Abstract:
Methods and systems for controlling an HVAC actuator using a single output control signal are disclosed. In one illustrative embodiment, the single output control signal may be a digital signal that serially encodes desired position data (either an absolute position or a relative position) for the HVAC actuator. In some cases, the single output control signal is provided by a controller remote from the HVAC actuator, and is received by the HVAC actuator. The HVAC actuator may include a controller for decoding the serially encoded data contained in the single output control signal, and for controlling the HVAC actuator accordingly.

Description:
FIELD 
     The present invention relates generally to HVAC actuators, and more particularly to a method and system for controlling an HVAC actuator with a single output control signal. 
     BACKGROUND 
     HVAC actuators are used in a wide variety of HVAC systems and applications. Such actuators can include, for example, air flow damper actuators, water valves, gas valves, as well as other actuators. In many cases, a motor is used to move the actuator, and a controller is used to provide control signals to cause the motor to drive the actuator to a desired actuated position. 
     HVAC actuator controllers produced today typically either provide analog output control signals or “floating” binary output control signals to control the position of the actuator. Analog output control signals are conventionally either 0-10 volt signals or 4-20 milliamp signals. HVAC actuator controllers that use analog output control signals must typically include a relatively expensive and accurate digital-to-analog (DA) converter. Furthermore, and during use in the field, analog output control signals can often be susceptible to electromagnetic noise that can affect the accuracy and/or reliability of the actuator control. Also, and at least in some cases, there may be a time lag due to the D/A conversion, which can effect the accuracy and/or reliability of the actuator control. 
     “Floating” binary output control signals can have some advantages over analog output control signals. For example, HVAC actuator controllers that provide floating binary output control signals do not typically require a digital-to-analog (DA) converter, are often less susceptible to electromagnetic noise, and are typically not subject to a time lag due to a D/A conversion. In a typical HVAC actuator that uses “floating” binary output control signals, the HVAC actuator controller provides two separate floating binary output control signals, each for commanding the actuated part to move in a particular direction (e.g. open or close). The term “floating” is used here to signify that the separate binary output control signals provide “relative position” control commands, rather than “absolute position” control commands to move the actuated part. 
     In one example one of the floating binary output control signals may be asserted high to move the damper actuator from whatever its current position is towards the “closed” position, while the other of the floating binary output control signals may be asserted to move the damper actuator from whatever its current position is towards the “open” position. Only one of the two floating binary output control signals is typically asserted at any given time. 
     In many cases, the amount or degree that the damper actuator is moved from its current position is dependent on the time interval that the floating binary output control signal is in the asserted state (e.g. high state). For example, if the controller asserts the floating binary output control signal that moves the damper actuator towards the “closed” position for 50 ms, the motor may move the damper actuator 2 degrees from its current position toward the “closed” position. As can be seen, and in this arrangement, the floating binary output control signals move the damper actuator relative to whatever its current position is, rather than commanding an absolute damper position (e.g. 60% open). The HVAC actuator controller must typically include software and/or hardware to indirectly keep track of the current position of the damper actuator, and make relatively position changes based on the desired position of the damper. 
     In today&#39;s market, the cost of an HVAC controller is typically directly related to the number of outputs on the controller. Even though floating binary outputs are cheaper to produce than analog outputs, a floating binary output controller still requires at least two separate outputs per HVAC actuator. What would be desirable, therefore, is a method and system for controlling an HVAC actuator that maintains the advantages of floating binary outputs, which includes high resolution with high noise immunity and lower cost, but requiring less controller outputs. 
     SUMMARY 
     The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
     The present invention relates generally to HVAC actuators, and more particularly to methods and systems for controlling an HVAC actuator with a single output control signal. In one illustrative embodiment, the single output control signal may be a digital signal that serially encodes desired position data (either an absolute position or a relative position) for the HVAC actuator. In some cases, the single output control signal is provided by a controller remote from the HVAC actuator. The HVAC actuator may include its own separate controller for decoding the serially encoded position data contained in the single output control signal, and controlling the position of the HVAC actuator accordingly. 
