JPS5826042B2 - Electric/pneumatic actuated current ↓-position conversion device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to current-to-position transducers used in industrial process control instrumentation, and more particularly to generating a corresponding pneumatic pressure output signal or changing the position of a driven element, such as a process control valve stem, by pneumatic means. The present invention relates to a current-position conversion device which is controlled proportionally.

It is well known in the process control instrumentation art to convert electrical input signals indicative of various control variables to pneumatic output signals that can be used for pneumatic instrumentation or as setpoint inputs for directly positioning valve stems.

A number of instruments have been developed over the years for this purpose.

In conventional instrument configurations, the input current is first converted into an equivalent force by the collapse of a voice coil or flat armature torque motor, and this converted force is then transferred across an element pivoted by a bellows. averaged.

An air actuated nozzle-flapper device is used to apply the required offset pressure to the bellows to maintain the pivot element in the null position.

An equilibrium condition is thus established between input current and output pressure.

The method of generating an output signal by pneumatic action in opposition to this torque is commonly referred to as a force balance device.

A feature of this device is that the movements between the various working parts, namely nozzle-flapper, pivot element and bellows, are almost imperceptible.

The range of motion of these parts is approximately 0.001 inches (approximately 0.0
25 mm).

This type of instrument is Foxborough's 69TA.
Type 546 manufactured by Fisher Governor are commercially available.

The main object of the present invention is to address the susceptibility of conventional electric/pneumatic position transducers to vibration errors caused by external forces and errors induced by the environment, such as the effects of cyclical changes in temperature. It is possible to eliminate defects such as sensitive points, to counteract the influence of unfavorable external elements, and to be simple, compact, and highly adaptable to many use cases. An object of the present invention is to provide a reliable electric/pneumatically actuated current-to-position transducer.

The transducer of the present invention operates in a so-called "motion following" manner, in which the nozzle follows the movement of the flapper and reaches a new equilibrium position in response to changes in the input current.

To achieve this objective, statically and dynamically balanced rotary motors are used whose output coils rotate a considerable distance (2-3 degrees in the preferred embodiment) over the transducer operating range. It shall be.

Also, the coil is mounted with flexural support at both ends.

The symmetrical arrangement of the motor and the flexure-supported coil mountings provide significant stability and balance to the motor and act to reduce equilibrated output errors when subjected to vibration.

At the same time, the normal amplitude of movement of the device is generally much larger than the amplitude of movement caused by the vibrations, so that the influence of mechanical displacement errors that may arise from vibrations or temperature changes can be minimized.

In a preferred embodiment of the invention, the input current is supplied to an electromechanical transducer consisting of a simple motor having a permanent magnet as a stator and a rotating coil restrained by a spring as a rotor.

A magnet is placed within the boundary of the coil, and a pair of flexible plates are coupled to the coil to be used not only as a pivot to rotate the coil around the magnet, but also as a spring restraint to balance the torque generated by the input current. do.

Therefore, an input current flowing through the coil induces a mechanical rotation of the coil around the central axis of the magnet in proportion to the input current.

A flapper arranged to cover the nozzle of the air circuit is fixed to the coil and moves in an arcuate manner together with the coil.

Applying current to the coil changes the angular position of the flapper over the nozzle, thus changing the back pressure in the nozzle circuit.

This changed pressure is amplified and then fed through a suitable feedback element to the control lever to which the nozzle is attached.

The pressure signal generated by this nozzle-flapper interaction therefore repositions the nozzle to maintain an essentially constant isolation relationship between the flapper and the nozzle.

Although there is no physical contact between the flapper and the nozzle, the motion of the flapper causes a one-to-one following motion of the nozzle, which in the case of the electro-pneumatic converter of the present application is proportional to the applied input current. proportional to size.

This control circuit therefore creates a so-called motion equilibrium of the interrelated components.

The air back pressure generated by the nozzle is proportional to the applied input current and can be used as an air output signal for any purpose.

In all configurations of the invention, high precision of measurement, especially in the presence of shocks and vibrations, is combined with a compact and symmetrical configuration, resulting in economical manufacture and increased flexibility in its application. .

