JP3060667B2 - Two-wire transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply from a load side via two transmission lines, converts a physical quantity to be measured into an electric signal, and processes the electric signal by a microprocessor to process the transmission line. 2 as a current signal to the load side via
The present invention relates to a two-wire transmitter, and more particularly to a two-wire transmitter improved so as to obtain a backlight power supply of a liquid crystal display element mounted on the two-wire transmitter from a current signal.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a configuration of a conventional two-wire transmitter. In this case, an example of a differential pressure transmitter is taken as an example of a two-wire transmitter, but it is converted into a flow signal by using another transmitter, for example, a vortex frequency changes corresponding to a flow rate. The same applies to a two-wire eddy flow transmitter that transmits a current signal to a load. Reference numeral 10 denotes a two-wire transmitter that converts a physical quantity such as a process variable into an electric signal and transmits the electric signal. The electrical signal is transmitted as a current signal I _L through the transmission lines L1, L2 through the output terminal T _1, T _2,
A process variable is known by detecting a voltage change occurring between both ends of the load 12.

[0003] The current signal _IL is, for example, 4 to 1 from a two-wire transmitter 10 set in a range corresponding to the pressure in the pipe.
It is converted into a unified current of 0 mA and transmitted. In this case, for example, when it is desired to change the pressure range or to perform a predetermined display, it is convenient if it can be operated from outside the two-wire transmitter.

For this reason, the handheld terminal 13 is connected to the transmission lines L1 and L2 as necessary using the connection lines L1 'and L2', and the two-wire transmitter 10 is used for exclusive data communication with the handheld terminal 13. Have a function,
Digital data such as parameter change is transmitted from the handheld terminal 13 to the two-wire transmitter 10. Also,
An interface 14 connected to a host controller is connected to both ends of the load 12, and communication is performed via the interface 14.

Next, each component configured as described above will be described in detail. Of these, the two-wire transmitter 10
Is configured as follows. SR1 is a sensor that detects pressure / differential pressure and converts it into an electric signal. The converted analog signal is converted into a digital signal by an analog / digital converter ADC1, and is converted into a random signal in a memory MEM1 via a microprocessor μP1. Access memory (R
AM) part. The microprocessor μP1 executes a predetermined operation such as linearization using the stored digital signal according to an operation procedure written in, for example, a read-only memory (ROM) portion of the memory MEM1. And outputs it to the output circuit OPC.

On the other hand, a predetermined calculation result in the microprocessor μP1 is digitally displayed in a necessary number of digits on a built-in monitor LCD1 (liquid crystal display element). The output circuit OPC converts the voltage signal converted into an analog signal by the digital / analog converter DAC1 into a unified current signal I of 4 to 20 mA.
_It is converted to L and transmitted to the load 12 via the transmission lines L1 and L2. Further, the output circuit OPC make power of an internal circuit of two-wire transmitter 10 using a portion of the current signal I _L.

The IFC is an interface for performing data communication with the handheld terminal 13 and is connected between the transmission lines L1 and L2 and the microprocessor μP1 to convert digital signals from the transmission lines L1 and L2 into parallel data. It has a function of transmitting the data from the microprocessor μP1 to the transmission lines L1 and L2 as a serial signal.

[0008] Next, the handheld terminal 13 is as follows.
It is configured as follows. SER is operated by operator
It is a setting device and has a built-in monitor. Two-wire transmitter
10 model requirements, change of display cycle, change of range,
Normal detection or current signal I _LVarious settings such as displaying the
It can be specified and requested. μP ′ is a microprocessor
The data from the setting device SER, for example.
In accordance with the processing procedure stored in the memory MEM '.
The digital signal is transmitted to the two-wire transmitter 10 through the terface IFC '.
Transmits a tall signal. Also, the microprocessor μP ′
Responds from the two-wire transmitter 10
The data is loaded into the memory MEM 'through the chair IFC', and further
Decoding according to the processing procedure stored in the memory MEM ',
It is displayed on the monitor of the setting device SER.

