CN103903412B - CAN (Controller Area Network) bus to 4-20mA data signal conversion device for NOx sensor - Google Patents

Abstract

The invention belongs to the field of industrial control, and specifically relates to a CAN protocol-based digital quantity signal that can be converted into an industrial general-purpose 4-20mA signal, which is suitable for converting the CAN bus of a NOx sensor to 4-20mA data based on the CAN protocol. Signal conversion device. The present invention includes a NOx sensor 1, a first CAN bus interface 2, a second CAN bus interface 3, a data processing module 5, a first photoelectric isolation module 4, a second photoelectric isolation module 6, and a 4-20mA output circuit 7. The signal transmission of the NOx sensor in the device of the present invention can adopt two working modes. When the redundant data conversion mode is adopted, one data transmission can be switched to the other after failure to ensure the reliability of the system operation.

Description

A data signal conversion device for converting CAN bus to 4-20mA for NOx sensors

technical field

The invention belongs to the field of industrial control, and specifically relates to a CAN bus for converting NOx sensors to 4-20mA data, which is suitable for converting digital signals based on the CAN protocol into industrial general 4-20mA signals based on the CAN protocol. Signal conversion device.

Background technique

With the development of society and the improvement of environmental awareness, the world has become more and more strict on the emission of NOx in the exhaust emission of internal combustion engines. In order to quickly and accurately detect the NOx content and solve the NOx emission problem, the application of NOx sensors has become more and more common. At present, most NOx sensors have a CAN bus control unit inside, which outputs the NOx concentration through the CAN bus. CAN bus has a high bit rate, high anti-electromagnetic interference and strong error detection and correction capabilities, and has the characteristics of low cost, high reliability, and low installation and maintenance costs. It has been widely used in automobiles and ships. Industry, transportation, industrial control and other fields.

However, in the field of industrial control applications, especially in PLC control systems, CAN bus is not widely used, even if there is a CAN bus module, its price is not cheap. In the industrial control system, 4-20mA analog signal is widely used, it uses 4mA to represent the zero signal, 20mA to represent the full scale of the signal, and the signal lower than 4mA and higher than 20mA is used for various fault alarms. The 4-20mA analog signal has the advantages of long output distance, strong signal anti-interference ability, and convenient use.

In order to apply the NOx sensor to the field of industrial control, it is necessary to realize the conversion between the CAN bus data of the NOx sensor and the 4-20mA analog signal, so a data conversion device is also required. Chinese patent application number 201020661289.9 proposes an analog output device, including a power supply, a microprocessor, a CAN bus unit, a photoelectric isolation circuit, and a DA conversion circuit, which converts received digital signals into analog signals to realize signal processing. Chinese patent application number 201120349179.3 proposes a photoelectrically isolated 4~20mA output device, including a microprocessor, a switch optocoupler, a shaper, a DA converter and a 4~20mA circulation generator, and the error-free conversion of digital signals is 4~20mA. 20mA analog signal. Due to the relatively high reliability requirements in the industrial field, the above-mentioned patents are all single-channel conversion devices, which have low reliability, poor environmental adaptability, and limited applications.

Chinese Patent No. 200710132579.7 proposes a dual-channel 4-20mA DC analog output device, which is composed of a high-speed optical isolator, a digital/analog converter, an operational amplifier, and a voltage reference source; among them, the high-speed optical isolator, digital The analog-to-analog converter and the operational amplifier are connected in series in sequence. This circuit can simulate a dual-way SPI communication line through the IO port of the FPGA, and convert the parallel digital information given by the microprocessor into a serial digital stream output required by the DAC to realize 4- 20mA DC analog output. The defect of this conversion device is that when a failure occurs along the way, the other side corresponding to it will be paralyzed, and the severe one will cause the whole device to fail to work normally. The signal transmission of the NOx sensor in the device of the present invention can adopt two working modes. When the redundant data conversion mode is adopted, one data transmission can be switched to the other after a fault occurs, so as to ensure the reliability of the system operation.

Contents of the invention

The object of the present invention is to provide a data signal conversion device for converting the CAN bus of the NOx sensor to 4-20mA.

The purpose of the present invention is achieved like this:

The present invention includes a NOx sensor 1, a first CAN bus interface 2, a second CAN bus interface 3, a data processing module 5, a first photoelectric isolation module 4, a second photoelectric isolation module 6, a 4-20mA output circuit 7, and a NOx sensor 1 The output digital signal is transmitted to the data processing module 5 through two CAN buses through the signal isolation of the photoelectric isolation module 4, and the signal of the data processing module is sent to the 4-20mA output circuit 7 through the second photoelectric isolation module 6 and converted into a 4- 20mA analog signal.

The photoelectric isolation module adopts high-speed optical coupler TLP521-4, and the data processing module adopts 16-bit microprocessor MC9S12XDP512,

The beneficial effects of the present invention are:

The signal transmission of the NOx sensor in the device of the present invention can adopt two working modes. When the redundant data conversion mode is adopted, one data transmission can be switched to the other after a fault occurs, so as to ensure the reliability of the system operation.

