JP2528054B2 - How to add measurement transmission equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to an existing measuring sensor for measurement.
A new detection signal for measurement using a log signal transmission device
By adding a signal transmission device for measurement
About the method.

[0002]

2. Description of the Related Art When a detection signal is newly required in various instrumentation systems, a new converter is conventionally installed and a new transmission line is laid to transmit a signal from the new converter. . However, it may be extremely difficult to perform this wiring work. For example, in an explosive environment such as a petrochemical factory, it is often impossible to carry out wiring work without suspending the operation of the factory. At a petrochemical plant,
Since the outage period is often once every 1 to 2 years, the opportunity to perform additional wiring work is limited. In addition, it is often difficult for large department stores to do large-scale wiring work.

If a newly added converter needs to redraw the power supply wiring, the chance of the wiring is small for the same reason as described above.

[0004]

According to the present invention, there is already
New detection on the provided 2-wire analog transmission device
In the case of adding additional conversion function and a transmission function, upper
The output of the new detection conversion function is converted to a digital signal and
Configure the digital transmitter, and an output side of the digital transmitter
Connect a series circuit of coil and Zener diode in parallel
The zener diode on both sides of the digital signal.
Connect to the operating power supply terminal of the transmitter and connect the above series circuit to the above 2
Insert in series at one end of the two-wire transmission line of a two-wire analog transmission device
Input the analog signal of the above two-wire type analog transmission device.
Based on the above, a predetermined voltage is generated in the Zener diode,
It is common to operate the digital transmitter with the specified voltage.
The digital signal output from the digital transmitter to the two wires
To the other end of the two-wire type transmission line,
DC cutoff of digital receiver that receives output digital signal
Expansion work by connecting via a capacitor
Things can be done quite easily.

[0005]

FIG. 1 shows an embodiment of the present invention. An operation output signal (for example, DC 4 to 20 mA) from the controller 11 as an analog transmitter is converted into an analog DC signal on the line 12.
It is supplied to the two-wire type transmission line 12 composed of a and 12b, and its operation output signal is supplied to the electropneumatic converter 13 which is an analog converter through the two-line type transmission line 12.

The nozzle-flapper is controlled according to the current flowing through the control coil 14 in the electropneumatic converter 13, and the converter 1
An air pressure output corresponding to the operation output signal from 5 is supplied to the operation end (for example, a control valve). In contrast to the state in which such an analog transmission device is already provided, in this embodiment, the temperature transmitter 16 is added to the electropneumatic converter 13 side, and the detection output of the temperature transmitter 16 is transmitted as a digital signal. Then, the digital signal is sent to the digital receiver 1 on the controller 11 side.
This is the case where the data is received at 7.

Therefore, the AC blocking coil 18 is inserted in series with the control coil 14, and the AC bypass capacitor 19 is connected in parallel with the control coil 14 and the AC blocking coil 18. Further, a series circuit of an AC blocking coil 21 and a Zener diode 22 as a power supply voltage generating means is inserted in series with the two-wire type transmission line 12, and the Zener voltage obtained by the Zener diode 22 is used as a power supply voltage for resistance / resistance.
The voltage is applied to the voltage conversion circuit 23 and the A / D conversion circuit 24. AC blocking coil 21 and Zener diode 22
In parallel with, a transistor 26 is connected through a resistor 25.

The resistance value of the resistance temperature detector 27 is converted into a voltage signal by the resistance / voltage conversion circuit 23, and the voltage signal is A / D.
It is converted into a digital signal by the converter 24. In addition to the coded serial pulse signal corresponding to the voltage signal, this digital signal has a digital signal whose frequency changes in proportion to the voltage signal and a pulse ON / OFF ratio which changes in proportion to the voltage signal. There is a digital signal. Further, the digital signal may be transmitted while taking a rest period instead of continuously transmitting the digital signal.

The transistor 26 is intermittently controlled by the output digital signal from the A / D conversion circuit 24, and the digital signal is superimposed on the two-wire transmission line 12. The analog DC signal (operation output signal) passes through the Zener diode 22 and is not affected by the digital signal. Further, based on this analog DC signal, the operating power supply voltage for the temperature transmitter 16 can be obtained by the Zener diode 22 without affecting it.

On the controller 11 side, the two-wire transmission line 12
An AC blocking coil 28 is inserted in series with the AC blocking coil 28, a resistance load 31 is connected in parallel with the AC blocking coil 28 via a DC blocking capacitor 29, and a D / A conversion circuit 32 is connected to the resistance load 31. The digital signal superimposed and transmitted on the analog signal via the two-wire type transmission line 12 is input to the D / A conversion circuit 32 and converted into an analog signal of DC 4 to 20 mA. Instead of the D / A conversion circuit 32, for example, the signal is converted into a signal that can be easily received by a personal computer and input to the personal computer. The analog DC signal for operation output passes through the AC blocking coil 28 and is not affected by the connection of the digital receiver 17.

