Bus AD/DA conversion data acquisition scheme: use Sunyuan ISO 4021 and ISO DA products in pair

Release time：2021-09-29 03:42:53 Number of views：616次

The data collector is a field bus system PLC, DCSAO module analog quantity directly controls the remote communication interface conversion equipment. Industrial field control causes signal attenuation and distortion due to long-distance transmission, and sometimes signal errors due to interference from other external signals. The RS485 differential digital signal transmission using the ISO 4021 and ISO DAO remote analog signal output modules can effectively improve the system's anti-interference ability. Through the RS485 bus communication baud rate and address settings, in some cases, it can also reduce wiring and reduce equipment control costs. And improve system reliability.

This article introduces the use of ISO 4021 module to convert 4-20mA analog quantity to RS485/232 digital quantity (AD conversion), remote communication through MODBUS RTD bus system, and then pairing with ISO DAO module to restore RS232/485 to analog quantity (DA conversion) ), to achieve the purpose of collecting data and remote monitoring between sensors, instruments and control systems.
Introduction to the application scheme of analog signal remote monitoring. The analog current or voltage signal output by the industrial field PLC, PCC AO module or SCADA, DCS system usually directly controls the remote execution equipment, and the signal is often attenuated due to long-distance transmission. , Distortion, and sometimes signal errors caused by other external signal interference, which affects the normal operation of the entire system. The RS485 differential digital signal transmission using ISO 4021 and ISO DAO remote analog signal output module can effectively improve the system's anti-interference ability, and through the RS485 bus communication baud rate and address settings, in some cases, it can also reduce wiring and reduce equipment Control costs and improve system reliability. With the continuous advancement of science and technology, people use various controllers to perform work and production, such as controlling the temperature of the heating furnace, controlling the flow of irrigation, and controlling the distance of movement of objects. The analog current or voltage signal output by the PLC's AO module or the DCS system directly controls the remote execution equipment, which will often cause signal attenuation and distortion due to long-distance transmission, and sometimes signal errors due to other external signal interference. The normal operation of the entire system. Therefore, ISO 4021 can convert the analog signal output by the sensor into a digital (A/D conversion) signal, use RS232/RS-485 communication to remotely transmit the signal or GPRS for wireless data transmission, and then use the remote analog signal output module ISO DAO to convert the signal. The digital signal is converted into an analog (D/A conversion) signal, and the restored output analog signal is obtained. These technologies have been increasingly used in data collection and remote monitoring.

一、Signal A/D (analog to digital) conversion and remote transmission technology
The ISO 4021 signal A/D (analog to digital) converter can realize the signal acquisition between the sensor and the host to detect analog signals or control remote equipment. Through software configuration, it can be used for a variety of sensor types, including: analog signal input, analog signal output, and digital signal input/output (I/O). It is widely used in RS-232/485 bus industrial automation control system, 4-20mA / 0-5V signal measurement, monitoring and control, small signal measurement, industrial field signal isolation and long-term transmission, etc.

ISO 4021 signal A/D (analog to digital) converter includes power isolation, signal isolation, linearization, A/D conversion and RS-485 serial communication. Each serial port can connect up to 256 ISO 4021 series modules. The communication method adopts ASCII code communication protocol or MODBUS RTU communication protocol. Its instruction set is compatible with ADAM modules. The baud rate can be set by code and can be linked to other manufacturers' control modules. On the same RS-485 bus, it is convenient for computer programming.

The ISO 4021 signal A/D (analog to digital) converter is an intelligent monitoring and control system based on a single chip microcomputer. All user-set calibration values, addresses, baud rates, data formats, checksum status and other configuration information are stored In the non-volatile memory EEPROM. ISO 4021 series products are designed and manufactured in accordance with industrial standards, with isolation between signal input and output, and can withstand 3000VDC isolation voltage, with strong anti-interference ability and high reliability. Operating temperature range-45℃～+85℃.

Brief introduction of ISO 4021 analog-to-digital (A/D) converter function:

ISO 4021 signal A/D (analog to digital) converter block diagram, as shown in Figure 1.