Description of drawings

Fig. 1 is a structural schematic diagram of the present invention.

Fig. 2 is a working schematic diagram of the present invention.

FIG. 3 is a redundant data failure processing process of the present invention.

Fig. 4 is an optocoupler isolation output circuit of the present invention.

Fig. 5 is the CAN receiver circuit of the present invention.

Fig. 6 is the 4-20mA conversion circuit of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

The present invention is to provide a kind of data signal conversion device that the CAN bus that is used for NOx sensor turns 4-20mA, and specific implementation scheme is as follows:

CAN bus to 4-20mA data signal conversion device for NOx sensor, including NOx sensor 1, CAN bus interface 2, 3, data processing module 5, photoelectric isolation module 4, 6, 4-20mA output circuit 7, working mode Set 8 and LED lights indicate fault alarm 9 and so on. The signal transmission between the above modules starts with the NOx sensor 1, and passes through the CAN bus interface 2, 3, the photoelectric isolation module 4, the data processing module 5, the photoelectric isolation module 6, and the 4-20mA output circuit 7, so that the digital signal is converted into 4-20mA analog signal.

By setting the jumper 8 in the working mode, the device realizes two working modes of dual-channel independent and redundant data conversion.

NOx sensor 1 outputs a digital signal, which is converted into a 4-20mA analog signal after data processing, 4mA represents the starting point of the NOx sensor range, and 20mA represents the end point of the NOx sensor range.

The data processing module 5 can judge and process the data of the NOx sensor 1, adapt to the device working in different working modes, and ensure the reliability of the device. If the data processing module 5 judges that a fault occurs, the LED lamp indicates a fault alarm 9 and sends a light alarm message prompt.

The photoelectric isolation modules 4 and 6 isolate and process the input and output data, so that the device has good environmental adaptability and strong anti-interference ability.

In Fig. 1, NOx sensor 1, CAN bus interface 2, 3, photoelectric isolation module 4, 6, data processing module 5, 4-20mA output circuit 7, working mode setting 8 and LED lamp indication fault alarm 9.

The structure of the present invention is shown in Figure 1, mainly including NOx sensor 1, CAN bus interface 2, 3, data processing module 4, photoelectric isolation module 5, 6, 4-20mA output circuit 7, working mode setting 8 and LED light indicating failure Alarm 9 etc. The signal transmission between the above modules starts with NOx sensor 1, passes through CAN bus interface 2, 3, photoelectric isolation module 4, data processing module 5, photoelectric isolation module 6, 4-20mA output circuit 7, and the NOx sensor 1 output Digital signal is converted to 4-20mA analog signal output.

The present invention works as shown in Fig. 2, mainly includes power supply circuit, reset circuit, crystal oscillator circuit, microprocessor, optocoupler circuit, two-way CAN transceiver, switch quantity input and output, analog quantity output composition. The two CAN transceivers exchange data with the microprocessor through the optocoupler circuit, and the microprocessor processes the input data and outputs 4-20mA analog signal. Switch input and output include microprocessor working mode setting and sound and light alarm signal output, etc.

The core of the data processing module 5 of the present invention is a microprocessor, and the microprocessor has more than two independent CAN controllers, which set receiving interrupts for the two CAN buses, give corresponding interrupt priorities, and allocate different receiving data buffers , Send the data buffer, and complete the data protocol conversion work. The data processing module 5 receives the data transmitted by the NOx sensor, stores it in the buffer area, and converts it according to the protocol.

The device of the present invention has more than two signal conversion functions, and by setting 8 jumpers in the working mode, two working modes of dual channel independence and redundant data conversion can be realized. In the working mode of independent data conversion, each channel can work independently to realize two input and output; in the working mode of redundant data conversion, two channels of NOx sensors collect data of one point, after data processing and fault judgment, the data processing module 5 Convert a relatively correct data and output it to two channels to realize channel redundancy and ensure the reliability of the device.

When the present invention adopts the redundant data conversion working mode to work, the data processing module 5 receives two CAN bus data at the same time, and for each channel, the data processing module 5 first judges whether the data exceeds the upper and lower limits, and then converts the previous multiple measurement data of this channel The average value of the current data is compared with the current data, and if it exceeds the set threshold, the fault is judged; when the data of the two CAN buses differ greatly, for each channel, the data of this time and the previous measurement data of this channel are extrapolated Compare the predicted values, take the path with the smaller error as the correct value, and the other path as a fault; when a fault occurs, the LED light indicates a fault alarm 9 and sends out a light alarm.

The device receives the NOx sensor signal, and the two CAN buses are isolated by the signal of the photoelectric isolation module 4 and transmitted to the data processing module 5 . The photoelectric isolation module adopts high-speed optical coupler TLP521-4, so that the voltage fluctuation on the bus will not affect the control module. The output circuit of the photoelectric isolation module is shown in Figure 4.

