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Posted on 08 May 2019

Selecting Current Transducers

 

 

 

 

 

 

 

The article "Transducers - Basic Principles of Selection" outines general criteria for selection of tranducers. Below is a more detailed listing of important criteria to be considered when choosing a suitable current transducer for a given application.

Some applications of current transducers have a high level of complexity and combine several potentially critical elements such as:

  • electromagnetic interference
  • significant common mode voltage transients (dv/dt)
  • mechanical disturbances (vibration, shock, etc.)
  • special isolation or partial discharge requirements
  • compliance with specific standards, etc.

Obviously, the best method of determining if a transducer is appropriate for a given application is to perform tests in the specific application environment. If this is not reasonable or feasible, one should provide the manufacturer with a diagram of the intended installation and a detailed description of the transducer operating conditions (e.g. description of the environmental conditions, graph of the waveform to be measured, nearby potentially disturbing elements such as inductors, current carrying conductors, the presence of magnetic materials or the desired location of other transducers). Electrical, dynamic operating and environmental parameters, as well as mechanical interfaces should be considered when selecting current transducers.

1.) Electrical parameters

Type of current:

  • DC, AC or complex waveform current
  • Selection of the adequate technology

Range of current to be measured encompasses:

  • Nominal current
  • Peak current
  • Transient current overloads
  • Not to be measured is the maximum peak value and the duration

Required output signal

  • Current or voltage output
  • Output value at nominal or peak current
  • For current output transducers, selection of the necessary or desired output load impedance

Measurement accuracy

  • Required accuracy at 25 °C, taking into account the DC offset and non-linearity of the output signal
  • Global accuracy within the operating temperature range, adding the accuracy at 25 °C, the offset drift and, if applicable, the gain drift.

Available power supply

  • Power supply voltage, including tolerances
  • Maximum allowable current consumption

Voltage

  • Primary working voltage
  • Applicable standard for isolation (design or test)
  • Compliance to the relevant standards
  • Single or reinforced insulation
  • Dielectric withstand voltage (e.g. 4 kVRMS, 60 Hz, 1 min.)
  • Pollution degree (e.g. class 2)
  • Overvoltage category (e.g. 0V cat. 1)
  • Impulse withstand voltage (e.g. 8 kV with 1.2/50 μs)
  • Partial discharge extinction level and electric charge

2.) Dynamic operating parameters

Frequency range

  • Frequency range to be measured
  • Fundamental operating frequency
  • Harmonic content (e.g. drive’s switching frequency)
  • Current Harmonics not to be measured but likely to create transducer losses (e.g. drive’s ringing current)

di/dt

  • Match between the di/dt to be measured and the transducer’s response and rise
  • Maximum possible di/dt overloads, to be withstood by the transducer, but not to be measured
  • Maximum transducer recovery time after a di/dt overload

dv/dt

  • Maximum error allowed during dv/dt disturbance
  • Maximum transducer settling time after a dv/dt disturbance

 3.) Environmental parameters

Temperatures

  • Minimum and maximum working temperatures where the transducer performance is applicable
  • Extreme storage temperatures

 Vibration & shock

  • Standards and levels to be considered (when applicable)

 Presence of external fields

  • External current identical to the one being measured
  • Other currents of similar or greater amplitude
  • Fields from transformers or inductors
  • Fields from magnetized materials in the area

4.) Mechanical Interfaces

Primary electrical connection

  • Printed wiring board (PWB/PCB) pins
  • Through-hole aperture size and shape
  • Busbar dimensions
  • Other connections (e.g. screw terminals)

Secondary electrical connection

  • Printed wiring board pins
  • Connector
  • Faston tabs
  • Screw lugs
  • Other connections (e.g. screw terminals)

External dimensions

  • Maximum specified dimensions
  • Aperture/primary location
  • Connector/secondary location
  • Required creepage/clearance distances

Package fastening

  • Printed circuit mount
  • Panel mount
  • Aperture (cable or busbar) mount
  • DIN rail mount

 

For more information, please read:

Transducers - Basic Principles of Selection

Selecting Voltage Transducers

Concerns When Using Transducer Measurement Devices

Characteristics of  Closed Loop Current Transducers

Open Loop Hall Effect Current Transducers

Handling Core Losses of Open Loop Transducers

 

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