Polygraph Description

A General Description of a Polygraph Machine (Lie Detector)
A polygraph machine, commonly known as a lie detector, is a machine that monitors and records changes in a person 's physiological characteristics. It is often used for criminal investigations, though employees in a high security career, such as military personnel, may have to undergo polygraph testing as well. While they cannot specifically detect lies, a polygraph machine can record physical responses from a person that are often associated with deception, such as increased blood pressure, sweating, and respiratory rate. Some models can also detect things such as arm and leg movement, but the rates described are the three most common attributes monitored in a polygraph machine.

Parts
A polygraph has four major sections: the pneumographs, the bellows, the blood pressure cuff, and the galvanometers.
Pneumographs and bellows
The pneumographs are two rubber tubes filled with air that are placed on the subject 's chest and abdomen. As the chest and abdominal muscles expand, the air inside the tubes are pushed through a bellows, which is a device that is made to contract as the tube expands. This bellows mechanism is attached to a mechanical arm, which is attached to a pen that is moved to scribble on paper by the effect of the bellows. This in turn records the subject 's breathing rate, making it easy to see where faster, more nervous breathing has occurred.
Blood pressure cuff and bellows
A blood pressure cuff is placed around a subject 's upper arm. The tubing from the cuff is connected to the polygraph, and as the blood pumps in the subject 's arm a sound is made. The changes in pressure cause by the sound displaces the air in the tubes and causes another bellows mechanism to react, which again moves another pen on the machine. This pen records a person 's pulse, again, making it easy to see where a faster heart rate was triggered.

The polygraph is turned on and the pens moved by each of the mechanisms begin recording the data from the subject 's breathing rate, heart rate, and sweat generation. The tester then begins to ask several basic questions, such as “Is your name X?”, to record the subject 's normal breathing, pulse, and sweat when answering. Then the tester begins asking questions pertaining to the reason why the polygraph test is being taken. The subject 's responses are all recorded on rotating paper with pens moved by his or her breathing, heart rate, and sweating. When the test is over, the polygraph tester examines the results on the paper to find overlap in the subject 's spikes of increased heart rate, sweating, and breathing. The spikes recorded usually indicate that the person was exhibiting deceptive behavior at the question asked during that time, which means that she or he