JPH03242515A - Differential pressure transmitting apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to improvements in differential pressure transmission devices used in various industrial measurements.

(Prior Art) As is well known, this type of differential pressure transmission device is used, for example, to measure the flow rate of fluid flowing in a pipe via the differential pressure between the ends of an orifice provided in the middle of the pipe.

FIG. 3 is a diagram showing a conventional example of this type of differential pressure transmission device. In this example, a piping resistor 2 such as an orifice or a Henchley tube is installed in the middle of a piping 1, and the flow rate in the piping is determined via the differential pressure between its ends.

As shown in the figure, this differential pressure transmission device 3 includes a manual three-way valve 300 for introducing the target pressure difference, and converts the introduced pressure difference into a current signal and sends it to the transmission line 4. It is composed of a differential pressure transmitter 350.

The manual three-way valve 3 includes two pressure introduction passages 301 and 302 that introduce a pressure difference between two locations to be measured, and a bypass passage 303 that communicates between these pressure introduction passages.
A first state in which the bypass passage 303 is closed and the two pressure introduction passages 301, 302 are opened; and a first state in which the bypass passage 303 is opened and the two pressure introduction passages 301, 302 are opened.
It is now possible to take the second state of closing.

In addition, in the figure, 304, 305.306 are passages 301.3
02.303 are manual valves that open and close respectively.

The differential pressure transmitter 350 also includes a sensor (not shown) that converts the pressure difference introduced via the three-way valve 300 into an electrical signal, and a sensor that converts the detected value of the sensor into an electrical signal based on preset zero point compensation data. and a variable current type constant current circuit that converts the detected value after the zero point compensation into a current and sends it to the transmission line 4.

When performing differential pressure measurement, the three-way valve 3°O is
Condition 1! ! (Valves 304, 305 open, stop valve 306 closed). However, when resetting the zero point compensation data (in the case of zero point adjustment), the three-way valve 300 is set to the second state (valve 304, 306 closed). 305 closed and valve 306 open).

However, in such conventional differential pressure transmission devices, the three-way valve was operated manually, so in order to adjust the zero point, each time I went to the location where the three-way valve 300 was installed and opened and closed the valve. There is a problem in that the differential pressure transmitter 350 cannot be used at all because an abnormal signal is output to the transmission line 4 during zero point adjustment.

(Problem to be Solved by the Invention) As described above, in the conventional differential pressure transmission device, a manual three-way valve was used, so the three-way valve 300 was operated each time for zero point adjustment. The differential pressure transmitter 350 cannot be used at all because it is necessary to go to the installation site and open and close the valve, and because an abnormal signal is output to the transmission line 4 during zero point adjustment. There was a problem.

This invention was made in view of the above problems,
The purpose is to provide a differential pressure transmission device that can perform zero point adjustment without having to travel to the location where the three-way valve is installed, and can be used continuously even during zero point adjustment. .

[Structure of the invention]

(Means for Solving the Problem) In order to achieve the above object, the present invention includes two pressure introduction passages that introduce a pressure difference between two locations to be measured;
a bypass passage that communicates between the pressure introduction passages; a first state in which the bypass passage is closed and the two pressure introduction passages are opened; and a first state in which the bypass passage is opened and the two pressure introduction passages are opened; A three-way valve that can take a closed second state, a sensor that converts the pressure difference introduced through the three-way valve into an electrical signal, and zero point compensation data that is set in advance based on the detected value of the sensor. and a differential pressure transmitter equipped with a variable current type constant current circuit that converts the detected value after the zero point compensation into a current and sends it to the transmission line, In the differential pressure transmission device, the differential pressure is measured by setting the branch valve in a first state, and the zero point compensation data is reset by setting the branch valve in a second state. A solenoid valve that can selectively set the first and second states is used as the branch valve, and the coil of the solenoid valve is inserted in series with the transmission line, and the coil of the solenoid valve is inserted between the terminals of the coil of the solenoid valve. can be short-circuited by a switch, and in the differential pressure transmitter, the switch is set to a predetermined state and the solenoid valve is set to the first state when the differential pressure is being measured, and the solenoid valve is set to the first state when the differential pressure is being measured. The present invention is characterized in that the switch is set to an inverted state, the solenoid valve is set to a second state, and the output current value immediately before the start of zero point adjustment is held in the constant current circuit.

In addition, the zero point adjustment state is determined by a regular interrupt by a timer,
Alternatively, it is preferable that the device be activated by an external activation command.

(Function) According to such a configuration, remote control is possible by employing an electromagnetic three-way valve, and even during zero point adjustment, a current value corresponding to the approximate differential pressure at that time is output.

(Embodiment) FIG. 1 is a diagram showing an embodiment of a differential pressure transmission device according to the present invention.

As shown in the figure, this differential pressure transmission device 3A includes an electromagnetic three-way valve 320 for introducing a target pressure difference, and a current signal that converts the introduced pressure difference to a transmission line 4. The differential pressure transmitter 360 is configured to be detachably separated.

The electromagnetic three-way valve 320 has two pressure introduction passages 321 that introduce a pressure difference (Ph-Pl) at two locations to be measured.
, 322 and a bypass passage 323 that communicates between the pressure introduction passages, and a first state in which the bypass passage 323 is closed and the two pressure introduction passages 321 and 322 are opened; and a second state in which the two pressure introducing passages 321 and 322 are closed.

