Patent Abstract:
A circuit and apparatus for magnetically sensing fluid flow and applying voltage to a load. A valve disposed within a conduit is provided with a magnetic shield. A magnet is located on one side of the magnetic shield while a sensor, associated with the valve is located on the opposite side of the magnetic shield. The valve, and hence the magnetic shield, moves to permit fluid flow. When the magnetic shield moves due to fluid flow, the magnet activates the sensor. A load control circuit includes a supply terminal for receiving a supply voltage and a detector which detects a condition requiring the operation of a load. The detector causes a threshold voltage to be generated from the supply voltage, and a time delay controller controls the time required to generate the threshold voltage. A DIAC or equivalent element conducts to generate a first trigger signal once the threshold voltage is achieved, and a silicon-controlled rectifier (SCR) generates a second trigger signal in response to the first trigger signal. The circuit includes an opto-TRIAC and triac which are rendered conductive by the second trigger signal to cause a voltage to be provided to the load.

Full Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus for sensing fluid flow through a conduit and controlling a load based upon the sensing of the fluid flow. More specifically, the present invention is directed toward a fluid flow sensor and a load control circuit employing a variable time delay to control activation of an alarm circuit in a fire protection system. 
     BACKGROUND OF THE INVENTION 
     Numerous control circuits have been designed to apply a voltage or current to an electrical load after a time delay. Examples of such circuits are disclosed in U.S. Pat. No. 3,745,382 to Hoge et al., U.S. Pat. No. 3,597,632 to Vandemore, and U. S. Pat. No. 3,764,832 to Stettner. However, these and other known control circuits are relatively complicated and have numerous components, thus increasing manufacturing difficulty and costs. Further, these and other known control circuits typically provide relatively lengthy time delays, on the order of five minutes, and are unreliable when needed to be reduced to a lesser amount of time. 
     Control circuits are used in a variety of applications including, for example, to activate an alarm circuit in a fire protection system. Conventional fire protection systems typically include a source of water or other fire-extinguishing fluid, a detector for detecting the flow of the fire extinguishing fluid through a pipe or conduit, and an alarm circuit or other load that is activated when a sufficient flow is detected. 
     In such systems, the alarm is preferably not activated immediately upon detection of fluid flow in the conduit, because flow may occur due to a “water hammer” or fluid backwash within the system. If the alarm were activated immediately upon detection of a water flow, a large number of false alarms would result. 
     In order to reduce or eliminate such false alarms, a control circuit can delay the activation of the alarm for a predetermined time following detection of an alarm condition. Early detection and control circuits included simple mechanical devices, such as dashpots in which air was forced into and out of a chamber. The alarm would not sound until the air was completely out of the chamber, at which time a switch would close to activate the alarm. 
     These and other conventional detection mechanisms were designed to provide a delay in the range of 30 seconds to 90 seconds. However, these devices were unreliable and inaccurate, and were thus unsuccessful in eliminating false alarms. Accordingly, solid state electrical load control circuits were developed for fire protection systems such as the time delay circuit known as ICM/HMKS-W1104. These electrical load control circuits delay activation of the alarm until an electrical sensor or switch is rendered conductive. 
     It would be desirable to provide a relatively simple, reliable, and easy-to-install sensor circuit with minimal current draw, in order to detect a condition (such as fluid flow) which requires activation of a load such as an alarm. While certain flow sensing devices are known, such as those described in U.S. Pat. No. 3,749,864 to Tice, U.S. Pat. No. 4,791,254 to Polverari and U.S. Pat. Nos. 5,086,273 and 5,140,263 to Leon, these and other similar devices include relatively complex arrangements of moving parts. In addition, it would also be desirable to provide an accurate load control circuit which delays activation of a load by using an integrated circuit. 
     SUMMARY OF THE INVENTION 
     The present invention solves the foregoing problems, and provides additional advantages, by providing an apparatus for sensing fluid flow through a fluid-carrying conduit. According to exemplary embodiments of the present invention, a valve such as a flapper valve disposed within the conduit is provided with a magnetic shield. A magnet is located on one side of the magnetic shield while a sensor, associated with the valve is located on the opposite side of the magnetic shield. The valve, and hence the magnetic shield, moves to permit fluid flow. When the magnetic shield is removed from between the magnet and sensor, the magnet activates the sensor. Thus the sensor, which can be a Hall effect sensor, generates a signal when the valve is opened to permit fluid flow. 
