JP3156799B2 - Electro-pneumatic converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for transmitting a current signal, calculating a deviation between the current signal and a feedback signal and outputting a drive signal, and discharging air from a nozzle in response to the drive signal. An air pressure conversion means for converting a drive signal into a pneumatic signal, and a pressure-resistant explosion-proof container containing at least a pressure sensor for introducing an output pressure related to the pneumatic signal and converting the output pressure to a previous feedback signal. More particularly, the present invention relates to an electropneumatic converter improved so as to maintain a predetermined accuracy and eliminate corrosive gas entering from the outside.

[0002]

2. Description of the Related Art FIG. 2 is a configuration diagram showing an outline of the configuration of a conventional electropneumatic converter. Reference numeral 10 denotes an explosion-proof container, in which a control circuit 11 and a torque motor 1 are provided.
2, a pressure sensor 13 and the like are housed, and a pilot relay 14 is arranged outside the explosion-proof container.

[0003] The control circuit input terminal T ₁ to 11, a current signal 4~20mA of, for example, controllers via the T ₂ I _i
And a feedback signal _Vf is input from the pressure sensor 13. Then, the control circuit 11 outputs the current signal I _i
Is converted into a voltage signal Vi, a deviation between the voltage signal Vi and the feedback signal _Vf is calculated, and a drive signal _Id is output to an output terminal thereof.

[0004] The drive signal I _d is Torukumo - data 12 of beam - are output to Biingu coil 15 to generate a magnetic field to displace the flapper 16 of the magnetic member by the magnetic field. The flapper 16 is provided with a nozzle 17 opposed thereto, and is supplied with a supply pressure Ps via a throttle 18. The torque motor 12 and the nozzle 17 constitute air pressure converting means.

[0005] The nozzle back pressure Pb generated in the nozzle 17 is
The supply pressure Ps is amplified by the pilot relay 14 supplied via the pipe 19 and is output to the measurement chamber side of the pressure sensor 13 via the pipe 20 as the output pressure P0. The reference chamber side of the pressure sensor 13 is opened to the outside of the explosion-proof container 10 via a pipe 21 to provide a reference pressure Pr.

Further, the explosion-proof container 10 is provided with a breather 22 for discharging air discharged from the nozzle 17 to the outside. The breather 22 has a gap and a gap depth based on explosion-proof guidelines.

[0007] With the above arrangement, the control circuit 11 a drive signal I _d as the feedback signal V _f satisfies corresponds to the current signal I _i Torukumo - Change the nozzle back pressure Pb and outputs the data 12,
An output pressure P ₀ corresponding to the nozzle back pressure Pb is output from the pipe 20.

[0008]

However, since the electric circuit portion of the conventional electro-pneumatic converter as described above is housed in a pressure-resistant explosion-proof container, the air discharged from the nozzle 17 is supplied to the outside of the container. Although a breather 22 is provided for escape, the breather has a narrow gap based on explosion-proof guidelines so that the flame of the explosion inside the container does not leak to the outside and ignite the external explosive gas atmosphere. Therefore, it becomes a resistance element as an air circuit.

For this reason, in the operation state of the electropneumatic converter, the pressure inside the explosion-proof container becomes higher than the atmospheric pressure due to the air discharged from the nozzle 17, and the internal pressure increases due to a change in the flow rate of the discharged air. Change. Therefore, the pressure sensor 1
The pipe 21 on the side of the reference chamber 3 is opened to the outside through an explosion-proof skirt without being opened inside the pressure-resistant explosion-proof container, so that the reference pressure does not change.

However, with such a configuration, for example, when the electropneumatic converter is installed in an atmosphere of corrosive gas such as an outdoor coastline or a chemical plant, the reference chamber side of the pressure sensor is directly at atmospheric pressure. Since the pressure sensor is opened, there is a problem that the pressure sensor comes into contact with the corrosive gas to cause corrosion and cause an accident.

A control circuit for transmitting a current signal, calculating a deviation between the current signal and the feedback signal and outputting a drive signal, and converting the drive signal to an air pressure signal while discharging air from a nozzle corresponding to the drive signal. An electro-pneumatic converter, comprising: a pressure-resistant explosion-proof container in which at least a pneumatic pressure converting means for converting and an output pressure related to the pneumatic signal are introduced and a pressure sensor for converting the output pressure into the feedback signal are housed. An external chamber provided outside the pressure-resistant explosion-proof container and having a communication hole communicating with the atmospheric pressure, and the pressure-resistant bleeding air discharged from the nozzle to the external chamber via an explosion-proof ski or a flame arrester conforming to the explosion-proof guidelines. The bleed hole provided in the explosion-proof container, the reference pressure chamber of the pressure sensor, and the external chamber are connected to the external chamber via an explosion-proof ski or a flame arrester. ; And a reference pressure introduction hole formed in the Flameproof爆容unit leading, the pressure of the outside air chamber
Higher than atmospheric pressure, affecting the output of the electropneumatic converter
The communication hole is formed in such a size that the pressure is not enough.
It was done.

