METHOD AND APPARATUS FOR THERMOANALYTICAL INVESTIGATIONS

摘要

1484205 Temperature control METTLER INSTRUMENTE AG 21 Jan 1975 [25 June 1974] 2607/75 Heading G3R [ Also in Divisions F2 and H5] A combination of heating and cooling effects is used to control the temperature of specimens undergoing thermoanalytical investigation. The apparatus used consists of: an enclosure 16 for the specimens 22, 24, whose temperature is displayed at 48; heating means 18 for the enclosure; an adjacent (as shown, surrounding) chamber 26 for receiving cooling fluid; and means for controlling (a) the heat input to the enclosure 16 and (b) the temperature and rate of flow of the cooling fluid. The invention also includes a method of using such apparatus to vary specimen temperatures with time according to a predetermined program. In Fig. 1, the power input to the heating means 18 is controlled in dependence on the output of a temperature sensor 50. The rate of flow of cooling medium is adjusted by a valve 72 whose setting depends on the temperature at sensor 50, the temperature of the cooling medium measured by a sensor 62 and the setting of a 'desired temperature' control input 164. The inputs from 50, 62 and 164 are fed to a multi-branch bridge circuit 52 with two outputs, these outputs being fed via appropriate, including amplifying, pulse producing and PID control, units 54-58 and 64- 70 to control both the heating and cooling effects . conjointly. The circuitry of units 52, 54-58 and 64-70 is more fully depicted in Fig. 4 (not shown), which includes means for providing automatic variation of the set temperature in accordance with a desired program. The preferred cooling medium is liquid nitrogen. This is boiled in a chamber 28 from which it emerges at constant pressure, this pressure being measured at 44 and the output of an immersion heater 40 is automatically adjusted to control the rate of boiling in response to the pressure measurement. The heater 40 is depicted in detail in Fig. 3 (not shown, but see Division H5). The cooling fluid flow-rate control valve 72 vents to atmosphere at 34. The valve itself is depicted in Fig. 2 (not shown, but see Division F2). This valve is operated by a solenoid whose control is modified by a feed-back system responsive to detection of the valve element's position. Also, the temperature of the cooling medium downstream of the temperaturecontrolled chamber but upstream of the valve, is increased by a subsidiary temperature-control system 75, 77 to ensure that the valve is not 'frozen' by too-cold fluid.