Next, the interface 14 connected to the load 12 will be described. Digital signal with the current signal I _L from 2-wire transmitter 10 is also transmitted to the load 12. These mixed signals of analog signals and digital signals are separated by the signal conditioner SC of the interface 14, and the analog signals as PV values for which high-speed real-time performance is required are converted by the microprocessor CP.
Under the control of U, digital signals are interfaced to a high-speed bus via a communication card CMN under the control of a microprocessor CPU.

Conversely, a digital signal is sent from the host system to the two-wire transmitter 10 via the communication card CMN, the signal conditioner SC, the load 12, and the transmission lines L1 and L2, and bidirectional communication is performed. Has been realized.

FIG. 5 is a top view showing the appearance of the housing 15 of the two-wire transmitter 10 shown in FIG. A pair of pressure inlets 16 and 17 are provided on the upper part, a cylindrical terminal case 18 for connecting electric wires required for external wiring is provided on the right side, and a display 19 is provided on the upper part.
The measurement pressures P1 and P2 (however, hidden by the terminal housing and not visible) are applied from the right and left lower portions of the terminal housing 18 via the respective pipes.

FIG. 6 is an enlarged view showing the display 19 shown in FIG. 4 in an enlarged manner. The display 19 is fixedly installed on the housing 15. 20 is a digital display, 21
Indicates a bar graph display, 22 indicates an ALM display indicating that an error has occurred, 23 indicates an end display of the one-push zero operation, and 24 indicates a percentage display.

[0013]

However, the above-described two-wire transmitter 10 is supplied from the DC power supply 11 provided on the load 12 side while having many functions as described above. The operation has to be performed even with the minimum current of 4 mA. Therefore, the liquid crystal display element LCD1 shown in FIG. 4 cannot have a backlight function that requires electric power. For this reason, there is an inconvenience that the displayed contents cannot be recognized in the dark place as well as at night.

[0014]

According to the present invention, a physical quantity to be measured is converted into an electric signal by receiving power supply from two loads through two transmission lines. The signal is processed by a microprocessor and transmitted as a current signal to the previous load via the previous transmission line. In the two-wire transmitter, a predetermined voltage drop is generated by being serially connected to the previous transmission line. A voltage drop element, a connection terminal provided at both ends of the voltage drop element for connecting a light emitting element for a backlight, a display element driven by the microprocessor, and a backlight provided by the light emitting element. And a liquid crystal display element.

[0015]

[Operation] A voltage drop element for generating a predetermined voltage drop is connected in series with a load side and two transmission lines. And
Connection terminals are provided at both ends of the voltage drop element for connecting light emitting elements for backlight. In the liquid crystal display device, the display device is driven by the microprocessor and the backlight is provided by the light emitting device. Thus, the greatest disadvantage of the LCD can be solved without increasing the current consumption of the entire circuit.

[0016]

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 two-wire transmitter shown in FIGS. 4 to 6 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

Reference numeral 25 denotes a two-wire transmitter according to the present embodiment. The output terminal of the two-wire transmitter 25 is T _3, T _4, and the output terminal T ₃ Zener diode ZD1 to the output terminal T ₂ of the two-wire transmitter 10 shown in FIG. 4 is connected in series
Is, the output terminal T ₁ is connected directly as an output terminal T _4. However, the monitor LCD of the two-wire transmitter 10
Reference numeral 1 denotes a display element driven by the microprocessor μP1, which is separately drawn from the two-wire transmitter 10 for convenience of explanation.

A backlight element BLE is arranged on the back of the monitor LCD 1 which is a liquid crystal display element. Both ends of the backlight element BLE are connected to connection terminals C ₁ and C ₂ provided at both ends of the Zener diode ZD1. Thus, the liquid crystal display element LCD
2 are configured. If necessary, connection terminals C ₁ provided at both ends of the Zener diode ZD1,
Switch SW is connected to the C _2.

