JPH0458041B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a pulse pneumatic transducer used for process control and the like.

(b) Prior art As shown in Figure 1, a conventional pulse pneumatic converter converts an up pulse signal or a down pulse signal sent from a voltage pulse converter (not shown) in the control room into a pulse motor drive circuit. 1 is amplified and added to pulse motor 2, pulse motor 2
is moved in steps to displace the nozzle flapper 8 via the gears 3, 4, 5, 6 and the spring 7, and the gap between the nozzle flapper 8 and the nozzle 9 is controlled, and the output air pressure according to the input pulse signal is derived from the booster relay 10. There is something that I tried to do. In addition, this pulse air pressure converter detects the position of the pulse motor 2 via gears 4 and 11 with a potentiometer 12, and detects the position of the pulse motor 2 with a resistor-electrical signal converter 13.
The answer back signal is fed back to the control room via the This type of pulse pneumatic pressure converter has the advantage of being able to maintain the pneumatic signal in the state before the power outage during a power outage, but because it uses many mechanical moving parts such as pulse motors, potentiometers, and gears, The disadvantage was that the parts suffered severe wear and tear and had a short lifespan.

In order to overcome this drawback, a pulse pneumatic transducer has been proposed in which a piezoelectric element flapper such as a bimorph is used as a movable part, and the other parts are constructed of electronic circuits. However, devices using bimorphs cannot maintain output during power outages, so they must be battery-powered and backed up. However, if all the circuit parts are backed up with batteries during a power outage, the power consumption will be large and the batteries will have to be replaced immediately.

(c) Purpose In view of the above, an object of the present invention is to provide a pulse pneumatic pressure converter that has a long life, can maintain output pneumatic pressure even during a power outage, is miniaturized, and can prolong backup time.

(D) Configuration In order to achieve the above object, this invention uses a piezoelectric element flapper in an electro-pneumatic converter, divides the power supply into two systems, and uses only the circuit related to the piezoelectric element flapper that needs to be maintained during a power outage. I try to back up. That is, the pulse pneumatic transducer of the present invention comprises an electropneumatic transducer consisting of a piezoelectric element flapper and a nozzle that are displaced according to an applied voltage, a pilot valve that receives supply air pressure and supplies it to the nozzle and derives an output air pressure, and the pilot valve. A pneumatic converter that converts the output air pressure from the valve into an electrical signal, a counter that receives an input pulse signal and integrates it, and a D/A that converts the integrated output of this counter into an analog signal.
an input electric circuit comprising a converter and a comparator that receives and compares the output of the D/A converter and the output of the pneumatic converter, and applies a DC voltage to the piezoelectric element flapper to control the nozzle back pressure; and the pneumatic converter. an answer back circuit that derives the output of the device;
A first power supply circuit that supplies power supply voltage to circuits that do not require maintenance during a power outage, such as this answer back circuit; a second power supply circuit that supplies power supply voltage to the input electric circuit and the air converter; It consists of a battery that backs up two power supply circuits.

(E) Examples The present invention will be explained in more detail below with reference to Examples.

FIG. 2 is a block diagram of a pulse pneumatic transducer showing one embodiment of the present invention. In the same figure,
21 is a photocoupler, and this photocoupler 21 performs electrical isolation and waveform shaping of an up pulse signal or a down pulse signal according to an input voltage from a control room (not shown). Reference numeral 22 denotes an up/down counter that receives an up pulse signal or a down pulse signal and integrates it. The output of this up-down counter 22 is applied to a D/A converter 23 and converted into an analog value.
It is adapted to be applied to the plus (+) input terminal of the comparator 24. The output of the comparator 24 is amplified by a transistor 25 and applied to a piezoelectric element (bimorph) flapper 26, for example. One end of the piezoelectric element flapper 26 is supported by a fixed part 27, and a nozzle 28 is arranged at the other end, and the tip is displaced according to the applied voltage, changing the gap between the tip and the nozzle 28. , to change the nozzle back pressure.

29 receives the supply air pressure and directs it to the nozzle 28
This is a pilot valve that derives the output air pressure according to the back pressure. The output air pressure derived from the pilot valve 29 is converted into a signal voltage by a pneumatic converter 32 consisting of a pressure sensor 30 and a signal amplifier 31, and is applied to the negative (-) input terminal of the comparator 24. . Further, the output signal voltage of the pneumatic converter 32 is converted into a current signal Io by a voltage/current conversion circuit 35 (answer back signal circuit) consisting of an IC 33 and a transistor 34, and is fed back as an answer back signal.

36 is a DC voltage source provided externally;
DC 24V is supplied from this DC voltage source 36.
This DC voltage source 36 is usually formed by rectifying an AC voltage. The DC voltage source 36 may be built into the meter (pulse air pressure converter) using a battery, but in order to obtain 24V DC, several batteries must be used in series, so it is difficult to build it into a small device. Therefore, it is installed externally as described above.

The 24V DC from the DC voltage source 36 is applied to the first DC-
It is converted to a low voltage comparable to the battery voltage by a DC converter 37, and is connected to a battery 38 via diodes d1 and d2. first
The low voltage output from the DC-DC converter 37 or the voltage of the battery 38 is input to a second DC-DC converter 39 and converted to approximately 24V DC. The output voltage V2 (high voltage) of this second DC-DC converter 39 maintains the output air pressure through an input electric circuit including an up-down counter 22, a D/A converter 23, a comparator 24, etc., a pneumatic converter 32, etc. It is designed to be supplied only to the minimum necessary circuit elements to achieve this. On the other hand, the output voltage V1 (low voltage) of the first DC-DC converter 37 is supplied to circuits that are not particularly necessary for maintaining the output air pressure, such as the photocoupler 21 and the IC 33 of the voltage/current converter 35. It's summery. Note that the power supply voltage of the transistor 34 requires a high V level voltage due to the output load resistance (usually 0 to 800Ω), so the second
An output voltage V2 of the DC-DC converter 39 is provided.

