A Device and Method for Anticipating Failure in a Solenoid Pilot Operated Control Valve for a Fieldbus Manifold Assembly

Abstract

A fieldbus solenoid valve system has a solenoid operated control valve mounted and operated by a solenoid pilot. A direct current power source is connected to a coil of the solenoid pilot and a driver for actuating the coil. A resistive element is in series with the power source, the driver, the solenoid and a ground. A frequency generator is connected to the circuit for creating a frequency pulse train to the coil having a characterization so as not to cause the solenoid pilot to actuate. The voltage is measured between the coil and resistive element and the measured voltage is compared to a base voltage value measured from the same circuit location. An indicator signal is displayed on the fieldbus solenoid valve system or externally when the measured voltage increases to a predetermined amount from said base voltage over time.

Claims

1. A fieldbus control valve system characterized by: a communication module which is connected to at least one manifold member with a valve body having a solenoid operated control valve mounted and operated by a solenoid pilot having a coil; a direct current power source connected to the coil of the solenoid pilot; a driver connected in series with the direct current power source and the coil for actuating said solenoid pilot; a resistive element positioned in series with the direct current power source, said driver and said coil and a ground when the driver is actuated to power said coil; a frequency generator for creating a frequency pulse train of voltage superimposed onto a DC energization signal for the coil of a predetermined duration during actuation of said driver, said frequency generator creating said frequency pulse train having characteristics that do not cause the solenoid pilot to actuate in response to said frequency pulse train; the voltage being sensed is sent to the communication module and stored in a microcontroller unit in a fieldbus control valve system with subsequent measured voltage for subsequent pulse train measured and compared to a base voltage value stored in the microcontroller unit; an indicator signal displayed on said fieldbus control valve system when said measured voltage increases to a predetermined amount from said base voltage value.

2. A fieldbus control valve system as defined in claim 1, further characterized by: said indicator signal displayed on an I/O unit corresponding to said solenoid valve on said fieldbus solenoid valve system.

3. A fieldbus control valve system as defined in claim 1, further characterized by: said driver being a low side driver; and said resistive element interposed between said low side driver and said coil of said solenoid pilot.

4. A fieldbus control valve system as defined in claim 1, further characterized by: said driver being a low side driver; and said resistive element interposed between said low side driver and said ground.

5. A fieldbus control valve system as defined in claim 4, further characterized by: said microcontroller recording the measured voltage which is proportional to the reactance of the coil when initially installed and said measured voltage being used as the base voltage value.

6. A fieldbus control valve system as defined in claim 3, further characterized by: said microcontroller recording the measured voltage which is proportional to the reactance of the solenoid coil when initially installed and said measured voltage which is proportional to the reactance being used as the base voltage value.

7. A fieldbus control valve system as defined in claim 1, further characterized by: said frequency generator being powered to work the frequency pulse train of said actuation signal when said driver is to actuate said solenoid.

8. A fieldbus control valve system as defined in claim 1, further characterized by: said driver being a high side driver; and said coil interposed between said high side driver and said resistive element.

9. A fieldbus control valve system as defined in claim 1, further characterized by: said frequency pulse train having a short enough duration and high enough frequency in time so as not to cause the solenoid pilot to actuate in response to said frequency pulse train.

10. A field bus control valve system as defined in claim 1, further characterized by: said frequency pulse train having a low enough magnitude in voltage so as not to cause the solenoid pilot to actuate in response to said frequency pulse train.

11. A method of detecting degradation of a coil in a solenoid pilot in a fieldbus control valve system, said method characterized by: providing a power circuit with a direct current power source that powers said solenoid coil; providing a driver that communicates said power source to ground to close and open the power circuit; providing a resistive element in series with said direct current power source, said driver and said solenoid coil; generating a frequency pulse train to said driver having a characteristic so as not to affect actuation of said solenoid coil; measuring an initial voltage level during said frequency pulse trains between said solenoid coil and said resistive element; storing said initial voltage level in a memory device; measuring a subsequent voltage level during a subsequent frequency pulse train; comparing said subsequent voltage level to said initial voltage level; and providing an indicator warning when said subsequent voltage level has changed a predetermined amount from said initial voltage level.

12. A method as defined in claim 11, further characterized by: said initial and subsequent frequency pulse trains having a short enough duration and high enough frequency so as not to cause the solenoid pilot to actuate in response to said respective frequency pulse trains.

