Apparatus and method for predicting failure of an electromagnetic pilot operated valve of a fieldbus manifold assembly

Abstract

The fieldbus solenoid system has a solenoid operated control valve with a solenoid pilot mounted and operated by the solenoid pilot. A DC power supply is connected to the coil of the solenoid pilot and a driver for actuating the coil. A resistive element is connected in series with the power supply, the driver, the solenoid coil and ground. A frequency generator is connected to the circuit for generating a frequency burst to the coil with characteristics that do not actuate the solenoid pilot. The voltage between the coil and the resistive element is measured and compared to a reference voltage value measured from the same circuit location. When the measured voltage increases from the reference voltage by a predetermined amount over time, an indication signal is displayed on the fieldbus solenoid system or externally.

Description

TECHNICAL FIELD

[0001] The present invention relates to an early warning system for predicting electromagnetic valve control system failure of a fieldbus manifold assembly. BACKGROUND

[0002] Fieldbus systems containing valve manifold assemblies are commonly used in industrial manufacturing for selectively directing pneumatic pressure to various pneumatically operated field devices. Manifold assemblies are typically modular and are commonly assembled with multiple I / O modules, communication modules, and manifold blocks. Manifold blocks include one or more pneumatically controlled valves and are commonly referred to as valve stations of a manifold. The pneumatically controlled valves are typically operated by an electromagnetic pilot valve, commonly referred to as just a solenoid, which moves a spool in the control valve that controls the direction of pneumatic flow to operate the individual field device. These solenoids are actuated by an electrical current flowing through a coil of wire that creates a magnetic field that pulls and opens the solenoid to allow pressurized air to pass through to move the spool of the valve body. Manifold blocks typically have a common pilot pressure channel that is connected to the solenoids of the control valves that in turn control the flow of main pressure to the corresponding pneumatic field device. In other manifolds, direct operated valves are used where the magnetic field force created by the solenoid coil directly pulls the spool without the use of air pressure to control the spool. Field devices are typically cylinder assemblies with a piston that reciprocate between a retracted position to an extended position depending on the spool position of the valve.

[0003] These manifold assemblies are capable of incorporating multiple manifold blocks and valve stations that in turn operate multiple field devices in large manufacturing or industrial production lines. Each control valve needs to operate correctly to maintain proper operation of the corresponding field device. Failure of a single control valve can result in the entire manufacturing or industrial production line to stop operating. Control valve failures are typically caused by mechanical wear but are also affected by the degradation of the solenoid and associated coil. While the coil of the solenoid of a control valve can last a long time since it does not have any moving parts, it is still affected by environmental factors that reduce its useful life. The coil can be in a very toxic or dirty environment and can also be subjected to thermal temperature cycling, corrosive chemicals, vibration, or dust and dirt. As a result, environmental factors can degrade the coil, and in particular the insulating wrap around the wire, to the point that the control valve's functionality is affected.

[0004] Since unplanned shutdowns of an industrial production line can impact production and thus result in loss of revenue, it is very advantageous to prevent shutdowns by replacing affected solenoids (or entire control valves) when they first show signs of degradation, before complete failure of the solenoid (or entire control valve) occurs, and to replace them during regular maintenance and normal shutdowns that do not impact production. This early preventive maintenance can prevent unplanned shutdowns of a production line, and thus prevent production losses. If failure of a solenoid can be predicted, then the solenoid can be replaced ahead of time, before the solenoid completely fails. Prediction of failure is possible when the failure does not occur suddenly and provides some advance warning over time. In other words, prediction of an impending failure is possible if early degradation of abnormal behavior or performance can be detected as an early warning indicator.

[0005] Various monitoring methods for solenoid control valve systems have been proposed. One such approach is to monitor the position of the spool within the control valve body according to a specific time value. The position of the spool is detected by using a magnet mounted on the control valve spool and a Hall effect sensor or other sensor device to sense the proximity of the magnet as the spool moves between its two end positions. The movement is timed, and if the pressure and voltage values provided to the solenoid pilot and control valve are constant, if the measured time slows beyond a normal operating value, then the valve is considered to need replacement. Typically these timers, pressure sensors, and Hall effect sensors and other sensors are all provided within the control valve body. However, this approach requires that the control valve and / or manifold block be initially designed and constructed with the appropriate sensors and magnets, and it does not address the need to reduce the need for modifications to the valve and the inability to monitor many control valves and manifold blocks already installed on automated industrial assembly lines.

