The Gauribidanur Active Thermal Control System: Maintaining m0C stability over days in a 30 m3 volume!

Temperature variations in the ambient are often a nuisance for the experimenter, since they drive a variety of “noise” effects in experiments. Temperature variations are even more troublesome if they are periodic, especially if the period is the same as that of the primary signal being searched for (in which case the effects that they drive are termed “systematics”).

The Equivalence Principle Experiment at Gauribidanur, one of the most sensitive mechanical experiments being undertaken anywhere, has been seriously troubled by “systematics” caused by diurnal and semi-diurnal variations of temperature, with amplitude greater than 20 m0C. We have developed an Active Thermal Control System to suppress these temperature variations down to an amplitude of 1 m0C, in a volume greater than 30 m3.

We will present aspects of the design and performance of this Active Thermal Control System. The talk will cover important features of the mechanical and thermal design, our choice of the thermal sensors (NTC Thermistors, Yellow-Springs) and studies of their stability, the design of the control electronics, and the governing principles of the feedback control, before presenting our most recent results from the Under Ground Laboratory(UGL) at Gauribidanur. Of special interest for anybody implementing feedback control, is our development of a 32-channel Infinite Droopless Sample and Hold Amplifier board built around the Analog Devices chip AD5533.