In the above configuration, the current signal _IL is supplied from the DC power supply 11 provided on the load 12 side to the output terminals T ₃ and T _4.
Once transmitted through, the current signal I _L becomes that flows through the Zener diode ZD1, a voltage V _Z generated at both ends. This voltage V _Z is applied to both ends of a backlight element BLE using, for example, a light emitting diode (LED), and irradiates the back surface of the monitor LCD 1 which is a liquid crystal display element.

The power source of the backlight element BLE that irradiates the back surface of the monitor LCD 1 basically includes a current signal I _L
This irradiation does not increase the overall current consumption of the two-wire transmitter 25 while eliminating the greatest disadvantage of the monitor LCD 1 which is a liquid crystal display element.

[0021] However, the voltage V _S is significantly lower in the DC power supply 11, the voltage V _Z of the Zener diode ZD1, or when the drive voltage of the light emitting diode causes a problem, and thus to ensure the normal operation turns on the switch SW but, in general, in the field of industrial instrumentation, voltage V _S is above 24V, yet minimum operating voltage of the two-wire transmitter is 11V~
13V, and a light emitting diode (LED) 1
Since the voltage required to drive the individual is about 1.5 V,
It is rare that the voltage V _Z of the Zener diode ZD1 becomes a problem.

FIG. 2 shows a plurality of light emitting diodes LED1,
LED2, monitor LED1 connected in parallel with LED6
Backlight element B that uniformly illuminates the back surface of
2 shows the sequence of LE (P). If you use a as a voltage V _Z of the Zener diode ZD1 in this case 1.8V～2.0V, the current signal I _L is a 4~20mA, LED1, LED2, ..., to each of the LED 6,
Since a current of (4/6) to (20/6) mA flows, 1
The illuminance is lower than in the case of individual pieces, but the uniformity is improved.

FIG. 3 shows a light emitting diode LED1, LED
2,..., A backlight element BL in which LEDs 6 are connected in series and parallel to uniformly illuminate the back surface of the monitor LCD 1
2 shows the sequence of E (SP). In this case, those 3.6V~4.0V is used as the voltage V _Z of the Zener diode ZD1. In this case, each light emitting diode LED
1, LED2,..., LED6 have (4/3) to (20 /
3) mA current flows. According to this method, although it is brighter than the parallel connection shown in FIG. 2, there is a disadvantage that the voltage drop is large.

In the above description, the backlight element BLE
Although a light emitting diode is used as an example, a discharge tube or a light bulb may be used in principle, although there are problems in terms of life and power consumption.

[0025]

As described above, according to the present invention, the current signal flowing to the load is used as the power source of the backlight element, so that the current consumption of the entire circuit can be increased. The liquid crystal display element can be backlit without the need, and even in the case of a two-wire transmitter that is often placed in a dark place as well as at night, the display content of the liquid crystal display element driven by the microcomputer can be clearly recognized. .

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing an example of an arrangement of the backlight element shown in FIG.

FIG. 3 is a circuit diagram showing another example of the arrangement of the backlight elements shown in FIG. 1;

FIG. 4 is a block diagram showing a configuration of a conventional two-wire transmitter.

FIG. 5 is a top view showing the appearance of the casing of the two-wire transmitter shown in FIG.

FIG. 6 is an enlarged view showing the display shown in FIG. 4 in an enlarged manner.

[Description of Signs] 10, 25 Two-wire transmitter 11 DC power supply 12 Load 13 Handheld terminal 14 Interface 19 Display SR1 Sensor MEM1 Memory LCD1, LCD2 Display ZD ₁ Zener diode BLE backlight element

Claims (1)

(57) [Claims] 1. A physical quantity to be measured is converted into an electric signal by receiving power supply from two loads through two transmission lines, and the electric signal is processed by a microprocessor. A two-wire transmitter for transmitting a current signal as a current signal, a voltage drop element connected in series to the transmission line to generate a predetermined voltage drop, and a light emitting element for backlight connected to both ends of the voltage drop element. And a liquid crystal display element to which a display element is driven by the microprocessor and a backlight is provided by the light emitting element.