Also, rotating the coil in the highest flux region of the strong magnetic field increases the linearity of the output motion with respect to the input current, thus improving the overall accuracy of the meter.

Hereinafter, an example of the electric/pneumatically actuated current-position converting device of the present invention will be explained in detail with reference to the drawings.

In FIGS. 1-3, a motor 14 is secured to one end of a cylindrical instrument holder 12 of an electro-pneumatic current-to-position transducer 10. As shown in FIGS.

A flapper 16, positioned along an arcuate but generally vertical path by the motor 14, covers the nozzle 18 of the air circuit.

The pneumatic circuit includes a feedback bellows 20 and a relay 22, both of which are communicated by conduits 23, 24 in a known manner.

The upper end of the bellows 20 is rigidly attached to the bulk body 12 by a bedplate bracket 26, while its lower end interacts with a nozzle control lever 28.

This nozzle control lever 28 is supported by a pair of deformable plates 29, 30 for some pivoting movement.

Nozzle 18 is connected to lever 28 by brace 32, and current is applied to the motor to move flapper 16 in the direction of nozzle 18 (
This movement causes a corresponding pressure increase in the bellows 20, producing nozzle movement identical to and in the same direction as the flapper movement.

Next, referring to FIGS. 4 to 6, the motor 14 normally has a cylindrical container 40, and a cylindrical permanent magnet 41 is disposed in this container, and between this magnet and the container. An elongated normally rectangular coil 42 is provided.

The proper method for supporting this coil 42 is to first secure the magnet 41 to an electrical terminal block 43 having input current conductors 44, 45 along one end thereof.

The magnet is properly positioned within the cylindrical container 40 by a right angle bracket 46 which extends in the axial direction of the magnet to form a wedge between the magnet and the container.

In this way, the coil 42 can be rotated without coming into contact with the magnet 41 or the opening of the container 40.

Further, in order not to affect the magnetic field distribution state, the terminal block 43 and the right angle bracket 46 are made of non-magnetic material.

The magnet 41 is magnetized along its diameter so that its north and south poles are opposed to each other over the entire length of the magnet.

It is preferable that the cylindrical container 40 be made of a soft ferrous material to serve as a magnetic path and strengthen the magnetic fields at the north and south poles, respectively.

Furthermore, the enclosure 40 shields the rotating coil-magnet assembly from the effects of external magnetic fields.

The long sides of the coil 42 serve as its working sides and are placed adjacent to the north and south poles of the magnet so that most of the magnetic field passes through these working sides.

In order to support the coil 42 so as to rotate correctly around the magnet 41, the coil is mounted on a frame 47 having square-shaped flexible supports 48A and 48B fixed at both ends thereof.

This coil-frame assembly is then placed around magnet 41 which is mounted on terminal block 43.

A right angle bracket 46 is placed on top of the magnet 41 to form a connection point to a pair of flexure plates 49A, 49B (one layer on each end of the coil).

This entire subassembly is then inserted into a tubular container 40, and the coil 42 is placed so that the coil can rotate about the axis of symmetry of the magnet.
support.

A set screw (not shown) in the container that engages terminal block 43 is tightened to accomplish this final alignment and tightening.

Of course, the coils must be carefully sized so that they do not come into contact with the magnet or with the tip of the canister during rotation over the input span of the meter.

There are several advantages to a motor rotation configuration that rotates the coil outside of the magnet.

Because of the balanced and symmetrical design described above, there is little response to external translational vibrations resulting from unbalance due to manufacturing and/or assembly tolerances.

In addition, the entire coil is placed in a strong and uniform magnetic field to improve the rotational linear response characteristics of the motor.

Additionally, a short-circuited copper conductor is attached to the coil 42 to improve dynamic response.

This provides sufficient damping force to minimize ringing due to sudden input current and external vibration effects.

Now, let's explain the operation of the current/position converter.

A coil frame 47 close to the inner periphery of the cylindrical container 40
Two flappers 16 and 17 are formed by extending a portion of the container from both ends of the container in the longitudinal direction.