    
    
     
       BRIEF DESCRIPTION 
       The invention may be more completely understood in consideration of the following detailed description of various illustrative embodiments of the invention in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of an illustrative example of a controller that provides a single output control signal for controlling an HVAC actuator; 
         FIG. 2  is a graph of an illustrative single output control signal that may be provided by the controller to the HVAC actuator in  FIG. 1 ; and 
         FIG. 3  is a flow diagram showing an illustrative method of controlling the position of the actuated part  24  of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The detailed description and drawings show several embodiments which are meant to be illustrative of the claimed invention. 
       FIG. 1  is a schematic diagram of an illustrative example of a controller  10  that is adapted to provide a single output control signal  18  for controlling an HVAC actuator  20 . In some cases, the controller  10  is located remotely from the HVAC actuator  20 . In the illustrative embodiment, the HVAC actuator  20  includes a controller  22 , an actuated part  24  and an electric motor  26 . The actuated part  24  may be, for example, an air flow damper, a water valve, a gas valve, and/or any other suitable actuatable part. The electric motor  26  can be selectively activated by the controller  22  to move the position of the actuated part  24  to a desired position. 
     In some illustrative embodiments, the controller  10  may provide a single output control signal  18  that is a digital or quasi digital signal that serially encodes a desired position of the actuated part  24  (either an absolute position or a relative position). The controller  22  of the HVAC actuator  20  may then be configured to decode the serially encoded position data contained in the single output control signal  18 , and command the motor  26  to move the actuated part  24  to the desired position. 
     It is contemplated that the single output control signal  18  may be encoded with the serial position data in any suitable format or way. For example, the single output control signal  18  may include a series of strictly digital (i.e. DC) high and low voltage signals that collectively encode a desired position of the actuated part. Alternatively, the single output control signal  18  may include an AC signal, such as a 24 volt AC signal, that is cropped or otherwise modified during certain times (e.g. on half-cycles) to produce a series of “zeros” and “ones” (e.g. see  FIG. 2 ). More generally, and in the illustrative embodiment, the single output control signal  18  may be in any suitable format that is capable of serially encoding a desired position value to the HVAC actuator  20 . 
     In some cases, the motor  26  may already include a controller  22 . For example, many DC brushless motors include a controller (e.g. microprocessor or microcontroller) for controlling the commutation of the motor during operation of the motor. It is contemplated that the controller  22  of the DC brushless motor  26  may be configured, through software or hardware enhancements, to receive and decode the position data from the single output control signal  18  provided by the controller  10 . This may help reduce the cost of the overall system. However, it is contemplated that the controller  22  may be separate from the motor  26 , if desired. 
     It is contemplated that the controller  10  may have any desired configuration suitable for producing the single output control signal  18 , and in many cases, a single output control signal  18  that serially encodes a desired position of the actuated part  24 . In the illustrative embodiment shown in  FIG. 1 , the controller  10  includes a processor  12  (e.g. microprocessor or microcontroller), and a switch  16 . A 24 volt transformer provides a 24 volt AC signal to the switch  16 , and the processor  12  selectively opens and closes the switch  16  to either pass or not pass the 24 volt AC signal to the single output control signal  18 . In this embodiment, a “one” may be provided on the single output control signal  18  when the switch  16  is closed, and a “zero” may be provided on the single output control signal  18  when the switch  16  is open. The processor  12  may thus provide a series of “ones” and “zeros” onto the single output control signal  18  to encode a desired position (e.g. either an absolute position or a relative position) of the actuated part  24 . In the illustrative embodiment, the switch  16  may be Triac (triode alternating current switch) as shown, a relay, a transistor, combinations thereof, or any other suitable switching device as desired. 
     It is contemplated that the processor  12  may be any suitable controller device, implemented in either hardware, software or a combination thereof. In many cases, the processor  12  may implement a control schedule, and may receive inputs from various sensors (e.g. temperature sensors, humidity sensors, occupancy sensors, airflow sensors, air quality sensors, and/or any other suitable sensor as desired) and/or other components, and provide appropriate control signals to an HVAC system and/or HVAC system components, as desired. In some embodiments, the controller  10  may be an electronic thermostat. 
     In other cases, the controller  10  may be configured to communicate with one or more thermostat and/or other controllers and may receive heat, cool, ventilation and/or other calls. The controller  10  may be linked to the one or more thermostats and/or other controllers via a communication path, upon which the various calls may be communicated. In response to the various calls, the controller  10  may provide an appropriate single output control signal  18  to communicate a desired position of the actuated part  24  to service the call. In some embodiments, the controller  10  may also be configured to provide other control signals to other components of an HVAC system, such as fan, heat, cool and/or other control signals, if desired. 
