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Do I Need True RMS Multimeter (11 Factors To Get True RMS Multimeter)

Do I need true RMS multimeter, first question arises to mind When we choose the RMS multimeter. True RMS multimeters differ from RMS multimeters.

However, if you are new to the electronics world, you may wonder what differentiates these two. RMS stands for Root Mean Square, while True RMS stands for True Root Mean Square.

Both RMS digital multimeter and True RMS digital multimeter perform a similar function. However, they differ in the accuracy they give. Therefore, when you need accurate values in your measurement, you should pick up a true RMS multimeter.

The values given by the True RMS digital multimeter may not seem much different from that of the RMS digital multimeter in the short term. However, in the long run, the better readings you take will pay off.

While we know what makes True RMS multimeters stand out, you may experience a bit of dilemma in knowing when to pick them up as a beginner. This guide will explore everything that’ll help you understand why you need a True RMS Multimeter instead of just an RMS multimeter or clamp meter. 

Description of the True RMS Multimeter

True RMS meter is a device that helps with electronic and electrical measurement of the level of effectiveness of an alternating voltage or current. RMS – Root Mean Square – as a value is used in finding the effectiveness level of entities. On the other hand, the RMS digital multimeter displays an average value.

For better understanding, you can check out the youtube link below:

When measuring voltage, there are several units to use. Direct current is simple to use; only a single unit is measured – volts direct current (VDC). For instance, when a power supply gives a value of A12, it will produce only 12 volts of direct current.

On the other hand, alternating current depicts a level of voltage produced as sinusoidal waveforms. These sinusoidal waves are called Sine Waves. For example, a sine wave of 60Hz makes one cycle in 0.0167 seconds. This means that the wave experiences peak polarity every 0.0083 seconds.

Electrical utility’s True Root Mean Square produces about 110 volts of Alternating current. This is the same as the 155.6 volts peak (V-Pk). So when you take the true RMS of the peak level for the pure sine wave, it’s at 0.707. However, for impure sine waveforms, the 1:0.707 scale doesn’t apply.

In electronics, note that the word multimeter and multitester are frequently used interchangeably. However, they differ from one another. A multimeter is a device used to take measurements, while the multitester does as the name suggests – for testing.

There are several cases in which RMS multimeter meters can be used, especially in frequencies above 60 Hz. Even in frequencies way higher than this – ultrasonic – a True RMS meter can be used to calibrate and maintain equipment in need of very high accuracy. One such piece of equipment is the ultrasonic ranging machine of submarines.

When do I need true RMS multimeter?

True RMS digital multimeter does not rely on averaging when calculating alternating current or direct voltage. Instead, to calculate, the RMS multimeter’s processor leverages the root mean square formula to facilitate the accurate accommodation of distorted waveforms when taking measurements. Why is it so important? To get a proper explanation you can watch the video below.


Here are scenarios where using the True RMA Multimeter is a compulsion.

1. For Imaging Supplies

True RMS multimeters are the best option from printers to digital duplicators, fax machines, copiers, and other multifunctional devices. The True RMS multimeters will help measure the actual amount of voltage that the exposure lamps, copier parts, and other AC voltage-receiving systems receive In these imaging appliances.

Using an ordinary RMS multimeter will only give you an average value for the amount of AC voltage received. An average value makes it impossible to make an accurate AC voltage adjustment as a technician.

When you use a True RMS Multimeter, you improve your service call efficiency. The device also helps prevent improper adjustments, premature parts failure, damages to the machine, and poor copy quality.

2. Component-Level troubleshooting

When working on component-level troubleshooting, you need the True RMS multimeter. You need the device to measure voltages beyond 500 million cps. Component-level troubleshooting requires high accuracy.

Hence, the need for a device whose readings will provide performance indications. When you also need to isolate faulty components, the True RMS multimeter is your best option. It is a must-have if you run a repair workshop.

3. Low voltage systems

When working on low voltage systems, the True RMS multimeter is the best. Low voltage systems are those using 50 volts or less of electricity.

Examples of low voltage devices are doorbells, home security sensors, landscape lighting, garage door openers, and thermostats. These devices operate on either 48V, 24V, or 12V electricity. They are mainly residential appliances.

4. Variable frequency drives (VFD)

In taking measurements in Variable Frequency Drives, the True RMS multimeter is vital. This device will give you an accurate reading of the non-sinusoidal voltage’s heating effect.

However, there may be some limitations to older model True RMS multimeters when you aim to achieve even higher accuracy. This is because the True RMS will not agree with the motor controller’s output voltage reading, which only displays the fundamental component’s RMS voltage.

You can, however, mitigate this limitation by getting very recent True RMS multimeters, most of which come with the VFD mode and comprehensive feature sets. In addition, the incredible advancement in the technology powering the modern True RMS multimeters makes them easy to use while also ensuring immense stability for the long term.

Hence, when you are dealing with Variable Frequency Drives, get the modern True RMS multimeter to prevent any false reading.

5. Phase Control 

When doing phase control, the True RMS multimeter is highly vital. For example, the phase control technique is used to dim incandescent lights.

It would help if you had the True RMS multimeter to get the accurate RMS voltage value. With this device, you can get your voltage measurement to the nearest 0.1 volts, with 3-digit accuracy. An ordinary RMS multimeter won’t cut it in this case.

6. High-efficiency HVAC system

When dealing with high-efficiency HVAC systems, you’ll need the True RMS multimeter or HVAC multimeter. The high-efficiency HVAC systems have a complex system beyond just turning them on and off.

To measure loads of these systems, you’ll need the True RMS multimeter to prevent false readings due to ghost voltage. Ghost voltage is a reading that we do not expect.

