.
Types of Multimeter
There are different types of multimeters like Analog, and Digital multimeters. Each is designed to measure the same basic electrical values but differ in their method of measurement and display.
- Analog Multimeter
The Analog Multimeter or VOM (Volt-Ohm-Milliammeter) is constructed using a moving coil meter and a pointer to indicate the reading on the scale. The moving coil meter consists of a coil wound around a drum placed between two permanent magnets.
As current passes through the coil, the magnetic field is induced in the coil which reacts with the magnetic field of the permanent magnets and the resultant force causes the pointer attached to the drum to deflect on the scale, indicating the current reading. It also consists of springs attached to the drum which provides an opposing force to the motion of the drum to control the deflection of the pointer.
For the measurement of DC, the D Arsonval movement described above can be directly used. However, the current to be measured should be lesser than the full-scale deflection current of the meter. For higher currents, the current divider rule is applied. Using different values of shunt resistors, the meter can also be used for multi-range current measurements. For current measurement, the instrument is to be connected in series with the unknown current source.
For measurement of DC voltage, a resistor is connected in series with the meter, and the meter resistance is taken into account such that the current passing through the resistor is the same as the current passing through the meter and the whole reading indicates the voltage reading.
For voltage measurement, the instrument is to be connected in parallel with the unknown voltage source. For multirange measurement, different resistors of different values can be used, which are connected in series with the meter.
For measurement of resistance, the unknown resistance is connected in series with the meter and across a battery, such that the current passing through the meter is directly proportional to the unknown resistance.
For AC voltage or current measurement, the same principle is applied, except for the fact that the AC parameter to be measured is first rectified and filtered to get the DC parameter and the meter indicates the RMS value of the AC signal.
Advantages of an Analog Multimeter are that it is inexpensive, doesn’t require a battery, can measure fluctuations in the readings. The two main factors affecting the measurement are sensitivity and accuracy. Sensitivity refers to the reciprocal of the full-scale deflection current and is measured in ohms per volt.
- Digital Multimeters
We mostly used a multimeter is a digital multimeter (DMM). The DMM performs all functions from AC to DC other than analog. It has two probes positive and negative indicated with black and red color is shown in the figure. The black probe connected to COM JACK and the red probe connected by user requirement to measure ohm, volt, or amperes.
The jack marked VΩ and the COM jack on the right of the picture are used for measuring voltages, resistance, and for testing a diode. The two jacks are utilized when an LCD shows what is being measured (volts, ohms, amps, etc.). Overload protection prevents damage to the meter and the circuit and protects the user.
The Digital Multimeter consists of an LCD, a knob to select various ranges of the three electrical characteristics, an internal circuitry consisting of a signal conditioning circuitry, an analog to digital converter. The PCB consists of concentric rings that are connected or disconnected based on the position of the knob. Thus as the required parameter and the range are selected, the section of the PCB is activated to perform the corresponding measurement.
To measure the resistance, current flows from a constant current source through the unknown resistor, and the voltage across the resistor are amplified and fed to an Analog to Digital Converter and the resultant output in form of resistance is displayed on the digital display. To measure an unknown AC voltage, the voltage is first attenuated to get the suitable range and then rectified to DC signal and the analog DC signal is fed to an A/D converter to get the display, which indicates the RMS value of the AC signal.
Similarly to measure an AC or DC, the unknown input is first converted to a voltage signal and then fed to an analog to digital converter to get the desired output(with rectification in case of AC signal). Advantages of a Digital Multimeter are its output display which directly shows the measured value, high accuracy, ability to read both positive and negative values.
Advantages of analog multimeters:
- Possibility to carry out measurements at low temperatures down to -30 ° С.
- Fast operation with a large number of measurements, when high precision is not required.
- Do not require power consumption from the built-in power supply in the mode of voltage and current measurement.
- Instant display of the dynamics of the signal change.
Disadvantages and features:
- Non-linear scale and setting zero before starting measurements.
- Absence of automatic detection of voltage polarity.
- A small set of functions: most models can measure only DC and AC voltage, DC, and resistance.
- Low input resistance and, consequently, a high error in low-voltage measurements.
- Sensitivity to mechanical damage, vibration.
Advantages of digital multimeters:
- Maximum possible measurement accuracy.
- Automatic polarity detection: If the probes are connected incorrectly, the correct values with a minus sign appear on the screen.
- Possibility of automatic and manual selection of measuring ranges.
- Does not require mandatory zero adjustments.
- The accuracy of the meter reading does not depend on the battery charge.
- Resistance to mechanical damage.
- The ability to record measurement results in memory and synchronize with a PC.
Bear in mind that all multimeters take readings over some time and then give you the average, so you can expect the reading to fluctuate. In general, cheaper meters tend to average more harshly and respond more slowly, so keep that in mind when you note the readings.
Everyone can use a multimeter. If you don’t have one, it’s fine to start small and inexpensive. If you have a special use, you will likely need to invest in the right tool for that job.