Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B23/00—Testing or monitoring of control systems or parts thereof
  • G05B23/02—Electric testing or monitoring
  • G05B23/0205—Electric testing or monitoring by means of a monitoring system capable of detecting and responding to faults
  • G05B23/0218—Electric testing or monitoring by means of a monitoring system capable of detecting and responding to faults characterised by the fault detection method dealing with either existing or incipient faults
  • G05B23/0256—Electric testing or monitoring by means of a monitoring system capable of detecting and responding to faults characterised by the fault detection method dealing with either existing or incipient faults injecting test signals and analyzing monitored process response, e.g. injecting the test signal while interrupting the normal operation of the monitored system; superimposing the test signal onto a control signal during normal operation of the monitored system
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B9/00—Safety arrangements
  • G05B9/02—Safety arrangements electric
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T137/00—Fluid handling
  • Y10T137/0318—Processes
  • Y10T137/0396—Involving pressure control
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T137/00—Fluid handling
  • Y10T137/8158—With indicator, register, recorder, alarm or inspection means
  • Y10T137/8175—Plural
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T137/00—Fluid handling
  • Y10T137/8158—With indicator, register, recorder, alarm or inspection means
  • Y10T137/8225—Position or extent of motion indicator
  • Y10T137/8242—Electrical
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T137/00—Fluid handling
  • Y10T137/8158—With indicator, register, recorder, alarm or inspection means
  • Y10T137/8326—Fluid pressure responsive indicator, recorder or alarm