[0006] Other approaches involve timing functions from the control valve actuation to the final cycle position of the field device, such as the time it takes for a cylinder piston to move from a retracted position to an extended position. The field bus system, with its computing capability and memory, compares the run time signal value to a preset acceptable run time value, and if the run time value has changed beyond an acceptable value compared to the preset acceptable run time value, a warning or other indication is provided at the field bus module. However, this system does not specifically detect degradation of the solenoid before the control valve function fails.

[0007] None of the above schemes directly detect the health of the solenoid, as performance degradation can be caused by other factors such as low air pressure, air flow changes, slide and system leaks, power supply voltage variations, or increased component friction. Furthermore, as the solenoid degrades, the run time of the valve system does not necessarily change unless the spool is directly operated. Therefore, using the time and time variation of the cycle performance parameter to determine solenoid condition is ineffective.

[0008] Another proposed system predicts solenoid life by measuring the operating temperature of the solenoid, which requires a separate thermometer device and compares the temperature to an acceptable temperature parameter.

[0009] A more common method of predicting solenoid failure measures and compares the variation of the characteristic current curve of the solenoid each time the solenoid is energized. The variation of this characteristic curve can predict an impending solenoid failure, but the sensing devices and various measurements required to analyze the characteristic current curve are complex, expensive, require complex solenoid drive circuitry, and require significant computing power, which is not typically available in a field bus manifold.

[0010] While manufacturers typically state the inductance value of a solenoid, it has been found that solenoids often vary significantly from the stated inductance value, and some solenoids vary by more than 10% from the stated inductance value. This variation can hinder the determination of solenoid degradation from the stated inductance level when the initial inductance value can be significantly different.

[0011] However, if a proper control scheme is used in a standard driver system, the inductance of an installed solenoid can be measured during its energize / de-energize cycle. The proper control scheme reduces the need to measure the absolute inductance value of the solenoid and relies on comparing an initial baseline inductance value to subsequent measured values to indicate a change in inductance over time. Since the number of windings is directly related to the inductance value of the solenoid and the inductance, the inductance value of the solenoid will change accordingly if a short circuit exists between two or more windings. This change in inductance proportionally changes the measured inductance at a given frequency.

[0012] Since solenoids operate on direct current and the inductance is based on a measurement that can only be taken during a change in voltage over time (e.g., during an alternating current cycle), previous inductance monitoring systems require a separate power source and extensive circuit modifications, which make these systems impractical for retro-fit installation into existing production systems.

[0013] It would be desirable to have a system that can check the operational degradation of solenoids in a valve manifold system by using hardware that is already applied, readily available, and / or easily modified. Furthermore, it would be desirable to have a monitoring system that specifically detects the condition of the solenoid without requiring any significant movement of the valve during the energize / de-energize cycle.

[0014] It is desirable to have a sense of change in inductance detection system that can measure the health of an electromagnetic coil, which can be installed into an existing valve manifold system and use a direct current (DC) power supply that can also be used to actuate the electromagnetic coil. SUMMARY

[0015] According to one aspect of the present invention, a fieldbus solenoid valve system has a communication module connected to at least one manifold member having a valve body with an electromagnetically operated control valve installed with and operated by an electromagnetic pilot. A direct current power supply is connected to the coil of the electromagnetic pilot. The circuit is also connected to ground. A driver is connected in series to the direct current power supply, the coil of the electromagnetic pilot for driving the electromagnetic pilot, and ground. A resistive element is also placed in series with the power supply, the driver, the electromagnetic pilot, and ground.

[0016] In one embodiment, the algorithm of the driver is programmed to produce a frequency burst superimposed on the DC excitation signal to the coil for a predetermined duration during actuation of the driver, which is dependent on the inductance value of the coil. The burst created by the driver has characteristics that do not cause the electromagnetic pilot to actuate in response to the burst.

[0017] When the frequency burst is provided to the electromagnetic pilot coil, a voltage drop is detected in the circuit and the measurement is sent to a microcontroller that can also be used to control the driver. The measured voltage is compared to a reference voltage value that was previously taken and stored in the microcontroller unit in the circuit. Preferably, the microcontroller records the measured voltage at initial installation and uses this measured voltage as the reference voltage. The measured voltage drop is directly proportional to the inductance value of the electromagnetic pilot coil.

