Abstract:
A system having unified diagnostics where an electrical energy storage device may supply an actuator. Various techniques may be used to determine energy storage capacity and actuator current usage. Measured storage capacity and actuator current may indicate the health of the energy storage device and the actuator, respectively. Also, operation of a service switch for the actuator may be checked relative to its state.

Description:
The present application is related to U.S. patent application Ser. No. 12/553,795, filed Sep. 3, 2009, now U.S. Pat. No. 8,297,524, issued Oct. 30, 2012, and entitled “A Damper Control System”. U.S. patent application Ser. No. 12/553,795, filed Sep. 3, 2009, now U.S. Pat. No. 8,297,524, issued Oct. 30, 2012, is hereby incorporated by reference. 
     BACKGROUND 
     The invention pertains to actuators and particularly to powering of actuators. More particularly, the invention pertains to diagnostics of actuator systems. 
     SUMMARY 
     The invention provides a system having unified diagnostics where an electrical energy storage device may supply an actuator. Various techniques may be used to determine energy storage capacity and actuator current usage. Measured storage capacity and actuator current may indicate the health of the energy storage device and the actuator, respectively. Also, operation of a service switch for the actuator may be checked relative to its state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a diagram of one circuit of an energy storage powered actuator; 
         FIG. 2  is a diagram of a graph showing an example capacitor voltage and a signal representing an actuator current; 
         FIG. 3   a  is a flow diagram representing an illustrative example of a diagnostics algorithm; 
         FIG. 3   b  is a flow diagram representing an illustrative example of a diagnostics algorithm; 
         FIG. 4  is a diagram of one circuit of an energy storage powered actuator showing one possible version of a drive plus current/voltage converter; 
         FIG. 5  is a diagram of a graph illustrating a determination of an actuator current according to a voltage signal on a capacitor; 
         FIG. 6  is a diagram of one circuit of an energy storage powered actuator showing still another version of the drive and current/voltage converter; and 
         FIG. 7  is a diagram of a graph showing a back electromotive force from a motorized actuator used to determine a magnitude of current to an actuator. 
     
    
    
     DESCRIPTION 
     Capacitors of substantially large capacitance (also known as “super capacitors”) are becoming commercially available. One of their target applications is to store energy when power is available from a power source and use the accumulated energy to drive an actuator even at times when power from the power source would otherwise be insufficient. The actuator may be utilized to drive or control a damper or valve in an HVAC system. The actuator may also be utilized to drive or control a damper or valve for a water heater, stove, another appliance or equipment. Other kinds of components may be driven or controlled by the actuator. 
     The capacitors may suffer gradual loss of energy storage capacity over time. There is a need to monitor this capacity and indicate if it becomes too low to drive the actuator when the need arises—otherwise the actuator may not be driven all the way to the desired position. 
     One way may be to measure and analyze the voltage across the energy storage device (e.g., capacitor) prior, during, and after driving the actuator. This voltage may be a measure of the health (e.g., capacity) of the energy storage device. However, the voltage may also depend on actuator current consumption which in turn may indicate the health of the actuator assembly. 
     Therefore, there is a need to distinguish clearly if it is the capacitor or the actuator that degrades, and to advise the user accordingly to either inspect the electronics control unit containing the capacitor or the actuator assembly, respectively. By providing accurate diagnostics, field maintenance can be optimized. 
     The actuator may also contain a “service switch” which allows the user to disable automatic actuator control, move the actuator to the desired position manually and leave it there. Therefore, there is another need, which is fulfilled by the present system, to detect the status of the service switch by the electronics control unit without adding extra components to it. 
     The voltage across the storage device (capacitor) drops when driving the actuator as the stored energy is consumed by the actuator. A larger voltage drop may indicate either loss of capacitance or increased actuator consumption. Therefore, actuator current is also measured to distinguish the two failure modes. The voltage drop and the actuator current are then combined to calculate the storage device capacitance. 