       FIG. 2  is a graph of an illustrative single output control signal  18  that may be provided by the controller  10  to the HVAC actuator  20  of  FIG. 1 . In the illustrative embodiment, the controller  10  encodes a serial position command on the single output control signal  18  by modulating the switch  16  on and off. For example, the processor  12  of  FIG. 1  may switch the switch  16  between “on” and “off” states in a desired sequence to encode serial ones and zeros on the single output control signal  18 . For example, when the switch  16  is in the “on” state, the 24 volt AC signal provided by 24 volt transformer of  FIG. 1  is passed to the controller  22  of the HVAC actuator  20 , indicating a “one” bit. When the switch  16  is in the “off” state, the 24 volt AC signal is not passed to the controller  22  of the HVAC actuator  20 , indicating a “zero” bit. The processor  12  may modulate the switch  16  in a manner that creates a serial bit stream on the single output control signal  18  that represents a desired position for the actuated part  24 . The serial bit stream can then be decoded by the controller  22  of the HVAC actuator  20 , and suitable command signals can be sent by the controller  22  to the motor  26  to drive the actuated part  24  to the desired position. 
     One example serial bit stream is shown in  FIG. 2 . Graph  30  shows the 24 volt AC signal provided by the 24 volt AC transformer of  FIG. 1  before it is encoded by the switch  16  and the processor  12 . Graph  32  illustrates an encoded bit stream on the single output control signal  18  after being encoded by the switch  16  and the processor  12 . As illustrated, the processor  12  turns the switch  16  on and off in a certain sequence that corresponds to an encoded position command for the actuated part  24  of the HVAC actuator  20 . 
     In the example shown, the switch  16  is switched on by the processor  12  at times  32   a ,  32   c ,  32   e , and  32   g , representing logic “ones” in the serial bit stream on the single output control signal  18 . At times  32   b ,  32   d , and  32   f , the switch  16  is switched off by the processor  12 , representing logic “zeros” in the serial bit stream on the single output control signal  18 . In the illustrative embodiment, the switching on and off of the switch  16  encodes a serial position command that can be received and decoded by the controller  22  of the HVAC actuator  20 , and ultimately used to control the motor  26  of the HVAC actuator  20 , which in turn, may control the position of the actuated part  24 . 
     Graph  34  shows the serial bit stream produced by the signal shown in graph  32 . Graph  34  assumes that each bit of the serial bit stream corresponds to one half-cycle of the 24 volt AC cycle. If the switch  16  is open, then the corresponding bit is considered a logic “one”, and if the switch is closed, then the corresponding bit is considered a logic “zero”. This is just one example of how a serial bit stream can be sent by controller  10  across the single output control signal  18  of  FIG. 1 . However, it is contemplated that any suitable method may be used to encode a position signal on the single output control signal  18  of  FIG. 1 . For example, and in no way limiting, it is contemplated that DC digital signals may be sent (e.g. 24V DC for logic “one”, and 0V DC for logic “zero”) across the single output control signal  18 , or a serial bit stream may be modulated on top of a DC or AC signal, or any other suitable method may be used, as desired. In some cases, start and stop bits may be provided before and after the desired serial bit stream to indicate the beginning and end of an encoded position signal, but this is not required. 
     In another example, it is contemplated that the duration of having the switch  16  open and/or closed may communicate to the controller  22  a desired position of the actuated part  24 . For example, if the switch  16  open for 10 cycles of the 24 volt AC signal, the controller  22  may decode this to mean that the actuated part  24  should be set at a 10% open position. Likewise, if the switch  16  open for 80 cycles of the 24 volt AC signal, this may be interpreted by the controller  22  that the actuated part  24  should be set at an 80% open position. As can be seen, there are a wide variety of ways to communicate a desired position across the single output control signal  18 . 
       FIG. 3  is a flow diagram showing an illustrative method of controlling the position of the actuated part  24  of  FIG. 1 . The method begins by encoding a serial position command on a single output control signal, as shown at  42 . Next, and as shown at  44 , the serial position command that is encoded on the single output control signal is decoded. Then, the actuated part is actuated based on the decoded serial position command, as shown at  46 . 
     Having thus described the preferred embodiments of the present invention, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respect, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.