JPH0433445Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an electro-pneumatic positioner for controlling the stem position of a pneumatically driven valve in response to an input current, and in particular to control the control loop thereof. This article relates to an electropneumatic positioner with improved characteristics.

(Prior Art) FIG. 7 shows the configuration of a conventional electropneumatic positioner.
Input terminals 1 and 1' receive current output from a controller or the like as an input current Io, and 2 is a torque motor through which an input current Io is passed through a coil 201. Reference numeral 3 denotes a lever driven by the torque motor 2, which rotates around a fulcrum 301. 4 is a spring for regulating the lever 3 to the reference position. The lever 3 is driven in the direction of arrow A by the input current Io, with one end 302 of the lever 3 functioning as a flapper. A nozzle 6 is arranged at an end 302 of the flapper 3 so as to face each other.

8 is a non-bleed type pilot relay, and a stem 801 is fixed to a case 802 via diaphragms 803 and 804. A movable end 805 extends from the stem 801, and is fed back to the lever 3 via a spring 5 fixed to the movable end 805. When the lever 3 moves in the direction A in response to the input current Io, the nozzle back pressure Pb of the nozzle 6 increases and pushes the stem 801 downward, causing the movable end 805 to be displaced downward x and moving the flap 3 via the spring 5. Press down the nozzle back pressure
Lower Pb and apply negative feedback. This stabilizes the control loop.

The lower end of the stem 801 is connected to a valve stem 807 having an intake valve formed below and an exhaust valve formed above.
is in contact with the exhaust valve of the case 802 and is pressed via a spring 806 fixed to the case 802.

Supply air pressure Ps is applied between case 802 and diaphragm 803 via throttle 7, and supply air pressure Ps is applied between diaphragms 803 and 804 and on the intake valve side of valve rod 807, respectively.

When the nozzle back pressure Pb increases, the stem 801 is pushed down, and the lower end of the stem 801 and the valve stem 807
With the exhaust valve in contact with the valve, the valve stem 807 is moved downward to change the opening degree of the air supply valve and increase the pneumatic output Po.

The air pressure output Po is guided to the air chamber 901 of the diaphragm valve 9 and drives the valve stem 903 in the direction B against the spring 902. This displacement of the valve stem 903 is transmitted to the lever 10 via the crank pin 904.

The lever 10 has one end rotatably fixed around a fulcrum 11, and converts displacement of the valve stem 903 in the B direction into rotational displacement in the C direction. Lever 1
A spring 12 is connected to spring 12, which applies a force in the D direction to the lever 3 by the rotational displacement of the lever 10 in the C direction, and acts to pull back the displacement of the lever 3 in the A direction due to the input current Io. The system is in equilibrium.

With such a force balance system, the displacement of the valve stem 903 is controlled in response to the input current Io.

(Problem that the invention aims to solve) However, such conventional electropneumatic positioners require a high-precision torque motor that converts input current into force, and further converts the displacement of the valve stem into a force feedback signal. Both systems are mechanical components and tend to be relatively large, and the connection mechanism is also mechanical, resulting in a complicated structure and high cost.

Furthermore, there is a drawback that the system tends to become unstable due to a delay in response caused by the capacity of the valve and constants of the mechanical elements of the feedback mechanism.

Furthermore, in general, it is difficult to obtain a pressure-resistant and explosion-proof structure when using an electrical configuration.

(Means for Solving the Problems) In order to solve the above problems, this invention provides an electro-pneumatic positioner for controlling the stem position of a valve driven by pneumatic pressure in accordance with the input current. an input processing means for converting the signal into a voltage signal or a digital signal, and an actuator means for controlling the flapper of a pilot relay that drives the valve based on the difference between the output of the input processing means and the feedback signal, and is interlocked with the valve of the pilot relay. first displacement/electrical signal converting means for converting the stem displacement of the valve into an electric signal using a non-contact magnetic sensor and feeding it back to the input side of the actuator means; It incorporates a second displacement/electrical signal conversion means for obtaining a signal, the input processing means, the actuator means, the first displacement/electrical signal conversion means, and the second displacement/electrical signal conversion means, and an explosion-proof gap is provided. It is equipped with a sealed, pressure-resistant and explosion-proof container.

