The Model 22600 Polygraph instrument was introduced by the Stoelting Company of Chicago, Illinois in 1966. This instrument replaced the 22500 model with the most significant change being the replacement of old vacuum tubes with transistors which reduced the weight and size of the instrument along with eliminating the previous warm up time.

This model is a three pen instrument. The top channel was a mechanical recording channel for recording respiration. The instrument did not have any means of controlling tracing size, except for possibly adjusting the pneumograph tube. The G.S.R. channel was a 250,000 ohm amplifier, balancing a twenty three micro amp current to the subject to record changes in galvanic skin response. The bottom channel was used to record heart rate and changes in relative blood pressure. Due to the mechanical nature of the recording, optimum tracings were not always obtainable.

The 22600 was the last instrument produced by Stoelting which utilized the single pneumograph, and the six inch chart paper. A few years after the 22600 was introduced, Stoelting produced its first four pen polygraph, which incorporated a second pneumograph and a kymograph which recorded on eight inch paper.


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