Comment on “Implementing of a precision fast thermoelectric cooler using a personal computer parallel port connection and ADN8830 controller” [Rev. Sci. Instrum. 74, 3862 (2003)

Abstract

Eli Flaxer has described a feedback controlled circuit to drive a Peltier junction to control the temperature of a specimen in the range 0 to 50 °C in a room temperature environment [Rev. Sci. Instrum. 74, 3862 (2003)]. The amount of heat transferred per unit current by a Peltier junction varies substantially with the temperature difference across the Peltier junction. Flaxer’s circuit does not provide any mechanism to compensate for this variation. This means that if the proportional-integral-differential control loop he uses is optimized at any particular temperature differential, the control loop with be over-damped at lower specimen temperatures, and under-damped at higher specimen temperatures. A circuit using a second thermistor to monitor the temperature of the exhaust side of the Peltier junction, and a digital control loop, can minimize this problem [A. W. Sloman, Paul Buggs, James Molloy, and Douglas Stewart, Meas. Sci. Technol. 7, 1653 (1996)]. This circuit has the incidental advantage of offering ten times better temperature stability.