JPH05327555A - 2 line type transmitter - Google Patents

Abstract

PURPOSE:To limit currents even and to prevent the malfunction of an entire transmitter at the time of occurrence of the internal short circuited accident or the like of a peripheral element, by inserting and connecting a current limiting circuit between a microprocessor and the peripheral element. CONSTITUTION:An electronic display LCD 2 is connected through a current limiting circuit CRC with a microprocessor muP. The circuit CRC connects limiting resistances RP, R1, R2, RN, and RG between power supply terminals P-P, signal terminals A-A, B-B, and N-N which terminals are attached to the processor muP and the driver of a display LCD 2 respectively. Moreover, a capacitor C is connected between the power supply terminal P at the display LCD 2 side and a common terminal G, to constitute a noise removing filter with the capacitor C and the resistance RP. Thus, normally this device is operated without being affected by the insertion of the circuit CRC, and at the time of the occurrence of the accident such as the short-circuit at the inside of the driver of the display LCD 2, currents are limited by the circuit CRC, and the malfunction of the entire transmitter by creating an excessive current consumption is prevented. Therefore, signal currents are normally transmitted to a load.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention receives a power supply from a load side through two transmission lines, converts a physical quantity to be measured into an electric signal, and processes it by a microprocessor to form a transmission line. 2 as a current signal via the load side
More particularly, the present invention relates to a two-wire transmitter improved so as to prevent malfunction of the two-wire transmitter due to a failure of a peripheral element controlled by a microprocessor.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a configuration of a conventional two-wire transmitter. Reference numeral 10 is a two-wire type transmitter that converts a physical quantity such as a process variable into an electric signal and transmits the electric signal. Electric power is supplied from a DC power supply 11 via a load 12.

The electric signal is transmitted as a current signal I _L by the transmission lines L ₁ and L ₂ , and the voltage change occurring across the load 12 is detected to know the process variable. The current signal I _L is converted into a unified current of 4 to 20 mA and transmitted by the two-wire transmitter 10 set in a range corresponding to the pressure in the pipe, for example.

Next, the internal structure of the two-wire type transmitter 10 will be described. The SNR is a sensor that detects pressure / differential pressure and converts it into an electric signal, and the changed analog signal is converted into a digital signal by an analog / digital converter A / D. This digital signal is stored in the random access memory part of the memory MEM via the microprocessor μP.

The microprocessor μP uses the stored digital signal to execute a predetermined operation such as linearization according to an operation procedure written in, for example, the read-only memory portion of the memory MEM, and the digital / analog converter D / A. To the output circuit OPC via.

On the other hand, the predetermined calculation result by the microprocessor μP is digitally displayed in the required number of digits on the built-in monitor LCD 1 which is an electronic display. The output circuit OPC unified current signal I _L of the voltage signal converted to an analog signal by a digital / analog converter D / A 4 to 20 mA
To the load 12 via the transmission lines L ₁ and L ₂ .

Further, the current signal I _L is output from the output circuit OPC.
Is extracted and output to the constant voltage circuit CVC, and this constant voltage circuit CVC generates the circuit voltage V _B of all circuit power supplies of the circuit used in the two-wire transmitter 10. Since the current signal I _L is limited to the range of 4 to 20 mA, 2
The wire transmitter 10 is a 2-wire transmitter 10 with a current of 4 mA or less.
Need to operate normally.

[0008]

However, the two-wire type transmitter 10 as described above has the following problems. First, before using the monitor LCD 1 which is an electronic display as shown in FIG. 2, a moving coil type instrument in which a diode is connected in series is connected to the transmission lines L ₁ and L ₂ to connect the output current signal. Since I _L was read, the operation of the two-wire transmitter 10 itself was not affected even if a failure such as disconnection or short circuit of the instrument occurred.

However, when the monitor LCD 1 making full use of the electronic technology as shown in FIG. 2 is used, for example, as shown in FIG.
And the monitor LCD 1 include a power supply terminal P, signal terminals A, B, ...
Since it is connected by N, common terminal G, etc., when the driver of the monitor LCD 1 causes a short-circuit accident, for example, an excessive current i flows into the common potential point COM through a path shown by a dotted line, resulting in a large current consumption. Become.

As a result, the power supply voltage of the 2-wire transmitter 10 which must secure the operating power of the entire circuit with a small current of 4 mA or less becomes less than the specified value, and the circuit voltage required for normal operation can be obtained. The problem of disappearing arises.

