JPS62272399A - Differential pressure/pressure transmitter - 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] 3. Detailed description of the invention [Industrial application field] The present invention relates to a differential pressure/pressure transmitter having a communication function.

[Conventional technology]

In order to realize a differential pressure/pressure transmitter having a communication function, a method of communicating all information including process differential pressure or pressure information as multiplexed digital data;
As described in Japanese Unexamined Patent Publication No. 58-85649, a method has been proposed in which analog data containing information on differential pressure or pressure and digital data containing other communication information are alternately transmitted using the same line. .

[Problem that the invention seeks to solve]

Among the above-mentioned conventional techniques, the former method is not compatible with existing systems, such as industrial instrumentation, which transmit differential pressure or pressure information using analog data.

In the latter method, analog data is disturbed during digital data transmission, and information on differential pressure or pressure cannot be obtained during that time, requiring human considerations such as switching to manual control, especially in the control system. Alternatively, connect the communication device directly to the line that transmits power supply and analog data.
Since it is connected in parallel with the pressure transmitter and the power supply, there is a problem that a malfunction of the communication device may cause a disturbance in the power supply and the transmission of analog data, such as a short circuit condition.

An object of the present invention is to provide a differential pressure/pressure transmitter that eliminates the drawbacks of the above-mentioned prior art and makes it possible to transmit digital data without disturbing differential pressure or pressure information while transmitting analog data. Our goal is to provide the following.

[Means for solving problems]

The above purpose is to provide a transmission line that transmits digital data separately from a transmission line that transmits analog data, and to connect a communication device that transmits and receives digital data electrically with a part that functions to transmit differential pressure or pressure information. This is achieved by configuring it so that it is insulated.

[Effect]

Digital data is transmitted over separate transmission lines from analog data. Therefore, differential pressure or pressure information based on analog data is not affected by the transmission status of digital data.

Even if a problem occurs in a digital data communication device or a transmission line, such as a short circuit between the transmission lines, the transmission of analog data will not be hindered.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings. Figure 1 shows the composite sensor and central processing unit (hereinafter referred to as CPU)
This is an example of a differential pressure transmitter using

The differential pressure transmission 1li11 is the differential pressure sensor 3. A composite sensor 2 consisting of a static pressure sensor 4 and a temperature sensor 5;
A multiplexer 6 that selects the output of , an A'/D converter 7 that converts the selected output into digital data, a CPU 8 that processes the data, and a memory that stores various information used for data processing in this CPU. Memory 9 and CPU
A D/A converter 1o converts the digital data processed by 8 into analog data given by voltage changes.
and.

Furthermore, a part that functions to transmit differential pressure information as analog data consists of a current control element 11 that converts into analog data given by a change in current, and a pair of terminals 12 and 13 used for power supply and output of analog data. , a communication interface 14 that is under the control of the CPU and manages the transmission of digital data, and a first photocoupler 15 that transmits digital data from the digital data transmission line pair 28 and 29 to the communication interface 14.
a second photocoupler 16 that transmits digital data to the digital data transmission line pair 28 and 29; a switch mechanism 17 that controls the current flowing through the second photocoupler according to the digital data from the communication interface 14;
It is composed of a part functioning to transmit digital data, which is made up of another pair of terminals 18 and 19 used for inputting and outputting digital data, and a power supply circuit 20 that supplies power to each of the above parts.

Next, the operation will be explained. The detection information of each sensor of the composite sensor 2 is selected by the multiplexer 6 and sent to the A/D converter 7.
The data is taken into the CPU 8 via.

The CPU 8 uses information regarding the characteristics of the composite sensor 2 stored in advance in the memory 9 to calculate differential pressure data corrected for the effects of temperature and static pressure and non-linearity, and further stores the differential pressure data in the memory 9. It is processed using the range settings, damping time constants, etc. stored in the . The differential pressure data after processing is converted into an analog current signal between 4 mA and 20 mA by the D/A converter 10 and the current control element 11.