     According to one aspect of the present invention, the sensor and magnet can both be encased in a tube sealed with substantially watertight material and inserted into the conduit (e.g., by threading the encased sensor through a threaded pipe opening) near the valve. 
     In another exemplary embodiment of the present invention, a load control circuit includes a supply terminal for receiving a supply voltage and a detector which detects a condition requiring the operation of a load. The detector causes a threshold voltage to be generated from the supply voltage, and a time delay controller controls the time required to generate the threshold voltage. A DIAC or equivalent element conducts to generate a first trigger signal once the threshold voltage is achieved, and a silicon-controlled rectifier (SCR) generates a second trigger signal in response to the first trigger signal. The load control circuit includes an opto-TRIAC and a TRIAC or similar switches which are rendered conductive by the second trigger signal to cause a voltage to be provided to the load. According to an alternate embodiment of the present invention, multiple electrically isolated loads can also be controlled. 
     If the supply voltage is an AC (alternating current) voltage, the load control circuit also includes a rectifying diode or equivalent element for converting the AC voltage to a DC (direct current) voltage. The time delay controller may include a potentiometer (variable resistor) to vary the delay time required to generate the threshold voltage. Additionally, the time delay controller can be implemented via a digital implementation. When digitally employed, a dip switch is used in combination with a digital control to vary the amount of time delay from zero to ninety seconds. 
     For implementation in a fire protection system in accordance with the present invention, the detector may be a magnet operated reed switch, or a Hall effect sensor, for detecting a threshold fluid flow in a conduit and the load is an alarm for indicating the threshold flow in the pipe. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the present invention will be more fully understood upon reading the following Detailed Description of the Preferred Embodiments in conjunction with the accompanying drawings, in which like reference indicia indicate like elements, and in which: 
     FIG. 1 illustrates a block diagram of the sensor circuit and load control circuit in accordance with an exemplary embodiment of the present invention; 
     FIG. 2 illustrates a schematic diagram showing an exemplary implementation of a fluid flow sensor of the present invention; 
     FIGS. 3A and 3B illustrate schematic diagrams of the fluid flow sensor and the magnetic shield in accordance with an exemplary embodiment of the present invention; 
     FIG. 4 illustrates a schematic diagram of a reed switch in accordance with an exemplary embodiment of the present invention; 
     FIG. 5 illustrates a circuit diagram illustrating the load control circuit in accordance with an exemplary embodiment of the present invention; 
     FIG. 6 illustrates a circuit diagram of the load control circuit with multiple loads in accordance with an exemplary embodiment of the present invention; 
     FIG. 7 illustrates a circuit diagram of the load control circuit implementing a digital time delay implementation in accordance with an exemplary embodiment of the present invention; and 
     FIG. 8 illustrates a schematic diagram of a fire protection system in which the circuit of the present invention may be implemented. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, an exemplary embodiment of an alarm circuit according to the present invention is shown. A sensor circuit  10  is implemented in a fire protection circuit. The fire protection circuit also includes a load control circuit  14  which further comprises a delay circuit for controlling the activation of a load such as an alarm circuit in a fire protection system. In such a system, the flow of water or other fire suppression fluid through the pipes of a building sprinkler system (to prevent or minimize fire damage) is detected, causing a switch to close and apply an operating voltage to the alarm circuit after a time delay to guard against false alarms. 
     According to the invention, sensor circuit  10  is connected as shown between a neutral wire  12 , an input of a load control circuit  14 , and a terminal  16  of a load L (e.g., an alarm, which can be embodied by one or more lights, sirens, motors, solenoids, or other loads) which is connected between a power input terminal  18  and the load control circuit  14 . The power input terminal receives an input voltage of, for example, 24-130 volts A.C. The sensor circuit  10  senses fluid flow through a pipe, and when fluid flow is sensed, the sensor circuit  10  generates an output signal and supplies this signal to the load control circuit  14 . The load control circuit  14  then operates to apply the supply voltage across the terminals  12  and  18 , thereby applying the supply voltage to the load  16  and activating the alarm. The sensor circuit  10  can be implemented using a Hall effect sensor or other suitable sensor such as a reed switch, as will be described in more detail with respect to FIGS. 2-4 below. It will be appreciated that the time delay circuit is useful for preventing false alarms. 