The second flapper 17 extending rearward will be described later.

When a positive input current is supplied to the coil 42, a torque is generated due to the interaction with the magnetic field, and this torque causes the coil to rotate clockwise. When the torque is balanced with the restraining force, the rotation is stopped.

The resulting angular rotation is essentially proportional to the magnitude of the applied input current.

It is therefore immediately apparent that the pivoting flexure plate serves a dual purpose: suspending the coil around the magnet and providing a tightly controlled spring rate that determines the magnitude of rotation.

The angular rotation of the flapper is nominally 7 degrees over the normal operating range of the instrument.

1-3, a current-to-position transducer converts an electrical input into a corresponding pressure output.

When a current signal is applied and flapper 16 approaches nozzle 18, backpressure within the nozzle increases due to flow restriction.

This back pressure is amplified by relay 22 and supplied to feedback bellows 20 by conduit 24.

As mentioned above, the bellows 20 is incorporated into a structure fixed to the instrument stand 12, and a control lever 2B restrained by a spring is provided in the large body 12, and the nozzle 18 is attached to this lever 28 by a support brace 32. It is communicated.

As the pressure in the bellows 20 increases, the nozzle control lever 28 deflects against the restraining force created by the leaf springs 29, 30 and moves the nozzle in the same direction as, or away from, the flapper until equilibrium is again established. urge

In this newly established equilibrium state, the pressure within the bellows increases and is directly proportional to the input signal.

Thus, as the input current increases, the output pressure within the bellows will increase.

As an example of a meter according to the present invention suitable for use in an industrial process control device, when the input current is 4 to 20 milliamps,
A corresponding output signal of 3 to 15 pounds per square inch was generated.

Inserting a diode 51,52 between the input terminals of the coil creates an escape route for the energy stored in the coil in the case of an open input signal, thus increasing safety when using the instrument in explosive environments. will give.

The overall symmetry of the current-to-position transducer 10 configuration, particularly the angular rotational relationship of the motor flapper nozzle, facilitates accurate meter adjustment.

The motor assembly is mounted on a pair of conical pivots 33, 34 (see Figure 3) to adjust the zero point of the instrument.

The flange 35 is secured to the rear cover of the motor 14 such that a spring loaded zero screw 36 acts on the flange 35.

When the screw 36 is rotated, the motor 14 pivots) 33,3
4, the flapper 16 deflects accordingly, and the output pressure then changes.

A load spring 38 inhibits adjustment of the motor.

Therefore, simply turning the zero screw 36 will accurately produce a low pressure (zero) output (eg, 3 pounds per square inch) for a low current input (eg, 4 milliamps).

If the measuring range changes substantially, it will be necessary to replace the plates 29, 30 and/or the bellows 20 with others having a different spring rate.

However, minor span adjustments can easily be made in the factory and/or in the field to account for tolerance variations during manufacturing.

A pair of locking nuts 54,55 are provided on the screw jacks 56, which are firmly attached between the bedplate bracket 26 and the span bracket 58, and thus also attached to the bulk body 12, so that the entire feedback bellows assembly is essentially connected to the flapper 16. so that they pivot in parallel to each other.

Adjustment of the nuts 54, 55 along the screw jack 56 causes the trapezoidal bracket 26 to flex and move the nozzle 18 in a direction across the flapper 16, ie, while substantially maintaining the spacing therebetween.

This adjustment changes the effective rotation radius of the motor 14,
The span changes as the lever arm ratio between the flapper and the nozzle changes as the instrument is affected by the balance of movement of the working parts.

When this double nut arrangement is tightened, further vibration resistance is created.

To demonstrate the increased flexibility of a transducer constructed in accordance with the present invention, the threaded jack 56 is attached to the trapezoidal bracket 26.
Then, remove the span bracket 58 and the strap 59, and take out the entire motor assembly from the instrument body 12.

The motor is then reversed and reinserted so that the other flapper 17 covers the nozzle 18.

