GB640711A - Improvements in or relating to pyrometers - Google Patents

Abstract

640,711. Automatic temperature control systems. MINNEAPOLIS - HONEYWELL REGULATOR CO. March 28, 1947, No. 8533. Convention date, March 29, 1946. [Class 38 (iv)] In a pyrometer for measuring relatively low temperatures the temperature of the housing is maintained constant at a temperature higher than that of surrounding objects or alternatively the housing is maintained at the same temperature as that of the body being measured, so as to minimize errors due to ambient temperature variations. The pyrometer comprises a body structure A, Fig. 1, in which are mounted a thermopile B and a lens C. The thermopile B is supported in a metallic housing D, the hot junction being located in a small chamber D<SP>2</SP>, whilst the lens may be mounted in the housing D or in the pyrometer housing (Fig. 3, not shown). The thermopile connections are taken from binding posts D<SP>3</SP>. A thermostat F and a heating element E surrounding the structure A are also provided. The thermostat F. is in the form of a mercury thermometer and is such that at a predetermined temperature the mercury will close contacts F<SP>1</SP> and F<SP>2</SP> connected externally to a binding post H<SP>1</SP>. The thermopile connections are brought to a binding post H<SP>2</SP> whilst the heater connections are brought to a binding post H<SP>3</SP>. The heater is energized by supply lines 1, 2 through a relay contact G<SP>2</SP> enclosed in a controller G, the operating coil 5 of the relay being connected in the thermostat F circuit and energized when contacts Fl and F<SP>2</SP> are made. The thermopile contacts H<SP>2</SP> are connected to an indicator unit I also energized from supply lines 1, 2. The temperature of the housing is then maintained at a constant level since if this temperature is exceeded the controller G will operate to disconnect the supply to the heater. In a modification, a thermocouple type of thermostat with a suitable controller may be used instead of the mercury thermometer type of thermostat F. In a further embodiment the temperature of the housing is maintained at the same level as that of the body X which is being measured, Fig. 5. The thermocouple L in this case provides a measure of the temperature of the body X and is connected to an indicator I. The thermopile B and heater E are connected to a controller GA, responsive to the difference between the hot and cold junction temperatures of the thermopile, and arranged to energize the heater so that the cold junction is maintained at the same temperature as the hot junction. In modifications a compensating voltage is introduced to compensate for hot and cold junction difference temperatures when the temperature of the body X varies rapidly (Figs. 6 and 7, not shown). In a further modification the radiation responsive element may be one arm of the resistance bridge of a bolometer (Fig. 8, not shown). U.S.A. Specification 2,357,193 is referred to.