[0018] Preferably, an indication signal is displayed on the fieldbus solenoid valve system when the measured voltage increases from the reference voltage value by a predetermined amount. In one embodiment, the indication corresponding to the control valve on the fieldbus control valve system is displayed on its communication or I / O unit. In one embodiment, the driver is a low side driver and the resistive element is placed between the low side driver and the coil of the solenoid valve.

[0019] In another embodiment, the driver is a high side driver and the coil is placed between the high side driver and the resistive element.

[0020] In one embodiment, the burst has a duration and a frequency that are sufficiently short and high, respectively, so as not to cause the electromagnetic pilot to actuate in response to the burst. In another embodiment, the burst has a voltage amplitude that is sufficiently low so as not to cause the electromagnetic pilot to actuate in response to the burst.

[0021] In accordance with another aspect of the present application, a method of detecting coil degradation in an electromagnetic coil in a fieldbus valve system includes the steps of providing a power supply circuit having a direct current power supply to power the coil, providing a driver to communicate the power supply with ground to turn the power supply circuit on and off, providing a resistive element in series with the direct current power supply, the driver, and the electromagnetic coil, generating an initial frequency pulse to the driver having characteristics that do not affect actuation of the electromagnetic coil, measuring an initial voltage drop level during the frequency pulse between the electromagnetic coil and the resistive element, storing the initial voltage level in a storage device, measuring a subsequent voltage level during a subsequent frequency pulse, comparing the subsequent voltage level to the initial voltage level, and providing an indication warning when the subsequent voltage level has changed from the initial voltage level by a predetermined amount. BRIEF DESCRIPTION OF DRAWINGS

[0022] Referring to the drawings wherein:

[0023] Figure 1 is a perspective and partially schematic view according to one embodiment of the present application;

[0024] Figure 2 is Figure 1 a cross-sectional view of a valve housing and manifold block as shown;

[0025] Figure 3 is a schematic view of a circuit according to one embodiment of the present application; and

[0026] Figure 4 is a schematic view of a second embodiment of the present application; and

[0027] Figure 5 is a schematic view of a third embodiment of the present application. DETAILED DESCRIPTION

[0028] Referring now to Figure 1 , the 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, which are interconnected together with a communications module 14 and a series of I / O modules 16. The communications module 14 can be connected to a fieldbus network 17 controlled by a programmable logic controller (PLC) and communications card 15. The specific number of manifold units 12 depends on the application and the capacity of the circuitry installed in each unit 12. As Figure 2 shown, each manifold unit 12 includes a manifold block 19 on which one or more control valves 18 can be mounted on the upper surface 13 thereof.

[0029] Referring to Figure 2 and Figure 3Each manifold block 19 has a fluid supply passage 24 and fluid discharge passages 20 and 22, which extend laterally through the manifold block and communicate with adjacent manifold blocks 19. Each manifold block also has working ports 21 and 23 extending to the outer wall 29 for use with fluid supply passages 20 and 22. Figure 1 The two pneumatic conduits 32 and 34 shown are connected to the pneumatically operated field device 30. Each manifold block also has a lateral pilot pressure passage 25. Each passage 20, 21, 22, 23, 24 and 25 is connected to corresponding ports 40, 42, 48, 46, 44 and 49 located on the upper surface 13 of the manifold block 19, which communicate with corresponding ports 50, 52, 58, 56, 54 and 59 in the valve 18.

[0030] Circuit board 60 is mounted in manifold block 19 in a well-known manner and supplies power to solenoid coil 64 of pilot valve 65 to actuate solenoid valve 18 by moving valve spool 66 through valve port 69 via pneumatic pressure from port 59. As valve spool 66 moves axially in valve port 69, it controls the fluid pressure communication between ports 50-58, i.e., controls the opening and closing of ports 50-58. Valve spool 66 can be biased in one direction by spring 68 in a well-known manner. Although the illustrated embodiment is a single solenoid valve system, it should be understood that commercially available dual solenoid valve assemblies can also be used. In short, when using dual solenoid valves, return spring 68 is canceled, and fluid pressure is provided by operating a second solenoid pilot to return valve spool 66 (towards...). Figure 2 (As shown on the right).

[0031] Figure 1 The field device 30 is typically operated by a piston and cylinder assembly 70, which has a piston 72 connected to a piston rod 73, the piston rod 73 extending from one end 76 of a cylinder 74. The piston 72 is in the retracted position (piston in...) Figure 1 (right side of the piston) and extended position (piston in) Figure 1 The piston 72 is slidably accommodated within the cylinder housing 74 between the left and right sides of the piston rod 73. Pneumatic conduits 32 and 34 are connected to opposing ends 75 and 76 and communicate with opposing internal pressure chambers 77 and 78 to provide fluid pressure to either of the chambers 77 and 78 to cause the piston 72 to circulate forward and backward within the cylinder housing 74, thereby retracting or extending the piston rod 73.

