Energy multimeter: What is it?

The energy multimeter is an electronic, microprocessor-based device capable of measuring electrical quantities in a circuit. It allows access to measurement information through an available Human-Machine Interface (HMI), and has several variants in terms of capacity, quantities measured, accessories, functionalities and local or remote interfaces.

Energy multimeter, electrical quantity multimeter, multimeter, or simply, meter, are the most used terms and almost always refer to the same type of equipment, with the same objective, to measure different electrical quantities, and hence the adjunct term “MULTImeter”, thus carrying out the measurement of “MULTI-quantities”.

What is an energy multimeter for?

SThere are two main reasons why we use an energy multimeter, and its application may be necessary and possible at any energy consumption point, from the entry point to the Concessionaire Coupling Point (PAC), where there is even a meter dedicated to billing, to panels and loads distributed throughout any infrastructure. If there is an electrical energy point, it is possible to measure it with a multimeter.

Monitoring and visualization: Electricity monitoring is performed where there is a concern with energy management (increased consumption, demand, etc., cost, ICMS, apportionment, etc.), or there is a need to visualize an electrical panorama of a point. In these cases, it is common, and often necessary, to apply more than one meter, expanding to a system, where possibly a software that manages all the data collected will be present, helping in the analysis and management of whoever operates it.

Monitoring and Control:

A multimeter is necessary in automation and control systems as an enabler of controllable parameters, when an electrical quantity is involved in a process.

Meter and measured electrical quantities

A multimeter measures the main electrical parameters, such as:

Line voltage (between phases), or/and phase voltage (between phase and neutral);Electric current;Power (Apparent, Active, Reactive) (Per phase and/or three-phase);Power factor (Per phase and/or three-phase);Frequency;DHT (Total Harmonic Distortion of voltage and current DHTu and DHTi);Energy (Active and reactive, capacitive and inductive);Consumption (active and reactive, capacitive and inductive);Demand (active and reactive);Among others.

Types of energy multimeters

Some are more basic and others more complete, there are several models, therefore, there are several measurement capabilities, that is, one model can measure more parameters than others, including some aspects of energy quality, such as DHTs, for example.

In general, we can divide them according to their characteristics, so the table below suggests the main differences between them, helping in decision-making for application.

• Interface AspectsHas Display;Has Keyboard;

• Mechanical AspectsFor panel door;For panel bottom;Portable;

• Current SensingVia CT;Direct;With Rogowski Coil (Flexible Sensor);

• Measured QuantitiesHow many and which quantities does it measure;

• Communication AspectsRS485 port;ETHERNET port;No communication;

• Mass MemoryMemory for records;No memory;

• Multimeters have several user interfaces, the most obvious being: Display/alphanumeric or graphic screen, and communication interfaces for insertion into local networks and the internet for use with software for data analysis and generation of reports and graphs.

For each application, a type of equipment may be more suitable and viable, depending on the design and measurement needs, the model with the correct characteristics.

Important accessories and devices

Calibration key

When installing multimeters, it is highly recommended to use calibration switches. They allow maneuvers of meters and sensors/current transformers, acting as an intermediate switch that separates the circuits, keeping the CT secondary free from operation with an open secondary, which can cause accidents. The calibration switch facilitates maintenance maneuvers, speeds up the operation, and provides safety to the specialist involved.

Current sensors and their types

Current sensors allow multimeters to read the current. As there are different capacities, magnitudes and values, the sensors are devices sized according to mechanical aspects (if they fit in the available space in a pre-existing installation, for example), precision (if used for protection or measurement, which is the focus here), and measurement capacity (range/scale). There are several types of current sensors, and each one is adapted to a specific application.

Current Transformers – CT

It is a device that transforms the value of the electric current, allowing high currents to be transformed into smaller currents, proportionally. In short, it consists of an iron core, primary winding (input), and secondary winding (output), which have a sufficient number of turns to obtain a nominal current of the order of 1, 5 or 10A at its output (secondary). The secondary winding delivers its current (reduced) based on a current of the order of 10 or 100 times greater in the primary winding (input).

Imagine that the multimeter will be installed on a bar or cable that carries a current of up to 2000A. The current transformer receives this current in its primary winding, and supplies a current 400 times smaller in its secondary, which allows the meter to read, which in turn normally accepts currents of around 5A.

We call this CT in the example a 2000/5A CT, and there are numerous possible currents in the primary, and obviously, changing the “size” of the device. Larger currents require more turns and larger cores, so we have transformers that are larger in size and volume.

It is common to find two types of current transformers, namely: Split and window, with different sizes and acceptable current values.

We can choose according to ease of installation, cost-benefit, precision, material it is made of, and mainly its nominal currents.

Bipartite Type CT

Transformer with a split core (mountable), which allows it to be disassembled, facilitating installation. To install this type of transformer, it is not necessary to disassemble the circuit to be measured.

Window Type CT

Transformer with a solid, solid core that does not allow opening. In this case, it is necessary to disassemble the circuit to be measured so that the conductor can pass through the transformer.

Flexible current sensor

Flexible current sensors are devices that work based on the Rogowski coil theory. Basically, this type of sensor has a series of advantages over current transformers. High accuracy;

Ease of installation due to the possibility of deformation and adaptation to the available space;Signal converted from A to mV, reducing the need to use calibration keys;Increased operational safety.

Additional features

Communication

For various applications in management systems, or in process automation, it is necessary for a multimeter to communicate with other devices, be they computers, servers, PLCs, or even data concentrators and/or modems.

Communication allows us to move beyond the scope of a device to an online system, or rather, a more autonomous solution, which allows us to optimize actions and, in turn, costs. Therefore, we have the participation of the multimeter in a system, with other assets, other multimeters, and with a much broader and more vital application. There are a variety of communication ports and protocols available, with MODBUS TCP/IP, encapsulated in an ETHERNET output – RJ45 or even RTU via RS485, being the most widely used worldwide.

A very common example is the use of meters in energy and utility management software, which allow viewing of quantities in real time, apportionment, comparison, issuing of reports, graphs, among dozens of other applications.

Relay outputs

In many applications, the user may need to perform some type of control or activation based on triggers, activated based on the multimeter measurement. Turning on the output based on a voltage above 127V, turns it off if the current exceeds 52A or 100kW. These are examples of trigger activation.

In addition to this type, it is also possible, in some cases, to turn the lights on or off depending on the time of day. We can think of a store window, for example, which should be turned off at the end of the working day and turned on at dusk, thus ensuring optimized and linear (predictable) consumption.

Digital inputs

Multimeters with digital inputs allow readings of other quantities from meters that have pulse outputs. This type of input allows counting of pulses from water meters, gas meters or other fluids, etc., thus enabling the management of non-electrical quantities using the same multimeter equipment.

Multimeter example Various models

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