     Fluid flow can be sensed by the use of a sensor, (e.g. Hall effect sensor), a magnetic shield, and a magnet used in combination. The particular Hall effect sensor discussed above is approximately {fraction (3/16)}″×{fraction (3/16)}″×{fraction (1/16)}″, and the magnet can have a ¼″ diameter and a thickness of ⅛″. Due to the relatively small size of both the Hall Effect sensor and the magnet, each element can be inserted into a threaded tube (made of, e.g., plastic), and the tubes can be covered with epoxy or some other suitable material to provide a substantially watertight seal for the contents of the tubes. Each of the threaded tubes can then be rotated into the fluid-carrying conduit through a threaded orifice in the conduit such that the end of each tube, one containing the sensor and one containing the magnet are located in close (e.g., within approximately ⅛″) proximity to each other. Alternatively, the tubes need not be threaded. The tubes containing the sensing device and magnet can be lowered down through holes to ensure that they are correctly positioned, and tightened through the use of a nut or rubber gasket. 
     FIG. 2 illustrates a (not to scale) view of a tube  47  inserted into a pipe defined by pipe wall  40 , and having a check valve with a hinged clapper  42 . The pipe contains a fluid flowing in the direction indicated by the flow arrow. Threaded tubes  46  and  47  (shown in FIG. 3A) are inserted into similarly-threaded holes in pipe wall  40  and this connection is sealed by a suitable seal  46 . The tube  47  includes a Hall Effect sensor  44  and is encased in a suitable substantially water-tight material. Tube  46  (not shown in FIG. 2) includes the magnet  45  which is encased in a suitable substantially water-tight material. Hinged clapper  42  is provided with sealing portions  48   a  which cooperate with corresponding portions  48   b  of the pipe  40  when the clapper is in a closed position. Magnetic shield  50  is attached to the hinged clapper  42  so that the magnet is prevented from actuating the Hall Effect sensor  44  when there is no flow of water through a valve. As shown in FIGS. 2 and 3A, the magnetic shield  50  is located between the encased magnet  45  and Hall Effect sensor  44 . While the magnetic shield  50  can be made of any material that is able to shield the magnetic field of the magnet from the sensor, it is advantageous for the material to be composed of approximately 3 percent Nickel Iron to prevent oxidation of the shield. 
     As illustrated in FIG. 3B, when there is substantially no fluid flow in the pipe, hinged clapper valve  42  is in a closed position as its associated magnetic shield  50  is positioned between the encased Hall Effect  44  sensor and the magnet  45  to substantially neutralize the magnet  45 . When there is fluid flow within the pipe, the flapper valve  42  is moved in the direction of the flow arrow shown in FIG. 2, and the magnetic shield  50  is moved away from the Hall effect sensor  44  and magnet  45 , thereby freeing the magnet to bias the sensor such that the sensor conducts to enable the operation of the sensor circuit  10  and load control circuit  14 . The remainder of the sensor circuit  10  can consist of three additional components (such as a zener diode, a capacitor and resistor) which act as a power supply to the Hall effect sensor. These elements are described in detail in commonly assigned application Ser. No. 09/001,216, incorporated herein by reference. Additionally, the sensor circuit  10  can also include an indicator circuit also described in detail in the above-mentioned commonly assigned application. 
     It should be appreciated that the sensor of the sensor circuit  10  illustrated in FIG. 1 can alternatively be embodied by a reed switch associated with a magnet such that motion of the valve or other indication of fluid flow causes the reed switch to close, thereby supplying an input to the time delay circuit  14 . The reed switch is set up within the valve in the same manner as described above with respect to the Hall effect sensor. However, the manner in which the switch is activated differs slightly. As illustrated in FIG. 4, a reed switch  60  encased in tube  47 , in this embodiment, can be biased in an “on” (conductive) state by its associated magnet  45  encased in tube  46 . The reed switch  60 , as is known within the art, consists of two electrodes maintained within a glass tube. When a magnet is close to the reed switch  60 , the magnet attracts the reed switch electrodes to contact and thus provide a closed circuit. As illustrated in FIG. 4, the reed switch magnet  45  is substantially neutralized by the use of the magnetic shield  50  when the valve is in a closed (no fluid flow) state. When the magnetic shield  50  is removed from the reed switch, the magnet  45  causes the reed switch  60  to close thereby providing power to the sensor circuit  10  and load circuit  14 . This alternative has the advantage of lower cost and a reduced number of parts when compared to employing the Hall effect sensor. 
