Constant temperature controller

Abstract

A constant temperature controller inexpensive and easy to operate, yet capable of accurately controlling the temperature with significantly reduced heat energy consumption, is provided. An operation mode of a cooler is switched between an idling mode and a loaded mode, based on a difference in temperature between a first temperature sensor and a third temperature sensor. For switching the operation mode, cooling power of the cooler is adjusted by changing a frequency of an inverter driving a compressor. Under the loaded mode, the cooling power of the cooler is adjusted by an aperture of an electronic expansion valve such that a difference between a temperature of a second sensor and a target temperature of a heater becomes a constant value.

1 . 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.    
   
   
       2 . The constant temperature controller according to  claim 1 , wherein the cooler operation mode switches a frequency of an inverter driving a compressor incorporated in the refrigerator cycle of the cooler, so as to switch the cooler operation mode.  
   
   
       3 . The constant temperature controller according to  claim 1 , wherein the target difference in temperature of the cooling power controller is set such that the heat medium fluid temperature at the outlet port of the cooler becomes lower than the target temperature of the heater by a predetermined value.  
   
   
       4 . The constant temperature controller according to  claim 1 , wherein the cooling power controller includes an electronic expansion valve incorporated in the refrigerator cycle of the cooler, so as to adjust the cooling power by controlling the aperture of the electronic expansion valve.  
   
   
       5 . The constant temperature controller according to  claim 4 , wherein the cooling power controller including the electronic expansion valve includes a feedback control function based on the temperature of the heat medium fluid at the outlet port of the cooler.  
   
   
       6 . The constant temperature controller according to  claim 5 , wherein the feedback control function includes dividing the heat medium fluid temperature at the outlet port of the cooler into a plurality of temperature zones in advance, and adjusting the cooling power of the cooler according to the respective temperature zones.  
   
   
       7 . The constant temperature controller according to  claim 1 , wherein the heater includes a feedback control function based on the temperature of the heat medium fluid at the outlet port of the heater.  
   
   
       8 . The constant temperature controller according to  claim 7 , wherein the feedback control function includes a PID control function.