Mercury-In-Rubber Strain Gauge
"Originally described by Fisher and colleagues (1965), the first circumferential measure, the mercury-in-rubber strain gauge, was adapted from a similar transducer used by Shapiro and Cohen (1965). The device consists of a hollow rubber tube filled with mercury and sealed at the ends with platinum electrodes. The operation of the mercury-in-rubber strain gauge depends upon penile circumference changes that cause the rubber tube to stretch or shorten, thus altering the cross-sectional area of the column of mercury within the tube. The resistance of the mercury inside the tube varies directly with its cross-sectional area, which in turn is reflective of changes in the circumference of the penis. Variations of the mercury-in-rubber gauge have been described by Bancroft et al. (1966), Jovanovic (1967), and Karacan (1969)."From Janssen, E., Prause, N., & Geer, J. (2007). The sexual response. In J. T. Cacioppo, L. G. Tassinary, & G. G. Berntson (Eds.), Handbook of Psychophysiology, 3rd ed. New York: Cambridge University Press.
Electromechanical Strain Gauge
"Another type of penile strain gauge is the electromechanical strain gauge developed by Barlow and co-workers (1970). This device is made of two arcs of surgical spring material joined with two mechanical strain gauges. These gauges are flexed when the penis changes in circumference, producing changes in their resistance. The resistance changes are in turn coupled through a bridge circuit to a polygraph or computer. The electromechanical gauge does not fully enclose the penis. For this reason, it is more sensitive to movement artifacts and less suitable for studies on nocturnal penile tumescence (NPT) than the mercury-in-rubber gauge. However, mechanical strain gauges are quite sensitive and more rugged than their rubber counterparts."From Janssen, E., Prause, N., & Geer, J. (2007). The sexual response. In J. T. Cacioppo, L. G. Tassinary, & G. G. Berntson (Eds.), Handbook of Psychophysiology, 3rd ed. New York: Cambridge University Press.