Patent Publication Number: US-2010127088-A1

Title: Electronic thermostat with main parameters that are rapidly settable even during operation of the plant under control

Description:
The present invention relates to an electronic thermostat with main parameters that are rapidly settable even during operation of the plant under control. 
     Rapid and precise setting is of fundamental importance to optimise the operation of the plant to which said thermostat is applied. 
     The continuous operating interruptions to the thermostat cause transitory operating situations of the plant to be multiplied that can lead to a fault in the thermostat and to a consequent fault in the plant to which the thermostat is connected. 
     Currently, thermostats of bimetal sensors are used that are suitable for measuring temperatures that are not below 30° C. Said sensor is, however, not precise, has a reduced temperature measuring range and, above all, after a temperature has been measured, it never returns to the exact start position. 
     This permits a fixed intervention temperature, so as many bimetal sensors are required as there are intervention temperatures. 
     Further, the bimetal sensor comprises a blade of conductive metal that expands as the temperature changes, closing a contact; said blade is subject to wear. A given temperature change is not matched by the same blade expansion, so the temperature data are not precise. 
     The object of the present invention is to make a thermostat with a simple construction but which is more precise than known thermostats and in which it is possible to act on setting means without having to stop the plant to which it is connected and the temperature of which it has to control. 
     According to the present invention this object is achieved with an electronic thermostat comprising a connector provided with means for sealing an outer body provided with a cavity within which there is housed a circuit card, said thermostat comprising a temperature sensor exposed to ambient temperature under control and connected to said circuit card, characterised in that said temperature sensor is a semiconductor sensor and is housed inside a cavity of a flange fixed to the outer body removably, the circuit card is provided with a memory and the thermostat comprises setting means housed inside the cavity of the outer body and comprising at least one button, said connector being connected to the lateral surface of the outer body and said cavity of the outer body communicating through an opening placed at the head of said body and normally covered by a removable cover to enable the operator to reach said setting means. 
     The presence of the laterally place connector enables the inside of the cavity to be accessed easily. The connector does not have to be removed as it is sufficient simply to remove the cover, which has no effect on the action of the thermostat, thus enabling the plant to be able to continue to operate even during setting of the thermostat. 
    
    
     
       These and other features of the present invention will be made clearer from the following detailed description of a practical embodiment thereof given by way of non-limiting example in the attached drawings, in which: 
         FIG. 1  shows an axially partially sectioned front view of the thermostat according to the present invention; 
         FIG. 2  shows a section view according to line II-II in  FIG. 1 ; 
         FIG. 3  is a schematic bottom view according to the line III-III in  FIG. 1 ; 
         FIG. 4  is a partially sectioned schematic view only of the lower part of the thermostat in  FIG. 1 ; 
         FIG. 5  shows the main part of the circuit card of said thermostat; 
         FIG. 6  shows a supply and cutout circuit comprised in said circuit card; 
         FIG. 7  shows a temperature signal input circuit provided by the temperature sensor. 
     
    
    
