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Constant temperature controllerRelated Patent Categories: Heat Exchange, With Timer, Programmer, Time Delay, Or Condition Responsive Control, Having Heating And Cooling Capability, Temperature Sensor Controlling Temperature, Area Receives Conditioning From Simultaneously Operated Heating And Cooling Means (e.g., Opposed And Compensating Heating And Cooling, Etc.)Constant temperature controller description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060225876, Constant temperature controller. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to a constant temperature controller for maintaining the temperature of an external heat load apparatus constant, and more particularly to a constant temperature controller that circulates a heat medium fluid of a constant temperature so as to maintain the temperature of the external heat load apparatus constant, employed for a chiller incorporated in a semiconductor manufacturing apparatus, or the like. DESCRIPTION OF THE RELATED ART [0002] A conventional constant temperature controller, generally called a chiller, is designed to circulate a heat medium fluid through a pipeline arranged in a loop through a cooler, a heater and an external heat load apparatus, so as to once supercool the liquid medium heated by the external heater with the cooler, and to heat the supercooled liquid medium with the heater thus to supply the external heat load apparatus with the liquid medium of a predetermined temperature specified by the external heat load apparatus. [0003] In such controller, normally the cooler is constantly outputting the rated cooling power irrespective of whether the external heat load apparatus is working. This leads to continuous consumption of a large power, especially when a refrigerator is employed as the cooler. Therefore, JP-A 2004-169933 proposes a constant temperature controller that can switch between an operation mode and an energy-saving mode according to the operation status of the external heat load apparatus. [0004] Also, the cooler of the constant temperature controller is usually set such that the liquid medium is cooled to the specified temperature at the outlet port of the cooler. However, the temperature of the liquid medium often becomes considerably higher (overshoot) or lower (undershoot) than the specified temperature after once reaching the specified temperature, because of slow heat transmission of a coolant gas (such as a CFC gas) in the refrigerator cycle of the cooler. This requires a larger capacity of the heater, and hence a larger heater capable of controlling a wider temperature range has to be employed. [0005] Accordingly, JP-A 2001-153518 proposes providing a temperature controller, outside the constant temperature controller and close to the external heat load apparatus, for micro-adjusting the temperature of the heat medium. [0006] [Patented document 1] JP-A 2004-169933 [0007] [Patented document 2] JP-A 2001-153518 [0008] The JP-A 2004-169933 discloses a chiller controller that employs a computer that pre-reads recipe information on a process sequence of a plasma etching processor, so as to switch the chiller to the operation mode or to the energy-saving mode, when the etching process enters a certain duration of downtime or when the etching process is resumed. [0009] Such chiller controller, however, requires the computer and associated wires and so on, for constantly monitoring the operation status of the apparatus under the temperature control, and transmitting the status information to the control system of the chiller. [0010] The JP-A 2001-153518 discloses a temperature control system that includes a second temperature controller separated from the chiller and located close to the processing apparatus to be controlled, for setting the temperature at the outlet port of the chiller and micro-adjusting the temperature of the heat medium supplied to the processing apparatus, depending on the temperature of the processing apparatus. Such system, however, incurs a greater heat energy loss because of including two temperature controllers which naturally requires two power supply systems. The system also requires two signal line systems for operating the two controllers, thus making the operation process more complicated. [0011] Accordingly, it is an object of the present invention to provide a constant temperature controller having an operation mode switching function that enables performing the energy-saving operation. [0012] It is another object of the present invention to provide a constant temperature controller inexpensive and easy to operate, yet capable of accurately controlling the temperature with significantly reduced heat energy consumption. SUMMARY OF THE INVENTION [0013] The present invention provides a constant temperature controller that circulates a heat medium fluid through a fluid path arranged in a loop through a cooler, a heater and an external heat load apparatus so as to maintain the external heat load apparatus at a predetermined constant temperature, comprising a cooler operation mode switch that selects one of the cooler operation modes at least including an idling mode of outputting a minimal cooling power to maintain the temperature when the external heat