JPH076289A - Intelligent transmitter - Google Patents

Abstract

PURPOSE:To provide the transmitter for detecting a fault of a reception filter circuit and for giving an alarm to a host side by measuring a frequency characteristic of a built-in reception filter circuit with respect to an intelligent transmitter. CONSTITUTION:A transmission current with an accurate frequency is flowed through a load resistor 14 in a 2-wire loop to generate a reference voltage signal and an attenuation guantity caused by passing the signal through a reception filter 7 is compared with an attenuation in the case of a previously normal reception filter by a comparator 6, and when the both are coincident, it is detected by the generation of an interruption to a microcomputer 1. The frequency of the transmission current in this case indicates the frequency characteristic of the reception filter 7 and it is compared with a reference value and the presence and the absence of a fault is discriminated. Since the internal reception filter characteristic is independently diagnosed by the intelligent transmitter, the reliability is improved and the maintenance and management are facilitated.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A two-wire system is the mainstream for intelligent transmitters, and as shown in FIG.
5 and the load resistor 14 are connected to form a two-wire loop, and a handheld terminal, a distributor, a host, etc. are connected between the outputs (+) and (-) for communication. As a communication method, there is a method of superimposing a digital signal current for communication on an analog current of 4 to 20 mA flowing in a two-wire loop, and a method of transmitting a signal by switching the analog current itself. In either method, it is necessary to remove a noise component through a filter circuit before separating / detecting a digital signal from an analog signal. There are various types of noise components depending on the installation environment, such as commercial power supply frequency noise, switching power supply high frequency noise, inductive noise superimposed on the loop, etc., but as a filter for removing these, a high-pass filter of second order or higher and a first order or higher order are usually used. In many cases, it is configured in combination with the low pass filter of. However, if it is installed in an environment that exceeds the noise tolerance, communication becomes almost impossible, and it becomes impossible to access the self-diagnosis function from an external device such as a handheld terminal, either due to a failure of the transmitter itself or due to external noise. It is difficult to identify the cause of communication failure.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an intelligent transmitter having a function of self-diagnosing the frequency characteristic of a reception filter circuit incorporated in the intelligent transmitter.

[0004]

The above object can be achieved by using a programmable timer which a microprocessor with an intelligent transmitter has and a detection circuit which has an interrupt processing function and a receiving function. On the other hand, for simple diagnosis, instead of the programmable timer,
This can be achieved by directly using the serial transmission function built in the microprocessor.

[0005]

The programmable timer outputs a signal having a constant frequency to superimpose the transmission current on the two-wire loop to generate an echo voltage in the load resistance. This echo voltage is attenuated by the reception filter and then compared with the threshold voltage of the detection circuit. If the two match, an interrupt signal to the microprocessor is generated, so the microprocessor receives the signal by sweeping the output frequency of the programmable timer. The frequency characteristics of the filter can be measured.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
Will be explained. In FIG. 1, the D / A converter 4
Drives the transistor 16 according to the data sent from the microprocessor 1 to control the analog 4-20 mA loop current to a constant value. The loop current is converted into a voltage by the feedback resistor 11 and fed back to the voltage / current conversion circuit 8. During normal operation, the microprocessor 1 selects the A channel of the multiplexer 17 to select the transmission signal Tx.
Is input to the addition / subtraction circuit 5 to be added / subtracted from the output signal of the D / A converter 4, and the transmission current signal I
It is converted to d and superimposed on the analog 4-20 mA current. On the other hand, during self-diagnosis, the microprocessor 1 is the multiplexer 1
Channel B 7 is selected to generate a transmission current signal Id on the loop by the PTM output signal of the programmable timer. The transmission current signal Id flows into the load resistor 14 and is converted into an echo voltage signal. The voltage signal has its DC component removed by AC coupling by the capacitor 9 and passes only the communication signal component, and is then attenuated by the reception filter 7 before being input to the non-inverting input terminal of the detection comparator 6 and its inverting input terminal. Side reference threshold voltage. For the threshold voltage, the reference voltage Vref is applied to the resistor 12
And the value divided by 13 is given by Vth = Vref × R ₂ (R ₁ + R ₂ ). At the point where the echo voltage attenuated by the reception filter 7 exceeds the threshold voltage Vth, the output of the comparator 6 changes from "L" to "H" and the microprocessor 1
This can be detected by applying an interrupt IRO to. The overall operation will be described with reference to FIG. The figure shows 200Hz and 1.5k
This is the case of a reception filter that combines a second-order high-pass filter with a cutoff frequency characteristic of Hz and a first-order low-pass filter, and the threshold voltage of the comparator 6 is Vth.
= 50 mV, load resistance 14 is 250Ω, transmission signal current I
The standard values are d = ± 0.5 mA and communication frequency fo = 600 Hz. When the reception filter 7 operates normally according to the above specifications, the echo voltage generated in the load resistor 14 by the transmission current signal Id is 0.5 mA × 2.
Since 50Ω = 125 mV is input to the reception filter 7, the gain at the frequency at which the signal after passing the reception filter 7 matches the threshold voltage Vth of the comparator 6 decreases by 20 log (50 mV / 125 mV) = 8 db f _L And f _H , and in FIG. 2, f _L = 126 Hz, f _H
= 3.75 kHz. Accordingly, when gradually sweeps upward direction the frequency of the programmable timer output signal from the frequency lower than f _L, at the time of passing through the f _L, the output signal of the comparator 6 transits from "L" to "H" Micro Since the processor is interrupt-activated, f _L can be detected. Similarly, f _H can be detected by sweeping the frequency of the programmable timer output signal downward from a frequency higher than f _H.