This flapper 17 is located opposite to the flapper 16 and rotates on the same axis, so when the current signal increases, the flapper 17
7 moves away from nozzle 18 and the output pressure within bellows 20 decreases.

Whenever an inverse relationship between input and output is observed during field assembly, this unique double-ended motor configuration allows rotation to be reversed without changing current polarity with a simple modification.

If the currents were reversed, the polarity of diodes 51, 52 would also need to be reversed, thereby compromising their inherent safety value for the entire meter.

Of course, if the motor is removed in this manner, the zero and span of the gauges will probably have to be adjusted slightly as described above.

7 to 11 show other embodiments of the current-position transducer according to the present invention.

The transducer is configured to control the position of the process control valve stem.

The illustrated example is very similar to the current-to-position transducer of FIGS. 1-3 described above.

The entire instrumentation configuration is the same, especially the motor that receives the input current signal.

The change in the converter described below from the previous example is the feedback circuit that includes the valve stem position control.

Further use of the unique design of this motor flapper assembly demonstrates the wide range of applicability of this overall configuration as used in electro-pneumatic actuation techniques.

Complete motor assembly 14 with flapper 16 as described above.
is the same as the previous example, but the nozzle 70 of the air circuit
is mounted on a bar 71 with an L-shaped return, and the lever 71 is pivotally connected to the body mounting plate 72 by a cross deflection plate 73, so that the pivot axis is perpendicular to the plane of FIG. 8. .

When current is supplied to motor 14, flapper 16 rotates to cover nozzle 70 and create back pressure on relay 74 (see FIG. 10).

The output pressure from the relay 74, which increases in response to this, is supplied to the valve drive pressure chamber and causes the valve stem to move.

Valve drive assemblies are well known in the art and are not shown here.

The operation of the valve driver is disclosed in US Pat. No. 2,661,725.

The linear movement of the valve stem is converted into a rotation of the position return shaft 75 in a conventionally known manner, namely by means of a lever.

A rotatable shaft 75 extends from a bearing 76 into the instrument holder 12 and is connected to an intermediate assembly 77.

This intermediate assembly 77 has a bracket 78 as shown in FIG. 11, one end of which is fixed to the shaft 75, and the other end to which a roller 81 is fixed.

The roller 81 supports the lever 71 at a position offset laterally from the pivot axis of the lever 71.

A coil spring 82 is provided between the lever 71 and the body mounting base plate 72 to press the lever 71 against the roller 81 over the operating span of the position adjuster.

Thus, as shaft 75 rotates, the action of intermediate assembly 77 converts the rotation into a vertical angular displacement of the nozzle.

With the rollers 81 arranged as shown in FIG. 7, rotation of the shaft 75 will cause the nozzle 70 to deflect and thus remain in equilibrium until the whole device receives a new current input and is again in equilibrium, i.e. the output pressure is stabilized and the valve drive is stopped. The flapper 16 moves until it stops (8th
(see figure).

Therefore, by using the position return shaft 75, the pivot return lever 71, other auxiliary levers, etc., it is possible to provide a current input to the transducer to obtain a proportional valve stem position.

FIG. 11 shows the compatibility of this embodiment of the present invention.

FIG. 11 shows a block 79 screwed onto the leadscrew 80.
A roller 81 is shown fixed to.

Simply adjusting this lead screw 80 shifts the point of contact between roller 81 and lever 71 and thus changes the ratio between the rotation of position return shaft 75 and the angular displacement of nozzle 70.

Such adjustments can accommodate changes in valve stem movement for the same motor movement.

In fact, if the bearing point is moved to the opposite side of the center point, ie towards the front of the meter, it may be possible to change the direction of the valve stroke with respect to the output pressure without reversing the current polarity.

