EP2699806A1 - Electropneumatic position controller - Google Patents

Abstract

The invention relates to an electropneumatic position controller having a controllable valve group (9, 10, 13) arranged in the position controller and having at least one valve (9, 10), by means of which in normal operation either compressed air supplied by means of a compressed air supply line (6) can be fed to an exhaust connection (8) or air fed by means of the exhaust connection (8) can be discharged to the outside, depending on the actuation of the valve group. In order for the valve group to be brought in a safe position, even in the event of a leak in one of the components thereof, said group is arranged in a gas-tight housing (14) within the position controller and means (15) are provided for monitoring the pressure in the housing (14) and for actuating the valve group (9, 10, 13) such that if the pressure in the housing (14) exceeds a predefined threshold value, said group is brought in the predefined safe position.

Description

description

Electropneumatic positioner

The invention relates to an electropneumatic positioner with a supply air connection for connecting a compressed air supply line, with at least one exhaust port for connecting a pneumatic actuator of a control device and arranged in the positioner controllable valve group according to the preamble of claim 1.

For the control of process valves pneumatic actuators are often used as actuators in which a on an actuator, such as a connected to a closing body lifting rod, acting membrane using a gas ^¬ shaped medium, for which hereinafter generally the term "air" is used , is acted upon by variable pressure to He generation of movements. the pressure is restored ^¬ deposition can take place on one side, wherein the membrane on the other side is loaded with a spring, or two-sided, with different pressures cause on both sides of the membrane deflection. the scheme the one or more pressures by an electropneumatic positioner, in which at least one controllable valve under pressure ste ^¬ rising supply air distributed depending on the control of one or two exhaust ports to the one or both sides of the membrane in the actuator.

From DE 10 2004 048 689 B3 a two-stage pilot valve for use in an electropneumatic positioner is known. In a first stage, four flow resistances, of which at least one flow ^{resistance is} variable, are arranged in a bridge circuit. Two opposite circuit points of the bridge circuit are connected to supply air or exhaust air to the environment. Between the other two circuit points is a variable in magnitude and sign pressure difference ready, the pneumatic output signal of the so in the first Stu fe realized electro-pneumatic converter for driving the downstream second stage is used. In the second stage there is a valve group which has an actuatable by the Druckdif ^¬ ference control piston. By this a pneumatic valve in the valve assembly is actuated, the hinleitet depending on the control over the supply air supplied to either compressed air to the exhaust port to the actuator or supplied via the same exhaust port to the outside air ^¬ SEN derived. For example, the pneumatic drive of a control valve is connected to the exhaust air connection. at

Failure of the pneumatic energy (compressed air) is often gefor ^¬ changed that the driven by the positioner drive the process valve automatically in a safety position, ie a safe in the environment of each process position, usually "open" or "close" brings.

Increasingly si possible ^¬ cheres reaching the predetermined safety position is also used if other error in electro-pneumatic positioners in the context of functional safety, which is classified in safety performance levels or "Safety Integrity Level" (SIL) required. Namely, when a defect evaluation between hazardous Defects in which the safety position can no longer be approached due to the error or a request, and non-dangerous errors in which the device is no longer functional, but is put into the specified safety position The valve group, in particular ^¬ in the seals or membranes commonly used on valves, can often lead to dangerous errors in electropneumatic positioner.

From DE 42 39 431 AI a positioner and an actuator with such a positioner are known. For monitoring purposes, if the actuator has a seal, in particular a sliding seal, a leakage chamber is provided on the side of the seal facing the pressure, which is connected to a pressure switch which, when a set pressure is exceeded, sends a signal to the sensor Positioner generated. As a seal, in particular, the usual in control valves fabric bushing comes into question. With the help of the pressure switch can be monitored whether a leakage above the allowable pressure is formed in the leakage chamber due to leakage. The signaling can be used to generate an alarm or perform a safety routine.

The invention has for its object to provide an electropneumatic positioner, which is characterized by increased functional safety.

To solve this problem, the new electropneumatic positioner of the type mentioned in the characterizing part of claim 1 features. In the dependent claims advantageous developments of the invention are described.

The invention has the advantage that a much larger number of possibly occurring error cases can now be classified as harmless errors. The ratio Zvi ^¬ rule hazardous errors and dangerous errors is therefore much cheaper.

The invention is based on the finding that material ^¬ wear, usually initially expressed with seals or membranes that are in valves of a valve assembly used as a compressed air leakage on the valves and sub ^¬ brin supply in a gas-tight housing leads to an increase in pressure within the housing at its , If a gradual or sudden leakage, for example at rupture of a membrane within the housing, so that it ent ^¬ standing pressure increase by means of a pressure switch is detected ^¬ which cooperates with the valves of the valve group and controls them so that the valve group in a predetermined safety position is offset.

