The use of isolated transmitters in industrial instrumentation

I. INTRODUCTION A variety of automated instruments, computers, and corresponding actuators are used in production process monitoring and control. The signals in the process range from small signals as small as millivolts to large signals as large as tens of volts, and even signals as high as several thousand volts and hundreds of amps have to be processed. From the frequency point of view, there are DC low-frequency range, there are high-frequency / pulse spikes. Mutual interference between equipment and instruments becomes a problem that must be solved in system debugging. In addition to electromagnetic shielding, solving the "ground" of various equipment meters, that is, the potential difference of signal reference points, will become an important issue. Because the signals of different equipments and meters need to be transmitted and sent to each other, there is a signal reference point problem. In other words, for the complete transmission of signals, ideally the signals of all equipment meters have a common reference point, ie the potential difference between the reference points of all equipment meter signals is “zero”. However, in the actual environment, this is almost impossible. In addition to the voltage drop caused by the wiring resistance between the “grounds” of the various equipment meters, there are various types of equipment meters that suffer from different interference in different environments. As well as wire contact points subjected to wind and rain leading to a drop in the quality of contacts and many other factors, resulting in a difference between each "ground".

Industrial field instrumentation In the industrial production process control system, it is necessary to monitor the electrical signals transmitted by the front-end sensors, and also transmit the processed signals to the control center host. In order to ensure the reliability and stability of the signal transmission, it is necessary to consider the signal ports. Isolated processing to eliminate the problem of ground potential difference after the meter is connected to the system.

Second, the general composition of industrial field instruments.

Industrial field instrumentation is applied to the industrial production process control system. Its role is to sample the on-site sensor signal, calculate the sampled value according to a preset algorithm to obtain the value of the monitored physical quantity at the actual site, and communicate the actual field physical status to the communication bus or The 4~20mA current signal is output to the main control center. The sensor signal is input to the industrial instrumentation. The first is the EMC protection circuit. Because the electrical environment at the industrial site is complex, there are strong electrical equipment and high-frequency switching equipment. These equipments will start and stop when they move. Larger surges and spikes are generated. This type of interference contains relatively large amounts of energy. Such interference is absorbed by EMC protection devices such as varistors, TVS tubes, and other devices to protect subsequent circuits from such interference. Cause damage. After the sensor signal is passed through the EMC protection circuit, the isolation amplifier input to the input terminal performs signal isolation and conditioning. The signal isolation can ensure that the internal circuit of the instrument and the external sensor form a ground line to block and eliminate common mode interference, thereby eliminating the ground line caused by the ground potential difference. Circulation, on the one hand, ensures that the sampling accuracy of the sensor signal is not affected by interference. On the one hand, it can protect the internal MCU system from damage caused by large common-mode voltages; the signal conditioning will convert the sensor through signal type conversion and signal amplification. The signal is linearly amplified to meet the signal type and range of the ADC sampling, to ensure that the signal range after conditioning and the input range of the ADC signal match to ensure the ADC sampling accuracy. The MCU digitally computes the digital signal after the ADC has been digitally quantized. After a series of operations such as digital filtering and linear operation, the MCU obtains the actual status of the physical quantity on the site and outputs it to the display panel. At the same time, the field physical value obtained is proportional to the linear ratio. Output to the DAC circuit, DAC circuit output voltage signal, in order to form a 4 ~ 20mA current signal, but also through the output side of the isolation amplifier to isolate the voltage signal conditioning into a 4 ~ 20mA current signal output. Of course, the signal output terminal also needs to design an EMC protection circuit.

Field Application Haiyan Jinhan Electronic Technology Co., Ltd. specializes in the production of FPD series DC isolated transmitter using ASIC chip (special thick film transmitter transmitter), super-linear voltage, current transformer and a full set of high-quality components, together with a full set of high-precision production equipment And computer check calibration system, in strict accordance with the international quality assurance system ISO 9001:2000 assembly production, full specifications, high taste, high degree of integration, work more reliable, with excellent temperature characteristics and long-term stability, good resistance to electric shock Performance and overload capabilities, high level of accuracy and linearity, are ideal third-generation power transmitters that do not require regular calibration and maintenance and are completely reliable. FP series transmitters meet the requirements of IEC, ANSI, BEAMA and other related standards and reach the advanced level of similar international products. FODH DC isolation is an instrument that converts a DC voltage or current signal in a linear scale into different DC voltage or current signals that are electrically isolated from each other. It can be used to measure generator rotor voltage and current, and it can be widely used in various other applications.