The nulling of this embodiment is accomplished in the same manner as the transducer example of FIG.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of the electric/pneumatically actuated current-to-position transducer of the present invention, and FIG. 2 is a diagram showing the large instrument body removed to more clearly show the relationship between operating parts. 3 is a side elevation view of the converter of FIG. 1, also with the instrument holder removed showing details of the air return assembly, and FIG. 4 is a side elevation view of the converter of FIG. Partially cutaway perspective view of the assembly, No. 5
The figure is a partial cross-sectional elevation view showing the motor assembly of Figure 4,
7 is a perspective view showing a suspension device for a motor assembly; FIG. 7 is a partially cutaway perspective view showing another embodiment of a current-position conversion device adapted to control the position of a valve stem; and FIG. 7 is an end elevation view of the converter of FIG. 7 with the instrument holder removed, and FIG. 9 is a side elevation of the converter of FIG. 7 with the instrument holder removed showing details of the return assembly. Figure 10 is a route diagram of the converter shown in Figure 7 showing the elements in the feedback circuit when the converter is used for valve position control, and Figure 11 is a range adjustment mechanism of the converter shown in Figure 7. FIG. 10 is an electric/pneumatic actuated current-position transducer, 14 is a motor, 16 and 17 are flappers, 18° and 70 are nozzles, and 20
is feedback bellows, 22.74 is relay, 28
is a nozzle control lever, 41 is a permanent magnet, 42 is a coil, 46 is a right angle bracket, 56 is a screw jack,
71 is a return lever, 75 is a position return shaft, and 81 is a roller.

Claims (1)