13. A method as defined in claim 11, further characterized by: said initial and subsequent frequency pulse trains having a low enough magnitude in voltage so as not to cause the solenoid pilot to actuate in response to said respective frequency pulse trains.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Reference now is made to the accompanying drawings in which:

[0023] FIG. 1 is a perspective and partially schematic overview of one embodiment according to the invention;

[0024] FIG. 2 is a cross sectional view of the valve housing and manifold block shown in FIG. 1;

[0025] FIG. 3 is a schematic illustration of a circuit according to one embodiment of the invention; and

[0026] FIG. 4 is a schematic illustration of a second embodiment of the invention; and

[0027] FIG. 5 is a schematic illustration of a third embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] Referring now to FIG. 1, a fieldbus manifold system 10 is modular in nature and has a plurality of valve manifold members also referred to as valve stations or manifold units 12 interconnected together with a communication module 14 and a series of I/O modules 16. The communication module 14 may be connected to a fieldbus network 17 controlled by a Programmable Logic Controller (PLC) and communication card 15. The particular number of manifold units 12 is dependent on the application and the capacity of the circuitry installed in each unit 12. Each manifold unit 12 includes a manifold block 19 which may mount one or more control valves 18 on its upper surface 13 as shown in FIG. 2.

[0029] Referring to FIGS. 2 and 3, each manifold block 19 has fluid supply 24 and fluid exhaust passages 20, 22, that extend laterally through the block to be in communication with an adjacent block 19. Each manifold block also has working ports 21 and 23 that extend to an outer wall 29 for connecting to a pneumatically operated field device 30 through two pneumatic conduits 32 and 34 as showing in FIG. 1. Each manifold block also has a transverse pilot pressure passage 25. Each passage 20, 21, 22, 23, 24, and 25 connects to a respective port 40, 42, 48, 46, 44 and 49 at the upper surface 13 of the manifold block 19 which are in communication with respective ports 50, 52, 58, 56, 54, and 59 in valve 18.

[0030] A circuit board 60 is mounted in the manifold block 19 in known fashion and supplies electric power to the solenoid valve coil 64 of the pilot valve 65 for actuating the solenoid valve 18 by moving its spool 66 through a valve bore 69 by the force pneumatic pressure from port 59 via pilot valve 65. When the spool 66 axially moves in the bore 69, it controls the fluid pressure communication between the ports 50-58, i.e. the opening and closing of ports 50-58. In a well-known fashion, the spool 66 may be biased to one direction by a spring 68. Although the embodiment shown is a single solenoid valve system, it will be understood that commercially available dual solenoid valve assemblies may also be used. Briefly, when a dual solenoid valve is used, the return spring 68 is eliminated and a second solenoid pilot is operated to provide fluid pressure to return the spool 66 (to the right as shown in FIG. 2).

[0031] The field device 30 in FIG. 1 is commonly operated by a piston and cylinder assembly 70 which has a piston 72 connected to a piston rod 73 that extends out of one end 76 of cylinder 74. The piston 72 is slidably housed within the cylinder housing 74 between a retracted position (piston to the right in FIG. 1) and an extended position (piston to the left in FIG. 1). The pneumatic conduits 32 and 34 are connected to opposite ends 75 and 76 and in communication to opposite internal pressure chambers 77 and 78 to provide fluid pressure to either chamber 77 and 78 for cycling the piston 72 back and forth within the cylinder housing 74 to either retract or extend the piston rod 73.

[0032] Two position sensors 80 and 81 are mounted on cylinder housing 74. These position sensors 80 and 81 may be Hall-effect, inductive or other sensors types which sense the presence of a magnetic field or the position of the piston. The piston 72 may have a magnet 83 mounted thereon which when in proximity to either sensor 80 or 81 triggers the sensor to send an output signal.

[0033] The position sensors 80 and 81 are each electrically connected to a separate input port 82 and 84 of the respective I/O unit 16 corresponding to the valve 18 that is pneumatically connected to the field device 30. The connection is through two electrically conductive cables 86 and 88. Wireless communication is also foreseen as a possibility.

[0034] The general operation of the disclosed embodiment is discussed in U.S. Ser. No. 16/468,898 filed on Jun. 12, 2019 which is hereby incorporated by reference.

