CONTROL VALVE

Abstract

The invention relates to a control valve for adjusting a process fluid flow of a process plant, comprising a valve housing (8) with a valve seat (14) and a valve member (16) connected to a valve rod (18), which cooperates with the valve seat (14) for opening and closing the control valve (2), wherein the valve rod (18) is electrically connected to the valve housing (8) through a contact device (42,43, 45). The invention is characterized in that a measuring device (26) for the ohmic transition resistance measurement of the contact device (42, 43, 45) is provided, and that the measuring device (26) is arranged in a measuring line (24) that connects the valve housing (8) to the valve rod (18).

Claims

1. Control valve for adjusting a process fluid flow of a process plant, comprising a valve housing (8) with a valve seat (14) and a valve member (16) connected to a valve rod (18), which cooperates with the valve seat (14) for opening and closing the control valve (2), with the valve rod (18) being electrically connected to the valve housing (8) through a contact device (42, 43, 45), characterized in that a measuring device (26) for ohmic transition resistance measurement of the contact device (42, 43, 45) is provided, and that the measuring device (26) is arranged in a measuring line (24) that connects the valve housing (8) to the valve rod (18).

2. Control valve according to claim 1, characterized in that the measuring line (24) extends from the valve rod (18) to the valve housing (8) via the measuring device (26) and a yoke (6) connected to the valve housing (8), or via an actuating drive (4) connected to the valve housing (8).

3. Control valve according to claim 1, characterized in that the measuring line (24) extends from the valve rod (18) to the valve housing (8) via a stroke pick-up member (28) of a positioner (22) on the valve rod (18), a rotary lever (36) of the positioner (22) which is connected to a stroke pick-up member (28) on the valve rod (18) via an elevating roller (38), a shaft (30) of the stroke pick-up means (34) guided by the positioner (22), a sliding contact (35) engaging the shaft (30), the measuring device (26) and the positioner (22) permanently connected to the actuating drive (4).

4. Control valve according to claim 1, characterized in that the measuring line (24) extends from the valve rod (18) to the valve housing (8) via a stroke pick-up member (28) of a positioner (22) on the valve rod (18), a rotary lever (36) of the positioner (22) which is connected to a stroke pick-up member (28) on the positioner (22) via an elevating roller (38), a shaft (30) of the stroke pick-up means (34) guided by the positioner (22), an electrically conducting torsional spring (32) which extends around an electrically conducting shaft (30) of the stroke pick-up means (34) guided by the positioner (22), the measuring device (26) and the positioner (22) permanently connected to the actuating drive (4).

5. Control valve according to claim 4, characterized in that the measuring line (24) comprises a contact point for mounting an electrical circuit board in the positioner (22), or a contact point on the interior wall of the positioner (22).

6. Control valve according to claim 1, characterized in that the measuring device (26) for measuring the ohmic transition resistance comprises a first transformer (50) and a second transformer (52), wherein the measuring line (24) forms a secondary winding of the first transformer (50) and a primary winding of the second transformer (52), whereby a voltage pulse impressed on the first transformer (50) by a pulse source (54) delivers a measured value on the secondary winding of the second transformer (52), which measured value is dependent on th resistance of the ground loop formed by the contact device (42, 43, 45) and the measuring line (24).

7. Control valve according to claim 1, characterized in that an evaluation device (46) is connected to the measuring device (26) for measuring the ohmic transition resistance, said evaluation device (46) being configured to calculate the measured value of the resistance of the ground loop and to output it via a display device (48).

8. Control valve according to claim 7, characterized in that a display device (48) for displaying the measured values is provided directly on the positioner (22).

9. Control valve according to claim 7, characterized in that a switching threshold of e.g. 10 ohms is defined in the evaluation device (46), and that the evaluation device (46) is configured to emit, in particular to display and/or to send, an alarm signal if the switching threshold is exceeded.

10. Control valve according to claim 7, characterized in that the evaluation device (46) is configured to transmit the measured values to an evaluation station or to a control room via a bus system or a wireless connection.

11. Control valve according to claim 3, characterized in that the measuring line (24) comprises a contact point for mounting an electrical circuit board in the positioner (22) or a contact point on the interior wall of the positioner (22).