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

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

[0034] The general operation of the disclosed embodiments is discussed in U.S.S.N. 16 / 468898, filed June 12, 2019, which is hereby incorporated by reference.

[0035] In this way, an increase in the level of prediction available for the preventive maintenance algorithm is achieved by having the signal that initiates the cycle also turn on the timer, and timing the cycle from the moment the signal is initiated until the piston reaches its final position. Any combination or issue that can cause a change in the system cycle time, all of which can be caused by the timing of the valve movement, the cylinder and piston, the pneumatic tubing 32 and 34, or other combined parts connected to the piston rod 73, can be detected. The cycle is monitored from start to finish. Parameters that can affect the cycle time include leaks in the valve, cylinder, joints, and tubing. Additionally, for example: manual changes to flow control, manual changes to pressure regulators, changes in load, sticking of the cylinder and piston assembly due to wear or rod side load, wear of the valve, wear of the cylinder, weakness of the return spring in the solenoid valve, sensor faults, input module faults, and other changes or faults in the system.

[0036] The cycle time from the change in actuation voltage sent to the coil to the end of the piston reaching its end can be used in a monitoring function, and if any changes over time and deviations from the prescribed proper time are detected, then a proper alarm can be issued to provide a warning that something in the line from the coil and valve to the field device is not operating as designed and set standards.

[0037] Reference is now made to Figure 3 , which shows a circuit 91 that quickly directs diagnostic test measurements specifically to detect changes in the inductance of the coil 64 driving the solenoid pilot valve 65. The coil 64 is connected to a DC power supply 93 (which can be set to 24V, for example), a resistive element (labeled detection resistor) 94, and a low-side driver 96 embedded in the valve driver printed circuit board (PCB). The driver has internal resistances represented schematically as resistive elements 98 and 99. The downstream end is then grounded at 100, completing the current path of the circuit.

[0038] The commercially available coil 64 can have a direct current resistance (DCR) of 865 ohms and a specified inductance value L of 1600 mH. The resistive element 94 can have a resistance low enough not to affect the operation of the coil 64, but high enough to enable measurement of any change in voltage drop. A 100 ohm resistive element can be suitable for the coil 64 described above.

[0039] Reference is now made to Figure 4 Figure 8, which shows an alternative circuit 191 that rapidly directs diagnostic test measurements specifically to detect changes in the inductive reactance of the coil 64 driving the solenoid valve 65. The coil 64 is connected in series to the low side driver 96 embedded in the valve driver printed circuit board. The driver has internal resistance schematically represented as resistive elements 98 and 99. The downstream end is then connected to a resistive element (labeled detection resistance) 194, which in turn is connected to ground 100, completing the current path. In addition to the voltage sensor 102, an additional voltage sensor 104 can be installed between the low side driver 98 and the resistive element 194.

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

[0041] X L = ωL = 2πfL

[0042] where X L is the inductive reactance, f is the frequency of the variable voltage, and L is the inductance. It is known that the voltage follows Ohm's law with the following equation:

[0043] V = IR

[0044] The following is a numerical example illustrating the inventive concept. The power supply 93 is a DC power supply and is set to 24 V, the detection voltage at the sensor 102 is 24 volts when the driver 96 is open and in equilibrium, and the sensing voltage at the sensor 102 is practically 0 V when the driver 96 is closed resulting in valve actuation and reaching equilibrium.

[0045] The low side driver 96 can be provided or programmed with a test algorithm to provide a burst of pulses, i.e., a burst of frequencies can be applied to the driver 96 to open and close the driver at a predetermined frequency for a short period of time. A frequency of 1000 Hz can be used for a short time, for example, 1 / 1000 of a second. The duration and frequency are short enough not to affect the actuation of the solenoid coil. The average voltage is detected at the sensor 102 or 104 and recorded at the communication module 15. The burst of pulses can reoccur at regular intervals, for example, every 10 minutes, to continuously monitor for changes.