Since valve groups in electro-pneumatic positioners are usually housed in a separate housing anyway the, the invention is associated with only a small overhead. The existing housing must namely be supplemented only by a suitable housing seal.

In principle, the pressure switch and the actuation of the valve group can to enable them at too high a pressure in interior housing Si ^¬ cherheitsstellung, by electronic or electromechanical means, for example a pressure sensor with a downstream electromagnet can be realized. Preferably, however, these are exclusively operated pneumatically, such that required in an advantageous manner able to operate any electric auxiliary energy, only be ^¬ restricts into ^¬ special case of field devices of the process instrumentation, which are operated with 4 to 20 mA interface is available. In addition, in such a realization, the safety position is approached completely independently of the operability of the electronics of the electropneumatic positioner and thus the functional safety ^¬ further increased.

Since a small leakage is permissible up to a certain limit without Be ^¬ drive degradation, a diaphragm for venting the housing with a predetermined maximum air flow can be provided in a particularly advantageous embodiment of the invention. The housing interior is then connected via the aperture as a flow resistance with the environment of the electropneumatic positioner. In one embodiment, the aperture may be sized so that an air flow of one liter per minute leads to a pressure increase of 0.8 bar in the housing interior, in which the pressure switch responds and the valve group in safety ^¬ set position.

In one embodiment of an electropneumatic positioner in which the valve group is preceded by an electropneumatic converter, preferably the exhaust side of the orifice is connected to the exhaust outlet of the converter. This has the advantage that in addition to the monitoring of the valve group on compliance with the permissible leakage and the exhaust air outlet the electro-pneumatic converter is tested for free continuity, since clogging of the output, for example, due to icing or contamination of the outlet opening, even with low leakage leads to an increase in the housing ^¬ inner pressure and thus even in this disorder, the Ven ^¬ tilgruppe is placed in the safety position , Hence a closure of the output of elektropneumati ^¬ rule converter can be classified as non-hazardous errors that could otherwise lead to the ineffectiveness of the control of the valve group and therefore a dangerous error of Stel ^¬ development regulator.

According to an advantageous development of the invention, the position of the valve group is detected by an electronic controller, which is usually present in electropneumatic positioner, so that it outputs a signal for displaying a fault condition, for example in the form of an alarm ^¬ message via a field bus, when the Valve group is in the safety position, this state, however, does not correspond to the control of the valve group by the controller electronics and any of these downstream electro-pneumatic converter. In an automation device or a control station as a receiver of the alarm, this can be further processed and issued to an operator ^¬ so that can be initiated by this maintenance or other appropriate actions to handle the reported error condition.

Reference to the drawing, in which an embodiment of the invention is shown, the invention and refinements and advantages are explained in more detail below.

In the figure, only the contributing to understanding of the invention parts of an electropneumatic positioner and a connected thereto pneumatic drive 1 for a control device 2, here a process valve shown. The pneumatic positioner has a pilot valve 3 and a controller electronics 4. An air supply connection 5 serves to connect a compressed air supply line 6, via which, for example, compressed air at 6 bar pressure to the pre ^{¬ control} valve 3 is supplied. The upper chamber 7 of the on ^¬ drive 1 is connected to an exhaust port 8 of the pilot valve. Depending on the control of the chamber 7 is supplied either by means of a supply air valve 9 compressed air from the compressed air ^¬ supply line 6 or derived from the pressure chamber 7 by means of an exhaust valve 10 via a valve outlet 11 into the environment. By a suitable locking ^¬ mechanism, which is not shown for clarity in the figure, it is ensured that the two valves 9 and 10 are never opened simultaneously, otherwise compressed air could escape unused into the environment. To control the position of the actuator 2 via the in the

Pressure chamber 7 of the drive 1 set pressure serve the controller electronics 4, an electropneumatic converter 12, which is designed in a known manner as a bridge circuit of flow resistances, and a booster drive 13 for Be ^¬ actuation of the supply air valve 9 and the exhaust valve 10 ent ^¬ speaking the with Help of the electropneumatic converter 12 set pressure difference.

By a pressure regulator 19, the supply pressure of, for example, 6 bar to a regulated pressure of, for example, 1.4 bar, which is applied to the bridge circuit of the electropneumatic converter 12, reduced.