[0012]

[Operation] A current signal is transmitted to the control circuit, and a deviation between the current signal and the feedback signal is calculated to output a drive signal.
The air pressure conversion means converts the previous drive signal into an air pressure signal while discharging air from the nozzle in response to the drive signal. The pressure sensor receives an output pressure associated with the pneumatic signal and converts the output pressure to a previous feedback signal. The outer chamber is provided outside the pressure-resistant explosion-proof container in which at least the control circuit, the air pressure converter, and the pressure sensor are housed, and communicates with the atmospheric pressure through the communication hole.

The bleed hole is provided in the pressure-resistant explosion-proof container and bleeds the air discharged from the nozzle through the explosion-proof ski or the frame arrestor conforming to the explosion-proof guide to the external chamber. The reference pressure introducing hole bridges the reference pressure chamber of the pressure sensor and the outer chamber to the outer chamber via an explosion-proof ski or a frame arrestor.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of one embodiment of the present invention. Parts having the same functions as those of the conventional electropneumatic converter shown in FIG. 2 are denoted by the same reference numerals, and the description thereof will be appropriately omitted.

In the explosion-proof container 23, the printed board 2
4 mounted on the side wall of the explosion-proof container 23.
Mechikkushi - Le like control circuit 11 to which the current signal I _i is introduced by the transmission line via a Torukumo changing the drive signal the displacement - motor 12, such as a pressure sensor 13 for converting the output pressure into an electric signal are housed . Projection chambers 25 and 26 projecting to the outside are formed on one side wall of the pressure-resistant explosion-proof container 23, and the projection chamber 25 is a bridge that discharges internal air to the outside.
In the projection chamber 26, a reference pressure introducing hole 28 for introducing an external reference pressure Pr is formed.

The bleed hole 27 and the reference pressure introducing hole 28 are covered with an outer chamber 29 covering the bleed hole 27 and the reference pressure introducing hole 28. The outer chamber 29 has a communication hole 30 communicating with the outside atmosphere. ing. Further, on the side wall of the explosion-proof container 23 opposite to the outer chamber 29, a projecting chamber 31 projecting to the outside,
32 is formed, and the nozzle back pressure hole 33A for outputting a nozzle back pressure Pb of the nozzle 17, the protruding chamber 32 and an output pressure hole 33B to derive the output pressure P ₀ are respectively formed in the projecting chamber 31 .

The projecting chambers 25, 26, 31, and 32 each have a through hole formed in the center of the lid portion, and cover the through hole with a cylindrical arrestor having a flame-extinguishing function satisfying an explosion-proof standard. 34, 35, 36 and 37 are arranged respectively. It is a matter of course that a structure having an explosion-proof ski and a depth satisfying the explosion-proof standard may be used instead of the frame arrester.

The plug 35 is connected to a reference pressure chamber 39 of the pressure sensor 13 fixed to the printed board 24 via a pipe 38. The output pressure chamber 40 side of the pressure sensor 13 is connected to the inside of the plug 37 via a pipe 41. The pressure sensor 13 outputs to the control circuit 11 mounted to the feedback signal V _f corresponding to the output pressure P ₀ to the printed board 24.

The nozzle 17 is connected to a plug 36 through a pipe 42.
Connected to the nozzle back pressure hole 33A via the throttle 18.
The supply pressure Ps is applied, and the nozzle back pressure Pb from the nozzle 17 is obtained. The nozzle back pressure Pb is amplified by the pilot relay 14 to which the supply pressure Ps is supplied, and is amplified by the output pressure P0.
Is supplied to the plug 37 via the pipe 43 and is output to the outside via the pipe 44.

The operation of the signal system of the electropneumatic converter thus configured is basically the same as the circuit shown in FIG. Next, an output error generated by the electropneumatic converter configured as described above will be described. Assuming that the radius of the communication hole 30 is r and the length of the communication hole is L, the relationship between the air flow rate Q passing through the communication hole 30 and the differential pressure ΔP between the external chamber 29 and the atmospheric pressure Pr is expressed by the following equation. Can be manifested.

