JPH05259941A - Intelligent transmitter - Google Patents

Abstract

PURPOSE:To detect the fault of a loop and to give the alarm to the host side with an intelligent transmitter by measuring the resistance value of the load and the voltage value of the power supply in a double line type loop. CONSTITUTION:When the power voltage value E and the load resistance value RL are calculated in a double line type loop, the different loop constant current levels are selected at two points and at the same time the real current IL and the inter-transmitter output terminals voltage V are measured. Thus the occurrence of a loop fault is decided when no coincidence is secured between the loop constant current level and the current IL. The voltage V undergoes the conversion of potential by the voltage dividing resistances 14 and 15, and the current IL undergoes the conversion of voltage by a feedback resistance 13. These converted voltage and current are fetched by an A/D converter 4 to be turned into the digital value and then undergo the arithmetic processing by a microprocessor 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the diagnostic function of an intelligent transmitter incorporating a microprocessor.

[0002]

2. Description of the Related Art The two-wire type is the mainstream for intelligent transmitters, and as shown in FIG.
1 and a load resistor 22 are connected to form a two-wire loop, and a handheld terminal is connected between output terminals for communication. As a communication method, 4-2 flowing in the two-wire loop
There are a method of superimposing a digital signal current for communication on an analog current of 0 mA, and a method of transmitting a signal by switching the analog current itself. The relationship between the voltage of the constant voltage power supply 21 and the load resistance 22 is limited to the range shown in FIG. If used with a power supply voltage or load resistance that is out of range, the transmitter itself will not operate, or communication with the handheld terminal will not be possible even if the transmitter is operating. In order to make the system intelligent, if existing wiring equipment is diverted and only the transmitter is changed to an intelligent transmitter, it often happens that the power supply and load resistance allowable conditions shown in Fig. 4 are not satisfied. .. As a result, communication becomes impossible and the operating state inside the transmitter cannot be confirmed using the handheld terminal. In addition, since the existing wiring equipment is complicated to route, re-inspection is extremely troublesome, and it is difficult to identify the cause.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to measure the voltage value and load resistance value of a power supply connected in a two-wire loop and send them to the host side by display or communication. , To provide an intelligent transmitter having a function of diagnosing a power supply condition in a two-wire loop.

[0004]

The above object is to use a loop check function of an intelligent transmitter capable of flowing an arbitrary constant current within a current value in the range of 4 mA to 20 mA in a two-wire loop. Can be achieved with.

[0005]

When there is no error in the constant current value IL flowing in the two-wire loop due to the loop check function, the load resistance R _L in the loop is measured by measuring the voltage V between the loop current output terminals of the transmitter. It can be calculated. The voltage V is measured using an A / D converter inside the transmitter. On the other hand, if the error in the constant current value I _L is generated, for measuring the constant current value I _L with voltage V. The constant current value I _L can also be measured using an A / D converter inside the transmitter.

[0006]

Embodiments of the present invention will be described below with reference to FIGS. 1 and 2. In FIG. 1, the D / A converter 8 drives the transistor 11 according to the data sent from the microprocessor 6 to control the loop current I _L to a constant value. The loop current I _L is converted into a voltage by the feedback resistor 13 and fed back to the D / A converter 8. The loop current I _L is supplied from the external power supply 19, the positive side filter circuit equivalent resistance 16 inside the transmitter, and the transmitter internal circuit equivalent resistance 1
2, through the transistor 11, the feedback resistor 13, the negative side filter circuit equivalent resistor 17, and the external load resistor 18 to the external power source 19. A part of the loop current I _L is supplied to the transmitter internal power supply circuit 9. Since the transmitter output terminals (+) and (-) are open to the outside, noise and surge may be superimposed on the terminal voltage, and the terminal voltage V after passing through the filter circuit is detected. .. The voltage V is P
The voltage value V ′ that can be input to the GA (Programmable Gain Amplifier) 3 is divided by the resistors 14 and 15 and enters the input switching circuit 2 via the buffer amplifier 10. Sensor 20
When measuring the output voltage of the channel a of the input switching circuit 2,
b and c are selected, and the channel d is selected by the microprocessor 6 when the voltage V'is measured. Then PGA3
Is amplified to a voltage value capable of A / D conversion by the A / D converter 4, converted into a digital value by the A / D converter 4,
Is taken into. The voltage V when the loop constant current I _L1 flows is V ₁ , and the voltage V when the loop constant current I _L2 flows is V
_{If the value is 2} , the following equation holds for the external power supply voltage E.
However, I _L1 ≠ I _L2 .

