With the continuous development of the digitalization of the electronics industry, a digital system has become the main form. A/D and D/A converters are receiving increasing attention as interfaces to analog and digital circuits. With the rapid development of digital technology, the requirements for A/D and D/A converters are getting higher and higher, and new analog/digital and digital/analog conversion technologies are emerging. Through these conversions, people can use various controllers for remote monitoring, such as controlling the temperature and humidity of a certain space, controlling the liquid level and flow of the liquid, and controlling the displacement, speed and pressure of the object. In the actual working environment, the analog current or voltage signals output by various sensors, PLC AO modules or DCS systems are weak (many are mV or mA), and generally have low load capacity. Directly used to monitor remote execution equipment, often due to long-distance transmission caused by signal attenuation, distortion, and sometimes due to other external signal interference caused by signal errors, affecting the normal operation of the entire system.
Therefore, to ensure the reliability of the monitoring system, it is first necessary to isolate, amplify and convert the analog signals output by various sensors, multi-channel PLCs, DCS, etc. in the system. In some cases, remote transmission without distortion is required through various communication carriers. ISO 4021 (A/D conversion) can convert the analog signal output by the sensor into a digital signal, remotely transmit the signal by RS232/485 communication or wirelessly transmit data by GPRS or GMS, and then use the remote analog signal output module ISO DAO ( D/A conversion) Converts digital signals into analog signals for remote monitoring and control with reduced analog signals. These technologies have been used more and more in SCADA data acquisition and FCS remote monitoring.
First, signal A / D (analog to digital) conversion and remote transmission technology
The ISO 4021 Signal A/D (Analog to Digital) converter enables signal acquisition between the sensor and the host to detect analog signals or control remote devices. The software is configured for a variety 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.
The 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 mode adopts ASCII code communication protocol or MODBUS RTU communication protocol. The instruction set is compatible with ADAM module. The baud rate can be set by code and can be linked with 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 single-chip microcomputer. All user-set calibration values, address, baud rate, data format, checksum status and other configuration information are stored. In a non-volatile memory EEPROM. ISO 4021 series products are designed and manufactured according to industry standards. The signal input/output is isolated, can withstand 3000VDC isolation voltage, strong anti-interference ability and high reliability. Operating temperature range - 45 ° C ~ +85 ° C.
Introduction to the ISO 4021 analog to digital (A/D) converter function:
A block diagram of the ISO 4021 signal A/D (analog to digital) converter, as shown in Figure 1.
Figure 1 ISO 4021 signal A / D (analog to digital) converter block diagram
The ISO 4021 signal isolation acquisition module can be used to measure one voltage or current signal, or it can be used to measure two current or voltage signals that can be grounded together without interfering with each other.
1, analog signal input
24-bit acquisition accuracy, all signal input ranges have been calibrated before leaving the factory. When in use, users can also easily program their own calibration. For the specific current or voltage input range, please refer to the product selection. When measuring two signals, the two input selections must be the same.
2. Communication protocol
Communication interface: 1 standard RS-485 communication interface or 1 standard RS-232 communication interface, please specify when ordering.
Communication Protocol: Supports two protocols, the character set defined by the command set and the MODBUS RTU communication protocol. The communication protocol can be programmed to enable network communication with various brands of PLC, RTU or computer monitoring systems.
Data format: 10 digits. 1 bit 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 communication network can be up to 1200 meters long and connected by twisted pair shielded cable.
Communication interface with high anti-interference design, ±15KV ESD protection, communication response time less than 100mS.
3, anti-interference
The checksum can be set as needed. The module has a transient suppression diode inside, which can effectively suppress various surge pulses, protect the module, internal digital filtering, and also can effectively suppress the power frequency interference from the power grid.
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