Description

[0026] Throughout the description, the claims and the drawings, those terms and associated reference characters are used as are indicated in the List of Reference Characters which follows below. In the drawings

[0027] FIG. 1 is a side view of an inventive control valve according to a first embodiment of the invention;

[0028] FIG. 2 is a detail view of an area of the inventive control valve according to a second embodiment, which view shows the area of the control valve where contact is made to the valve control rod;

[0029] FIG. 3 is a detail view of an area of the inventive control valve according to a third embodiment, which view shows the area of the control valve where contact is made to the valve rod;

[0030] FIG. 4 is a circuit diagram of a measurement and elevation circuit used in the inventive control valve.

[0031] The control valve 2 shown in the drawings comprises an actuating drive 4 and a valve housing 8 connected to the actuating drive 4 via a yoke 6 and having an inlet 10 and an outlet 12 and a valve seat 14 which can be closed or opened by means of a valve member 16, and which is actuated by a valve rod 18 connected to the valve member 16 and the actuating drive 4. For this purpose, the valve rod 18 is connected to a diaphragm working element 20 of the actuating drive 4. In known manner, the control valve 2 is completed by a positioner 22.

[0032] In control valves of this type, the valve rod 18 is electrically connected to the valve housing 8 via a contacting device 42. According to the invention, the transition resistance of the electrical contacting device 42 is constantly monitored by measuring the transition resistance between the valve rod 18 and the grounded housing 8.

[0033] A measuring line 24 is provided as a conductor path between the valve rod 18, or a component of the control valve 2 that is electrically connected to the valve rod 18, on the one hand, and the grounded valve housing 8, or a component of the control valve 2 that is connected to the valve housing, on the other hand.

[0034] As seen in FIG. 1 and/or FIG. 4, the measuring line 24 (shown as a dashed line) extends from the valve rod 18 via a schematically shown measuring device 26 to the actuating drive 4 connected to the valve housing 8. In particular, the measuring line 24 extends through the stroke pick-up member 28 of the positioner 22 on the valve rod 18, the measuring device 45 to the positioner 22 which is permanently connected to the actuating drive 4. As an alternative, the measuring line 24 may extend to the yoke 6 connected to the valve housing 8.

[0035] As seen in FIG. 2, the measuring line 24 (FIG. 4) extends to the valve housing 8 from the valve rod 18 via a stroke pick-up member 28 of a positioner 22 on the valve rod 18, a rotary lever 36 of the positioner 22 which is connected to the stroke pick-up member 28 on the valve rod 18 via an elevating roller 38, a shaft 30 of the stroke pick-up 34 guided by the positioner 22, a sliding contact 35 engaging the shaft 30, the measuring device 26 and the positioner 22 permanently connected to the actuating drive 4. More specifically, the measuring device is connected to the interior wall of the positioner 22, or to a contact point for mounting an electrical circuit board (not shown) in the positioner 22.

[0036] As seen in FIG. 3, the measuring line 24 (FIG. 4) extends from the valve rod 18 to the valve housing 8 via the stroke pick-up member 28 of a positioner 22 on the valve rod 18, the rotary lever 36 of the positioner 22 which is connected to the stroke pick-up member 28 on the positioner 22 via an elevating roller 38, the shaft 30 of the stroke pick-up means 34 guided by the positioner 22, a torsional spring 32 which extends about the shaft 30 of the stroke pick-up means 34 guided by the positioner 22, the measuring device 26 and the positioner 22 permanently connected to the actuating drive 4.

[0037] In the above described control valves 2 according to the invention, the stroke pick-up member 28, the elevating roller 38, the rotary lever 36, the shaft 30 and the sliding contact 35 and/or the torsional spring 32 are made of an electrically conductive material and are insulated with respect to the positioner, and are connected to the positioner 22 and/or the valve housing 8 via the insulated measuring device 26. Although an additional transition resistance is added between the valve rod 18 and the sliding contact 35 or the torsional spring 32, the device will be safe if the total transition resistance is less than 10 ohms.

[0038] The contact points on the housing of the positioner 22, on the yoke 6 or on the actuating drive 4, or on the valve housing 8 itself are designed to have a low transition resistance. Connection can be made either via uncoated spots on the mountings or via an additional ground line.