ΔP = 9.8 × 10 ⁵ xπxr ⁴ xΔP / 8ηL where ΔP (Kgf / cm ² ), r (cm), L (cm),
Q (cm ³ / s), η (viscosity coefficient of air) = 1.82 × 1
0 ^-4 p (20 ° C.). Since the flow rate of the air flowing out of the nozzle 17 is usually about 2 liters / min, r =
If 0.1 and L = 0.3, then ΔP = 4.7 × 10 ⁻⁵ . That is, the outer chamber 29 is 4.7x higher than the atmospheric pressure.
The pressure increases by 10 ⁻⁵ (Kgf / cm ² ).

Therefore, when the nozzle 17 is completely closed and the air flow rate Q becomes 0 and ΔP = 0, the error ε generated in the pressure sensor 13 due to the change in the pressure of the reference pressure chamber 39 is reduced by the electric current. the span of the output pressure P ₀ of the pneumatic transducer e.g. ^{0.8Kgf / cm 2 (0.2~1.0Kgf / cm} 2)
Then, ε = 407 × 10 ⁻⁵ × 100 / 0.8 = 0.005% error, which is a negligible value.

[0023]

As described above, according to the present invention, the bleed hole 27 and the reference pressure introducing hole 2 are provided.
8 is covered with an external chamber 29. In the external chamber 29, a communication hole 30 communicating with the outside atmosphere is provided.
Large enough not to affect the output of the electro-pneumatic converter
As a result, the outer chamber 29 can be maintained at a high pressure with respect to the atmospheric pressure. Therefore, the invasion of corrosive gas from the outside can be prevented. The reliability is improved without touching. Further, since the sufficiently smaller than the output pressure of the rise is electropneumatic transducer for atmospheric pressure external chamber 29, the external chamber 2
The error of the pressure sensor due to the change in the pressure of No. 9 can also be ignored.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of one embodiment of the present invention.

FIG. 2 is a configuration diagram showing a configuration of a conventional electropneumatic converter.

[Explanation of symbols]

 10, 23 Explosion-proof container 11 Control circuit 12 Torque motor 13 Pressure sensor 14 Pilot relay 17 Nozzle 25, 26, 31, 32 Projection chamber 27 Bleed hole 28 Reference pressure introduction hole 29 External chamber 30 Communication hole

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Minoru Midorikawa 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Corporation (72) Inventor Yasuo Kasahara 2-9-132 Nakamachi, Musashino-shi, Tokyo Next to (72) Inventor Akira Inoue 2-9-132 Nakamachi, Musashino City, Tokyo Yokogawa Electric Corporation (72) Inventor Hiroshi Hayashi 2-9-132 Nakamachi, Musashino City, Tokyo Yokogawa Electric Examiner in the corporation Taketo Sato (56) References JP-A-50-28884 (JP, A) Japanese Utility Model Application No. 2-9909 (JP, U) Japanese Utility Model Application No. 3-61546 (JP, U) Japanese Utility Model Application No. 2 -7540 (JP, U) JP-A-61-1810 (JP, U) JP 2-41892 (JP, Y2) (58) Fields investigated (Int. Cl. ⁷ , DB name) F15B 5/00 G01D 5/42

Claims (1)

(57) [Claims] 1. A control circuit for transmitting a current signal, calculating a deviation between the current signal and a feedback signal, and outputting a drive signal. The control circuit outputs air pressure from a nozzle while discharging air from a nozzle corresponding to the drive signal. An electro-pneumatic converter comprising: a pressure-resistant explosion-proof container in which at least a pneumatic pressure converting means for converting the pressure into a signal and an output pressure related to the pneumatic signal are introduced and a pressure sensor for converting the output pressure into the feedback signal are housed. Bleeding the air discharged from the nozzle into the external chamber via an explosion-proof ski or a flame arrestor conforming to the explosion-proof guidelines, and an external chamber provided outside the pressure-resistant explosion-proof container and having a communication hole communicating with atmospheric pressure. A bleed hole provided in the pressure-resistant explosion-proof container, a reference pressure chamber of the pressure sensor and the external chamber are connected to the external chamber via an explosion-proof ski or a frame arrestor. A reference pressure introduction hole provided in the explosion-proof container to bleed, and the pressure of the outside air chamber is
Higher than atmospheric pressure, affecting the output of the electropneumatic converter
The communication hole is formed in such a size that the pressure is not enough.
Pneumatic transducer collector, characterized in that the.