The polygraph machine or “lie detector” is an instrument or device that produces recordings of physiological phenomena that could be used to diagnose the truth or deception using a reliable technique. There are no specific physiological reaction linked to lying. The instrument can only record the physiological phenomena/changes that occur when the subject is deceptive. It cannot detect lies or deception. The examiner simply uses the instrument to attempt to detect deception.
Two Kinds of Polygraph Instrument
Most polygraph machines measure four to six physiological reactions that are recorded by three different medical instruments that are combined into one machine.
Major Components of the Polygraph Instrument
The polygraph instrument is composed of four major parts: the pneumograph, the galvanograph, the cardiosphygmograph, and the kymograph. These components work simultaneously and help in the administration of the examination.
pneumograph detects the thoracic and abdominal breathing patterns
galvanograph measures the subject’s skin resistance to a very small amount of electricity
cardiosphygmograph measures the changes in the subject’s blood pressure and pulse rate
kymograph chart recording unit of the polygraph instrument
Note, however, that the digital polygraph no longer has the kymograph. Instead, it has the computerized polygraph.
Additionally, the digital polygraph also has the activity sensor seat pad to monitor the activity on the lower body of the subject.