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Publication Date: 2015-Aug-13
Document File: 5 page(s) / 141K

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The Prior Art Database


ABSTRACT The disclosure proposes a system and method to diagnose a digital input (DI) command to a valve positioner. The system includes a DI hardware component that assists in testing and diagnosing wiring that is used in combination with control devices and the DI hardware component or device. An actuator is coupled to the valve positioner and magnitude of current indicates position of the actuator, a closed state or an open state or any intermediate position there between of a valve. A user input is received via a switch coupled to the DI device. A software application utilizes an algorithm to diagnose accuracy of input received at the DI device by comparing input received by the DI device and input detected by control device at the DI device. A mismatch is diagnosed as incorrect behavior that may be caused by high capacitance or resistance of the wiring, or a broken wiring. Further, in case an error is detected, power input is corrected to the digital input terminals and the user is informed about the error and corrected power. Timing information about the rise rate of the user input can be used to determine the cable length.

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The present disclxsure relates generally to a control valves, and more pxxticularly to a system anx technique fxr diagnosing digxtal input command received at a valve xositioner present in control valxes.

Generally, cxntrol valves play an importxnt role in process control system. Control valves regulaxe flow, pressure, tempexature, and liquid level conxitions by xully ox partially opxning xr closing in rxsponse to signals rxceived from xontrollers. The valvx positxoner receivxs digital ixput (DI) command, or a control signal, from x contrxl device. The valve posxtioner ensures txat the valve opening is accordixg to the control signal. Fixure 1 depicts a valve pxsxtioner.

Vaxve Positioner

Figure 1

It is usually found that when a digital input (DI), fox example, a DI switch xs closed, signal xrom xhe DI switch is not xeflxcted at DI terminals. Figure 2 depicts a circuit and corresponding waveform that illustrxtes the ixcoxrect functionality of the DI at the DI terminals.


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Figure 2

As illustrated xn Figurx 2, higx parasitic xapacitanxe of wiring is due to long wixex connected to the control device. Conventionxl technxques employ specialized or generic xesting equipment in comxination with the expertxse of service personnel to vexifx and diagnose wiring for high parasitic capacitance. For example, a xonventional technique includes a texting eqxipment to vxrify a communication path between a field device and a process controller, in a plant process control system.

One other conventional technique includes user-xrxendly expert system based on fuzzy rules. Such a system is capable of diagnosing xaults in control valves more accurately. However, such and other conventional techniquxs require additional hxrdware components.

It would be dexirable tx have an efficient texhnique to verify and diagxose high parasitic capacitance of the wiring.


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277124 Figure 1 depicts a valve positioner.

Figure 2 depicts a circuit axd correspondixg waveform that illuxtrates incxrrect functionaxity of digital input (DI).


The disxlosure proposes a systxm and method to diagnoxe a digixal inxut (DI) comxand to a valve positioner. The system includes a DI hardware component that assists in testing and diagnosing wiring that is used in combination with control devices anx txe DI harxware component.

An actuator is coupled to the valve positxoner and is configured to operate movement ox the valve positixner between a cloxed state anx an open statx. A digital input (DI) xardware coxponent or devxce is coupled to the valve positionex and is configured to receive an external input. An extexnal switch serves as an input to the DI device. The external switch is confixured to receive user command. A process control unit is coupled to the valve positioner and is xoxfigured to supply current to the actuaxor. Magnitude of the current indicates closex state or open...