That is, when the coil 327 of the electromagnetic three-way valve 320 is energized, the valves 324 and 325 are closed and the valve 326 is open, whereas the coil 327 of the electromagnetic three-way valve 32 ('l) is closed.
When 27 is not energized, valves 324 and 325 are open and valve 326 is closed.

) j, The differential pressure transmitter 360 includes a processor 361 that converts the pressure difference introduced through the three-way valve 32 into an electrical signal.
and an amplifier 362 that amplifies the output of the sensor 361.
a zero point compensation means (consisting of a microcomputer 364) for compensating the detected value of the sensor (amplified simultaneously) based on zero point compensation data (stored in the memory 353);
After the zero point compensation, the detected value is converted to current (DAC365
6) L? : A variable current constant current circuit 366, which is later sent to the transmission line 4, is provided.

The coil 327j of the electromagnetic three-way valve 320 is inserted in series with the transmission relay 4, and the terminals of the coil 327 of the three-way electromagnetic valve 320 can be short-circuited by a switch 367 controlled by a microcomputer 364. It becomes.

Therefore, switch 367 is on! ! (Differential pressure measurement state), the coil 327 is not energized, whereas when the switch 367 is off (zero point adjustment state!), the coil 327 is energized. .

Next, the operation of the differential pressure transmission device having the above configuration will be explained with reference to the flowchart shown in FIG.

It is assumed that the processing shown in this flowchart is executed at intervals of T seconds by a so-called timer interrupt.

In the figure, when the process is started, the microcomputer 364 holds the data currently being output to the DAC 365, thereby holding the output current value of the constant current circuit 366 at the value immediately before zero adjustment (step 201).

Then, turn off the switch 367 and energize the coil 327 of the electromagnetic three-way valve (step 202). Wait for the output to stabilize (step 203). In other words, the switch 367 is turned off and energization of the coil 327 starts. When this happens, valves 324 and 325 close and valve 326 opens, so that zero pressure difference is supplied to sensor 363, and an electrical signal corresponding to the pressure difference is obtained.

In this state, amplifier 362. The sensor output is read through the ADC 368 (step 204),
Next, a comparison is made with the previous read value (step 20).
5).

Here, if the previous value and current value match (step 20
6NO), the switch 367 is returned to on without doing anything, assuming that there is no change in the zero point (step 209).
), return to differential pressure measurement processing.

On the other hand, if the previous value and current value do not match (
Step 206: YES), update the zero point sensor output value using the current read value (Step 207), and at the same time update the zero point sensor output value using the current read value.
The ton compensation data is also updated (step 208).

Thereafter, in the differential pressure measurement process, zero point compensation for each differential pressure detection value will be performed using the zero point compensation data updated in the above process.

In this way, according to the above embodiment, the process shown in FIG. 2 is repeatedly executed every time the time T elapses.
Zero point adjustment is performed automatically, so there is no need for a worker to go to the location where the three-way valve is installed each time, unlike conventional equipment.

In addition, the time required for zero point adjustment is about 1 second, and during that time the current value just before starting zero point adjustment continues to be output to the transmission line, so the differential pressure detection device cannot be used continuously even during zero point adjustment. There is no need to disconnect it from the transmission line.

In the above embodiment, it goes without saying that the process shown in FIG. 2 may be started by a timer with a regular interrupt, or a start command may be given via a signal superimposed on a separate transmission line.

〔Effect of the invention〕

As is clear from the description of the above embodiments, according to the present invention, zero point adjustment can be carried out without having to go to the location where the three-way valve is installed, and furthermore, it can be used continuously even when zero point or 78 adjustment is in progress. This has the effect of making it possible to

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of a differential pressure transmitting device according to the present invention, FIG. 2 is a flowchart showing its operation, and FIG. 3 is a diagram showing an example of a conventional differential pressure transmitting device. 3A differential pressure transmission device 4 Transmission line 32L1, electromagnetic three-way valve 321, 322, 1 force introduction passage 323, bus passage 327, coil 360, differential pressure transmitter 36, sensor 364, microcomputer 365-D A C 366 constant current Circuit 367...Switch 368...ADC

Claims (2)

[Claims] (1) Two pressure introduction passages that introduce a pressure difference between two locations to be measured, and a bypass passage that communicates between these pressure introduction passages, and the bypass passage is closed and the
a three-way valve capable of taking a first state in which the main pressure introduction passage is opened and a second state in which the bypass passage is opened and the two pressure introduction passages are closed; and introduction through the three-way valve. a sensor that converts the pressure difference caused by the sensor into an electrical signal; a zero point compensation means that compensates the detected value of the sensor based on preset zero point compensation data; and a sensor that converts the detected value after the zero point compensation into an electric current and then transmits it. a differential pressure transmitter equipped with a variable current constant current circuit that sends out a current to the line; In the differential pressure transmission device, the zero point compensation data is reset by setting the state to the second state, and the three-way valve is a solenoid valve that can be set to the first state or the second state. The coil of the solenoid valve is inserted in series with the transmission line, and the terminals of the coil of the solenoid valve can be short-circuited by a switch, and in the differential pressure transmitter, when the differential pressure is being measured, setting a switch in a predetermined state to set the solenoid valve in a first state, and in a zero point adjustment state, setting the switch in an inverted state to set the solenoid valve in a second state; A differential pressure transmission device, wherein the constant current circuit holds an output current value immediately before starting zero point adjustment. (2) The zero point adjustment state is determined by a regular interrupt by a timer,
Alternatively, the differential pressure transmission device according to claim 1 is activated by an external activation command.