Brief introduction of the hottest intelligent elec

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Brief introduction of intelligent electric quantity sensor/transmitter

I. overview

electric quantity isolation sensor/transmitter is a small volume and high-performance electric quantity test component (product) developed for electric quantity detection (monitoring) in engineering and improving the overall anti-interference ability of the system

the electric quantity isolation sensor/transmitter can isolate, measure and transform the electric parameters such as high current, high voltage, power, frequency, phase angle and electric degree on site, and can also isolate, amplify and transform all kinds of weak signals (such as all kinds of bridge signals). After conditioning, it can be transformed into simulation signals such as voltage, current and frequency that meet the international general standards, or transformed into digital quantity, switching value status and other signals for output. These output signals can be connected with traditional pointer instruments, as well as modern digital automatic control instruments, various a/d converters and calculator systems, so as to form a highly reliable industrial detection (monitoring) or control system

due to the application of electric quantity isolation sensor, users do not need to do secondary development work. High voltage or high current signals can be directly connected to the product (input through terminals, pins or perforations), and the corresponding output signals can be obtained. Therefore, as a functional module of signal conditioning, isolation and transformation, electric quantity isolation sensor is an ideal transmitter product in industrial control and data acquisition system

with the continuous development of science and technology, industrial control or detection (monitoring) systems have higher and higher requirements for electrical isolation sensors, especially in terms of product stability, detection accuracy and function. Due to the performance and functions of digital products, such as nonlinear correction and small signal processing, simulation products are incomparable. Therefore, the digitization of electric quantity isolation sensor is an inevitable trend

the following is a brief description of the working principle of the electric quantity isolation sensor and its digital technology for your reference

II. Basic working principle of electric quantity isolation sensor

since the detected objects of electric quantity isolation sensor products are mainly current and voltage signals, the following mainly introduces the detection principle of current and voltage signals

AC signal detection principle

AC signal is divided into AC voltage and current signals. Figure 1 is the detection principle block diagram of AC current signal, and Figure 2 is the detection principle block diagram of AC voltage signal. The signal is isolated by CT and Pt. The current is the perforation input mode, and the voltage is the terminal wiring input mode

among them, CT is current transformer, Pt is voltage transformer, and the output is generally 0~5v or 4~20ma

2. DC signal detection principle

Figure 3 is the block diagram of DC signal detection principle

Figure 3 Schematic diagram of DC signal product

DC signal is divided into DC voltage and DC current. DC current is generally sampled through resistance, and DC voltage is generally reduced by resistance, and an isolated power supply supplies power to the preamplifier

it can be seen from the above principle block diagram that the input and output of both AC and DC signals are completely isolated. Generally, the field input signals are high current or high voltage, so that the electric quantity isolation sensor can completely isolate the field signal from the low-voltage data acquisition system, avoid the interference of strong signals, and improve the reliability of the system

III. digitalization technology of electric quantity isolation sensor

Figure 4 is the combined block diagram of an AC signal digital electric quantity isolation sensor, which is composed of transformer, data processing, interface, t/v transformation and output

Figure 4 schematic block diagram of AC signal digital electric quantity isolation sensor

the transformer has two parts: current transformer and voltage transformer. Aging and loosening of parts is a problem caused by long-term use of the equipment. The current transformer is generally perforated, and the voltage transformer generally needs to add current limiting resistance at its original side

the data processing part is the core part of product digitization. At present, MCU with a/d converter is generally selected, such as PIC16C74, MSP430 or adcuc812. Therefore, the circuit can be very simple. If you choose ADuC812 single chip microcomputer, you can directly output 0~5v voltage signal, because it contains two 12 bit d/a converters

the interface part is the conversion circuit of digital signal output. At present, RS-485 bus interface is widely used. The most commonly used interface chip is adm483, which can connect 32 nodes at most. Of course, there are many other similar chips now. There are generally two ways to realize RS-232 interface, one is to add an rs-485/rs-232 converter to the RS-485 network, and the other is to directly put the RS-232 interface chip in the product. The disadvantage of the latter is that the application of the product will be limited, and it can not form a network structure, but only point-to-point communication. CAN-bus is a bus with rapid development at present. Its advantage is that the transmission distance is long, it can reach 10km, there will be no bus conflict, the multi master working mode, and the communication protocol has good universality. Of course, its cost is high

t/v transformation 6. The end of the experiment of bellows ring stiffness tester is to be compatible with the simulation signal acquisition and input system. At present, PWM mode is generally used for output, and then through t/v transformation, 0~5v or 4~20ma simulation signal is output

the software mainly includes three functional modules, data acquisition, data processing and communication protocol. Among them, data acquisition is mainly to read the conversion results of a/d. Because the MCU has its own a/d, the program is relatively simple

data processing mainly completes the operation of AC to DC. Because the operation speed of single chip microcomputer is limited, we use the frequency tracking method to complete the calculation of transformation

therefore, since its inception at the beginning of this century, the demand has soared. Communication protocols are generally selected by users, such as Modbus protocol, ASCII format, etc

IV. conclusion

the above briefly introduces the basic working principle and digital technology of the electric quantity isolation sensor. Because the digital electric quantity isolation sensor can directly output digital quantity, for many application systems, the a/d acquisition module can be omitted, so the system cost can be reduced. Therefore, the digitalization of electric quantity isolation sensor can not only improve the stability of products, but also enable users to further reduce costs

because there are many kinds of electric quantity isolation sensors, this paper only introduces a digital technology of AC signal electric quantity isolation sensors. There are many ways to realize the digitalization of electrical isolation sensors. At present, the most common is to use the performance of waste foam granulator with single-chip microcomputer technology for higher R & D and skill investment, because its application is very flexible and can realize various functions. With the continuous development of integrated circuits, there have been many special chips, such as watt hour meter products. There are many special chips available, including digital interface and pulse output

this paper makes a superficial discussion on the digitization of electric quantity isolation sensor products, which is only for the reference of relevant personnel, hoping to play a role in attracting jade and accelerating the greater development of digital technology of electric quantity isolation sensor. (end)

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