     It should also be appreciated that the sensor circuit  10  of the present invention can also be implemented using a push-button or pressure switch, such as in commonly used to provide interior lighting control for example, a refrigerator or automobile door. In such an embodiment, the closed clapper of the valve exerts pressure on the pressure-sensitive switch to indicate an open condition (that is, would provide no output to the delay circuit). When the valve is opened, indicating fluid flow through the pipe, the pressure exerted by the clapper on the pressure switch is reduced or eliminated and would indicate a closed condition (that is, would provide an indicator signal to the delay circuits). It should also be appreciated that alternative conventions of the reed switch can be used (i.e., the sensor switch can be a normally open or normally closed). 
     Referring to FIG. 5, according to another embodiment of the present invention load control circuit  14  is shown in detail. The load control circuit includes a neutral terminal  12  connected to ground and a supply terminal  18  connected to a standard A.C. power source of between 30 and 120 volts at 60 Hz. A load  70  is connected to the supply terminal  18  to receive the supply voltage. The load control circuit  14  is connected between the load  70  and the neutral terminal  12  to selectively connect the load between the supply terminal  18  and the neutral terminal  12 . In this embodiment, it is assumed that the load  70  draws a maximum of 6 amps; it will be readily appreciated that the circuit may be readily modified to accommodate loads having a current draw greater than 6 amps. The load control circuit  14  includes a switch  75 , a diode  80 , and a first capacitance  85  connected in series between the load  70  and the neutral terminal  12 . In a preferred embodiment, the diode  80  is a 1N4005 diode, and the first capacitance  85  is a 33 micro farad (MFD) capacitor rated at 160 volts D.C. (VDC). It will be appreciated that other suitable diodes and other suitable charge storing elements may be used for diode  80  and first capacitance  85 , respectively. 
     The first capacitor  85  is connected in parallel to a resistance  87 . A second capacitance  105  and a time delay setting circuit  90  are connected in series, in a circuit path that is in parallel with resistance  87  and in parallel with first capacitance  85 . Resistance  87  functions to discharge capacitance  85  when operation of the load control circuit is completed. Resistance  87  can be a fixed 10 kilo ohm (kΩ) resistor rated for 2 watt (W) or other suitable resistor. The second capacitance  105  may be a 47 MFD capacitor rated at 50 VDC or other suitable charge storing element. 
     Time delay circuit  90  includes two paths. The first path includes diode  97  while the second path includes a potentiometer  95 . The potentiometer  95  functions to adjustably control the charging rate of capacitor  105  to delay activation of the load  70 . 
     The time delay circuit  90  further includes a DIAC  110 . The DIAC  110  is preferably an MBS 4991 DIAC having a trigger voltage of 10 volts, though any suitable triggering element may be used. As will be appreciated by those skilled in the art, a DIAC (DIode AC switch) is a bidirectional diode which may be rendered conductive when a “breakover” or “trigger” voltage is exceeded in either direction by an applied voltage or trigger spike. Suitable DIACs are available from numerous suppliers, including Motorola Corporation. 