Definitions

• the invention relates to the maintenance of safety devices.
• the invention per- tains to the verification of the correct performance of actuator-controlled safety devices comprising movable parts, especially so-called emergency shutdown valves and their control devices, in such a manner that neither production continuity nor the standby state of the devices is impaired.
• valves In the industry, particularly in the petrochemical process industry, systems are used wherein process equipment likely to cause hazards upon failure is provided with valves and other mechanical means designed to bring the process quickly into a safe state if preset process parameter limits are exceeded.
• a system usually includes valves with sin- gle-action actuators, the opening or closing of which releases a built-up overpressure, diverts a hazardous process stream into a holding tank, or the like.
• valves are referred to as shutdown valves (being emergency valves having a closing or an opening function).
• the general safety of shutdown valves is not considered satisfactory when prior art equipment and methods are used.
• the greatest disadvantage in present systems is, that an existing failure - for example, a mechanical component getting stuck - is not necessarily observed when the system is in a standby state, and in an emergency situation the system may be impaired or inoperative.
• To verify proper performance it is common to test e.g. shutdown valves in a manner simulating a real emergency situation. This practice may in fact cause huge risks, as the workability of the shutdown valve system is temporarily blocked, and if the device is not properly activated, the situation may remain permanent.
• One method of testing a shutdown valve is to mechanically limit its travel, thus preventing it from having any significant effect on the process, and check the mobility of the valve within certain limits.
• This procedure requires the use of, for example, a physical key, and activation of the emergency system is prevented during the testing procedure, at least as far as the relevant unit is concerned.
• the test is carried out at preset intervals, for example twice a year, but the test only proves that the devices are workable at the moment of testing. A fault may develop shortly after the test and persist until the next test. This manner of testing is not a reliable way of verifying operability of the system.
• Valve diagnostics using present sensor and digital technology is a fast developing field.
• methods are disclosed for surveillance of the condition of control valves using sensors in the actuator and control means of the valve and the analysis of signals from said sensors in a microprocessor to analyze the workability of the valve unit as a whole.
• a method according to claim 1 has been invented, which provides for the verification of error-free operation of a mechanical safety device, for example a shutdown valve, while the standby state of the safety system is constantly maintained without impairment.
• the safety function and the surveillance or diagnostics function are combined in real time, the safety function nevertheless having a higher priority than the diagnostics function.
• a component fitted directly to the safety device for activating the safety function is controlled by the plant's high-level safety system which is responsible for safety operations, or alternatively by a logic unit integrated into the device according to the invention, a diagnostics unit being adapted to said activating component.
• the diagnostics unit is allowed to perform diagnostics not disturbing the process functions whenever the process is in a normal state.
• the diagnostics unit In an emergency situation, the diagnostics unit is bypassed, whereby for example neither a fault or disturbance in the diagnostics testing nor an ongoing routine test can impair the safety function.
• the scope and periodicity of the diagnostics can be programmed into the system in order to achieve a desired level of reliability.
• a device is provided enabling the verification of undisturbed operation of a mechanical safety device while the standby state of the safety system is fully maintained.
• the field unit of a safety system comprises a microprocessor providing for preset self-testing and diagnostics procedures.
• the field unit further includes a control unit providing for the control of an actuator.
• said control unit is connected to, on the one hand, the high-level safety system or the logic unit integrated into the field unit, and on the other hand to the supply of energy to the safety device, e.g. a compressed air supply.
• the high level safety system or the integrated logic unit activates the safety function directly, bypassing the diagnostics function.
• another main component of the safety system is a monitoring unit.
• the communication link from the high level safety system is routed through the monitoring unit.
• the task of the monitoring unit is to monitor the status of the field unit on-line, and provide the means for presenting status information to the user.
• FIG. 1 is a schematic representation of a system for implementing the method of the present invention
• FIG. 2 is a representation of a field unit according to the present invention connected to a valve actuator in a normal situation;
• FIG. 3 is a representation of a field unit and actuator according to the present invention in an emergency situation.
• (1) represents a monitoring unit of a system according to present invention and (2) is a field unit comprising a control unit (7) according to the invention, a communication interface (3), an electronics unit (19) including a microprocessor, and the required sensors and pneumatic components (not shown).
• the control unit (7) controls a safety device (24) comprising an actuator (8) and a valve (22).
• the communication between monitoring unit (1) and control unit (7) is preferably maintained through communication link (5) as described below.
• Communication link (5) can be analogous or digital or a combination of both by means of, for example, a paired cable.
• the system includes a barrier unit (6).
• Field unit (2) is supplied with power voltage, preferably 24 V, from the high level safety system (18) in charge of safety functions or, in case the safety system according to the present invention includes a logic unit, from a digital communication link.
• the moni- toring unit (1) is provided with indicator lights reflecting the state of the field unit, controlled by the signal provided by communication link (5) and relay outputs (21) corresponding to said indicator lights.
• a green light may indicate the signal being normal and the safety system according to the invention being in a standby state.
• the microprocessor included in electronics unit (19) carries out diagnostics. Thereby the signal in link (5) changes, as indicated by, for example, a yellow light.
• the diagnostics When the diagnostics has revealed a fault, this is correspondingly indicated by, for example, a red light.
• the signals corresponding to the indicator lights can be forwarded through, e.g., relay outputs (21).
• the performance of the light indicators and the relay outputs may for example be checked by means of a local push button on the monitoring unit.
• the monitoring unit (1) is connected to a computer (23) running a safety system maintenance program, enabling the determination of the character of a fault by analysis of data stored by the diagnostics system.
• the communication required by this function is preferably also provided by communication link 5.
• the monitoring unit housing preferably includes means (for example, a keyboard and a LED display) for local control of the microprocessor included in electronics unit (19).
• the task of the communication interface (3) is to separate the signals, described below, transmitted by communication link (5). In addition, it may incorporate the logic unit inte- grated in the field unit.
• the communication link splits into a direct link (10) to th ⁇ control unit (7) and a link (25) to electronics unit (19). Further, the electronics unit (19) is connected (26) to the control unit.
• test on the control unit (7) and the safety device (24) are performed at defined intervals under the control of the program residing in the microprocessor within the electronics unit (19). Tests can also be performed ad hoc by means of computer (23).
• the signal is carried directly from the high level safety system (18) via links (5) and (10) to control unit (7), for example in a manner described below.
• a logic unit integrated into communication interface (3) may transmit a signal along link (10) directly to control unit (7).
• (7) is the main valve of field unit (2).
• the figure represents a normal operating situation: As connection (10) is live with 24 V control voltage, pneumatic control valve (11) stays closed and slide (14) stays pushed to the right against spring (15). Hereby the operating air pressure of the actuator acts freely through connections (12) and (13), and the valve actuator cylinder (8) is pressurized, spring (9) being compressed.
• Microprocessor (17) within electronics unit (19) is allowed to carry out diagnostics by means of pneumatic control valve (16) as described below.
• Figure 3 represents a situation where the safety function has been activated.
• the voltage in connection (10) has fallen to zero, and the pressure is released through valve (11).
• Spring (15) pushes slide (14) to the left, the actuator pressure is released through aperture (20), and actuator (8), by means of the energy in compressed spring (9), brings the shutdown valve into its safety position, which may be open or closed.
• the function of microprocessor (17) has no influence on the situation.
• the microprocessor is de-energized in this situation, as it is supplied with power from the same connection as control valve (11).
• the field electronics unit (19) of the shutdown valve is normally provided with nonvolatile memory circuits able to store measurement data relating to the safety function before power disappears.
• Microprocessor (17) receives at least the following input data:
• Microprocessor (17 ) can be programmed to perform diagnostics functions at preset intervals, for example 15 ms - one week. In the preferable embodiment described below, these comprise a so-called hysteresis test. Before starting the test, the microprocessor transmits, by altering the signal of communication link (5), a message to monitoring unit (1) which shifts to indicate that a test is in progress. Next, the control pressure is lowered by means of valve (16) during a previously defined time interval to a preset level and back to the starting level, whereby a corresponding decrease in actuator pressure shall be observed within a defined time delay, as indicated by sensors (not shown).
• microprocessor (17) transmits, by altering the signal in communication link (5), a message to monitoring unit (1) which shifts to indicate failure alarm.
• the movements of the shutdown valve during the test cycle are limited in order not to interfere with the process.
• diagnostics include other functions outside the scope of the present invention, e.g. internal diagnostics of electronic components and characterization of valve leakage and valve movement using a separate acoustic sensor.
• all communication between field and control room can take place along the same communication link (5).
• this is a paired cable for a) maintaining the control voltage, e.g. 24 V, of the high level safety system (18), simulta- neously maintaining the standby state of field unit (2); b) controlling the indicator lights and relay outputs of monitoring unit (1) by means of signal changes c) communication between the safety system maintenance program in computer (23) and' electronics unit (19) using, for example, the HART protocol well known to persons skilled in the art.
• the above arrangement is preferable because retrofitting of the system into existing plants is convenient.
• the present invention provides the following advantages: -
• the "intelligent" components are located in the field, which enables the connection of safety devices to a field bus system.
• the safety function is not unconditionally activated, but maintenance is possible and the plant may remain in operation.
• the main standby signal (e.g., the 24 V main voltage in the above example) is not affected during testing, but direct contact with the system in charge of safety functions is always maintained. Testing is carried out using a dedicated signal and separate wiring.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Automation & Control Theory (AREA)
• Testing And Monitoring For Control Systems (AREA)
• Safety Devices In Control Systems (AREA)
• Alarm Systems (AREA)
• Burglar Alarm Systems (AREA)
• Fluid-Pressure Circuits (AREA)
• Numerical Control (AREA)
• Indication Of The Valve Opening Or Closing Status (AREA)

