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| Solutions | Current and Energy Measurement Technology | Glossary | Solutions | Current and Energy Measurement Technology | Glossary



Arithmetic Mean Value

Sine current

+ Sine current

Mean square current

+ Mean square current

The arithmetic mean value (also average) is the quotient of the sum of all measured values detected and the number of measured values.

For periodic variables (e.g., sine waves) the arithmetic mean is zero. For this reason, it is not meaningful for use with periodic variables, or it only provides information about a possibly present constant. For DC variables, the arithmetic mean value corresponds to the average measured value viewed over time

Mean Square Value

The mean square value — RMS (root-mean-square), also the TRMS (true root-mean-square) — is the square root of the quotient of the sum of squares of the measured values and number of measured values (square root of the average of the measured value).

In electrical engineering, the effective value of an periodic quantity corresponds to the effective value of the DC variable. It is characteristic of the power transformed in the consumer.

A differentiation is frequently made between the terms RMS and TRMS. This is merely historical conditioning, so that newer measuring procedures are preferred over form factor based methods. In principle, WAGO measures according to the TRMS method. However, no special differentiation is made, as both terms describe the same mathematical equation, and one merely indicates the specific accuracy of the measurement.

Digital Processing

Digital Processing

+ Digital Processing

During digital processing, the signal is sampled in defined, very short time intervals (digitized). The sampled values are processed and, e.g., converted into an analog standard signal.

Digital processes are becoming increasingly common, since high reproducibility and signal-authentic mapping can be guaranteed due to the high sampling rates. In addition, further processing or transmission of the digitized information is easier, less susceptible to interference and more flexible, due to the software.

Analog Processing

During analog processing, the input signal is fed directly to a processing unit and prepared according to a fixed transfer function.

The processing takes place using an operational amplifier (OpAmp) and a few passive components.

Apparent Power

Apparent Power

+ Apparent Power

Active Power

+ Active Power

Reactive Power

+ Reactive Power

Apparent power (S) is the total power of a transmission network. It is composed of active power (P) and reactive power (Q).

A positive apparent power, which is in the interest of the consumer, means that the power is drawn from the grid. A negative apparent power, however, means that power is fed back into the grid.

Active Power

The active power (P) is the power actually consumed. It has no phase shift between current and voltage and relates to a resistive load.

For an alternating voltage, the active power results from the multiplication of the RMS values for current and voltage.

Reactive Power

Reactive power (Q) refers to a load on the power grid, which acts against the power flowing from the producer to the consumer.

Reactive power is the product of voltage and current flowing through a reactance. Reactive power is generated by any device that is connected to an AC grid. Any electrical equipment generates an electromagnetic field when a voltage is applied. The magnetic field is constantly being built up and then dismantled again by the alternating voltage. The energy created when the field is being dismantled is fed back into the power grid, which increases the resistance to the current flow.

A positive apparent power, which is in the interest of the consumer, means that the power is drawn from the grid. A negative apparent power, however, means that power is fed back into the grid.


50 Hz fundamental frequency

+ 50 Hz fundamental frequency

150 Hz harmonic frequency

+ 150 Hz harmonic frequency

non-sinusoidal curve shape

+ non-sinusoidal curve shape

Harmonics are currents having frequencies that are multiples of the 50 Hz fundamental frequency. The harmonic degree is defined as the relationship between harmonic and fundamental frequency.

Harmonics are created by devices with non-linear characteristic curve (e.g., transformers, rectifiers, televisions, computers, halogen lighting). The non-sinusoidal currents of these devices result in a voltage drop in the network impedance, which distorts the network nominal voltage and affects the proper operation of the device. The impacts of harmonics contamination include: failures of protective devices, thermal overload and premature ageing of electrical equipment, loss of mechanical stability, performance loss, measurement errors, higher noise level, hard drive failures, system crashes, operational breakdowns, etc.

If many devices are operated within a network that generates the third harmonic, a very high current load of the neutral conductor might be the consequence. Neutral conductor currents caused by harmonics in TN-C power networks travel within the entire equipotential bonding system via water and heating pipes, grounding systems, shields of data lines, video lines, and communication systems, and can lead to increased corrosion or pitting on piping systems. Therefore, a continuous harmonics and neutral conductor analysis is required for guaranteeing both power supply and overvoltage protection, as well as fire safety.

Shunt Measurement (AC/DC)

High-Side Method

+ High-Side Method

Low-Side Method

+ Low-Side Method

Transformer Principle

+ Transformer Principle

Hall Effect Sensor

+ Hall Effect Sensor

Rogowski coil

+ Rogowski coil

Current measurement is performed using a low-ohm resistor (shunt), which is connected in parallel to a voltmeter.

The current is proportional to the current measured at the shunt resistor, I = V/R.

The shunt can be located upstream or downstream of the load (high-side/low-side method). WAGO products are equipped for both methods, giving users the freedom to decide where the conductor section should be disconnected. In addition to DC and AC currents, shunt measurements are also suitable for measuring superimposed signals (DC + AC). Accuracies of 0.1 % and better can be achieved. WAGO's 855 Series Plug-In Current Transformers with predefined division ratio can be used to expand the measurement range for pure AC measurements.

Shunt Measurement in Combination with Plug-In Current Transformer (AC)

Plug-In Current Transformers are used at higher measurement currents.

They function according to the transformer principle and expand the range of an existing measurement system (usually a shunt transformer). The number of secondary windings mirrors the fixed setting of the division ratio. The electrically isolated output AC is proportional and in phase with the input AC. The measuring error typically lies below 1 %.

Hall Effect Sensors (AC/DC)

A soft-magnetic core is applied around the conductor. The core has a small air gap in which the Hall effect sensor is located.

A magnetic flux is generated in the ring-shaped core by the current flowing through the conductor. The magnetic flux also flows through the Hall effect sensor, which outputs a voltage signal proportional to the current measured. This signal is prepared and forwarded for processing. Using the Hall method, different signals (AC/DC) and measuring ranges can be mapped, depending on the design. Measurement accuracy lies between 0.5 % and 1 %.

Rogowski Coil (AC)

A closed-air coil, i.e., coil without iron core, is applied around the conductor to be measured.

The AC current flowing through the conductor induces a proportional voltage in the Rogowski coil. The output voltage is amplified and conditioned. A measurement error of less than 2 % and a response threshold of only a few amps guarantee a straightforward measurement of high to very high AC currents.

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