(Function) According to the present invention, the input current is converted into an electric signal or a digital signal by the input processing means, and the pilot relay is controlled by the voltage difference between the input current and the feedback signal given as a voltage signal or digital signal, and the output is used to control the valve. is driven. The displacement of the valve stem is converted by the second displacement/electrical signal converting means into a voltage or digital feedback signal to balance the output of the input processing means. The displacement of the stem interlocked with the valve of the pilot relay is converted into an electrical signal by a first displacement/electrical signal conversion means composed of a non-contact magnetic sensor, and the feedback is fed back to the input side of the actuator, thereby stabilizing the system.

Since the electrical components are housed in the flameproof explosion-proof container, they have flameproof and explosion-proof properties.

(Example) Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. Note that parts having the same functions as those in FIG. 7 are designated by the same reference numerals, and their explanations will be omitted as appropriate.

Reference numeral 16 denotes an input processing means, which converts the input current Io into a voltage signal Vi. A differential amplifier 17 amplifies the difference between the voltage signal Vi and the feedback signal Vf.
The output of this differential amplifier 17 and the pilot relay 8
The piezoelectric actuator 18, which displaces the flapper 3, is driven by the differential voltage Vc of the feedback signal Vp related to the displacement x of the stem 801. The configuration from the nozzle 6 to the valve 9 via the pilot relay 8 is the same as the conventional configuration.

The displacement of the valve stem 903 is converted into a feedback signal Vf by the displacement-to-electrical signal converter 19. This displacement-electrical signal converter 19 is composed of a vibrating force sensor means, and a pair of piezoelectric elements 193 and 194 are arranged on an etched vibrating part 192 of a cantilever beam 191 fixed at one end. By causing the amplifier 197 and the two piezoelectric elements to form a closed loop, self-oscillation of the natural frequency of the vibrating section 192 can be generated, and the cantilever beam 191
A valve stem 903 is attached to the other end via a spring 196.
By converting the displacement into force and inputting it, a vibration output at a frequency related to the displacement of the valve stem 903 can be obtained. The signal processing circuit 195 has a function of converting the oscillation frequency into a voltage signal Vf.

The displacement-electrical signal converter 21 has a magnet 211 fixed to a stem 801 that is linked to a valve of the pilot relay 8, and a magnetoresistive element 21 facing the magnet 211.
2, 213 are arranged in a non-contact manner, and magnetoresistive elements 212, 213 and resistors 214, 2
15 constitutes each side of the bridge circuit, one end of the magnetoresistive element 212 and the resistor 214, and one end of the magnetoresistive element 2
13 and one end of the resistor 215 are each connected to a constant voltage Eb.
is applied, which causes the magnetoresistive elements 212 and 2
A deviation voltage Vd corresponding to the displacement x is obtained at the other end of the resistor 13 and the other ends of the resistors 214 and 215. FIG. 2 shows the relationship between the displacement x and the corresponding deviation voltage Vd. This deviation voltage Vd is subtracted by the deviation voltage Vd corresponding to the midpoint in FIG. 2 in an amplifier 216, and is negatively fed back to the output Vo of the differential amplifier 17 as a voltage signal Vp.

Note that a Hall element or the like may be used instead of the magnetoresistive element as the non-contact magnetic sensor.

This feedback loop is intended to improve the stability of the system, and can eliminate instability factors caused by valve capacities, component constants, etc.

This displacement-to-electrical signal converter 21 can be realized with a device having lower precision than 19.

The driving power source for the amplifier, displacement-electrical signal converter, etc. can use the constant voltage Eb obtained from the Zener diode 161 of the input processing means.
Does not require special power supply.

Reference numeral 22 designates a pressure-resistant explosion-proof container, which houses input processing means 16, actuator means 18, and displacement/electrical signal conversion means 19, 21, as shown by the two-dot chain line in FIG. That is, as shown in FIG. 3, the magnet 211 and the magnetic resistance 212 of the displacement/electric signal conversion means 21,
The wall of the container 22 is arranged between the container 213 and the container 213 .
In this way, since the electrical components are housed in a sealed, pressure-resistant, explosion-proof container that does not have an explosion-proof gap by using a non-contact magnetic sensor, a device with good flame-proof and explosion-proof characteristics can be obtained.

FIG. 4 shows the configuration shown in FIG. 1 as a block diagram to make it easier to understand.