By comparing f _L and f _H detected by the above processing with the standard value stored in the memory 2, it is possible to diagnose whether the characteristic of the reception filter 7 is abnormal.
Since f _L and f _H can be measured independently, if an abnormality is detected, is it an abnormality on the secondary high-pass filter side?
It is possible to determine whether there is an abnormality on the next low pass filter side.

FIG. 3 shows an embodiment in which the diagnosis of the reception filter circuit is executed by utilizing the original communication function without using the programmable timer. Since the serial communication frequency is generally limited to 75 × 2 ^ n (n = 0 to 8) Hz, accurate measurement cannot be performed as in the example of FIG. 1, and the simple diagnosis function for discrete frequencies is limited. To be done. In the example of the reception filter in FIG. 2, when the transmission signal frequency is 75 Hz, the output of the comparator 6 is “L”, but the transmission signal frequency is 1
The transition to "H" can be detected when switching to 50Hz, so the second-order high-pass filter characteristic is 75Hz ≤ f
_It can be confirmed that _L ≤ 150 Hz. Similarly, by switching the transmission signal frequency from 4.8 kHz to 2.4 kHz, the primary low-pass filter characteristic is 2.4 kHz ≦ f _M
Since it can be confirmed that ≦ 4.8 kMz, it can be used as a simple diagnostic function.

In the embodiment shown in FIGS. 1 and 3, the characteristics of the original reception filter are stored in the memory 2 in advance, and f _L ,
Since f _M is already known, it is not necessary to sweep the transmission signal over all frequencies, and it suffices to sweep nearby frequencies including f _L and f _M , so that the processing time of the microprocessor 1 is less burdened. . In the case of the embodiment shown in FIG. 1, f _L and f _M can be displayed on the display 3 and transferred to an external handheld terminal via a two-wire loop line. f
If the measurement results of _L and f _M are not within the specified range,
It is determined that the reception filter is abnormal, the information is stored in the memory 2 and then displayed on the display 3, and is transmitted to the host side or the handheld terminal to warn of the abnormality.

[0010]

As described above, according to the present invention, in the circuit block built in the intelligent transmitter, the self-diagnosis of the reception filter circuit, which has a relatively large number of components and causes a large number of defects, can be self-diagnosed. The reliability of the container is improved and the initial defects can be reduced.

[Brief description of drawings]

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

FIG. 2 is a frequency characteristic diagram for explaining the operation of FIG.

FIG. 3 is a circuit configuration diagram showing a second embodiment of the present invention.

[Explanation of symbols]

1 ... Microprocessor, 2 ... Memory, 3 ... Indicator, 4
... D / A converter, 5 ... addition / subtraction circuit, 6 ... converter, 7 ... reception filter, 8 ... voltage / current exchange circuit, 9 ...
Coupling capacitors 10, 11, 12, 13, 1
4 ... Resistor, 15 ... External power supply, 16 ... Transistor, 17
… Multiplexer.

Claims (4)

[Claims] 1. A microprocessor for executing various kinds of arithmetic processing according to an input signal, a memory circuit for storing and storing the arithmetic result, a display for displaying the result, and a two-wire loop for the result. A transmission circuit for transmitting to the outside via
A reception filter circuit that removes noise components from the communication signal superimposed on the two-wire loop, a detection circuit that converts the communication signal into a digital signal, and a constant current in the two-wire loop according to an instruction from the microprocessor. In an intelligent transmitter composed of a flowing voltage / current converter, means for sweeping the frequency of a transmission current signal superimposed on a two-wire loop is provided, and the voltage waveform generated on the load side by the current at each frequency is After passing through the reception filter circuit, the presence or absence of a reception signal is determined using the detection circuit, the determination result is compared with a reference value in the memory, the comparison result is stored again in the memory, and the display unit displays the result. Display,
An intelligent transmitter characterized in that it is transmitted and output by the transmitting circuit. 2. The intelligent transmitter according to claim 1, wherein the number of frequency points to be swept is four. 3. The intelligent transmitter according to claim 1, wherein the memory circuit is incorporated in the microprocessor. 4. The intelligent transmitter according to claim 1, wherein the loop for superposing the transmission signal is of a 4-wire type.