A valve group of the electropneumatic positioner, which consists in the embodiment shown from the supply air valve 9, the exhaust valve 10 and the booster drive 13 is disposed in a gas-tight housing 14 within the position ^¬ controller. By a pressure switch 15, the pressure prevailing within the housing 14 is monitored for maintaining a predetermined threshold value of, for example, 0.8 bar. All free inner spaces within the gas-tight device covers 14, 13 entge ^¬ gengesetzten areas, the area around the valves 9 and 10, spring chambers located in the valve group and the area around the locking mechanism of the valves are the pressure chambers of the booster actuator 9 and 10 pneumatically interconnected. Occurs in the valve group a leak, such as a crack in a membrane of the booster drive 13, so escapes compressed air through the leak in the gas-tight interior of the housing 14 and leads to a pressure increase, which is detected by the pressure switch 15. As long as the pressure does not exceed a threshold value of 0.8 bar, the pressure monitor 15 does not intervene in the regulation of the position of the actuating device 2. However, as soon as the pressure rises above the limit value, the pressure monitor 15 opens the exhaust air valve 10. The supply air valve 9 is closed at the same time by the locking device, not shown in the figure, so that the pressure in the pressure chamber 7 of the drive 1 drops rapidly and the actuator ^¬ 2 device in the safety position, which speaks in the embodiment shown, an "Open" of the process valve corresponds, is added. the required switching state of the valve group is also as safety position ^¬ be distinguished.

Notwithstanding the described embodiment, it is of course possible in an alternative embodiment, the process valve to be arranged so that it "closes" at pressure ^¬ waste in the chamber 7. In a further modification of the embodiment, additional components, such as the electropneumatic converter 12, the Pressure Reg 19 and / or the pressure switch 15, are additionally integrated into the housing 14.

Minor leaks on the valve group in the housing 14 do not necessarily lead to functional impairments. In order to avoid that the safety position of the actuator 2 is taken even at low leaks, a diaphragm 16 is provided, which also referred to as throttle or Strö ^¬ tion resistance can be and is connected between the In ^¬ nenraum of the housing 14 and an exhaust air outlet 17 of the electropneumatic converter 12. The orifice 16 is for example adjusted so that a leakage of one liter per minute leads to a pressure increase of 0.8 bar in the housing 14. The pressure monitor 15 therefore only responds when the air flow through the throttle 16 exceeds one liter per minute. rises or when the exhaust outlet 17 of the converter 12 is clogged, for example, due to icing or contamination. To carry out the control, the current position of the valves 9 and 10 is taken into account in the controller electronics 4. In order to detect a response of the pressure switch 15 and thereby caused starting the safety position by the valve group with the valves 9 and 10, is additionally checked in the controller electronics 4, whether the position of the supply air valve 9 and the exhaust valve 10 with the by the control electronics 4 via the electro-pneumatic transducer 12 corresponds to the predetermined position. A lack of agreement with simultaneous taking of the safety position by the valve group evaluates the controller electronics 4 as a fault condition and generates a corresponding alarm message, for example, via a fieldbus 18, with which the electropneumatic positioner is integrated into an automation ^¬ network automation plant, for example, to a parent Control station ^{¬ is} given, so that in response to the error occurred appropriate measures can be initiated to remedy this.

Claims

claims 1. Electropneumatic positioner with a supply air connection (5) for connecting a compressed air supply line (6), with at least one exhaust air connection (8) for connecting a pneumatic drive (1) of a control device (2) and with a arranged in the positioner controllable valve group (9, 10, 13) with at least one valve (9, 10) through which in normal operation depending on the control of the valve ^¬ group fed either via the compressed air supply line compressed air to the exhaust port (8) or via the exhaust port (8) supplied to the outside is ^¬ off, characterized, that the controllable valve group (9, 10, 13) in a gas-tight housing ^¬ (14) is integrally ^¬ arranged within the positioner, in that means (15) are provided for monitoring the pressure prevailing in the housing and for actuating the valve group (9, 10, 13) such that the valve group (9, 10, 13), when the pressure in the housing exceeds a predetermined threshold, into a predetermined safety position is ver ^¬ sets, and an aperture (16) is provided for venting the housing (14) with a predetermined maximum air flow. 2. Electropneumatic positioner according to claim 1, characterized in that the means (15) for monitoring and control realized pneumatically and are adapted to control the valve group (9, 10, 13) pneumatically. 3. Electropneumatic positioner according to claim 2, characterized in that the valve group (9, 10, 13) an electropneumatic converter (12) is connected upstream and that the exhaust side of the diaphragm (16) connected to the exhaust outlet (17) of the converter (12) is. 4. Electropneumatic positioner according to one of the preceding claims, characterized in that the Stel ^¬ ment of the valve group (9, 10, 13) by a controller electronics (4) can be detected and that the controller electronics (4) is formed to a signal (18) to output a Fehlerzu ^¬ states when the valve group (9, 10, 13) is in the safety position and this does not correspond to the control of the valve group (9, 10, 13) by the controller electronics (4).