Operation of the Polygraph.
a. The polygraph does not ring a bell, flash a light, or produce some other
quick response when the examinee tells a lie. What it does is record within on a
paper strip or chart the changes of relative blood pressure, pulse rate, galvanic
skin reflex (skin resistance), and respiration cycles of examinees under controlled
conditions. There are several types of polygraphs available. They all basically
operate in the same manner. They all have as the most important factor involved in
their use, the ability and integrity of the examiner.
b. The operation and attachment of the polygraph instrument is as follows:
(1) Pneumograph Components.
The pneumgraph tubes are ten-inch corrugated
rubber tubes that are fastened around the examinee's chest and abdomen. During the
test, as the examinee's lungs expand with each inhalation of air, the tubes
stretch, and as the examinee exhales, they contract.
This movement produces
pressure changes in the tubes that are transmitted through rubber hoses to
recording units which move pens on the chart paper.