In this embodiment, a temperature transmitter is used as the transmitter to be added, but the variable (physical quantity) to be input to the transmitter may be pressure, position, or any other desired value.
Further, the electropneumatic converter 13 may be an operation part driving device such as an electropneumatic positioner or an electropneumatic positioner. FIG. 2 shows another embodiment of the present invention, in which parts corresponding to those in FIG. 1 are designated by the same reference numerals. A DC voltage source 33 is inserted in series at one end of the 2-wire transmission line 12, a receiving resistor 34 is inserted in series with the DC voltage source 33, and a 2-wire analog transmission is made at the other end of the 2-wire transmission line 12. 35 is connected, an analog DC signal flows in proportion to the input of the analog transmitter 35 in the two-wire type transmission line 12, and the DC signal is received by the analog receiver 36 connected in parallel with the receiving resistor 34. This is a case where a temperature transmitter 16 and a digital receiver 17 are added as in the case of FIG. 1 when an analog signal transmission device for receiving is provided.

In this case, only the capacitor 19 is connected between the connection points of the analog transmitter 35 and the two-wire transmission line 12,
The temperature transmitter 16 and the digital receiver 17 are connected in the same manner as in FIG. 1, and the digital signal bypass capacitor 37 is connected in parallel with the reception resistor 34. In FIG. 1, the controller 11
When the power required by the temperature transmitter 16 cannot be obtained from the operation output signal flowing through the two-wire type transmission line 12 because the internal power supply voltage is low, the signal is converted one-to-one as shown in FIG. 3A. It suffices to insert a power amplifier 38 capable of supplying a sufficient power supply voltage. The power amplifier 38 serves not only the purpose of power amplification but also the purpose of direct current isolation between input and output of signals and level conversion between input and output signals (for example, converting 4 to 20 mA DC to 10 to 50 mA DC). realizable.

As shown in FIG. 3B, the transmitter to be added is 2
It may be a table (16, 41) or more. Instead of the digital receivers 17 and 42 that receive a digital signal and output DC 4 to 20 mA, a converter that switches the digital signal and digitally transmits it to another device may be provided. In FIG. 1, the capacitor 19 and the AC blocking coil 18 are provided in the existing electropneumatic converter 13, but without such modification,
The capacitor 19 and the coil 18 may be attached to the outside as shown in FIG. 2, or may be built in the newly installed temperature transmitter 16.

As a means of transmitting a plurality of detection data using existing wiring, there is a smart converter that transmits a plurality of detection signals by using a single converter by using both analog signals and digital signals. Already in use. But,
The transducer can only use the detection signal that has been captured for that purpose. That is, for example, in the case of a differential pressure transmitter, the pressure and the temperature of the transmitter main body are detected in addition to the differential pressure, and only that value can be digitally transmitted. Therefore,
It is not possible to freely select and transmit detection signals having completely different purposes.

Further, even if there is a smart type converter suitable for the purpose, it is necessary to replace the converter with a new one, resulting in extra cost.

[0016]

As described above, according to the present invention, it is possible to use an existing analog signal transmission device without newly laying a transmission line, and to use an ordinary digital signal even if the variable has no relation to the transmitter. An additional transmitter can be installed to superimpose and transmit a digital signal on the analog signal of the analog signal transmission device, which can be received by a digital receiver.
In addition, the power supply voltage for the digital transmitter is created by using the DC signal in the analog transmission device, there is no need to provide a special power supply for the digital transmitter to be additionally installed, and it has no effect on the existing analog transmission. Absent.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram showing another embodiment of the present invention.

FIG. 3 is a block diagram showing still another embodiment of the present invention.

Claims (1)

(57) [Claims] 1. A method for adding a new detection conversion function and a transmission function to an already installed 2-wire type analog transmission device, wherein the output of the new detection conversion function is converted into a digital signal and digitally converted. A transmitter is configured, and a series circuit of a coil and a Zener diode is connected in parallel with the output side of the digital transmitter, and both ends of the Zener diode are connected to the operation power supply terminal of the digital transmitter, and the series circuit is The Zener diode is inserted in series at one end of the 2-wire transmission line of the 2-wire analog transmission device to generate a predetermined voltage in the Zener diode based on the analog signal of the 2-wire analog transmission device, and the digital signal is generated at the predetermined voltage. While operating the transmitter, the output digital signal of the digital transmitter is supplied to the two-wire transmission line, and the other end of the two-wire transmission line is Expansion method for measuring transmission apparatus including the, connected through an output digital signal DC blocking capacitor digital receiver for receiving.