Editorial Feature

What is a Voltage Detector?


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Article updated on 09/03/20 by Jo Finchen-Parsons

A voltage detector is a device that determines the presence or absence of an electrical charge in an object. It can be a simple, pen-shaped piece of testing hardware that indicates the existence of electricity or an advanced tool that detects precise voltage levels in electrical systems.

This detector employs visual or audio cues to alert the user if a voltage is present. Certain types of detectors use lights and numbers for indicating the voltage level.

The detectors are tested and rated to use within certain ranges of voltage. Using the voltage detector on a higher voltage than that for which it is designed will provide inaccurate results and could also be dangerous.

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Types of Voltage Detectors

The following are the four different types of voltage detectors:

  • High-frequency AC voltage detector (Spark tester) – this detector employs a Tesla coil to produce high voltages. It is usually mains powered, and it can detect electrical charges over 50,000 V. During operation, a blue brush discharge can be observed around an electrode. The discharge will change into a single white spark when a fault is detected. One problem encountered with this type of equipment is the capacitive loss effect.
  • Low-frequency AC voltage detector – this type of detector uses transformers to step up the mains voltage to the desired level. It is larger and has the potential to deliver excess amounts of voltage. However, the output of the detector is low-frequency AC voltage. This type displays problems similar to that of high-frequency AC voltage, but to a lesser extent.
  • Pulsed DC voltage detector – this type of detector is light-weight and battery-powered. It works on the principle that a capacitor is charged up to 400 V and discharged into a high voltage coil for producing a high voltage pulse of a short duration.
  • Continuous DC voltage detector – this portable, battery-powered detector can provide an output that can be as low as a few hundred volts up to 40,000 V. It is operated based on the principle that the battery triggers a high-frequency oscillator that converts the battery voltage from 12 V DC to a high AC voltage.

Working Principle

A voltage detector measures the flux lines of the electric field formed between the earth’s potential and a live component of the system.

Displacement current is produced when the electric field is interrupted by an operating head of the high-voltage detector.

The current starts to flow via the test electrodes E1 and E2. A downstream electronic circuit identifies and measures this current. The high-voltage detector generates a visual and audio signal if the displacement current exceeds the threshold value thereby indicating the presence of a voltage.


Some of the major applications of voltage detectors:

  • Battery voltage monitoring
  • Brown-out protection of the system
  • Level discrimination
  • Switching circuit in battery back-up
  • Microprocessor reset.

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