With this device, you’ll accurately register the amount of work that can be accomplished by an equal amount of DC voltage or current. The accuracy of the measurements makes the True RMS multimeter the best option for a system with variable speed motor or switching systems.

In the HVAC system, the voltage and current signals are mainly sine waves perfect sine wave is said to be a sinusoidal waveform in shape; the loads are generated from AC motors. Therefore, you might say the non-true RMS meter will give you an accurate reading for the sine waves.

However, you shouldn’t forget that the HVAC systems also feature heaters, fan motors, and several control signals that end up distorting the sine waves. This distortion results in a non-sine waveform.

Hence, it necessitates a True RMS multimeter when measuring the equal amount of DC voltage or current needed as an alternative power source.

7. Elevators

When dealing with Elevators, you need the True RMS multimeter. Elevators are always busy, especially those in commercial buildings. This is because so many people depend on these elevators.

Hence, as the technician working on it, you must ensure that downtime is very close to zero.

You need the True RMS multimeter when working on elevators because they comprise Variable Frequency Drives. These VFDs are the Motor Drives of the elevator and facilitate the transformation of constant voltage from the main Alternating Current power supply to variable voltage, hence, controlling motor torque and speed.

True RMS multimeters are used to troubleshoot drives.

8. Controller boards

Controller boards form a connection between devices and objects to computers, giving them the ability to serve as peripheral controllers. With these controllers, actions and events in these systems can be controlled by the peripheral controllers.

Accurate measurement is critical in this case. Only a True RMS multimeter can give you the needed level of accuracy when taking measurements.

9. Conveyors

Conveyor Systems are premised on accurate measurements and details. Hence, you need the True RMS multimeter. These mechanical devices transport materials from one point to the other with minimal effort.

Slight inaccuracies in measurement value can be costly in the long term. Examples of conveyor systems include; pneumatic, belt, roller, and screws.

10. High tech and IT environments

When you are working with the latest advancements in engineering and technology, you need your measurements to be beyond accurate. You can’t rely on the average values provided by RMS multimeters or clamp meters in this case. Instead, you need the True RMS multimeters.

11. Solid-State Electronics

These electronic devices are part of our daily lives. The most common form of these is Transistors. The crystal radio was also one of the first solid-state devices created.

These devices work with frequencies and signals that vary. Hence, you need a voltage measurement device that’ll give accurate measurements per time.

If your repair or maintenance work involves any solid-state electronic devices, a True RMS multimeter is a must-have to measure true RMS voltage. Invest in getting one.

There are several other cases in which you can use the True RMS multimeter. These include; industrial motors, power supplies, motor controls, Machine tool drives, Pumps.

Crest Factor in True RMS Multimeter

Before you pay for a True RMS multimeter device, ensure that you check for the RMS Crest Factor signals. Crest factor is the ratio measurement of the peak amplitude of a waveform instantaneously to its RMS value.

Peak amplitude refers to the instantaneous peak current required per load. In essence, the RMS crest factor depicts how off a waveform is.

When the sine wave is perfect, the crest factor is always 1.414. However, when the wave is distorted, the crest factor value changes. This is because the distortion of the sine wave is directly proportional to the crest factor value.

Hence, if you see your multimeter with a crest factor value of 1.5, you are bound to get inaccurate results. On the other hand, if the multimeter has a crest factor value of 3 or more, you should make accurate measurements, irrespective of the waveform’s degree of distortion.

Tips to Making More Accurate RMS Measurements

If you are looking to make more accurate measurements with your True RMS multimeter, here are some tips to help.

Understand your Device

As a technician, the best thing to do for yourself is to understand the workings of your device perfectly. Not the general workings now; know the peculiarities of your True RMS Multimeter. You may not be able to use other people’s devices, but you must understand yours.

There are four main technologies used in True RMS multimeters;

● Thermal AC to DC Converters

● Analog AC to DC converters

● Digital Sampling AC converters

● Peak and Averaging AC converters

Know what technology powers your device.

Beware of Measurement Errors

When making measurements with your True RMS multimeter, you should ensure that you note the following factors. They can lead to errors in your readings.

●       Harmonic Content: When signals are rich in harmonic content, they can lead to low measurement readings. Especially when fewer of the components are included in the measurements. 

On the other hand, when you measure only the fundamentals, you may end up with values higher than normal. 

You can avoid these errors by cross-checking the datasheet of your multimeter. The datasheet will guide you on the appropriate bandwidth to use. 

●       Low-level measurement errors: When taking AC measurements less than 100mV, external noise sources can cause errors. For instance, when a test lead is exposed, it can serve as an antenna, which influences the reading by your multimeter. 

You can get rid of these errors by using shielding techniques. You can also reduce the antenna’s area. You should also ensure that both the multimeter and source of AC are connected via the same electrical point outlet. This will minimize ground loops. 

●       First-Reading Accuracy: Your True RMS multimeter probably features a large DC blocking capacitor in the input. This can lead to errors in your first readings. Hence, before taking the first readings, allow the device some time to charge, especially when dealing with low-frequency signals. 

●       Measurement Not Up to Full Scale: New multimeters specify the AC inputs down to about 5 or 10% of the full scale. You can mitigate this by ensuring that your measurements are as close to the full scale as possible. 

It would be best if you overrode auto-scaling on your device. Though, ensure care when your measurement involves high crest factor signals. Overloading may result in the saturation of the input circuitry of the meter. 

Informative Visual link

An informative video you can watch and gather knowledge about TRMS multimeter.


Summarily, when you need to take voltage and current measurement of AC signals, which aren’t pure sine waves, you need a True RMS Multimeter.  

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