Polygraph instrument | Lie detector apparatus

The polygraph instrument is an apparatus capable of registering psycho-physiological changes in the human body.

The polygraph, also popularly known as lie detector, is normally composed of a Data Acquisition System and sensors that collect information from different organs like longs, heart and skin.

Other sensors can also be included in polygraphs although for decades, skin conductance, heart rate and respiration have been the basis of the data collected by a polygraph.

In the following images you will be able to see some of the sensors that are normally used in polygraphs. The images used is from Polygraph manufacturer P.O.L.A.R. Polygraph with whom Polygraph India has a partnership agreement.

Polygraph parts in images:

Polygraph sensors explanation:

Polygraph Instrument Kit
  • DAS (Data Acquisition System)

This is the central part of the polygraph, where information is acquired, transformed in digital format and later transmitted to a computer.

  • Pneumographs

The pneumographs measure respiratory activity using 2 sensors placed on the abdomen and upper chest of the examinee.

  • Electro Dermal Activity Sensor

The electro dermal activity sensor, also known as Galvanic Skin Response Sensor registers the activity of the sweat glands. It normally consists of two metal plates that are placed on two fingers of the hand.

  • Sphygmomanometer

The sphygmomanometer consists of a manometer and a blood pressure cuff. The cuff is normally placed on the upper arm of the examinee and measures, blood pressure, blood rate and blood volume.

  • Photo Plethysmograph

The photo plethysmograph measures peripheral cardiovascular activity from the palmar surface of skin.

  • Movement sensor

The movement sensor is used to detect any movement that could alter the natural readings caused by the Autonomic Nervous System. It is a component that helps the polygraph examiners spot any unnatural changes in physiological registrations.

Polygraph instruments can have additional or less sensors but these are the most common used sensors in a polygraph instrument used for lie detection.

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