Abstract:
A controller for controlling a heater associated with the crankcase of a compressor senses electrical current flowing through the heater. The sensing is preferably accomplished by a transformer in combination with an amplifier providing a feedback signal to the controller. The transformer is installed in the line which carries the electrical current flowing through the heater. The controller checks for the presence of an appropriate voltage level from the amplifier. In the event that the voltage level is not above a threshold level, the controller sends an alarm signal indicating that the heater is not operating properly.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to the control of a heater associated with the crankcase of a compressor. In particular, this invention relates to monitoring the status of such a crankcase heater.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0002]    Compressors are utilized in many modem heating, cooling, and refrigeration applications. These compressors require oil to lubricate the moving parts of the compressor. The oil is often housed in a crankcase where it can be drawn up into the moving parts of the compressor. Heaters have been previously provided to heat the crankcase oil so as to boil off liquid refrigerant in the oil and maintain an appropriate viscosity of the oil for lubricating the moving parts of the compressor. The crankcase heater may run continuously or it may be activated in response to sensed conditions either in the crankcase or in other areas of either the compressor or the system in which the compressor operates. An example of the latter type of control is disclosed in commonly assigned U.S. Pat. No. 5,012,652 entitled “Crankcase Heater Control for Hermetic Refrigerant Compressors” issued to Kevin Dudley. The above described crankcase heater control as well as other heater controls all require one or more invasive sensors to sense conditions that are to be fed back to the control. These controls also do not necessarily provide a quick check as to whether a crankcase heater is operating properly shortly after it has been turned on since there is a lag between activation and changes to the sensed conditions fed back to the control.  
           [0003]    It would be preferable to obtain information as to the operation of a crankcase heater without resorting to the use of invasive sensors. It would also be preferable to be able to quickly determine whether a crankcase heater is operating properly even if other systems may be deployed that use invasive sensors.  
           [0004]    Briefly, the present invention senses the current flowing through a resistance heater. The resistance heater may be either located in the crankcase or external to the crankcase. The sensing is preferably accomplished by a transformer in combination with an amplifier providing a feedback signal to the programmed microprocessor. The transformer is installed in the line which carries the electrical current flowing through the resistance heater. The microprocessor checks for the presence of an appropriate voltage level from the amplifier. In the event that the voltage level is not above a threshold level, the microprocessor sends an alarm signal indicating that the crankcase heater is not operating properly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    For a fuller understanding of the invention, reference should now be made to the following detailed description thereof taken in conjunction with the accompanying drawings, wherein:  
         [0006]    [0006]FIG. 1 illustrates a system for monitoring the operation of a heater, which heats crankcase oil for a compressor; and  
         [0007]    [0007]FIG. 2 illustrates the process implemented by a processor within the system of FIG. 1. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0008]    Referring to FIG. 1, a crankcase heater in the form of a resistance heater  10  is disposed within the crankcase  12  of a compressor  14 . It is to be appreciated that the resistance heater could be external to the crankcase  12  and still heat the oil. In this regard, the heater could for instance be wrapped or mounted to the outer shell of the crankcase. It is also to be appreciated that the crankcase heater could be an inductance heater or any other type of heater that draws electrical current.  
         [0009]    A microprocessor  16  switches a triac  18  on so as to cause current from an AC power source  20  to flow through the resistance heater  10 . It is to be appreciated that switching devices other than a triac could be used to cause the current to flow from the AC power source  20 . For example a relay contact switch could be used. Current flowing through the resistance heater  10  also flows through the primary winding of a transformer  22  located downstream of the resistance heater  10 . An amplifier  24  associated with the secondary winding of the transformer  22  provides a voltage level signal to the microprocessor  16  indicative of the amount of current flow through the primary winding. As will be explained in detail hereinafter, the processor  16  examines the voltage produced by the amplifier  24  in order to determine whether the resistance heater  10  is operating properly. In the event that the heater is not operating properly, the processor sends an alarm signal to an alarm display  26 . The alarm display  26  may be a light emitting diode on a control panel, a computer screen having the ability to display an alarm message, or any other suitable communication device capable of transmitting an appropriate message.  