     The DIAC  110  is connected to a gate  120   a  of a silicon controlled rectifier (SCR)  120  through a resistance  115 . The resistance  115  may be a fixed 690Ω resistor rated for 0.5 watts or other suitable resistance element. SCR  120  is preferably an EC103B SCR, available from numerous manufacturers, including the Teccor Corporation of Dallas, Tex. The anode  120   b  of the SCR  120  is connected to the cathode of the second capacitor  105 , resistance  87 , and between the cathode of first capacitance  85  and the cathode of the diode  80 . The cathode  120   c  of the SCR  120  is connected to pin  2  of an MOC3020 opto-TRIAC  125 . As a result, light emitting diode  127  connected between pins  1  and  2  of opto-TRIAC  125  is caused to emit light thereby exciting optical triac  129  connected between pins  4  and  6  of opto-TRIAC  125 . Pin  1  of the light emitting diode is connected via resistor  140  to neutral line  12 . Once optical triac  129  is excited, a trigger pulse is provided to the gate of triac  130 . The pulse is supplied via the load  70  in series with resistor  135 . Triac  130  then turns on the load  70 . Resistor  135  can be a fixed 100 ohm resistor or other suitable resistance element. 
     As will be appreciated by those skilled in the art, a silicon controlled rectifier (SCR) is rendered conductive when a proper signal is applied to its gate. The SCR remains conductive when the gate signal is removed, and is turned off by removing the anode voltage, reducing the anode voltage below the cathode voltage, or making the anode voltage negative, as on the alternate half-cycles of an A.C. power source. A TRIAC (TRIode AC switch) is a gate-controlled bidirectional thyristor or SCR which is rendered conductive in both directions when a proper signal is applied to its gate. TRIAC  130  is preferably a Q4006L4 TRIAC available from numerous suppliers including Teccor Corporation. 
     The load control circuit of FIG. 5 may be used, for example, in a fire suppression system. In such an arrangement, the switch  75  may be a Hall effect transistor in combination with a power supply circuit as described above or a magnet operated reed switch on a vane type water flow detector as discussed above with respect to FIG. 4, and the load  70  may be an alarm circuit which causes bells, horns, lights, etc., to be activated in response to a threshold fluid flow in a conduit with a reed switch. It will be appreciated that the circuit of the present invention may be used in connection with other types of switches or detectors and/or with other types of loads. Suitable reed switches are available from numerous suppliers, including the C. P. Clare Corporation of Chicago, Ill. and the Hammlin Corporation of Lake Mills, Wis. 
     Using the example of a fire suppression system, the operation of the load control circuit  14  of the present invention will now be described. When water or fire extinguishing fluid starts to flow through the pipes of a sprinkler system in a building to prevent fire damage, a small permanent magnet as described above is enabled to activate switch  75  to cause closure. 
     The closing of the switch  75  contacts applies the supply voltage potential to the rectifying diode  80 . In the embodiment of FIG. 1, the supply voltage is between 24 and 120 volts A.C. (alternating current). 
     The diode  80  rectifies the alternating current to provide a half wave rectified current equivalent to a D.C. (direct current) voltage which rapidly charges capacitance  85  to a voltage of about 160 volts D.C. (based on an input voltage of 120 volts A.C.). Diode  80  and capacitance  85  thus have the effect of converting the A.C. voltage source into a D.C. power source. It will be appreciated that if a D.C. power source with correct polarity is used, a rectifying function does not need to be performed, and the diode  80  is therefore unnecessary. In this case, the closing of the switch causes capacitance  85  to be rapidly charged directly by the power source. 
     The charge stored by capacitance  85  slowly charges the second capacitance  105  through potentiometer  95  and resistance  100 . It will be appreciated that an RC circuit is formed by second capacitance  105 , potentiometer  95 , and fixed resistor  100 , and that the RC time constant and thus the charge time of capacitance  105  may be adjusted by potentiometer  95 . According to one embodiment of the present invention, potentiometer  95  is a trim pot and allows the delay time of time delay circuit  90  to be adjustable between about zero seconds and approximately 90 seconds. A dial or other input device (such as a screw head slot, not shown) connected to the potentiometer  95  may be used to adjust the resistance and thus the time delay. Diode  93  discharges capacitor  105  when power is removed. 
     If not for the presence of DIAC  110 , capacitance  105  would be charged to approximately 170 volts (based on a 120 volt A.C. supply voltage). However, when the charge stored in second capacitor  105  reaches 10 volts D.C., the break over voltage of DIAC  110  is achieved, causing DIAC  110  to conduct and generate a first trigger signal. The first trigger signal is supplied to gate  120   a  of SCR  120  through the resistor  115  which causes SCR  120  to conduct and generate a second trigger signal. 
