A Multimeter as the name suggests is an instrument that can do the function of many meters. Over a century ago, electrical measurements of current was done by an ammeter, a voltmeter was used to measure voltage, an ohmmeter to measure resistance. Carrying 3 instruments to do measurements was cumbersome & laborious. This led to the invention of Analog Multimeters initially.
Analog Multimeters could measure AC A, V, & resistance. More functions such as DC. A, V, were added. With development of semiconductors, more functions were added to Analog Multimeters. Safety features were added to protect the multimeters. Analog Multimeters reigned the market for over 5 decades. With digital technology being introduced in the 80’s, the Analog Multimeters gave way to Digital Multimeters. Digital Multimeters are superior to analog multimeters because of their better accuracy in measurements, sensitivity to very small changes in input voltages and clear and easy to read displays. Digital multimeters need a power supply as batteries or a main supply.
The Multimeter consists of a display, buttons, a dial that allows us to move through different scales and input jacks. Digital Multimeters have varying levels of display values depending on the model. Depending upon the number of digits the resolution increases. And also accuracy. Digital Multimeters are categorized based on their use.
CAT I – for electronic devices that are not connected directly to the building’s power supply
CAT II – for appliances, PC’s, and TVs that are plugged into the building’s power supply
CAT III – for motors, lighting systems in large buildings, and power distribution lines
CAT IV – for three-phase connections by electricity providers
For safety reasons we should be careful to use the correct category of Multimeter for our application. The higher categories have high energy fuses that protect devices connected to high voltage input services. These fuses prevent the high voltage from passing to the tested devices and burning them out and also the user.
New technology Multimeters have high safety ‘UL’ listing with transient protection upto 12KV which protect the device being tested and also the user.
Most commonly available Multimeters can measure AC Voltage, DC Voltage, AC Current, DC Current, Resistance, Continuity, Diode Test, Capacitance Frequency, Temperature. These DMMs are used by hobbyists. They do not provide high degree of accuracy. They give a general idea of what’s working.
Handheld Multimeters are used by HVAC. Specialist, electricians, electrical contractors, maintenance personnel in factories. Hand held DMMs are used when mobility is required.
Advance hand held DMMs have added functions such as VFD measurements, Conductance, 4-20mA signals. Square wave output pulse, graphical display, data logging function, PC connectivity.
High grade of Multimeters, have higher resolutions to be able to measure minute signals such as nano amperes, nano volts. They are available in both hand held types & bench types. These instruments are extremely precise and have a variety of advance functionality including the ability to program, automation and interface with other instruments. They can also be interfaced with PC to store for future analysis. New DMMs also have Bluetooth feature to capture the readings on mobile phones.
How to choose a Multimeter?
When it comes to choosing a Multimeter which will be best for your present & future needs, there are a number of factors for consideration. What is the application? What is the maximum range of any parameter to be checked? What functions are to be measured? What is the circuit energy level? What is the accuracy? Do you need precise or approximate readings? How long do you propose to use it? What is the budget you have? Is there any limitation to size?
Once the above questions are answered, then it becomes easy to select the right DMM.