This analog current signal is connected to the analog data transmission line pair 20.
21 and is transmitted as a voltage drop across the resistor 22 to the receiving device 23, typically a recorder, controller, or the like.

The analog data transmission line pair 20.degree. 21 also serves as a power supply line, and power is supplied from the power supply device 24 to each section via the power supply circuit 20.

The above operation functions as a conventional two-wire differential pressure transmitter.

On the other hand, digital data is transmitted and received by the components within the dotted lines. The switch ta17 is normally in the 17a side, and since an analog current having differential pressure information flows from the current control element 11 to the photodiode 16a of the second photocoupler 16, the phototransistor 16 is in a conductive state.

Here, when a digital signal due to intermittent current is sent from the communication device 30 via the transmission line 28.29 connected to the terminal pair 18.19, it is sent from the oil flow interface 14 to the CPU 8 via the first photocoupler 15. It is said that.

In Figure 1, as a means of intermittent current, the current of constant current source 25 is controlled by photocoupler 26 (control system diagram not shown), when digital data is transmitted from differential pressure transmitter 1 to communication device 2. The CPU 8 controls the switch mechanism 17 via the communication interface 14. When the switch mechanism 17 is in the 17a side, an analog current having differential pressure information flows to the photodiode 16a of the second photocoupler 16, and the phototransistor 16b becomes conductive. In the state on the side 17b, no current flows through the photodiode 16a, so the phototransistor 16b is in a cutoff state. In FIG. 6, the contact information of the phototransistor 16b is given to the communication device E30 as digital data.
7 (reception system diagram not shown).

Here, the analog current with differential pressure information is the switch mechanism 17.
Regardless of the state of the current, the current flows to the analog reception system consisting of the resistor 22 and the power supply 24.

According to this embodiment, the current flowing through the digital data transmission line is supplied from the communication device, and an analog current signal with differential pressure information is used for its control, so differential pressure transmission has a communication function configuration with low power consumption. It is possible to realize a vessel. Furthermore, since a composite sensor is used, information on external pressure and temperature other than differential pressure can be transmitted and used as digital data.

Furthermore, this embodiment has advantages in terms of implementation as shown in FIG. la, lb...1c are differential pressure transmitters installed in separate locations, respectively, and are connected to each power supply unit 24.
A, 24b, . . . , 24c transmit differential pressure information in the form of analog data to the power supply system. On the other hand, the plurality of differential pressure transmitters 1a, lb...1c are connected to one communication device I! 3
When communicating with each differential pressure transmitter individually, an address is assigned to each differential pressure transmitter using software, and the address is sent from the communication device 30. Selection information is sent to select only one device, and the others are prevented from receiving digital data by software until the communication is completed.

This mounting structure has the advantage that one communication device can handle a plurality of differential pressure transmitters, and only two transmission lines for digital data transmission are required from the control room to the site.

Furthermore, as shown in Figure 3, multiple differential pressure transmitters are connected to the power supply unit 2.
4. Resistor 22. By sharing the receiving device 23, it becomes a communication device!
! If only one unit selected by 30 transmits differential pressure information, the configuration can be further simplified.

Although the above embodiments have been described using a differential pressure transmitter as an example, the operation and effect are the same when the pressure transmitter is used.

〔Effect of the invention〕

According to the present invention, while transmitting differential pressure or pressure information using analog data, digital data can be transmitted without disturbing the information.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIGS. 2 and 3 are block diagrams of implementation examples of the present invention.

Claims (1)

[Claims] 1. A detection unit that converts the differential pressure or pressure in the process into an electrical signal, a central processing unit that processes the electrical signal from this detection unit, and a receiving device that receives the signal from this central processing unit via a pair of transmission lines. , comprising a power supply circuit connected to the pair of transmission lines, and a communication device connected to the pair of transmission lines via electrical insulation means.
pressure transmitter.