In the pulse pneumatic converter configured as described above, when 24V DC is supplied from the DC voltage source 36, a predetermined power supply voltage is supplied to each circuit section, so an up pulse signal or a down pulse signal is transmitted through the photocoupler 21. are added, the up-down counter 22 integrates these pulse signals. This integration result is converted into an analog value by the D/A converter 23 and input to the comparator 24. Therefore, if the input voltage is large and many up pulses are transmitted,
The integrated value of the up-down counter 22 also becomes large,
When the analog output value of the D/A converter 23 becomes large and, conversely, the input signal becomes small, the analog output value of the D/A converter 23 also becomes small.

The analog output value of the D/A converter 23 is compared with a signal voltage corresponding to the output air pressure from the pneumatic converter 32 by a comparator 24. As the output air pressure at that point is small and the input voltage is large, the output signal of the comparator 24 becomes large, and a large DC voltage is applied to the piezoelectric flapper 26 via the transistor 25, displacing the tip of the piezoelectric flapper 26 to a large extent. , narrows the gap with nozzle 28, increases nozzle back pressure, and increases output air pressure. As the output air pressure increases, the pneumatic converter 32
Since the output signal voltage of comparator 2 becomes large,
4 becomes smaller, the degree of displacement of the piezoelectric element flapper 26 becomes smaller, and eventually the gap between the piezoelectric element flapper 26 and the nozzle 28, which derives the output air pressure corresponding to the input voltage, balances out.

Conversely, when the input voltage is smaller than the output signal voltage of the pneumatic converter 32, the piezoelectric element flapper 26 is displaced in the direction in which the gap between the piezoelectric element flapper 26 and the nozzle 28 opens, and the nozzle back pressure becomes smaller. The output signal voltage of the pneumatic converter 32 is reduced and balanced.

Also, the output signal voltage of the pneumatic converter 32 is IC33
and drives the transistor 34. As a result, the output signal voltage is converted to a current Io, and an answer back signal corresponding to the output air pressure is fed back to the control room side.

When a power outage occurs in the AC power supply and the DC voltage is no longer input to the first DC-DC converter from the DC voltage source 36, its output voltage V1 becomes 0, and power supply voltage is no longer supplied to the photocoupler 21, IC 33, etc. . Therefore, the transistor 34 is no longer driven by the IC 33, and even if the output voltage V2 of the second DC-DC converter 39 is applied to the transistor 34, the current Io does not flow, and the power consumption in this part is 0. Become.

On the other hand, due to a power outage, no voltage is input from the first DC-DC converter 37 to the second DC-DC converter 39, but the voltage from the battery 38 is input instead and backed up. The second DC-DC converter 39 derives an output voltage V2. Therefore, the up-down counter 22, the D/A converter 23 and the comparison circuit 2
4. Furthermore, the power supply voltage is supplied to the pneumatic converter 32 to maintain the circuit function. Therefore, the piezoelectric element flapper 26 maintains the displacement corresponding to the input voltage at the time of the power outage, and the output air pressure also maintains the value at the time of the power outage.

(F) Effects According to the pulse pneumatic transducer of the present invention, since the only movable part is the piezoelectric element flapper, there is almost no mechanical wear and tear, so that a long life can be obtained. In addition, since the circuits that need to maintain the output air pressure are backed up by batteries, the current output air pressure can be maintained even in the event of a power outage.Furthermore, the circuits that are not required to maintain the output air pressure are not backed up by batteries, so they can be backed up by batteries. It is possible to minimize power consumption and extend backup time.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional pulse pneumatic pressure converter, and FIG. 2 is a block diagram of a pulse pneumatic pressure converter showing an embodiment of the present invention. 22...Up-down counter, 23...D/
A converter, 24... Comparator, 26...
Piezoelectric element flapper, 28... Nozzle, 29... Pilot valve, 32... Pneumatic converter, 35... Voltage/current conversion circuit, 37... First DC-DC converter, 38... Battery, 39... …Second DC
-DC converter.

Claims (1)

[Claims] 1. An electro-pneumatic converter consisting of a piezoelectric flapper and a nozzle that are displaced according to applied voltage, a pilot valve that receives supply air pressure and supplies it to the nozzle to derive output air pressure, and converts the output air pressure from the pilot valve into an electrical signal. A pneumatic converter for converting, a counter for receiving and integrating an input pulse signal, a D/A converter for converting the integrated output of this counter into an analog signal, and a D/A converter for receiving the output of the D/A converter and the output of the pneumatic converter. An input electric circuit consisting of a comparator that applies a DC voltage to the piezoelectric element flapper to control the nozzle back pressure, an answer back circuit that derives the output of the pneumatic converter, and this answer back circuit, etc., are maintained during a power outage. a first power supply circuit that supplies power supply voltage to circuits that do not require
A pulse pneumatic converter comprising a second power supply circuit that supplies power voltage to the input electric circuit and the pneumatic converter, and a battery that backs up the second power supply circuit.