Data acquisition is a fieldbus system PLC, DCSAO module analog direct control of remote communication interface conversion device. Industrial field control due to long-distance transmission caused by signal attenuation distortion, and sometimes also because of other external signal interference caused by signal errors. Application of ISO 4021 and ISO DAO remote analog signal output module RS485 differential digital signal transmission can effectively improve the system's ability to resist interference, through the RS485 bus communication baud rate and address settings, on some occasions you can also reduce wiring, reduce equipment control costs and improve system reliability.

        This paper introduces the ISO 4021 module will be 4-20mA analog into RS485/232 digital (AD conversion), through the MODBUS RTD bus system for remote communication, and then paired with the ISO DAO module will be RS232/485 reduced to analog (DA conversion), to achieve the sensors and instruments, control systems, between the collection of data, remote monitoring purposes.

        Analog signal remote monitoring application program introduction, industrial field PLC, PCC AO module or SCADA, DCS system output analog current or voltage signals usually go directly to the control of the remote implementation of the device, often because of long-distance transmission caused by the attenuation of the signal, distortion, and sometimes because of other external signal interference caused by the signal error, affecting the normal operation of the entire system. Application of ISO 4021 and ISO DAO remote analog signal output module RS485 differential digital signal transmission can effectively improve the system's anti-jamming ability, and through the RS485 bus communication baud rate and address settings, in some occasions can also reduce wiring, reduce equipment control costs and improve system reliability. With the continuous progress of science and technology, people use a variety of controllers to work and production, such as controlling the temperature of the heating furnace, controlling the flow of irrigation, controlling the distance of movement of goods and so on. PLC's AO module or DCS system output analog current or voltage signals directly to control the remote implementation of the device, often because of long-distance transmission caused by signal attenuation, distortion, and sometimes because of other external signal interference caused by signal errors, affecting the normal operation of the entire system. Therefore, ISO 4021 can convert the analog signal output from the sensor into digital (A/D conversion) signal, apply RS232/RS-485 communication to transmit the signal remotely or GPRS for wireless digital transmission, and then use the remote analog signal output module ISO DAO to convert the digital signal into analog (D/A conversion) signal, and then get the analog signal of the restored output. These technologies have been increasingly used in data acquisition and remote monitoring.

I. Signal A/D (analog to digital) conversion and remote transmission technology
ISO 4021 Signal A/D (Analog to Digital) Converters enable signal acquisition between sensors and host computers for detecting analog signals or controlling remote devices. Configured by software, it can be used for a wide range of sensor types, including: analog signal input, analog signal output, and digital signal input/output (I/O). Widely used in RS-232/485 bus industrial automation control system, 4-20mA / 0-5V signal measurement, monitoring and control, small signal measurement, and industrial field signal isolation and long line transmission and so on.

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 be connected to a maximum of 256 ISO 4021 series modules, communication using ASCII code communication protocol or MODBUS RTU communication protocol, its instruction set is compatible with the ADAM module, the baud rate can be set by the code, and can be hooked up to the same RS-485 bus with the control modules of other manufacturers, which is convenient for computer programming.

ISO 4021 signal A/D (analog to digital) converter is an intelligent monitoring and control system based on microcontroller, all the user-set calibration values, address, baud rate, data format, calibration and status configuration information are stored in non-volatile memory EEPROM. ISO 4021 series products are designed and manufactured in accordance with the industrial standards, the signal input/output isolation, can withstand 3000VDC isolation voltage, high reliability. ISO 4021 series products are designed and manufactured in accordance with industrial standards, with signal input/output isolated and can withstand 3000VDC isolation voltage, strong anti-interference ability and high reliability. Operating temperature range - 45℃～+85℃. 

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

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

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

ISO 4021 Signal Isolation Acquisition Module can be used to measure one voltage or current signal, or two current signals or voltage signals that can be grounded and will not interfere with each other. 

1、 Analog signal input 

24-bit acquisition accuracy, all signal input ranges have been calibrated before delivery. In use, the user can also easily program their own calibration. Specific current or voltage input range, please see the product selection, measurement of two signals must be the same for both input selection. 

2、 Communication protocol 

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

Communication protocol: Support two protocols, the character protocol defined in the command set and MODBUS RTU communication protocol. It can be programmed to use that kind of communication protocol, which can realize network communication with PLC, RTU or computer monitoring system of many brands. 

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

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

Communication interface high anti-interference design, ±15KV ESD protection, communication response time of less than 100mS.　　 

3、 Anti-interference 

Checksum can be set as required. Transient suppression diode inside the module, can effectively inhibit a variety of surge pulses to protect the module, the internal digital filtering, can also be very good suppression of industrial frequency interference from the power grid.

二、  signal D / A (digital to analog) conversion and restore monitoring technology 

ISO DAO signal D/A (digital to analog) converter can realize the host RS-485/232 interface digital signal isolation into a standard analog signal, used to control remote equipment. Widely used in RS-232/RS-485 bus industrial automation control system 0-20mA/4-20mA/0-5V/0-10V and other standard analog signal reduction output, used to control the industrial field of the implementation of equipment, control equipment, and display instrumentation 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 be connected to a maximum of 256 ISODA series modules, communication using ASCII code communication protocol or MODBUS RTU communication protocol, its instruction set is compatible with most similar modules, baud rate can be set by the code, and can be linked with other manufacturers of control modules in the same RS-485 bus, easy to computer programming. 

ISO DAO signal D/A (digital to analog) converter is a microcontroller based intelligent monitoring and control system, all user set calibration values, address, baud rate, data format, checksum and status configuration information are stored in non-volatile memory EEPROM. 

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

ISO DAO digital to analog (D/A) converter function introduction: 

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

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

ISO DAO signal isolation D/A converter module, can be used to output one way voltage or current signal, also can be used to output two ways can be common ground current or voltage signal. 

1、Analog signal output and working power 

12-bit output precision, all signal output ranges have been fully calibrated before the product is shipped from the factory. In use, the user can also be very easy to program their own calibration, so the application in the field is more flexible. Signal output temperature drift: ±20 ppm/°C (±30 ppm/°C, max). Operating power supply, +8 ~ 50VDC wide power supply range, internal anti-reverse connection and over-voltage protection circuit. Power consumption: less than 1.5 W. Isolation withstand voltage: between communication interface/output: 3KVDC, 1 minute, leakage current 1mA, where communication interface and power supply are common ground. 

2、Communication protocol 

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

Communication protocol: Support two protocols, the character protocol defined in the command set and MODBUS RTU communication protocol. It can be programmed to use that kind of communication protocol, which can realize network communication with many brands of PLC, RTU or computer monitoring system. Because it supports the universal MODBUS RTU protocol, it can be widely used in the industrial control field. 

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

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

Communication interface high anti-interference design, ±15KV ESD protection, communication response time of less than 100mS.        

3、Anti-jamming 

Checksum can be set as required. Transient suppression diode inside the module, can effectively inhibit a variety of surge pulses, protection module, the internal digital filtering, can also be very good suppression of industrial frequency interference from the power grid.

Related Product Technical Information

1.  Data Acquisition ,AD Analog to Digital Isolated Transmitters: ISO 4021 Series：http://0032.psznh.cn/products_35/60.html

2、Data Acquisition DA Digital to Analog Isolated Transmitters: ISO DA Series ：http://0032.psznh.cn/products_35/61.html