     If the capacitance drops substantially compared to either previously stored values or an absolute threshold, it is concluded that the storage device is compromised. 
     If the actuator current during actuator drive is increased substantially compared to either previously stored values or an absolute threshold, it is concluded that the actuator assembly is compromised. 
     If the actuator current is substantially zero during actuator drive, it is concluded that the service switch is open. 
     Alternatively, if the voltage across the storage device stays substantially constant during actuator drive, it is concluded that the service switch is open. 
     The techniques of monitoring voltage across storage device as well as current in an actuator may be used stand-alone. The present approach may combine the two measured values to provide accurate system diagnostics that indicate which system component needs maintenance. 
     The present scheme may be realized using an electronics circuit built around a microcontroller. The microcontroller may provide signals to drive the actuator, and use an analog-to-digital (AD) converter input to measure the voltage across the storage device. The microcontroller may also measure a voltage proportional to the actuator current by another AD converter input. This voltage may be obtained by a current-to-voltage conversion. 
     In one approach, a resistor in series with the actuator is used for the conversion. This technique may be used in the motor control field. In another approach, the conversion may be done by measuring a voltage drop across a known capacitor while disconnecting the actuator from the storage device temporarily. In this case, the microcontroller may provide signals to drive the measuring sequence and use the AD converter again to measure the voltages. 
     In case the actuator involves an electrical motor, yet another approach is possible where the actuator current may be monitored by measuring the back electromotive force (BEMF) generated by the motor while disconnecting the actuator from the storage device temporarily. Again, the microcontroller may provide signals to drive the measuring sequence and use the AD converter to measure the voltages. 
     The microcontroller may then calculate the storage device capacitance and actuator current based on measured voltages, compare the value to values stored during previous run cycles or to a suitable threshold, and decide if the storage device and/or the actuator assembly is compromised. 
     If the health of the storage device or the actuator is detected as insufficient to further position the actuator reliably, the microcontroller may decide to leave the actuator in a desirable position and indicate the failure to the user. For example, if diagnostics finds out that the capacitor or the actuator have failed such that moving a flue damper to the closed position can not be guaranteed, the system may decide to leave the flue damper open from that time on. This may allow the system to keep on working safely (flue is open) although with reduced energy efficiency (flue stays open even when a main valve is off and only a standing pilot flame is burning, heat escapes up the flue). User is notified but still gets hot water when needed so the repair is not urgent. If the system left the damper in closed position instead, the main valve would not be allowed to turn on and user would get no hot water and would need to get it repaired urgently. 
     The present system relates to a millivolt damper disclosed in U.S. patent application Ser. No. 12/553,795, filed Sep. 3, 2009, now U.S. Pat. No. 8,297,524, issued Oct. 30, 2012, which is hereby incorporated by reference. 
       FIG. 1  is a diagram of one scheme of the present approach. A power source  11  may have an output with energy storage provided by a capacitor  12 . The output from power source  11  may go to a drive plus current/voltage converter  13 . An output from converter  13  may go to a service switch  14 . The service switch  14  may be connected to an actuator  15 . Service switch  14  may allow a user to disconnect actuator  15  and drive it manually to a desired position and leave it there. A microcontroller  16  may provide a drive signal to the drive plus converter  13 . The signal drive may be a control signal from microcontroller  16  that energizes actuator  15  and controls the current-to-voltage conversion. An AD1 line from microcontroller  16  may be connected to the energy storage line. An AD1 voltage may be a voltage signal corresponding to a voltage across an energy storage device  12 . An AD2 voltage signal may correspond to the current sunk by actuator  15 . 
       FIG. 2  is a diagram showing examples of signals for voltage across the energy storage device and current sunk by the actuator. Actuator  15  may be energized for a duration  17  of T time. Signal  18  corresponding to the voltage across the energy storage device  12  decreases as the storage device  12  is discharged by current going into actuator  15 . Signal  18  may be read directly by AD1 line of the microcontroller. Signal  19  representing current sunk by actuator  15  is constructed from measurements taken on AD2 line of the microcontroller. Different versions of drive plus converter  13  may lead to different algorithms to construct signal  19 , as will become apparent further below. Microcontroller  16  may take several samples of the AD1 and AD2 signals repeatedly during time  17 . 