     The electronic thermostat shown in  FIGS. 1 and 2  comprises an outer body  1  made of aluminium with a cylindrical cavity  60  having a pair of longitudinal grooves  61  that are removably engageable with the ends of an extractable flat circuit card  2 . 
     On the lateral surface of the body  1  a connector  6  is fixed that is provided with a transparent cover  30  and a removable plate  7  for sealing the cavity  60 . Inside the connector  6  there are located luminous warning LEDs  10 - 11  that are able to emit respectively a green and red light that is visible through the transparent cover  30 . The connector  6  is further traversed by electric wires  65  for the external electric connection of the circuit card  2 . 
     In the lower part of the body  1  a brass flange  100  is fixed that is provided with a cavity  101  in which a temperature semiconductor sensor  103  is arranged by a thread, preferably a semiconductor sensor of NTC type, with corresponding washer, below which there is a threaded fitting  106  for connecting to the plant at a temperature to be controlled. As is more visible in  FIGS. 3 and 4 , the flange  100  is fixable to the body  1  by means of screws that can be arranged in suitable threaded holes  200 . The threaded fitting may have various dimensions to adapt to various plants to be controlled. 
     Said flange  100  is disconnectable from the body  1  and in general is made of a material that is more resistant than the body  1  to be able to operate at very high operating temperatures. This is further replaceable with another flange made of various material that is variable according to the desired operating temperature. 
     The circuit card  2  supports setting means  4  comprising setting buttons  12 - 13 , a luminous warning LED  16  emitting a green light, a luminous warning LED  11  emitting a red light and a serial port  14  provided with connecting pins  15  for connecting by the wires  65  to an external personal computer or other data inputting/data gathering means. 
     Said buttons  12 - 13  are reachable by the operator through a threaded opening  73  located at the head of the body  1  and normally closed by a threaded removable cover  74 . 
     From a circuit point of view, said card  2  comprises a main circuit  17  ( FIG. 5 ), a supply and cutout circuit  18  ( FIG. 6 ) and an input circuit  19  for reading the signal coming from the temperature sensor  103  ( FIG. 5 ). 
     The main circuit  17  comprises switches  20 - 21  controlled respectively by the setting buttons  12 - 13 , a microprocessor  33  with an internal E 2 PROM memory and a feedback capacitor  32 , a switching transistor  34 , a power transistor  35 , the LEDs  11  and  16 , various resistances  22 , stabilising capacitors  31 , a Zener diode  60 , earth connections, an input  36  and an output  37 . 
     The supply and cutout circuit  18  comprises a pair of input terminals  45 - 46 , cutout diodes  42 - 43  protecting against voltage reversals, variable resistances  41 , a voltage stabiliser-converter  40 , resistances  38 , capacitors  44  and various earth connections. 
     Lastly, the input circuit  19  comprises input terminals S 1  and S 2  that are connected to the NTC semiconductor component of the temperature sensor  103 . The input circuit  19  comprises a filter  50 , consisting of a resistance  48  and a capacitor  49 ; the capacitor  50  is coupled between a supply voltage VDD and earth GND and has the terminals connected to the terminals S 1  and S 2  and the supply voltage VDD supplies the resistant component of the temperature sensor. The input circuit  19  comprises an overvoltage cutout circuit  51  comprising two diodes and connected to an output  52  that is in turn connected to the input  36  of the circuit part  17  in  FIG. 5 . 
     Setting the thermostat manually is rather simple. 
     The green LED  10  is associated with the electric supply circuit of the thermostat (non shown in  FIGS. 3-5 ) with the task of indicating the presence of power. 
     Let the thermostat be considered mounted on the plant or machine under control with the intervention temperature (for example 60° C.) taken to the desired operating value. This temperature is detected by the semiconductor sensor NTC  103 ; in fact, as the temperature varies there is a variation in the value of the resistant component of the sensor  103 . Said resistive component variation is in turn translated into an electric amplitude signal corresponding to the temperature detected at the output  52  of the input circuit  19  in  FIG. 7  and the input  36  of the microprocessor  33  of the circuit part  17  in  FIG. 5 . 
     In order to access the setting buttons  12 - 13 , it is sufficient to remove the cover  74 . It is not necessary to stop the plant or the machine at a temperature under control. When the thermostat is powered up the green LED  10  on the connector  6  switches on. 
     By keeping the button  12  pressed for at least three seconds the input  36  temperature value is acquired as an intervention value by the memory of the microprocessor  33 , with a consequent luminous confirmation by the green LED  16 . 
     Each acquisition of a new intervention value also automatically sets the reset threshold (hysteresis) according to a minimum hysteresis value. 
     In order to set a different reset threshold, the plant has to be taken to the desired reset temperature and then the white button  13  has to be kept pressed for at least three seconds. Also in this case the green LED  16  will light up to confirm that the reset value has been acquired by the microprocessor  33  and corresponding memory. 
     Once the thermostat has been set, the opening  73  can again be covered with the cover  74 . 
     During operation, the luminous red LED  41  located on the connector  6  lights up to indicate that the set switching value has been reached. In turn, the transistors  34  and  35  are switched by the microprocessor  33  in saturation or blocking status to indicate electrically to the exterior, by the wires  65 , the intervention or resetting status of the thermostat. 
     If it is necessary to program the instrument again it is merely necessary to repeat the aforesaid procedure with different temperature values. 
     Before a new value is acquired (intervention or reset) a test is run on the E 2 PROM memory. This test is indicated by the green LED flashing in rapid succession before the visual datum acquisition signal. 
     In addition to significant setting rapidity, said thermostat is very flexible inasmuch as there exists the possibility, by pressing the buttons  12 - 13  simultaneously for a few seconds, of transforming an operating mode with “normally open” contact (i.e. with output  37  in  FIG. 5  normally devoid of signal) into an operating mode with “normally closed” contact (i.e. with output  37  normally with a signal). In practice, two thermostats in one are obtained. 
     More precisely, the NTC sensor  103  detects the operating temperature of the plant to be controlled. As the temperature varies the resistive value of the sensor varies, creating a voltage variation on the output  52  in  FIG. 7  and the input  36  in  FIG. 5  and the application of a temperature signal to the microprocessor  33 . The latter then commands the blocking of the transistor  34 , which in turn leads to the blocking of the power transistor  35 . The red LED  11  commanded by the diode  41  lights up. 
     The card  2  is further provided with a cutout circuit  18  for possible short circuits and incorrect electric connections. 
     The opposite pattern, with saturation of the transistors  34  and  35  and switching of the red LED  11 , is caused by the return of the temperature below the reset threshold. 
     Lastly, the setting buttons  12 - 13  can be used to enter codes for locking/unlocking programming. The operator can perform setting operations only if he knows the set combination of buttons  12 - 13  (for example, button  12  is pressed twice, button  13  is pressed once and button  12  is pressed three times again). This code is managed by software integrated into the circuit card  2 . 
     The thermostat according to the present invention enables working with the greatest safety, the basic operating parameters to be set rapidly and frequent maintenance interventions to be avoided. 
     It is possible to obtain rapid programming of the thermostat without having to disconnect the supply and without using specific tools but only minimal pressure on the buttons by the operator. Further, the thermostat enables calibration to be performed on the plant and not in the workshop; in this manner it is possible to modify rapidly the calibrating values according to customer needs, 
     With the thermostat according to the present invention it is possible to have a wider range of temperature readings than with known thermostats, i.e. from −20° C. to 90° C. with precision of ±3° C.