[0035] In this fashion, by having the signal that initiates the cycle also turning on the timer and timing the cycle from the moment a signal is initiated until the piston achieves its end position achieves an improved level of prognostics which can be used for preventative maintenance algorithms. Any binding or problems with valve shifting timing, the cylinder and piston, the pneumatic tubing 32 and 34 or other binding parts of the field device connected to the piston rod 73 all of which could cause system cycle time changes can be detected. The cycle is monitored from its initiation to its end. The parameters that can affect the cycle time include leaks in the valve, cylinder, fitting and tubing. Also, for example; the manual change in the flow control, manual change in a pressure regulator, changes in load, binding in the cylinder and piston assembly caused by wear or rod side loading, valve wear, cylinder wear, weak return spring in the solenoid valve, sensor malfunction, input module malfunction and other changes or malfunctions in the system.

[0036] The timing of the cycle commencing with the actuating voltage change sent to the coil and ending with the piston reaching its end can be used to monitor the function and if any changes over time and deviations from the set forth proper time is sensed, an appropriate alarm can be sent to provide warning that something in the line from the coil and valve to the field device is not operating up to design and set standards.

[0037] Referring now to FIG. 3, circuit 91 is shown which expeditiously directs the diagnostic test measurement specifically to detecting changes in the inductive reactance of the coil 64 that drives the solenoid pilot valve 65. The coil 64 is connected to a DC power source 93 which for example can be set at 24 V, a resistive element (labeled as sense resistor) 94, and a low side driver 96 which is imbedded in a valve driver printed circuit board (PCB). The driver has internal resistance schematically indicated as resistive elements 98 and 99. The downstream end is then grounded at 100, completing the electrical current path of the circuit.

[0038] The coil 64 which is commercially available may have a Direct Current resistance (DCR) of 865 ohms and a stated inductance value L of 1600 mH. The resistive element 94 may have a resistance that is low enough so as not to affect the operation of the coil 64 but high enough to make measurement of any voltage drop variances practical. A resistive element of 100 Ohms may be suitable for the above described coil 64.

[0039] Referring now to FIG. 4, an alternate circuit 191 is shown that expeditiously directs the diagnostic test measurement specifically to detecting changes in the inductive reactance of the coil 64 that drives the solenoid valve core 65. The coil 64 is connected in series to a low side driver 96 which is imbedded in a valve driver printed circuit board. The driver has internal resistance schematically indicated as resistive elements 98 and 99. The downstream end is then connected to a resistive element (labeled as sense resister) 194 which in turn is connected to ground 100, completing the electrical current path. Beside voltage sensor 102, an additional voltage sensor 104 may be installed between low side driver 98 and resistive element 194.

[0040] It is well known that the inductive reactance of a coil is calculated by the following mathematical relationship:

X.sub.L=ωL=2πfL

Where X.sub.L is inductive reactance, f is frequency of variable voltage and L is inductance. It is also well known that voltage follows Ohms law by the equation

V=IR

[0041] A numerical example to illustrate the concept of the invention follows. While the power source 93 is a direct current supply and set at 24V, the sensed voltage at sensor 102 will be at 24 volts when the driver 96 is open and in an equilibrium state and practically at 0 when driver 96 is closed causing the valve to actuate and reach an equilibrium state.

[0042] A test algorithm may be supplied or programmed to the low side driver 96 to supply a pulse train, i.e. a frequency burst may be applied to the driver 96 to open and close at a predetermined frequency for a brief period of time. A frequency of 1000 Hz can be used for a short duration for example 1/1000 second. The duration and frequency are short enough so as not to affect the actuation of the solenoid. The average voltage is sensed at either sensor 102 or 104 and recorded at the communication module 15. The pulse train may re-occur at regular intervals such as once every 10 minutes during activation to continuously monitor changes.