FIG. 5 shows an embodiment of a system balanced by digital signals. The voltage signal Vi is converted into a digital signal Di by the analog-to-digital converter 28 and input to the microcomputer 30. On the other hand, the displacement-electrical signal converter 19' directly outputs a vibration frequency signal F related to displacement, and by counting clocks in the period counter 29, a digital feedback signal Df corresponding to the vibration period is generated.
is input into the microcomputer 30 as follows.

The deviation between these digital signals Di and Df is processed within this microcomputer 30, and the operation output Dm is transmitted as a digital signal. This operation output Dm is output from the digital-to-analog converter 31
The voltage signal Vo is converted into a voltage signal Vo, which is subtracted from a feedback signal Vp related to the stem displacement x of the pilot relay 8, and is input to an amplifier 17 that drives an actuator 18.

When the output of the displacement-electrical signal converter 19' is a frequency output, it is easy to realize a balanced system using such a digital signal, and by introducing the microcomputer 30, it is possible to calculate the relationship between the input signal and the valve stem displacement. It is also easy to perform calculations on specific functional relationships.

The embodiment shown in FIG. 6 shows a configuration in which system balance is achieved by phase comparison of frequency signals. 32 is a voltage-frequency converter that converts the voltage signal Vi into a frequency signal ω ₁ , and 33 is a phase comparison detector that outputs frequency signals ω ₂ and ω ₁ of the displacement-voltage converter 19' related to the displacement of the valve stem. A signal φ related to the phase difference is calculated, and the signal φ is converted into a voltage signal Vo and output.

The difference between this output Vo and the feedback signal Vp related to the stem displacement x of the pilot relay 8 is input to the amplifier 17.

As the phase comparison detector 33, it is possible to use a commercially available PLLIC.

This embodiment is also effective when the means for detecting displacement of the valve stem outputs a frequency signal.

(Effects of the invention) As described above in detail with the embodiments, according to the invention, the system does not rely on mechanical force balance like conventional positioners, but is balanced by electrical signals, so levers and Since mechanical parts such as bearings are reduced and a high-precision, large-sized torque motor is not required, it is possible to realize a positioner that is small, inexpensive, easy to assemble, and has improved hysteresis characteristics and earthquake resistance.

In particular, since the displacement caused by the slight force of the stem linked to the valve of the pilot relay is detected in a non-contact manner, an electro-pneumatic positioner with good response and frequency characteristics can be realized.

Therefore, the electrical components can be housed in a sealed flameproof explosion-proof container without creating an explosion-proof gap by using a non-contact magnetic sensor. There is no difficulty in machining or assembling an explosion-proof gap, and an inexpensive explosion-proof electro-pneumatic positioner with good flameproof characteristics can be obtained with a simple structure.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention;
Figure 3 is a characteristic diagram showing the characteristics of the main parts, Figure 3 is an explanatory diagram of the configuration of the main parts of Figure 1, Figure 4 is a block diagram of the configuration shown in Figure 1, Figure 5 is the second diagram of the present invention. FIG. 6 is a block diagram showing a third embodiment of the present invention, and FIG. 7 is a block diagram showing the structure of a conventional electro-pneumatic positioner. 1, 1'...Input terminal, 2...Torque motor,
3... Lever, 6... Nozzle, 8... Pilot relay, 9... Diaphragm valve, 16... Input processing means, 17... Differential amplifier, 18... Actuator, 19, 19', 21... Displacement - Electrical signal converter, 22... Flameproof explosion-proof container, 30... Microcomputer.

Claims (1)

[Scope of utility model registration request] In a pressure-resistant explosion-proof electro-pneumatic positioner for controlling the stem position of a valve driven by pneumatic pressure in accordance with an input current, an input processing means for converting the input current into a voltage signal or a digital signal;
Actuator means controls a flapper of a pilot relay that drives the valve based on the difference between the output of the input processing means and a feedback signal, and a non-contact magnetic sensor converts stem displacement linked to the valve of the pilot relay into an electrical signal. first displacement/electrical signal converting means for converting and feeding back to the input side of the actuator means; and inputting the stem displacement of the valve to obtain the feedback signal in the form of a voltage signal or a digital signal. The second displacement/electrical signal converting means, the input processing means, the actuator means, the first displacement/electrical signal converting means, and the second displacement/electrical signal converting means are incorporated, and no explosion-proof gap is provided. A pressure-proof explosion-proof electro-pneumatic positioner equipped with a sealed pressure-proof explosion-proof container.