JPH0447161B2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to improvements in electropneumatic positioners.

<Prior Art> An example of the prior art will be explained with reference to the configuration diagram in FIG. 6 and the block diagram in FIG. 7.

Reference numerals 1 and 1' denote input terminals that receive a current output I _p from an operating means such as a controller as an input signal, and 2 is a torque motor to which an input current I _p is applied to a coil 201 . 3 is a lever driven by a torque motor,
It is regulated to a reference position by springs 4 and 5, and one end 301 is driven as a flapper in the direction of arrow A by input current. A nozzle 6 is arranged opposite to this flapper, and its back pressure P _b increases.

7 is a throttle for the supply air source PS, which supplies air ejected from the nozzle. 8 is nozzle back pressure P _b
A pilot relay that amplifies its air pressure output.
P _p is guided into the air chamber 901 of the diaphragm valve 9 and drives the valve stem 903 in the direction of arrow B against the spring 902.

This displacement of the valve stem is transmitted to the lever 10 via the clamp 904 and clamp pin 905, and the shaft 11 is rotationally driven in the direction of arrow C by this lever. This shaft has 1 lever
2 are interlocked, and the rotational movement of this lever drives the lever 14 in the direction of arrow D via the range adjuster mechanism 13.

The lever 14 and the other end 302 of the leaf spring 3 are connected by a spring 15. Due to the displacement of the lever 14 in the D direction, the spring 15 is displaced in the direction of the arrow E, and due to this force, the input current I _p The system is balanced by acting to pull back the displacement of the leaf spring 3 in the A direction.

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

FIG. 7 shows such a system in the form of a block diagram.

<Problems to be solved by the invention> In an electropneumatic positioner using such a force balance meter,
A high-precision torque motor that converts input current into force is required, and a mechanism that converts valve stem displacement into a force feedback signal is also required, and both are mechanical components that tend to be relatively large. Since the coupling mechanism is also mechanical, it has the disadvantage of being complicated in structure and high in cost.

Additionally, due to the response delay due to the valve capacity and the constants of the mechanical elements of the feedback mechanism, there is a delay in the response of the actuator that controls the flapper.
The disadvantage is that the system tends to become unstable.

The present invention aims to solve these problems and provide an electro-pneumatic positioner that is small, inexpensive, and has excellent stability.

<Means for Solving the Problems> The structural feature of the present invention is that, in an electro-pneumatic positioner for controlling the stem position of a valve driven by pneumatic pressure in accordance with an input current, the input current is converted into a voltage signal. Alternatively, it has a signal conversion circuit that converts it into a digital signal and a constant voltage circuit that is connected in series to this signal conversion circuit and creates a constant voltage using the input current, and the constant voltage is applied to the electric circuit used in this electro-pneumatic positioner. An input processing means is used as a power supply voltage, and an amplifier calculates the difference between the output of the input processing means energized by the power supply voltage and a feedback signal, and based on this, a flapper of a pilot relay that drives the valve is controlled. an actuator means; a displacement-to-electrical signal converting means that converts a stem displacement energized by the power supply voltage and interlocks with the valve of the pilot relay into an electric signal and feeds it back to the input side of the actuator; and energized by the power supply voltage. and a displacement-to-electrical signal conversion means for inputting the stem displacement of the valve and obtaining the feedback signal in the form of a voltage signal or a digital signal.

<Operation> According to the present invention, the input current is converted into a voltage signal or a digital signal by the input processing means, and the pilot relay is controlled based on the difference from the feedback signal given by the voltage signal or digital signal. The output drives the valve. The displacement of the valve stem is converted into a voltage or digital feedback signal by the displacement-electrical signal converting means to balance the output of the input processing means, and the displacement of the stem interlocked with the valve of the pilot relay is converted into an electric signal. It is fed back to the input side of the actuator and balanced with the actuator drive signal.

<Example> An example of the present invention will be described with reference to FIGS. 1 to 5. 1 and 2 show a block diagram and block line of an embodiment for converting input current into a voltage signal,
Elements that are the same as those in FIG. 6 are given the same reference numerals and their explanations will be omitted.

16 is an input processing means, which converts the input current I _p into a voltage signal V _i . A differential amplifier 17 amplifies the difference between the voltage signal V _i and the feedback signal V _f .
The difference voltage V _c between the output of this amplifier and the feedback signal V _p related to the stem displacement of the pilot relay.
This drives the piezoelectric actuator 18 that displaces the flapper 3. The configuration from the nozzle 6 to the valve 9 via the pilot relay is the same as the conventional configuration.

The displacement of valve stem 903 is converted into a feedback signal V _f by displacement-to-electrical signal converter 19 . This transducer consists of a vibrating force sensor means and has a cantilever beam 19 fixed at one end.
A pair of piezoelectric elements 193 and 194 are arranged in one etched vibrating part 192, and the amplifier 197 and the two piezoelectric elements form a closed loop to generate self-oscillation at the natural frequency of the vibrating part 192. By converting the displacement of the valve stem 903 into force and inputting it to the other end of the cantilever via the spring 196, it is possible to obtain a vibration output at a frequency related to the displacement of the valve stem. The signal processing circuit 195 has a function of varying the oscillation frequency into a voltage signal V _f .

The displacement-electrical signal converter 20 is a converter having exactly the same configuration as the converter 19, and generates a voltage signal V _p related to the displacement of the stem 801 linked to the valve of the pilot relay 8, and outputs V of the differential amplifier. It has the function of giving negative feedback to _p . This feedback loop is intended to improve the stability of the system, and it is possible to eliminate unstable factors caused by valve capacities, component constants, etc.