[0043] However, during the test pulse by the low side driver, a pulse frequency is seen by coil 64 which in turn creates a reactance based on the known mathematical relationship X.sub.L=ωL=2πfL. Thus, with 1000 Hz pulsing a 1.6 H coil, an inductive reactance of approximately 10053 ohms is seen. By using the inductive reactance value plus its DC resistance (DCR value in FIG. 4) as a simple resistive element, a simple series circuit is created with the connected coil 64, valve driver PCB 96 and Sense Resistor element 194. Using Ohms law V=IR, the sum of all the voltage drops across each resistive element must equal the total applied voltage. Therefore, any resistance change in any of the resistive elements will create a voltage drop change that is proportional to the resistive element's value. Hence, if the inductance of coil 64 changes, it's inductive reactance changes and the proportional voltage change can be measured across any of the resistive elements of the series circuit while it is in its dynamic state. Using the sample values in FIG. 4 of 1000 Hz pulse frequency to a 1.6 H coil creates an inductive value of about 10053 ohms. Consequently, the voltage sensor 104 positioned in series between the coil 64, valve driver PCB 96 (resistive value assumed to be negligible) and resistive element 94 of 100 ohms, reads a voltage drop calculated by [Applied voltage (93)]/[inductive reactance (Xc)+DCR (865)+Sense Resistor element (194)]×[Sense Resistor element (194)]=24/(10053+865+100)×100=218 mV. Thus the sensor 104 will read a sensed voltage of 23.782 voltages. If the Valve Driver internal resistance is not negligible then the circuit 91 in FIG. 3 can be used and the voltage from sensor 102 could be used.

[0044] There may be situations where the combination of DCR, inductance value of the coil and required test frequency may cause the coil to energize during the diagnostic test measurement operation. In such situations, the direct source voltage 93 may be stepped down during the diagnostic test measurement operation to a lower magnitude, i.e., a lower voltage 192 as shown for example in FIG. 5. In the example shown in FIG. 5, the source voltage during diagnostic test measurement operation is stepped down to a lower magnitude of 3.3 V. In this situation, the lower magnitude of the supplied voltage prevents actuation of the solenoid valve. In either situation, the frequency pulse has a characteristic so as not to actuate the solenoid valve during the diagnostic test measurement operation. After the frequency pulse is sent and voltage drop measured, the DC power level can revert back to the 24 V level shown at 93 for normal operations.

[0045] As also shown in FIG. 5, the system can be used with a high side driver 196 which is situated upstream from the solenoid coil 64.

[0046] In all the above embodiments, the initial value of the voltage is sensed and stored in the memory controlled by the microcontroller of the fieldbus manifold communication module 14. Subsequent test compares the values of sensed voltage with the initial voltage and upon a change (i.e. increase) of a predetermined magnitude the communication module 14 transmits an indicator warning which can be read either at the PLC and its associated display (HMI) or at the appropriate I/O unit module 16 at display 92 or the display 90 of the communication module 14. Knowing the resistive value of the circuit and the resistive value of resistive element 94 or 194, the reactance X.sub.L of the solenoid coil 64 can be calculated by using the sensed voltage. The change in current in the series circuit made up of the reactance X.sub.L value of coil 64, the internal resistive value of the driver 98 and 99, and the value of the sense resistive element 94 or 194 is the factor that allows a base line for monitoring change. Since the inductance of coil 64 cannot be measured directly in a dynamic circuit, an indirect representative value is obtained by calculating its inductive reactance Xc. By comparing changes of Xc over time, indirectly measured by voltage drops of the Sense Resistor element 102 and 194 circuit, removes the need to empirically know the value of the coil 64 inductance. The critical measurement to determine degradation of the coil, now becomes the Vsense voltage change over time. Since the comparison of the initial value of the voltage drop, which is proportional to the coil's inductive reactance X.sub.L, is compared to successive measurements the variations or deviations of the actual inductance value of the coil from its nominal value becomes irrelevant in that only the change of voltage over time is indicative of coil degradation. The rate of voltage change (i.e. increase) over time determines the rate of degradation and thus can be used to optimize frequency of maintenance (replacement) that is required to achieve the maximum machine/component up-time or availability.

[0047] In this fashion, an easy modification that is retroactively installable in known circuitry can be done and using the direct current power source 24 that is normally used to actuate the coil 64, and by interrupting the driver with a high frequency pulse or a lower magnitude voltage pulse, a change of voltage can be sensed over time that indicates a potential degradation of the coil 64. The change of voltage sensed later in time from the initial voltage becomes an indicator that the inductance in the coil 64 must have changed because the values of power source voltage 93, driver internal resistive element 98 and 99, sense resistor element 94 or 194 and the diagnostic test measurement operation frequency remain the same. The change of inductive reactance X.sub.L is an indication that the inductance value of the coil has changed which, with all things being equal, points to a change in the number of wire turns that make up the coil and most likely caused by the failure of the insulation around the wire used to wind the solenoid coil.

[0048] Other variations and modifications are possible without departing from the scope and spirit of the present invention as defined by the appended claims.