Alternate method for achieving temperature control in the -160 to +90 degrees Celcius range
AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration
InventorKenneth R. Johnson
Life of this patent
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Abstract
A single-pass method for accurate and precise temperature control in the -160.degree. to +90.degree. C. range, and which exhibited minimal set-point overshoot during temperature transitions. Control to .+-.2.degree. C. with transitions between set-points of 7.degree. C. per minute were achieved. The method uses commercially available temperature controllers and a gaseous nitrogen/liquid nitrogen mixer to dampen the amplitude of cold temperature spikes caused by liquid nitrogen pulsing.
Claims15
A single-pass flow-through system for producing accurate and precise temperature control in the -160.degree. to +90.degree. C. temperature range comprising:
- (a) a first source for providing gaseous nitrogen at ambient temperature and constant pressure;
- (b) a first line for receiving gaseous nitrogen from the first source comprising an open-and-close solenoid valve, a first hand-controlled throttle valve for manually adjusting the flow of gaseous nitrogen in the first line to a predetermined constant flow rate, and an in-line electric heater for heating the gaseous nitrogen;
- (c) a second source for providing liquid nitrogen at constant pressure;
- (d) a second line for receiving liquid nitrogen from the second source comprising a fail-safe control open-and-close solenoid valve, a master control open-and-close solenoid valve, and a second hand-controlled throttle valve for manually limiting the flow of liquid nitrogen in the second line to a predetermined maximum flow rate;
- (e) a mixer for receiving gaseous nitrogen from the first line and liquid nitrogen from the second line, and for mixing the gaseous nitrogen and liquid nitrogen and forming a tempered gaseous nitrogen stream;
- (f) a third line for receiving the tempered gaseous nitrogen from the mixer;
- (g) a heat exchanger means for receiving the tempered gaseous nitrogen stream from the third line;
- (h) a fourth line for receiving gas from the heat exchanger means comprising an adjustable back-pressure control valve for adjusting the gas stream pressure in the fourth line, and a vent for venting the gas from the adjustable back-pressure control valve and from the system;
- (i) fail-safe controller means for sensing the temperature of a predetermined fail-safe point in the system which is no further upstream than the heat exchanger means, and for using the sensed temperature of the predetermined fail-safe point for turning off the power to the heater when the temperature of the predetermined fail-safe point exceeds a predetermined high-limit set-point temperature, and for closing the fail-safe control open-and-close solenoid valve when the temperature of the predetermined fail-safe point falls below a predetermined low-limit set-point temperature;
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- (j) master controller means for sensing the temperature of two predetermined master points in the system, for generating an average temperature signal from the two sensed temperatures, and for using the average temperature signal for controlling the master control open-and-close solenoid valve, and for controlling the power intensity to the heater, in such a manner that the system is operable for producing accurate and precise temperature control of the tempered gas received by the heat exchanger means in the about -160.degree. to about +90.degree. C. temperature range.
Dependencies are inferred from the claim text.