     The SCR  120  renders a negative pulse on pin  2  of opto-TRIAC  125 . The current through LED  127  thereby renders optical triac  129  conductive. When optical triac  129  is conductive, AC voltage is supplied to the TRIAC  130 . The TRIAC  130  is rendered conductive in response to A.C. voltage generated by the closure of the optical triac  129 . When the TRIAC  130  turns on, the A.C. voltage drop across the load control circuit  14  is only about 6 volts. The signal applied to the gate of TRIAC  130  is phase controlled such that TRIAC  130  is only about 95-98% conductive. If the TRIAC were 70% conductive, the voltage drop across the TRIAC would be greater than 6 volts, and the power supplied to the load would be reduced. If the voltage drop across the TRIAC is less than about 6 volts, the TRIAC may oscillate between conductive and non-conductive states, thus impairing operation of the load control circuit. It will be appreciated that the actual voltage drop across the TRIAC is approximately 6*(1/{square root over (2)}) which equals approximately 4 volts RMS. 
     Because of the low voltage drop across the TRIAC, the load  70  receives a voltage substantially equal to the supply voltage potential received at terminals  12  and  18 . If the supply voltage is 120 volts A.C., the load receives approximately 114 volts A.C., which is more than sufficient to operate horns, lights, motors, solenoids or any other component in the fire alarm circuit. 
     When the water or fire extinguishing fluid stops flowing, the switch opens and the capacitors  85  and  105  are discharged to ground. Capacitance  85  discharges through resistor  87  and neutral terminal  12 , and capacitance  105  discharges through diode  97  and neutral terminal  12 . It will be appreciated that other suitable elements may instead be used to allow the capacitances  85  and  105  to discharge. If capacitances  85  and  105  are not provided with an effective discharge path, any remaining charge stored on the capacitances will cause the delay time to be varied during a later operation of the circuit. Once capacitances  85  and  105  are discharged, the circuit is reset and ready for another load control operation. 
     Referring now to FIG. 6, an alternate time delay circuit according to the present invention is shown. In the embodiment of FIG. 6, a voltage supply may be selectively applied after a time delay to a second load. The circuit includes a first circuit having substantially the same arrangement of components as in the embodiment of FIG. 5 connected between a first input terminal  18  and a first neutral line  12 , and also includes a second circuit  150  connected between second load  155  located on input terminal  154  and second neutral line  152 . Second circuit  150  includes opto-TRIAC  160 , second TRIAC  165 , and resistance  170 , which is connected as shown. Second load  155  is connected to receive a second voltage supply via input terminal  154 . In operation, once SCR  120  is rendered conductive in the manner described above, the charge stored by first capacitance  85  is discharged to provide a negative pulse to pin  2  of opto-TRIAC  160 . As a result of the discharge of first capacitance  85 , light-emitting diode (LED)  175 , connected as shown between pins  1  and  2  of opto-TRIAC  160 , is caused to emit light. The output of pin  1  of opto triac  160  is provided to pin  2  of opto TRIAC  125  as shown in FIG.  5 . Thus light emitting diodes  127  and  175  are in series thereby causing each optical TRIAC  129  and  180  between pins pins  4  and  5  of opto-TRIACs  125  and  160 , to conduct. The conduction of optical TRIACs  129  and  180  causes trigger pulses to be provided to the gates  130   g  and  165   g  of TRIACs  130  and  165 , thereby rendering the TRIACs  130  and  165  simultaneously conductive and causing power to be applied to both the first and second load  70  and  155 . Resistances  170  is a current-limiting resistor to limit the current applied to gate  165   g  of second TRIAC  165 . 
     It will be appreciated that the first and second circuits in the time delay circuit of FIG. 6 are electrically isolated from one another, and therefore enable the time delay circuit to reliably control the operation of two loads. Because the first and second circuits are electrically isolated, the voltage sources connected to input terminals  18  and  154  may provide the same or different supply voltages. Alternatively, first and second neutral lines  12  and  152  may be the same neutral line. Further, input terminals  18  and  154  may be connected to the same voltage source. 