         [0010]    Referring now to FIG. 2, a flow chart of the process executed by the microprocessor  16  in controlling the resistance heater  10  or any other type of heater that draws electrical current is shown. The process begins with a step  30  wherein the microprocessor inquires as to whether the crankcase heater is on. This is preferably a check as to whether a signal has been sent to the output triac  18  so as to authorize power to the resistance heater  10 . In the event that a command to the output triac is not present, then the microprocessor will proceed along the no path to a step  32  and inquire as to whether a call has been initiated to turn the crankcase heater on. It is to be appreciated that such a call could occur as a result of any number of different processes being implemented by either the microprocessor  16  or some other control device. These processes could include a process which initiates a call in response to one or more sensors providing information indicating that the resistance heater should be turned on. These processes could also be an authorization to turn the resistance heater on before turning the compressor  14  on. It is to be appreciated that the routine of FIG. 2 could be implemented with respect to any of these external processes.  
         [0011]    The processor proceeds from step  32  to step  34  in the event that a call has been noted to turn the crankcase heater on. Referring to step  34 , the microprocessor turns the crankcase heater on by issuing a signal to the triac  18 . The processor proceeds in step  36  to initiate a time delay, which is preferably a clocked time count of a predetermined amount of time that would allow for the AC power to be applied to the crankcase heater  10  and for any transient current conditions to have passed. The processor proceeds from step  36  to a step  38 , which terminates the routine of FIG. 2. It is to be appreciated that the processor will execute various other control procedures before again returning to the routine of FIG. 2. At such time, the processor will again inquire in step  30  as to whether the crankcase heater is on. Assuming that the microprocessor  16  has issued a signal to the triac  18  so as to turn the crankcase heater on, the processor will proceed to a step  40  and inquire as to whether there is a call for turning off the crankcase heater. It is to be appreciated that such a call could originate from other processes being implemented by the microprocessor such as has been previously described. When such a call is noted, the processor will proceed to a step  42  and turn the crankcase heater off before continuing to step  38  and terminating the routine of FIG. 2.  
         [0012]    Referring again to step  40 , in the event that there is not a call to turn the crankcase heater off, the microprocessor will proceed along the no path to a step  44  and inquire as to whether the time delay of step  36  has passed. In the event that this time delay has not passed, the processor will proceed out of step  44  to step  38  and terminate the routine of FIG. 2. On the other hand, if the time delay has passed, the processor will proceed from step  44  along the yes path to a step  46  and read the output of the amplifier  24 . The processor will proceed to a step  48  and inquire as to whether the read amplifier output indicates the presence of current flow through the primary winding  22  of the current transformer. This is preferably a comparison of the read amplifier output to a threshold number stored in the microprocessor  16  indicative of the amount of voltage that should be present during a normal current flow situation in the primary winding of the transformer  22 . In the event that the read amplifier output does not favorably compare with the stored threshold value, then the processor will proceed along the no path from step  48  to a step  50  and issue an alarm signal to the display  26 . It is to be appreciated that the signal transmitted in step  50  can be either the authorization to a light emitting diode on a display panel or an authorization to display a message on a computer screen or an authorization to provide an appropriate message on some other communication device. In any event, the processor will proceed from step  50  to step  38  and terminate the routine of FIG. 2.  
         [0013]    Referring again to step  48 , in the event that the amplifier output does indicate the appropriate amount of current flow, then the processor will proceed along the yes path to step  38  and again terminate the routine of FIG. 2.  
         [0014]    It is to be appreciated that the microprocessor will execute other processes for which it has been programmed before returning to the routine of FIG. 2. These processes preferably include the microprocessor determining whether the resistance heater is to be turned on or off. The execution of these processes should occur in a short period of time preferably less than five milliseconds before returning to step  30  of the routine in FIG. 2. It is to be appreciated that this period of time is substantially less than the time delay implemented in step  36  so as to cause several executions of the logic after initiating the time delay of step  36 .  
         [0015]    Although a preferred embodiment of the present invention has been described and illustrated, it will be apparent to those skilled in the art that changes or modifications may be made without departing from the scope of the present invention. It is therefore intended that the scope of the invention be limited only by the following claims.