Priority Applications (7)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8549753

Family Applications (1)

Country Status (12)

Cited By (10)

Families Citing this family (53)

Citations (6)

Family Cites Families (8)

• 1997
  • 1997-10-17 FI FI973990A patent/FI116587B/fi not_active IP Right Cessation
• 1998
  • 1998-10-07 CA CA002306141A patent/CA2306141C/en not_active Expired - Fee Related
  • 1998-10-07 BR BRPI9815249-1A patent/BR9815249B1/pt not_active IP Right Cessation
  • 1998-10-07 EP EP98947574A patent/EP1027635B2/en not_active Expired - Lifetime
  • 1998-10-07 DE DE69829403.3T patent/DE69829403C5/de not_active Expired - Lifetime
  • 1998-10-07 WO PCT/FI1998/000784 patent/WO1999021066A1/en not_active Ceased
  • 1998-10-07 RU RU2000112092/09A patent/RU2223532C2/ru not_active IP Right Cessation
  • 1998-10-07 JP JP2000517323A patent/JP2001521213A/ja active Pending
  • 1998-10-07 CN CNB988112302A patent/CN1140858C/zh not_active Expired - Fee Related
  • 1998-10-07 ES ES98947574T patent/ES2236942T5/es not_active Expired - Lifetime
  • 1998-10-15 US US09/172,678 patent/US6176247B1/en not_active Expired - Lifetime
• 2000
  • 2000-04-14 NO NO20001974A patent/NO319522B1/no not_active IP Right Cessation

Patent Citations (7)

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