KidZone Science
The Polygraph MachineThe Polygraph Machine Image 1

The polygraph machine uses the following components in order to collect results on the subject’s reactions to questions related to the investigation:

Blood Pressure Cuff – measures the subject’s blood pressure, heart rate and blood volume, also known as their cardiovascular activity.  It is attached to the subject’s arm, around their brachial artery.

Pneumograph – this is a device that measures the respiratory activity (breathing patterns) of the subject.  A pneumograph is essentially a convoluted rubber tube; it uses ohms law to determine how much resistance there is in the chest cavity because there is more resistance in your chest when your lungs are filled with air.  During the polygraph test, two pneumographs are attached to the subject, one around their chest and the other around their abdominal area.

GSR – the galvanic skin response is a protruding electrode which is used to determine the changes in a subject’s anxiety.  An increase in anxiety will result in a decrease of the electrical resistance in the skin.  The galvanometer measures the small differences in electrical resistance and any shifts in a subject’s anxiety.  The polygraph test uses two galvanometers, which are attached to two of the subject’s fingers in order to obtain results from their electro dermal activity.