[0039] The above described measuring device 26 in the control valve according to the invention can also be used in a control valve which, in known manner, comprises an electrically conductive ground strap (not shown) that connects the valve rod 18 to the yoke 6 or to the valve housing 8, where a fracture of the ground strap is detected by the measuring device 26.

[0040] In the above described control valves 2 of the invention, the contact device between the valve rod 18 and the valve housing 8 may comprise a sliding contact 42 which engages a component connected to the valve rod 18, for example the stroke pick-up member 28, and is connected to the valve housing 8, as is shown in FIG. 1. The contact device may also comprise an electrically conductive stuffing box 43 between the valve rod 18 and the valve housing 8, as shown in FIGS. 2 and 3. Lastly, the electrical contact between the valve rod 18 and the valve housing 8 may also comprise the valve plate 20 connected to the valve rod, a positioning spring 44 of the actuating drive 4 which spring 44 is connected to the valve plate 20, and an actuator housing 45 being in contact with the positioning spring 44.

[0041] As shown in FIG. 4, for the purpose of measuring the ohmic transition resistance which is represented by the resistance 47 in FIG. 4, the measuring device 26 is arranged in the measuring line 24. The measuring device 26 is connected to an evaluation device 46 in which a measured value of the transition resistance of the contact device is calculated, and to a display device 48 which is provided for displaying the measured values directly on the positioner 22.

[0042] As seen in FIG. 4, the measuring device 26 comprises a first transformer 50 and a second transformer 53, with a ground loop being formed by the measuring line 43 and the contact device, the resistance of which consists of the line resistance 56 of the measuring line 24 and the transition resistance of the contact device and which extends through the first transformer 50 and the second transformer 52.

[0043] A voltage pulse impressed on the first transformer 50 by a pulse source 54 delivers a measured value to the second transformer 52 which value is dependent on the resistance of the ground loop. By way of transformers, a voltage pulse is thus impressed on the electrical connection to be monitored between the valve rod 18 and the valve housing 8. The wiring of the transformers is known per se, see EP 2 249 170 A1.

[0044] The required voltage pulse is of a length of about 1 s, and the primary voltage is small, i.e. typically smaller than 3V. In this case, the energy required for a pulse is smaller than 2 nJ (measured value). Even at a measuring rate of 500/s, the average power consumption for providing the pulse will thus be below 1 W (=2 nJ/2 ms). Only a very small voltage will thus be induced in the ground loop, typically smaller than 100 mV. This eliminates the risk of ignition when the measuring line 24 and/or the ground loop is open.

[0045] A pulse current of e.g. 100 mV/10 ohms=10 mA flows in the ground loop. This pulse current is detected by the second transformer. Since the induced voltage only depends on the number of turns of the primary winding, the output is directly dependent on the resistance of the ground loop.

[0046] In the evaluation device 46, a switching threshold is defined, for example 10 ohms, with the result that, if the transition resistance exceeds the switching threshold, an alarm signal will be emitted and displayed and/or sent. The measured values will therefore be transmitted to a display device 48, to an evaluation station or to a control room via a bus line (for example Hart, Profibus, CAN, Ethernet or the like) or through a wireless connection (for example Wireless Hart, Bluetooth, NC, WIFI, RFID or the like).

LIST OF REFERENCE CHARACTERS

[0047] 2 control valve

[0048] 4 actuating drive

[0049] 6 yoke

[0050] 8 valve housing

[0051] 10 inlet

[0052] 12 outlet

[0053] 14 valve seat

[0054] 16 valve member

[0055] 18 valve rod

[0056] 20 diaphragm working element

[0057] 22 positioner

[0058] 24 measuring line

[0059] 26 measuring device

[0060] 28 stroke pick-up member

[0061] 30 shaft

[0062] 32 torsional spring

[0063] 34 stroke pick-up means

[0064] 35 sliding contact

[0065] 36 rotary lever

[0066] 38 elevating roller

[0067] 42 sliding contact

[0068] 43 stuffing box

[0069] 44 positioning spring

[0070] 45 valve drive housing

[0071] 46 evaluation device

[0072] 47 transition resistance

[0073] 48 display device

[0074] 50 first transformer

[0075] 52 second transformer

[0076] 54 pulse source

[0077] 56 line resistance