Figure 1 Block diagram of ISO 4021 signal A/D (analog to digital) converter

The ISO 4021 signal isolation acquisition module can be used to measure one voltage or current signal, and it can also be used to measure two current signals or voltage signals that can share the same ground and will not interfere with each other.
1、 Analog signal input
24-bit acquisition accuracy, all signal input ranges have been calibrated before the product leaves the factory. When in use, users can also easily program and calibrate by themselves. Please refer to the product selection for the specific current or voltage input range. When measuring two signals, the two input selections must be the same.
2、 Protocol

Communication interface: 1 standard RS-485 communication interface or 1 standard RS-232 communication interface, specify when ordering and selecting.

Communication protocol: supports two protocols, the character protocol defined by the command set and the MODBUS　RTU communication protocol. The communication protocol can be set by programming, and it can realize network communication with PLC, RTU or computer monitoring system of various brands.

Data format: 10 bits. 1 start bit, 8 data bits, 1 stop bit.

The communication address (0～255) and baud rate (300, 600, 1200, 2400, 4800, 9600, 19200, 38400bps) can be set; the longest distance of the communication network can reach 1200 meters, connected by twisted pair shielded cable.

The communication interface has a high anti-interference design, ±15KV ESD protection, and the communication response time is less than 100mS.

3、 Anti-interference
The checksum can be set as required. There are transient suppression diodes inside the module, which can effectively suppress various surge pulses, protect the module, and the internal digital filtering can also well suppress the power frequency interference from the power grid.

二、 Signal D/A (digital to analog) conversion and restoration monitoring technology

The ISO DAO signal D/A (digital to analog) converter can realize the isolation and conversion of the digital signal of the host RS-485/232 interface into a standard analog signal for controlling remote equipment. It is widely used in the 0-20mA/4-20mA/0-5V/0-10V standard analog signal restoration output of the RS-232/RS-485 bus industrial automation control system, which is used to control the executive equipment, control equipment and Display instrument and so on.

ISO DAO signal D/A (digital to analog) converter includes power isolation, signal isolation, linearization, D/A conversion and RS-485 serial communication. Each serial port can connect up to 256 ISODA series modules. The communication method adopts ASCII code communication protocol or MODBUS RTU communication protocol. Its instruction set is compatible with most similar modules. The baud rate can be set by code and can be linked to other manufacturers' control modules. On the same RS-485 bus, it is convenient for computer programming.

ISO DAO signal D/A (digital-to-analog) converter is an intelligent monitoring and control system based on single-chip microcomputer. All user-set calibration values, addresses, baud rates, data formats, checksum status and other configuration information are stored In the non-volatile memory EEPROM.

The ISO DAO signal D/A (digital to analog) converter is designed and manufactured according to industry standards. The signal output/communication interface is isolated and can withstand 3000VDC isolation voltage. It has strong anti-interference ability and high reliability. Operating temperature range-45℃～+80℃.

Brief introduction of ISO DAO digital to analog (D/A) converter function:
ISO DAO signal D/A (digital to analog) converter block diagram, as shown in Figure 2.

Figure 2 Block diagram of ISO DAO signal D/A (digital to analog) converter

The ISO DAO signal isolation D/A conversion module can be used to output one voltage or current signal, or it can be used to output two current or voltage signals that can share the ground.

1. Analog signal output and working power supply

12-bit output accuracy, all signal output ranges have been calibrated before the product leaves the factory. When in use, users can also easily program and calibrate by themselves, so the application in the field is more flexible. Signal output temperature drift: ±20 ppm/℃ (±30 ppm/℃, maximum). Working power supply, +8 ~ 50VDC wide power supply range, internal anti-reverse connection and overvoltage protection circuit. Power consumption: less than 1.5W. Isolation withstand voltage: between communication interface / output: 3KVDC, 1 minute, leakage current 1mA, where the communication interface and the power supply share the same ground.
2、Protocol

Communication interface: 1 standard RS-485 communication interface or 1 standard RS-232 communication interface.

Communication protocol: Two protocols are supported, the character protocol defined by the command set and the MODBUS RTU communication protocol. The communication protocol can be set by programming, and it can realize network communication with PLC, RTU or computer monitoring system of various brands. Because it supports the universal MODBUS RTU protocol, it can be widely used in the field of industrial control.

Data format: 10 bits. 1 start bit, 8 data bits, 1 stop bit.

The communication interface has a high anti-interference design, ±15KV ESD protection, and the communication response time is less than 100mS.

3、Anti-interference
The checksum can be set as required. There are transient suppression diodes inside the module, which can effectively suppress various surge pulses, protect the module, and the internal digital filtering can also well suppress the power frequency interference from the power grid.