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Simple Time-Proportioning Temperature Controller

Department of Dairy and Food Science New York State College of Agriculture Cornell University Ithaca, New York

ABSTRACT

The construction of an adiabatic calorimeter requires a device capable of maintaining two points at the same varying temperature, since the sample must be surrounded by a heat-sink kept at the sample temperature. Devices for such applications should be accurate and simple to operate. This note reports such a device, used satisfactorily for 2 yr as an adiabatic shield control in calorimetry.

A diagram of the control system is shown in Figure 1. The hot junctions of a two-couple differential thermopile are located in the sample, along with the sample heater and temperature-measuring thermocouples. The cold junctions of the thermopile are cemented to the inner surface of an aluminum cup serving as the adiabatic shield. The signal from the thermopile is amplified^{1, 2} and fed to a combination phase-shifting and saturable reactor device³ controlling the firing delay of an inverse-parallel silicon-controlled rectifier (SCR) circuit (1). The fractional sine-wave output is placed across a 180 resistance heater wound on the outside of the shield.