This displacement-to-electrical signal converter 20 can be realized with a device having lower accuracy than 19.

The driving power source for the amplifier, displacement-electrical signal converter, etc. is the Zener diode 1601 of the input processing means.
It is possible to use the constant voltage E _b obtained from this method, and no special power source is required. In this case, the signal conversion circuit consisting of a potentiometer etc. and the constant voltage circuit consisting of a Zener diode etc. are connected in series, and their connection point (common potential point) and the other end of the constant voltage circuit are connected in series. Since the constant voltage E _b generated between is used as the power supply voltage of the circuit,
A constant voltage E _b is applied to the electric circuit that constitutes the electropneumatic positioner.
The return current of the current that is energized and flows through any part of this electric circuit returns to the common potential point.

Therefore, the signal conversion circuit connected in series with this constant voltage circuit has no input current, regardless of the power consumption in the electric circuit that constitutes the electropneumatic positioner.
All of I _p flows into the input processing means 16, and a voltage signal V _i , etc. that exactly corresponds to the input current I _p flows into the input processing means 16.
obtained from.

Figure 2 is a block diagram of the configuration shown in Figure 1. By comparing the voltage signal _Vi and the voltage feedback signal V _f , the system is balanced and the stem displacement of the pilot relay is adjusted to the input side of the actuator. It is characterized by the fact that the balance is realized by a double loop.

The means for realizing the displacement-electrical signal converters 19 and 20 can be applied such as a magnetostrictive potentiometer, a displacement magnetoresistive converter, or one that uses light or capacitance change. An example of implementation using .

The displacement signal of the valve stem 903 is transmitted by the expansion mechanism 21
The coil 22 is enlarged and coupled to the magnetostrictive wire 23 in a non-contact manner. 24 is a pulse generating means for supplying a pulse signal current from both ends of the magnetostrictive wire;
Reference numerals 5 and 26 denote pulse detection means provided at both outer ends, and an arithmetic circuit 27 processes the arrival time difference of the reflected pulses from the slider position to obtain a voltage signal V _f related to displacement as a feedback signal.

The actuator means for driving the flapper 3 may be configured to be driven by a moving coil or a moving iron piece means in addition to the piezoelectric element as in the embodiment.

FIG. 4 shows an embodiment of a system balanced by digital signals. The voltage signal V _i is analog/digital.
The signal is converted into a digital signal D _i by the 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 the period counter 2
By counting the clocks at step 9, the digital feedback signal _Df corresponding to the vibration period is inputted to the microcomputer 30.

The deviation between these digital signals D _i and D _f is processed within this microcomputer, and the operation output D _n is transmitted as a digital signal. This signal D _n
is converted into a voltage signal V _p by a digital-to-analog converter 31, subtracted from a feedback signal V _p related to the stem displacement of the pilot relay, and input to an amplifier 17 for driving the actuator 18.

When the output of the displacement-electrical signal converter is a frequency output, it is easy to realize a balanced system using such digital signals, and by introducing a microcomputer, the relationship between the input signal and valve stem displacement can be converted to a specific function. It is also easy to perform calculations on relationships.

The embodiment shown in FIG. 5 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 V _i into a frequency signal ω ₁ , and 33 is a phase comparison detector that detects the frequency signal outputs ω ₂ and ω of the displacement-voltage converter 19 ′ related to the displacement of the valve stem. ₁ and calculates a signal φ related to the phase difference, and converts it into a voltage signal V _p and outputs it.

The difference between this output V _p and a feedback signal V _p related to the stem displacement of the pilot relay is input to an 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 explained above, according to the present invention, all the circuit power necessary for the operation of the positioner is obtained from the input current, and at the same time, a signal is detected from this input current, and the detected signal is Since the equilibrium of the system is realized by an electric signal so that they match,
It is possible to realize a positioner with improved hysteresis characteristics and earthquake resistance while reducing the size of the electric circuit.

Furthermore, by employing double feedback, it is possible to realize a stable positioner that follows input signals well.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure is a block diagram, FIG. 3 is a block diagram showing another embodiment of the main part of the present invention, FIGS. 4 and 5 are block diagrams showing other embodiments of the present invention, and FIG. 6 is a block diagram showing another embodiment of the present invention. FIG. 7 is a block diagram showing an example of the prior art. 1, 1'...Input terminal, 3...Flapper, 8
...Pilot relay, 9...Valve, 903...
...Valve stem, 16... Input processing means, 17...
...Amplifier, 18...Actuator, 19,20
...Displacement-electrical signal converter.

Claims (1)

[Claims] 1. In an electro-pneumatic positioner for controlling the stem position of a valve driven by pneumatic pressure in accordance with an input current, a signal conversion circuit that converts the input current into a voltage signal or a digital signal is connected in series to this signal conversion circuit. and an input processing means for using the constant voltage as a power supply voltage of an electric circuit used in this electro-pneumatic positioner, and an input processing means that is energized by this power supply voltage. actuator means for calculating the difference between the output of the input processing means and the feedback signal using an amplifier and controlling the flapper of the pilot relay for driving the valve based on the difference; displacement-to-electrical signal converting means for converting the stem displacement of the valve into an electric signal and feeding it back to the input side of the actuator; An electropneumatic positioner comprising displacement-to-electrical signal conversion means for obtaining the feedback signal.