[0011]

In order to solve the above problems, the present invention converts a physical quantity to be measured into an electric signal by receiving power supply from the load side through two transmission lines. The present invention relates to a two-wire type transmitter that processes the signal as a current signal to the load side through the previous transmission line through the previous transmission line and is controlled by the previous microprocessor and independent of the previous current signal. It is equipped with a peripheral element that functions as such and a current limiting element that is inserted and connected between this peripheral element and the preceding microprocessor, so that the excessive current flowing due to the failure of the preceding peripheral element is limited by the preceding current limiting element. It is the one.

[0012]

[Operation] Peripheral elements are supplied with power from the load side via two transmission lines, convert the physical quantity to be measured into an electrical signal, and execute the processing under the control of a microprocessor that processes this signal. To do.

The current limiting element inserted and connected between this peripheral element and the preceding microprocessor limits an excessive current flowing due to a failure of the preceding peripheral element. As a result, even if a failure occurs in the peripheral element, the circuit power supply of the two-wire transmitter does not drop below the specified value, and at least a normal operation can be ensured for signal processing.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. It should be noted that parts having the same functions as those of the conventional two-wire type transmitter shown in FIG.

The two-wire transmitter 13 includes a sensor SNR, an analog / digital converter A / D, and a microprocessor μ.
P, memory MEM, digital / analog converter D / A,
It is composed of an output circuit OPC, a constant voltage circuit CVC, an electronic display LCD2 functioning as a peripheral element, and the like.

The electronic display LCD2 is connected via the current limiting circuit CRC when connecting to the microprocessor μP. The current limiting circuit CRC limits between the microprocessor μP and the driver of the electronic display LCD2 between the power supply terminal P-P, the signal terminals AA, BB, NN, and the common terminal NN, respectively. Resistance R _P , R ₁ , R ₂ , R _N , R
_G is connected.

Further, a capacitor C is connected between the power supply terminal P and the common terminal C on the electronic display LCD2 side,
The limiting resistor R _P and the capacitor C form a filter for removing noise.

[0018] In this case, the constant of the limiting resistor R _P is considering voltage drop limiting resistance R ₁ of the signal line, R _2, R _N is the signal waveform rounding condition, taking into account the time constant that is, each determined To do.

According to the above structure, the current limiting circuit CRC normally operates without being affected by the insertion, and even if an accident such as a short circuit occurs in the driver of the electronic display LCD2, the current is prevented. There is no case where the current is limited by the limiting circuit CRC and excessive current consumption is caused to cause an overall malfunction. Therefore, the signal current can be normally transmitted to the load.

The current limiting circuit CRC is as shown in FIG.
In the configuration shown in ( ₁₎ , the limiting resistors R _P , R ₁ , R ₂ , R _N , and R _G are used to realize, but the present invention is not limited to this, and the same effect can be obtained by using a constant current circuit, for example.

As the peripheral element connected to the microprocessor μP, in addition to the electronic display LCD2, for example, a digital signal of serial data for communication is taken in via the transmission lines L ₁ and L ₂ and is used as a modem. Even if the modem fails, the current signal I can be converted into a parallel signal via the microprocessor μP and taken in by the data.
_The current limiting circuit CRC shown in FIG. 1 can be applied to peripheral elements that do not affect _L.

[0022]

As described above in detail with the embodiments, according to the present invention, since the current limiting circuit is inserted and connected between the microprocessor and the peripheral element, even if a short circuit occurs inside the peripheral element. Even if such an accident occurs, the current is not limited and the entire transmitter does not malfunction.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration of a conventional 2-wire type transmitter.

FIG. 3 is an explanatory diagram illustrating a problem of the two-wire type transmitter illustrated in FIG.

[Explanation of symbols]

 10 2-Wire Transmitter 11 DC Power Supply 12 Load 13 2-Wire Transmitter SNR Sensor LCD1 Monitor LCD2 Electronic Display μP Microprocessor MEM Memory CRC Current Limiting Circuit OPC Output Circuit CVC Constant Voltage Circuit

Claims (1)

[Claims] 1. A physical quantity to be measured is supplied from a load side via two transmission lines to convert a physical quantity to be measured into an electric signal, and the signal is processed by a microprocessor to perform the signal processing on the load side via the transmission line. In a two-wire type transmitter for transmitting a current signal to a peripheral device, a peripheral element controlled by the microprocessor and functioning independently of the current signal, and a current limiting element inserted and connected between the peripheral element and the microprocessor And a current limiting element for limiting an excessive current flowing due to a failure of the peripheral element.