load is off, and a loaded mode of increasing or decreasing the cooling power according to the external heat load, based on a difference between a heat medium fluid temperature at an inlet port of the cooler and a heat medium fluid temperature at an outlet port of the heater; and a cooling power controller that adjusts the cooling power of the cooler such that the difference between the heat medium fluid temperature at an outlet port of the cooler and a target temperature of the heater becomes a predetermined target difference in temperature under the loaded mode. [0014] The cooler operation mode is switched based on the difference between the circulating heat medium fluid temperature at the inlet port of the cooler and the circulating heat medium fluid temperature at the outlet port of the heater. A reason of such arrangement may be described as follows. It is impossible to precisely foresee when the heat load that has been changed returns from the external heat load apparatus, i.e. the object of the temperature control. The target temperature of the heater, which is the target temperature of the constant temperature controller, is often changed depending on the operation status of the external heat load apparatus. Although the target temperature of the constant temperature controller is changed, the heat load that has been changed may not always return from the external heat load apparatus after the temperature of the heat medium fluid at the outlet port of the constant temperature controller has reached the newly set target and has been stabilized. The heat load that has changed may return during the transition of the temperature toward the target newly set by the constant temperature controller. [0015] Under the conventional control system of switching the operation mode based on the difference between the circulating fluid temperature at the inlet port of the cooler and the target temperature of the constant temperature controller, the heat load that has been changed may return during the transition of the target temperature of the constant temperature controller, i.e. before the circulating fluid temperature at the outlet port of the constant temperature controller reaches the newly set target, in which case the actual temperature becomes considerably higher (overshoot) or lower (undershoot) than the target temperature. [0016] To avoid this, the present invention switches the operation mode based on the difference between the circulating fluid temperature at the inlet port of the cooler and the circulating fluid temperature at the outlet port of the heater. Such method enables quickly detecting the fluctuation in the difference in temperature even during the transition of the target temperature of the constant temperature controller, to thereby quickly react the fluctuation of the lead load, thus allowing switching the operation mode under a stabilized situation without overshooting or undershooting the target temperature by far. As a result, the operation mode can be timely switched and therefore the operation status can be quickly stabilized. [0017] The difference in the circulating fluid temperature varies depending on the type or scale of the external heat load apparatus, as well as of the constant temperature controller, but may be usually set in a range of 1 to 5 degree centigrade. For measuring the temperature difference, a first temperature sensor is disposed at the inlet port of the cooler, and a third temperature sensor at the outlet port of the heater. [0018] The operation mode of the cooler may be switched by switching a frequency of an inverter driving a compressor incorporated in the refrigerator cycle of the cooler. Specifically, the compressor is driven by a low inverter frequency in the idling mode. Driving under a low frequency can reduce the cooling power. [0019] Also, driving the inverter with a low-frequency power reduces the power consumption. In the idling mode real-time adjustment of the cooling power is not required because the heat load scarcely returns from the external heat load apparatus, and it is sufficient to output a low cooling power generally constantly. Such operation mode can be performed over the entire rated temperature range of the constant temperature controller. [0020] In the loaded mode, the compressor of the refrigerator cycle is driven by a power of a high inverter frequency. Increasing the inverter frequency can increase the cooling power. However, since controlling the compressor by the inverter frequency does not provide a sufficiently quick response, the inverter frequency is fixed in the loaded mode, and an electronic expansion valve is employed for controlling the cooling power of the cooler. [0021] Another reason of fixing the inverter frequency of the refrigerator in the loaded mode is that the coolant gas (such as a CFC gas becomes temporarily unstable because of a fluctuation in the inverter frequency, thus degrading the temperature adjusting accuracy. Continue reading about Constant temperature controller... Full patent description for Constant temperature controller Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Constant temperature controller patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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