     The capacitance of storage device  12  may be estimated as: 
                     C   ≈         ∫   0   T     ⁢         I   ACTUATOR     ⁡     (   t   )       ⁢     ⅆ   t         Vdrop       =       Integral   Vdrop     .             (   1   )               
Microcontroller  16  may implement an algorithm to approximate the value of the integral of equation (1).
 
     An algorithm as diagrammed in  FIG. 3   a  may be implemented. It may be regarded as a diagnostics algorithm. A question, whether the integral (of equation 1) is equal to zero, may be asked at symbol  21 . If the answer is yes, then service switch  14  may be open, as shown at symbol  22 . If the answer is no, then a question of whether the integral is equal to a value larger than expected, may be asked at symbol  23 . If the answer is yes, then actuator  15  may have failed, as shown at symbol  24 . If the answer is no, then a question of whether C of the integral equation is smaller than expected may be asked at symbol  25 . If the answer is yes, then there may be a capacitor  12  failure, as indicated at symbol  26 . If the answer is no, then the algorithm process may be stopped or repeated. It may be noted that it is unlikely that two of the failures noted by the algorithm in  FIG. 3   a  would occur at the same time. Also, the order with which the questions are raised during algorithm execution may be changed as desired. 
     An alternative algorithm as diagrammed in  FIG. 3   b  may be implemented. The difference from the algorithm as diagramed in  FIG. 3   a  is that symbol  21  is replaced with a symbol  27  in  FIG. 3   b  which asks whether the voltage across the storage device is constant during an actuator drive. If the voltage is substantially constant, it is concluded that the service switch is open. Also, the order with which the questions are raised during algorithm execution may be changed as desired. 
       FIGS. 4 and 5  are diagrams for illustrating a conversion of an actuator current to a representative voltage signal with a capacitor. While actuator  15  is being driven, microcontroller  16  may turn switch  20  off temporarily, as indicated by drive signal  28  of a diagram in  FIG. 5 . The diagram of  FIG. 5  shows measurement signals taken during actuator current changes. A period of the switch being off is indicated by a notch  29  in drive signal  28 . While switch  20  is off (i.e., open) and service switch  14  is on (i.e., closed), actuator  15  current then may discharge a converter capacitor  31  of a known capacitance at a rate proportional to the level of the actuator current, as shown by a discharge indication  32  on an AD2 signal  33 . The current discharge rate may be measured by an A/D converter of microcontroller  16 . 
     Another way for measuring actuator current is by measuring back EMF in a situation where actuator  15  implements a motor.  FIG. 6  is a diagram of a circuit which may be used for performing actuator current measurements from a back electromotive force. While actuator  15  is being driven, microcontroller  16  may turn switch  20  off temporarily as indicated by an off portion  29  of signal  28  in  FIG. 7 . The motor of actuator  15  may keep on rotating due to inertia. The rotating of the motor may generate back electromotive force, which may be observable in a graph of  FIG. 7  as a steady voltage at portion  37  of signal  35  after some of the transients  36  disappear. Signal  35  may be sensed on the AD2 line of microcontroller  16  for processing. Lower BEMF may indicate higher motor current. A diode  34  at the input of actuator  15  may limit the magnitude of the transients  36 . 
     Several such current measuring sequences, as exemplified by  FIGS. 5 and 7 , may be executed during the course of energizing the actuator. Each such sequence provides AD2 signal that may be used by the microcontroller to calculate instantaneous actuator current levels. Microcontroller  16  may use the calculated consecutive current levels to construct signal such as signal  19  in  FIG. 2  and calculate the integral in Equation 1. 
     In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense. 
     Although the present system has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.