[Scope of Claims] 1. A motor having a rotatable output member that receives an input terminal and takes an angular position corresponding to the magnitude of the current, and a motor that is mounted on the output member of the motor in a radial direction from its rotation axis. a pneumatic nozzle-flapper comprising one element mounted at an offset position, the one element performing an arcuate movement with the rotational movement of the output member, carrying another element of the nozzle-flapper; a movable support member for moving said other element in response to movement of said element; means for generating an air output pressure signal in response to said nozzle back pressure; and air return means controlled by said output pressure signal. The return means includes a motion generating means connected to the movable support member, and the return means includes an electric motor for moving the other element while maintaining a small distance between the flapper and the nozzle.
Air actuated current-position transducer. 2. The motor includes a container made of soft magnetic ferrous material, and a cylindrical permanent magnet having N and S poles extending oppositely over the entire length and firmly attached within the container and separated from the container. , the output member has a coil pivotally movably suspended in the container and surrounding the magnet within the magnetic field of the magnet, and rotates around the magnet in response to a current flowing through the coil. The electric power supply according to claim 1, which is made to
Air actuated current-position transducer. 3. The coil has an actuating side located adjacent to the poles of the magnet in the majority of the magnetic field generated by the magnet, providing effective linearity between output motion and input current. 3. The electric/pneumatically actuated current-position conversion device according to claim 2. 4. The electric/pneumatically actuated current-to-position conversion device according to claim 3, wherein the coil has an elongated shape, and the actuating side surface is a longitudinal side of the coil. 5. An electro-pneumatic actuator according to claim 2, wherein the coil is suspended at each end by respective flexure plates which provide a precisely controlled spring rate to set the magnitude of the angular rotation of the coil. Current-position conversion device. 6. The electro-pneumatically actuated current-to-position converter according to claim 2, wherein a copper conductor forming a shorted winding and providing attenuation is attached to one end of the coil to improve the dynamic response of the converter. Device. I said flapper is mounted on one end of said coil;
3. An electro-pneumatically actuated current-to-position transducer as claimed in claim 2, wherein said nozzle is mounted on said movable support member. 8 a second flapper mounted on the other end of the coil, the second flapper being spaced apart and rotating about the same axis as and diametrically opposed to the first flapper; When the motor is mounted in the reverse direction within the converter, the second flapper covers the nozzle and sets an inverse relationship between the input current and the output position without changing the polarity of the input current. An electric/pneumatically actuated current-to-position conversion device according to scope 7. 9. An electro-pneumatically actuated current-to-position converter according to claim 7, wherein said motor is mounted at both ends on conical pivots to enable its rotation and zero adjustment of said converter. 10 includes a flange fixed to one end of the motor and a spring-loaded screw biased against the flange such that rotation of the screw rotates the motor and the first flapper to produce the output for a constant input current; 10. An electrically pneumatically actuated current-to-position transducer according to claim 9, which changes a pressure signal. 11. An electro-pneumatically actuated current-to-position transducer according to claim 2, including diode means attached to the input of said coil to provide open circuit protection and improve the intrinsic safety of said transducer. 12 The air return means includes pressure response means for receiving the output pressure signal and converting the pressure signal into a force applied to the movable support member, and coupled with the pressure response means to control the movable support member. 2. An electrically pneumatically actuated current-to-position transducer according to claim 1, comprising spring means adapted to proportionally correspond position to pressure and provide said pressure as an output signal proportional to said input current. . 13 The spring means includes a drawing board spring coupled to the movable support member to cause a slight pivoting movement of the support member when the force is applied, and the pressure responsive means comprises a bellows. An electric/pneumatically actuated current-position converting device according to claim 12. 14 a typically rigid and deformable support structure fixed to an end of the pressure responsive means remote from the movable support member, and coupled to the support structure to maintain constant spacing between the flapper and the nozzle; means for changing the lever arm ratio between the two while maintaining the lever arm ratio, the support structure supporting the springing means and being substantially parallel to the movable support member; 13. The electro-pneumatically actuated current-to-position transducer of claim 12, which achieves span adjustment of said transducer. 15 The lever-to-arm ratio changing means has a screw jack that connects the support structure at right angles to the conversion device, and the screw jack bends the support structure to adjust the nozzle to the nozzle.
A patent claim comprising a first adjustable nut that causes translational movement within an effective radius of the flapper, and a second adjustable nut that minimizes the effect of vibration on the span adjustment by fixing the translational movement within the radius. 15. The electric/pneumatically actuated current-position conversion device according to item 14. 16 The air return means includes a valve driver for producing movement of a valve stem in response to the output pressure signal, and a valve driver coupled to the movable support member to control the position of the valve stem and the movable support. 2. An electro-pneumatically actuated current-to-position conversion according to claim 1, further comprising means for proportionately matching the position of a member so that said valve stem occupies a position corresponding to said input current. Device. 17 a shaft connected to the valve stem and extending within the conversion device;
a bracket attached to the shaft and rotating therewith; and a roller attached to the other end of the bracket and riding on the movable support member, the shaft making rotational movement in response to the valve stem movement. , said movable support member is pivotally mounted to said transducer at a point laterally offset from the point of contact of said roller with said support member, said movable support member being pivotally mounted to said converting device to angularly offset said other element to direct said flapper and nozzle 17. The electrical conductor according to claim 16, which maintains the close spacing between the
Air actuated current-position transducer. 18. An electro-pneumatically actuated current-to-position transducer as claimed in claim 17, including means for adjusting said contact point to vary the magnitude and/or direction of said valve stem movement for a given current input. 19 A box, a container made of soft ferrous magnetic material attached thereto, and a permanent magnet having opposing N and S poles and firmly attached within the container and isolated from the container. a coil pivotally suspended within the container within the magnetic field of the magnet and rotating around the magnet in a space between the magnet and the container; and a coil mounted on and with the coil. a movable flapper; means for applying an electrical input current to said coil to cause angular rotation between said coil and said flapper; and a spring coupled to said coil to cause its position to be proportional to the magnitude of said applied current. means, a movable support member pivotally mounted on the stand adjacent the container, and a movable support member mounted on the support member and disposed in close proximity to the flapper so as to be covered by the flapper. an air nozzle adapted to produce a pressure signal as a stroke of separation between the flapper and the nozzle; and responsive to the pressure signal, applying a force to the movable support member to accommodate the position of the nozzle. an electro-pneumatically actuated current-to-position transducer comprising return means for varying the distance between the flapper and the nozzle to maintain an essentially constant spacing between the flapper and the nozzle. 20. The electric/pneumatic actuated current-position converter according to claim 19, wherein the flapper is mounted on the coil at a position offset in the radial direction from the rotation axis thereof, and performs an arcuate movement together with the rotational movement of the coil. Device.