An Automatic thermoelectric cooling method and computer-based recording system for supercooling point studies on small invertebrates

Abstract

An automatic controller is described for use with fluid-cooled thermoelectric assemblies and compatible bipolar controllers in supercooling point studies on small invertebrates. The automatic controller provides constant and repeatable cooling rates in the range of 0.4 to 3 °C min −1 from +25 to −50 °C; under manual control this range can be extended from less than 1 to 15 °C min −1. The controller includes a range of preset lower-limit temperatures and a reset function to heat the system between experiments to the start temperature (+15 °C) in less than 2 min. Supercooling points were sensed, observed, and recorded by a 12-channel, cold-junction-compensated, thermocouple convertor interfaced to a microcomputer, color monitor, and dot-matrix printer. Thermocouples were calibrated against a platinum resistance thermometer to derive polynomial descriptors which were incorporated into a microcomputer program (BASIC, Applesoft) to match thermocouples to ±0.2 °C. Each thermocouple was sampled at 3-sec intervals to ±0.1 °C and temperatures of insect-bearing sensors were plotted against time in distinguishing colors on the monitor, using a second computer program. On completion of an experiment all supercooling points for each thermocouple were printed on the dot-matrix printer; the graphical display could be stored on disk or output to a printer. The computer program can be readily modified to implement individual protocol requirements such as the range of temperatures and related information displayed on the monitor, and the thresholds (time and °C) for the recognition of supercooling points. The thermocouple convertor/microcomputer system could be used with any method of cooling.