[0007]

[Equation 1]

[0008]

[Equation 2]

From Eqs. 1 and 2, E and R _L are

[0010]

[Equation 3]

[0011]

[Equation 4]

[0012]

[Equation 5]

[0013] Here, I _L1 , I _L2 , R _f1 and R _f2 are known and stored in the memory 5 in advance as data. Therefore, when there is no error in the loop constant currents I _L1 and I _L2 , it is possible to obtain the values of the power supply voltage E and the load resistance R _L by measuring the voltage V twice and using the data and the formulas 3 and 4. it can. It is also possible to use equation 5 instead of equation 4. The values of E and _RL can be displayed on the display 26 and can also be transferred to an external handheld terminal via a two-wire loop line.

On the other hand, when the power supply voltage E or the load resistance R _L does not satisfy the specified value, or when an abnormal load is connected in the two-wire loop, the microprocessor 6 tries to flow it in the two-wire loop. An error occurs between the constant current value and the actual current value. In this case, the process of measuring the actual current is required. The loop current I _L is V _{I by the} feedback resistor 13.
Is converted into a voltage and is taken into the channel e of the input switching circuit 2 via the buffer 20. Data processing is voltage V
In the same manner as in the above case, the microprocessor 6 selects the channel e of the input switching circuit 2 to perform A / D conversion and digitize it. The processing procedure follows the flow shown in FIG. 2, and first outputs a loop current of an arbitrary value, then measures the actual current and compares the two values. When the comparison results are the same, there is no error in the loop constant current value, it is determined that the loop condition is normal, and the loop current measurement is omitted in the subsequent processing. After the arithmetic processing is completed, the values of E and _RL and the information that the loop condition is normal are stored in the memory and displayed on the display device. If there is a data transmission request from the handheld terminal, the data is transmitted. On the other hand, if there is an error in the comparison result, it is judged that the loop condition is abnormal,
The actual current I _L is measured and E and R _L are calculated using the measured value. The calculation result is stored in the memory together with the information that the loop condition is abnormal, then displayed on the display device and transmitted to the handheld terminal to warn of the occurrence of the abnormality. It is possible to express the content of the information together with E and _RL as an amount of error from the specified value shown in FIG.

[0015]

As described above, according to the present invention, the voltage value and load resistance value of the power source connected in the two-wire loop can be measured by the intelligent transmitter side and information can be transmitted to the host side. The loop status can be monitored at all times, improving system reliability. In addition, when an abnormality occurs, it is possible to distinguish between the defect side on the transmitter side and the defect on the loop side. This improves work efficiency.

[Brief description of drawings]

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

FIG. 2 is a flowchart illustrating a processing flow of the embodiment of FIG.

FIG. 3 is a connection diagram illustrating a wiring method of a two-wire transmitter.

FIG. 4 is a diagram that defines allowable values of a power supply connected to a transmitter and a load resistance.

[Explanation of symbols]

1 ... Sensor, 2 ... Input switching circuit, 3 ... PGA, 4 ... A /
D converter, 5 ... memory, 6 ... microprocessor, 7 ...
Display, 8 ... D / A converter, 9 ... Power / communication circuit, 1
0, 20 ... Buffer amplifier, 11 ... Transistor, 1
2, 13, 14, 15, 16, 17 ... Resistance, 18, 22
… Load resistance, 19, 21… External power supply.

Claims (2)

[Claims] 1. A switch circuit for selecting one sensor signal from a plurality of sensor signals, an A / D converter for converting the sensor signal into a digital value, and an operation according to output data of the A / D converter. A microprocessor that executes processing, a memory circuit that stores and stores the calculation result, a display that displays the result, a communication circuit that transmits the result to the outside through a two-wire loop, and the microprocessor In the intelligent transmitter composed of a voltage-current converter that causes a constant current to flow in the two-wire loop according to the instruction of, the voltage detection means between the transmitter output terminals of the two-wire loop, the loop current detection means, A switch circuit for switching the two detection results to a plurality of sensor signals and inputting them to the A / D converter is provided, and the transmitter output at two or more different loop current values is provided. The inter-child voltage and the loop actual current are measured, the power supply voltage and the load resistance value in the two-wire loop are calculated using the measurement data, the calculation result is stored in the memory, and displayed on the display, An intelligent transmitter characterized by transmitting and outputting by the communication circuit. 2. The intelligent transmitter according to claim 1, wherein the current detecting means is omitted by using a loop current set value instructed by the microprocessor instead of the loop actual current.