Let’s Know Digital Multimeter

TRMS multimeter is useful where there are non-linear loads and have a lot of disturbances in signal quality.

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Let’s Know Digital Multimeter

In the past, to measure different electrical parameters like Voltage, Current, Resistance, separate meters were required. The problem was more prominent where on-field testing was done, to carry all these meters was a hectic task. But eventually, as technology evolved all these parameters got combined into one product called Multimeter.

What is a Multimeter?
A Multimeter is an electronic instrument combining several different functions. It was also called as AVO meter as earlier it had three primary functions only, like measurement of Voltage, Current, Resistance. It used to have an analog pointer and was of big size.

As electronics evolved everything became compact. Multimeters also became compact. A lot of parameters got incorporated in Multimeter apart from Voltage, Current & Resistance like Capacitance, Frequency, Diode testing, Continuity testing, duty cycle, Temp. measurement.

So, to sum up, a Multimeter is a handheld device used for basic fault finding and service work in the field. It also comes in a benchtop type models with very high accuracy of the measurement.

The criticality of Usage of Multimeter
Abnormal power conditions occur at any point of time in home, industries. Such abnormal conditions can lead to damage of different equipment’s resulting in significant revenue losses.

A multimeter is often used to troubleshoot electrical glitches in a wide range of industrial and household devices such as motor controls, power supplies, electronic equipment’s, domestic appliances, and wiring systems

Basics of Multimeter
A multimeter has some parameters like Digits & Counts, Basic Accuracy, Average & Trms, Type of category protection in multimeter, Type of connections. One must know all these parameters in depth so as to select the right model of Multimeter. Let us understand these parameters in detail.

Digits & Counts
Usually whenever we purchase a Multimeter first thing that comes into mind is Digits & Counts. The number of digits decides the maximum value multimeter can display and counts decide when the range will be changed while taking various measurements. For Eg. If a Multimeter is 3 ½ digit and 2000 counts Multimeter, then it will display 3 full digits and first Most significant digit will be half like 0 or 1. As shown below:
3½ digits = 1 9 9 9 = 2000 Counts
3¾ digits = 3 9 9 9 = 2000 Counts
4½ digits = 1 9 9 9 9 = 20000 Counts

So, we can say as the number of digits and counts increases in a Multimeter so as the accuracy and range of the multimeter will also increase.

Basic Accuracy
The multimeter has the capability to measure various parameters, but when a basic accuracy of a multimeter is asked DC voltage accuracy is specified as per Industry norms. The reason why it is specified as basic accuracy since it is the best accuracy a multimeter can offer due to its design in which it processes the data.

As we can observe from fig.1 for giving data to analog to digital converter it is being converted into DC voltage as A to D converter only accepts DC voltage input. Hence all other parameter goes through the process of conversion whereas DC voltage is just attenuated and given directly to A to D converter. So highest accuracy is achieved while measuring the DC voltage and hence it is specified as basic accuracy of Multimeter.

Average & TRMS
There two types of Multimeter available popularly categorized as Average & TRMS. Basically, an average meter average outs the value of the signal and resultant average value is zero for pure sinusoidal wave. So an average multimeter is calibrated for the pure sine wave and it measures the RMS values of sinusoidal waves, thus it is also called as Average RMS. Here it is important to note that an average RMS multimeter treats all signals as sine wave and displays the readings. So, it does not read the values accurately for signals apart from sine wave. A TRMS Multimeter chops any type of wave takes the instantaneous values and calculates the root mean square value of the signal. Thus giving an accurate reading for any type of wave under measurement. So a TRMS multimeter is useful where there are non-linear loads and have a lot of disturbances in signal quality. Hence, it becomes very important to rightly select the multimeter according to the application and type of signal quality present in the premises.

Type of connections
It is very important to know how one should connect the multimeter while measuring the voltage and current as it can lead to serious accidents. Voltage is always measured in parallel, hence while measuring the voltage you can directly connect the two leads of multimeter into mains socket or any voltage measurement points of devices, as in this case multimeter is connected in parallel. Whereas current is measured in series, so a load has to be always connected across the multimeter while measuring current, if the multimeter is not connected in series, then a large amount of current will flow from the multimeter. This will result in the burning of multimeter and also cause danger to the human being. Some multimeter also provides terminal blocking system so as to avoid wrong connections and enhance the safety of the user.

Category Protection in Multimeters
Multimeters are hand-held devices and are often used for testing of live objects. There is a high probability, if a transient occurs in system it will also pass through them. Understanding this IEC 61010 devised protection called Category protection in which it states protection of multimeter against such transients at different voltage levels depending on the area of usage/application. There are four category protections like CAT IV, III, II, I categorized for different area of application with operating voltages like 600V, 1000V. The level of protection increases as we move closer towards the source from where electricity is generated. For e.g. If a multimeter has CAT protection of CAT IV 600V it can sustain a transient of 8kV for certain microseconds, thus it will be suggested for environment operation outside the industry. Thus, it is very important for one to select the multimeter with the right category of protection depending on the area of application.

Rishabh has a wide variety of Multimeters to offer to start from basic multimeters like Rishabh Young/iYoung, Rishabh 410 useful for Technical students, Electricians & Service industry, for industrial segment Rishabh 6k series, Multi series is available which have features like automatic terminal blocking system to avoid wrong connections, dual display facility, drop-proof meters, there is an advanced series of multimeters like Rishabh 60k series with Bluetooth catering to high-end applications like Axle counters, Automation, VFD drives etc. Thus, with a wide variety of range of multimeters Rishabh caters to different segments of customers, offering solution to each segment.

Contributed by:
Rishabh Instruments Pvt Ltd

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