The control module 5 adopts the 16-bit microprocessor MC9S12XDP512 of Freescale Company, which has rich resources on the chip and has 5 independent CAN bus controllers. The single-chip mode can meet the requirements, avoiding the expansion of the external bus and enhancing the reliability of the system. The processor has an XGATE module, which can undertake the processing tasks of CPU peripheral devices, support more deterministic interrupt processing, and avoid the conflict between core functions and interrupt processing when executing information receiving and sending, and communication conversion.

The data processing module 5 receives two CAN bus data and transfers them to the two CAN data buffer module TJA1050. The circuit is shown in Fig. 5 . The specific length of the received data can be determined according to the conversion rate, the baud rate of the CAN bus and the application layer protocol of the CAN bus. Provides the data segment of the complete application layer protocol.

The specific process of data processing in this device is as follows:

(1) Read data from CAN bus interface 2, 3;

(2) Propose the data In about NOx concentration from the read-in data;

(3) Convert In to NOx concentration Data, Data=In×0.005-200, the value range of Data is [0,1500];

(4) If Data>1500 or Data<0, an alarm will be issued;

(5) Output current through 4-20mA output circuit. When the 16-bit conversion circuit is used, the output value OUT=65535×Data/1500;

The specific process of redundant data fault handling of this device is as follows:

(1) Read data from CAN bus interface 2, 3;

(2) Obtain the NOx concentration data Data1 and Data2 processed by the two channels;

(3) If Data1<0 or Data1>1500, an alarm will be issued;

(4) If Data2<0 or Data2>1500, an alarm will be issued;

(5) If |Data1-Data2|≤E, output the data of CAN bus interface 1;

(6) If |Data1-Data2|>E, E is the set threshold, use the first three data obtained by CAN bus interface 1 to perform cubic equation interpolation, and obtain the predicted data value Data1* of CAN bus interface 1 this time; use CAN The first three data obtained by the bus interface 2 are interpolated by the cubic equation to obtain the predicted data value Data2* of the CAN bus interface 2;

(7) Calculate |Data*1-Data1| and |Data*2-Data2|, and take the channel data with the smallest error as the true value;

(8) If |Data*1-Data1|>E, and |Data*2-Data2|>E, an alarm is issued, and the process is shown in Figure 3.

4-20mA output conversion adopts AD421 chip, which is a single-chip high-performance digital-to-analog converter (DAC), powered by a current loop, 16-bit digital signal serial input, 4-20mA current output, in line with industrial control standard signals Output requirements, can better realize remote industrial control, the circuit is shown in Figure 6.

In addition, the noise in the system mainly comes from the power supply, and the power supply should be processed by a filter circuit to minimize the noise of the power supply. The utility model adopts the combined power filter BNX002 of muRata Company, which has relatively high insertion loss in the range of 0.5M-1GHz, and can suppress the noise of the power line and the ground line at the same time.

Claims (1)

1. a kind of CAN for NOx sensor turns the data-signal conversion equipment of 4-20mA, including NOx sensor (1), First CAN interface (2), the second CAN interface (3), data processing module (5), the first photoelectric isolation module (4), Two photoelectric isolation modules (6), 4-20mA output circuits (7), it is characterised in that：NOx sensor (1) exports digital quantity signal, Jing Signal isolation of the two-way CAN by photoelectric isolation module (4) is crossed, data processing module (5), data processing module is sent to Signal be sent to 4-20mA output circuits (7) through the second photoelectric isolation module (6) and be converted into 4-20mA analog signalses；

The photoelectric isolation module adopts high speed optocoupler TLP521-4, data processing module to adopt the microprocessor of 16 bit MC9S12XDP512；

Data processing detailed process is as follows：

(1.1) data are read in from CAN interface 2,3；

(1.2) data In about NOx concentration are proposed from the data read in；

(1.3) In is converted into into NOx concentration Data, the number range of Data=In × 0.005-200, Data is [0,1500]；

(1.4) if Data>1500 or Data<0, send warning；

(1.5) by 4-20mA output circuit output currents, using output valve OUT=65535 × Data/ during 16 conversion circuits 1500；

Redundant data troubleshooting detailed process is as follows：

(2.1) data are read in from CAN interface 2,3；

(2.2) NOx concentration data Data1 and Data2 that two passages are processed are obtained；

(2.3) if Data1<0 or Data1>1500, send warning；

(2.4) if Data2<0 or Data2>1500, send warning；

(2.5) if | Data1-Data2 |≤E, the data of CAN interface 1 are exported；

(2.6) if | Data1-Data2 |>E, E are given threshold, and the first three data obtained using CAN interface 1 is carried out Cubic equation interpolation, obtains prediction data value Data1* of this CAN interface 1；Before being obtained using CAN interface 2 Three data carry out cubic equation interpolation, obtain prediction data value Data2* of this CAN interface 2；

(2.7) | Data*1-Data1 | and | Data*2-Data2 | is calculated, it is true to take the minimum channel data all the way of both errors Value；

(2.8) if | Data*1-Data1 |>E, and | Data*2-Data2 |>E, sends warning.