Cooled, temperature controlled electrometer

Abstract

A cooled, temperature controlled electrometer for the measurement of small currents. The device employs a thermal transfer system to remove heat from the electrometer circuit and its environment and dissipate it to the external environment by means of a heat sink. The operation of the thermal transfer system is governed by a temperature regulation circuit which activates the thermal transfer system when the temperature of the electrometer circuit and its environment exceeds a level previously inputted to the external variable temperature control circuit. The variable temperature control circuit functions as subpart of the temperature control circuit. To provide temperature stability and uniformity, the electrometer circuit is enclosed by an insulated housing.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. An electrometer system for the purpose of measuring small currents at temperatures less than ambient room temperature including an electrometer amplifier coupled to a high impedance to form an electrometer circuit, said system further comprising: a thermal transfer system coupled to said electrometer circuit;   means for receiving a signal from an external source;   means for transmitting a signal from the electrometer circuit;   means for thermally coupling said electrometer circuit to said thermal transfer system where said thermal transfer system acts to cool said circuit by transferring heat from the electrometer circuit and its environment to an external environment;   means for regulating said thermal transfer system where said regulating means controls the temperature of said electrometer circuit by controlling the operation of said thermal transfer system; and   means for thermally insulating said electrometer circuit where said insulating means inhibits the transfer of heat to the electrometer circuit while increasing the stability of the temperature variation to which the electrometer circuit is exposed.   
     
     
       2. The electrometer system of claim 1 in which said thermal transfer system includes a conducting block attached to the external surface of said electrometer housing;   a thermoelectric cooler linked to said conducting block; and   a heat sink coupled to said thermoelectric cooler.   
     
     
       3. The electrometer system of claim 2 in which said means for regulating said thermal transfer system includes a resistance temperature detector coupled to said thermal conducting block, an external variable temperature control circuit coupled and responsive to said resistance temperature detector, and   a means for coupling said external controller circuit to said thermoelectric cooler where said thermoelectric cooler is responsive to said external variable control circuit.   
     
     
       4. The electrometer system of claim 3 in which said thermal insulating means includes a tetrafluoroethylene (TFE) insulating blanket enclosing an electrometer housing, a layer of thermal insulation wrapped around said TFE insulating blanket in such a manner as to envelop said TFE insulating blanket, and   a means for insulating said receiving means and said transmitting means.   
     
     
       5. A method for measuring small currents employing said electrometer system comprising: selecting a temperature for the operation of said electrometer circuit;   inputting said selected temperature to said external variable temperature control circuit;   sensing the temperature of the electrometer circuit by means of said resistance temperature detector which is responsive to the temperature of said electrometer circuit and its environment;   activating said thermoelectric cooler in response to said external variable temperature control circuit where said thermoelectric cooler removes heat from said conducting member and yields heat to said heat sink.