[0046] However, during the test pulses of the low side driver, the coil 64 can be subjected to a pulse frequency, which in turn is based on the known mathematical relationship XL = ωL = 2πfL also creates a reactance. Thus, with a 1.6 H coil pulsed at 1000 Hz, an inductive reactance of approximately 10053 ohms can be obtained. By using the inductive reactance value plus its DC resistance (DCR value) in Figure 4 , a simple series circuit with the coil 64, the valve driver PCB 96 and the sensing resistor element 194 connected is created. Applying Ohm's law V = IR, the sum of all voltage drops across each resistor element must equal the total applied voltage. Thus, any change in resistance in any resistor element will create a change in voltage drop proportional to the resistor element value. Thus, if the inductance of the coil 64 changes, its inductive reactance changes and a proportional voltage change can be measured by any resistor element in the series circuit that is in a dynamic state. Using Figure 4 , the sample value of 1000 Hz pulsed frequency to a 1.6 H coil will create an inductive value of approximately 10053 ohms. Thus, the voltage sensor 104 positioned in series between the coil 64, the valve driver PCB 96 (resistance value assumed to be negligible) and the 100 ohm resistor element 94 will show a voltage drop calculated by: [applied voltage (93)] / [inductive reactance (Xc) + DCR (865) + sensing resistor element (194)] x [sensing resistor element (194)] = 24 / (10053 + 865 + 100) x 100 = 218 mV. Thus, the sensor 104 will show a sensing voltage of 23.782 volts. If the internal resistance of the valve driver is not negligible, then the circuit 91 in Figure 3 can be used and the voltage from the sensor 102 can be used.

[0047] In some cases, the combination of DCR, inductance value of the coil and the required test frequency can cause the coil to be energized during the diagnostic test measurement operation. In this case, the DC supply voltage 93 can be stepped down to a lower magnitude during the diagnostic test measurement operation, i.e. to a lower voltage 192 as in the example shown in Figure 5 . In the example shown in Figure 5 , the source voltage during the diagnostic test measurement operation is stepped down to a lower magnitude of 3.3 V. In this case, the lower magnitude of the supplied voltage will prevent the activation of the solenoid valve. In either case, the frequency pulse has the characteristic of not actuating the solenoid valve during the diagnostic test measurement operation. After the frequency pulse is sent and the voltage drop is measured, the DC supply level can be restored to 24 V as shown in 93 for normal operation.

[0048] As also shown in Figure 5 , the system can be used with a high side driver 196 located upstream of the solenoid coil 64.

[0049] In all the above embodiments, the initial value of the voltage is detected and stored in a memory controlled by the microcontroller of the fieldbus manifold communication module 14. Subsequent tests will compare the value of the voltage with the initial voltage and, in the event of a variation (i.e. an increase) of a predetermined amplitude, the communication module 14 sends an indication of the warning which can be read on the PLC and its associated display (HMI) or at the display 92 of the appropriate I / O unit module 16 or at the display 90 of the communication module 14. Knowing the resistance value of the known circuit and the resistance value of the resistance element 94 or 194, it is possible to calculate the reactance X L of the electromagnetic coil 64 by using the detected voltage L The variation of the current in the series circuit consisting of the reactance X C value of the coil 64, the internal resistance values of the drivers 98 and 99 and the value of the detection resistance element 94 or 194 is the factor that allows the variation of the baseline to be monitored. Since the inductance of the coil 64 cannot be measured directly in a dynamic circuit, an indirect representative value is obtained by calculating its reactance X C By comparing the variation of X L over time, the voltage drop of the detection resistor element 102 and 194 circuit is measured indirectly without knowing empirically the inductance value of the coil 64. The key measurement to determine the coil degradation now becomes the variation of the voltage of the voltage sensor (Vsense) over time. Since the initial value of the voltage drop proportional to the reactance X L of the coil is compared with the successive measurements, the variation or deviation of the actual inductance value of the coil from its nominal value becomes irrelevant since only the voltage variation over time represents the coil degradation. The speed of the voltage variation over time (i.e. the increase) determines the speed of the degradation and therefore can be used to optimize the maintenance (replacement) frequency to achieve the maximum machine / component uptime or availability.

[0050] In this way, a simple modification can be made, which is traceable to be installed in a known circuit and, using the direct current power supply 24 normally used to actuate the coil 64, by interrupting the driver with high frequency pulses or voltage pulses of lower amplitude, it is possible to detect the voltage variation over time which indicates a potential degradation of the coil 64. The variation of the voltage detected subsequently with respect to the initial voltage becomes an indication that the inductance in the coil 64 has certainly changed since the values of the power supply voltage 93, the driver internal resistance elements 98 and 99, the detection resistance element 94 or 194 and the diagnostic test measurement operating frequency remain unchanged. The variation of the reactance X L indicates that the inductance value of the coil has changed, which, under all conditions being equal, indicates that the number of turns that make up the coil has changed, most likely due to a failure of the insulating layer around the wire that winds the electromagnetic coil.

