Abstract:
A circuit placed between an alternating current actuated device and a digital logic controller to isolate the digital logic controller from the AC line power and to provide a signal indicative of actuation of the alternating current device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to means for isolating an alternating current (AC) actuated device from a logic control device integrated therewith, combined with means for detecting when the AC actuated device is operational. 
     2. Description of the Related Art 
     Many AC devices which perform work are now controlled by digital logic devices such as microcontrollers, microprocessors, or programmable logic controllers (PLCs). Examples of this in the consumer field include numerous household appliances. In the industrial field, a common example would be in material handling operations where various sensors, motors, relays, solenoids, et al. are required to run the conveying and handling apparatus and may be controlled by one or more bus systems, programmable logic controllers, or on board microprocessors. In this instance, it is often critical that immediate detection of a fault condition in an actuated device is available to the operator in order to prevent mishandling, backups, crashes, etc; of the items on the conveyor line. 
     Further, because digital logic control is incompatible with the AC power required for the actuated devices, isolation between DC logic power and AC device power is highly desirable. 
     It is further highly desirable that an actuation sensor be accomplished inexpensively and reliably within a small package which can easily be added to or integrated within existing systems. 
     SUMMARY OF THE INVENTION 
     The present invention provides a means for isolating an AC actuated device and detecting its actuation via a digital controller which controls the actuation. The means generally comprises a circuit having an optocoupler or other suitable means for isolating an AC actuated device, or load, from a DC microcontroller or PLC; a diode network allowing current flow in first and second directions and for biassing the light emitter of the optocoupler; a device actuation switch between the device and the diode network which is controlled by the PLC and; resistor-capacitor (RC) RC charge and discharge paths connected between the phototransistor output of the optocoupler and the PLC to vary the state of an indicator output connection which the PLC can sense to determine that the load is present, i.e. the device is actuated when the device actuation switch is placed in the ON state. 
     The invention may further comprise suitable biassing and limiting resistors, connection points, DC power supplies and the like as necessary or desirable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully and completely understood from a reading of the Description of the Preferred Embodiment in conjunction with the drawings, in which: 
     FIG. 1 is schematic of the present invention in situ between a PLC and an AC actuated device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Throughout the Description of the Preferred Embodiment, like components will be identified by like reference numerals. 
     As seen in FIG. 1, the electronic circuit  11  of the present invention is used to sense the actuation of an AC powered device  13  through a DC powered programmable logic controller (PLC)  15 . The device  13  acts as the AC load upon the circuit  11 . While described as a PLC, the DC powered logic and control circuit may be a microcontroller, microprocessor, ASIC, or the like. The device  13  is powered by AC power lines L 1  and L 2  and connected to the circuit  11  through first and second AC connectors  17 ,  19 , respectively, of any known type. 
     The circuit  11  contains an electronic or electromechanical controllable switch  21  controlling current flow through the first AC connector  17 . The AC actuated device  13  is placed between second AC line L 2  and second AC connector  19 . It will be appreciated that the device may be placed in series with the first AC line L 1 , if desired. Between the pole side of switch  21  and the device  13  are connected a diode network  23  having a first line of two series diodes, D 1 , D 2  in parallel with a single second line having a reverse direction diode D 4 . A first leg  25  of the diode network  23  has a current limiting first resistor R 1  in parallel with series diodes D 1 , D 2  and connected to the anode  29  of the light emitter, or LED  31 , of an optocoupler U 1 . The second leg  27  of the diode network is connected to the cathode of the LED  31 . The optocoupler U 1  is used to isolate the AC power lines L 1  and L 2  of the device  13  from the DC powered half of the circuit  11  and its attendant PLC  15 . The optocoupler U 1  includes a phototransistor  35  in its internal circuitry as is common in the art. The optocoupler may be comprised of discrete components if desired. 
     The base of phototransistor  35  is connected through a second resistor R 2  to ground. The specific values and types of the electronic components will be recognized as variable according to the specific application selected by the ordinarily skilled artisan. A first side of a capacitor C 2  is connected to the collector of phototransistor  35  through a third resistor R 3  thereby forming an RC discharge path through the phototransistor  35  to ground, as illustrated by line  34 . A fourth resistor R 4  is connected between the DC power supply  37  and the junction  39  of capacitor C 2  and the third resistor R 3  to form an RC charge path, as illustrated by line  36 . Extending from the junction  39  is an indicator connection  41  to which is attached a sense pin  43  of the PLC  15  for the purpose of monitoring the voltage state of the indicator connection  41 . The emitter of the phototransistor  35  is connected to ground. The DC power supply  37  may be shared with the PLC  15  as indicated by the dashed line  45 . The PLC  15  also shares a ground with the DC side of the circuit as indicated by dashed line  44 . 
     The PLC  15  is connected through a second, or control, pin  47  to the controllable switch  21  whereby it controls activation of the device  13 . Suitable isolation between the AC and DC halves of the circuit is maintained by, e.g., relay operation or optocoupling (not shown) of the switch control function. 
     Activation of the device  13  by closing of the controllable switch  21  places a load on, i.e., causes current to flow through, the circuit  11  causing voltage to rise across the series diodes D 1 , D 2  during the positive half of the AC line cycle. When this voltage is sufficient, the LED  31  of the optocoupler U 1  turns on. Damage to the LED  31  is prevented by current limiting resistor R 1 . The phototransistor  35  then conducts causing the capacitor C 2  to discharge through the phototransistor  35 , making the voltage level at indicator connection  41  a logical low. The charge and discharge time constants determined by the values of R 4  and R 3 , respectively, can be sized to provide a slow charge time and rapid discharge time to facilitate detection of the low voltage state at indicator connection  41  in order to accommodate the polling duty cycle of the sensing algorithm of PLC  15  through pin  43 . When the PLC knows the controllable switch  21  has been activated and it then senses a low voltage at the indicator connection  41  it can decide that the device  13  is present and active. It can then report through its output “report pin”  49  the operative state of the device  13  to, for example, an operator interface indicator bulb  53 . 
     If a square wave corresponding to the half line cycles were desired at indicator connection  41  and the PLC sensing algorithm/duty cycle were adjusted accordingly, very fast sensing response may be obtained without the use of R 3  and C 2  to form a discharge path. 
     While the present invention has been shown and described with reference to preferred embodiments, many alternatives will become apparent to the ordinarily skilled artisan upon disclosure of the present invention. Therefore the present invention is only to be limited by the claims appended hereto.