     Preferably, the supply voltages provided on input terminals  18  and  154  are between approximately 24 and approximately 120 volts A.C., and first and second loads  70  and  155  draw a current of no more than approximately 6 amps. Opto-TRIAC  160  can be a 3047 opto-TRIAC available from numerous suppliers, and second TRIAC  165  can be a Q4006L4 TRIAC available from numerous suppliers. Resistance  170  can be implemented by a 100Ω resistor. It will be appreciated that other suitable components can be used. 
     Further, it will also be appreciated that the addition of the second circuit  150  may require changes in the component values of the first circuit. In the embodiment of the circuit of FIG. 6, first capacitance  85  is a 33 microfarad capacitor rated for 160 volts D.C. Further, in the embodiment of FIG. 6, resistance  87  is preferably a 10 kΩ resistor rated for 2 watts. Additionally, capacitor  105  would be changed to a 2200 MFD capacitor rated at 16 VDC. Other component values remain the same. It will be appreciated that other suitable component values or components can be used for the time delay circuit of FIG.  6 . It will further be appreciated that operation of more than two electrically isolated loads can be controlled according to a circuit of the type shown in FIG.  2 . 
     In yet another exemplary embodiment of the present invention, the time delay circuit  90  employed within the load control circuits illustrated in FIGS. 5 and 6 can be implemented digitally. As illustrated in the FIG. 7 embodiment which shows a load control circuit controlling two loads, when the switch  75  is closed, AC voltage is applied to diode  80 . The diode  80  changes the alternating current to direct current and charges the capacitor  85 . The capacitor in combination with a 1N965A zener diode  205  and resistor  210  form a power supply for a programmable digital IC timer  215 . The time delay can be adjusted by use of a dip switch  220 . The dip switch  220  can comprise any multiple pole dip switch which can be set so that a wanted time delay will elapse. Also, resistance  225  and capacitance  230  on the output of the dip switch  220  and connected to the neutral node  12 , form an oscillator circuit used with IC timers. The dip switch  220  adjustably controls timing the delay in the activation of load  70  in a range from 1 to 90 seconds. Upon timeout of the delay, a trigger signal is sent to SCR  120  via resistance  115  from digital IC timer  215 . As described above, the SCR  120  receives the trigger signal and provides a path for the voltage stored in the capacitor  85  to the opto-TRIACs  125  and  160 . The opto-triac conducts AC current in both directions providing power to the load. When the valve closes, the timer  215  immediately is reset and ready to initiate another time delay upon actuation of the switch again. With the implementation of the digital control the values of capacitor  85  would be changed to a 50 MF capacitor rated at 160 VDC while the resistance would optimally be a 3 Kilo-ohm resistor rated at 2 Watts or suitable resistance component. Additionally capacitor  227  is a 0.1 Micro-Farad capacitor while resistor  225  is optimally a 27 Kilo-ohm resistor or appropriate resistance element. All remaining elements within the multiple load control circuit remain the same values discussed with respect to FIG.  6 . 
     The digital timer, illustrated in FIG. 7 with multiple loads, would also be able to be implemented in a load control circuit containing a single load, illustrated with analog timing in FIG.  5 . Of course, the elements would need to be modified (to the values described with respect to FIG. 5) in order to ensure proper operation. 
     Referring now to FIG. 8, a fire suppression system including a load control circuit  14  according to the present invention is shown. When sufficient water flow through pipe  300  is detected by switch  75 , the switch closes the load control circuit  14  and causes a load, e.g., an alarm or warning light, to be turned on after a desired time delay. The time delay reduces false alarms by avoiding registration of an alarm condition which might occur due to back flow or other temporary movement of water in the pipe. The delay period is selectable by the user or manufacturer as described above to accommodate a given fire protection system. Of course, the time delay control circuit according to the present invention may be used in other applications using household or industrial current and voltage levels. For instance, the switch  75  could detect any of a number of conditions, such as gas flow, temperature (with a thermal switch), the open or closed state of an enclosure or movement of another physical object, to name but a few. 
     The foregoing description, while including many specificities, is intended to be illustrative of the general nature of the invention and not limiting. It will be appreciated that those skilled in the art can, by applying current knowledge, readily modify and/or adapt the specific embodiments described above for various applications without departing from the spirit and scope of the invention, as defined by the appended claims and their legal equivalents.

Technology Classification (CPC): 8