[0051] Other changes and modifications are possible without departing from the scope and spirit of the application as defined by the appended claims.

Claims

1. A fieldbus control valve system, characterized in that: A communication module is connected to at least one manifold component having a valve body having an electromagnetically operated control valve, the electromagnetically operated control valve being mounted with and operated by an electromagnetic pilot having a coil. A DC power supply is connected to the coil of the electromagnetic pilot. A driver, connected in series with the DC power supply and the coil, is used to actuate the electromagnetic pilot. A resistive element is connected in series with the DC power supply, the driver, the coil, and ground when the driver is actuated to supply power to the coil. The driver generates a frequency pulse train superimposed on a DC excitation signal for a coil of a predetermined duration during the actuation of the driver, and the frequency pulse train generated by the driver has the characteristic that it does not cause the electromagnetic pilot to be actuated in response to the frequency pulse train. The detected voltage is sent to the communication module and stored in the microcontroller unit of the fieldbus control valve system. Subsequently, the voltage for subsequent frequency pulse trains is measured and compared with the reference voltage value stored in the microcontroller unit. When the measured voltage increases from the reference voltage value to a predetermined amount, an indication warning is displayed on the fieldbus control valve system.

2. The fieldbus control valve system according to claim 1, further characterized in that: The warning indication is displayed on the I / O unit corresponding to the solenoid-operated control valve on the fieldbus control valve system.

3. The fieldbus control valve system according to claim 1, further characterized in that: The driver is a low-side driver; and The resistive element is connected between the coil of the low-side driver and the electromagnetic pilot.

4. The fieldbus control valve system according to claim 1, further characterized in that: The driver is a low-side driver; and The resistive element is placed between the low-side driver and the ground.

5. The fieldbus control valve system according to claim 4, further characterized in that: The microcontroller records a measured voltage proportional to the reactance of the coil during initial installation, and the measured voltage is used as the reference voltage value.

6. The fieldbus control valve system according to claim 3, further characterized in that: The microcontroller records a measured voltage proportional to the reactance of the coil during initial installation, and the measured voltage proportional to the reactance is used as the reference voltage value.

7. The fieldbus control valve system according to claim 1, further characterized in that: When the driver actuates the electromagnetic pilot, the driver is powered to generate the frequency pulse train.

8. The fieldbus control valve system according to claim 1, further characterized in that: The driver is a high-side driver; and The coil is connected between the high-side driver and the resistive element.

9. The fieldbus control valve system according to claim 1, further characterized in that: The frequency pulse train has a sufficiently short duration and a sufficiently high frequency, so as not to cause the electromagnetic leader to be actuated in response to the frequency pulse train.

10. The fieldbus control valve system according to claim 1, further characterized in that: The frequency pulse train has a sufficiently low voltage amplitude so as not to cause the electromagnetic pilot to be actuated in response to the frequency pulse train.

11. A method for detecting coil degradation in an electromagnetic pilot in a fieldbus control valve system, characterized in that: A power supply circuit is provided that has a DC power supply for powering the coil; A driver is provided to communicate the power supply with ground to turn the power supply circuit on and off; A resistive element is provided in series with the DC power supply, the driver, and the coil; Generate a frequency pulse train to the driver that has characteristics that do not affect the actuation of the coil; The initial voltage level is measured during the frequency pulse train between the coil and the resistive element; The initial voltage level is stored in a storage device; Measure the subsequent voltage level during the subsequent frequency pulse train; The subsequent voltage level is compared with the initial voltage level; and An indication warning is provided when the subsequent voltage level has changed by a predetermined amount from the initial voltage level.

12. The method according to claim 11, further characterized in that: The initial and subsequent frequency pulse trains have sufficiently short durations and sufficiently high frequencies so as not to cause the electromagnetic leader to be actuated in response to the frequency pulse trains.

13. The method according to claim 11, further characterized in that: The initial and subsequent frequency pulse trains have sufficiently low voltage amplitudes so as not to cause the electromagnetic pilot to be actuated in response to the frequency pulse trains.

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