Application Analysis of Analog Isolation Transmitter and Frequency Converter Technology

The analog signal isolation amplifier (also known as analog isolation transmitter) for input and output between industrial field sensors and PLC/FCS/DCS and instrumentation belongs to the category of analog signal conditioning. The analog signal isolation amplifier can effectively protect the control loops at all levels, eliminate or reduce the influence of environmental noise on the test circuit, suppress the interference of the common ground, the inverter, the solenoid valve and the surge pulse to the device, and have the signal voltage limit for the lower-level equipment. Turbulence function. It is a reliable protection device for transmitters, instruments, inverters, solenoid valves, PLC/DCS input and output and its communication interface. For some industrial sites with harsh environments, the control system is intricate, and the high temperature, vibration, humidity and interference signals coexist. Therefore, the input and output analog signals are amplified, converted, and transmitted remotely through the isolation amplifier, and the system loops are completely isolated. This is indeed the automatic control today. One of the effective measures against interference in the system.

The so-called bandwidth (also called bandwidth) refers to the amount of data that can be transmitted at a fixed time, that is, the ability to transmit data in the transmission pipeline. In digital devices, the bandwidth is usually expressed in bps, which is the number of bits that can be transmitted per second. In analog equipment instruments, bandwidth is typically expressed in transmission cycles per second or hertz (Hz). The bandwidth of a signal refers to the range of frequencies occupied by the various frequency components contained in the signal.

The frequency response is referred to as the frequency response, which is used in electronics to describe the difference in processing power of signals from different instruments such as instruments and PLCs. Like distortion, this is also a very important parameter indicator.

The test method of the bandwidth indicator is as follows. A frequency-adjustable sine wave analog signal is added to the input end, and the maximum frequency range at which the output can stably follow the input signal is the bandwidth. What is the engineering significance of the industrial signal isolation amplifier bandwidth indicator? How do we understand "bandwidth" in the application? The bandwidth metric reflects the response speed of the isolation amplifier to changes in the input signal. The larger the bandwidth, the faster the isolation amplifier responds to signal changes; the smaller the bandwidth, the more the isolation amplifier is insensitive to the transient response of the input signal, and in some cases it means stronger resistance to interference.

The working principle of the isolation amplifier and the isolation transmitter is to first modulate the standard signal transmitted or received by the sensor, instrument, PLC, etc., or the special signal such as temperature, displacement, frequency, and rotational speed through the semiconductor device, and then the light sense or the magnetic sense. The device performs isolation conversion and transmission, and then demodulates and restores the original signal with the same precision and linearity or transforms into other signals, and simultaneously isolates the working power of the signal before and after isolation to ensure signal input, signal output and auxiliary power supply. That is, the signal, power supply, and ground are separated before and after the conversion. Analog signal isolation amplifiers and isolation transmitters belong to a class of industrial instrumentation and sensor classification. Their main functions are analog isolation, amplification, conversion and transmission. Therefore, there must be a basic signal bandwidth and frequency response. Technical indicators.

Industrial site signal transmission interference processing reference scheme (inverter anti-EMC interference dedicated isolation amplifier):

Industrial sites have frequency conversion control equipment, high-power electromagnetic starting equipment, GPS high-frequency signal wireless transceivers and other systems with EMC interference sources. It is necessary to analyze and determine the interference signal processing solutions for different interference sources and system control signals.

1, the sensor output interference on the analog signal

The addition of ISO series analog signal isolation amplifiers at the sensor output can effectively solve the attenuation and EMC interference during the transmission of analog signals, and enhance the stability and reliability of the display control system. Analog signal isolation amplifier for inverter anti-EMC interference: ISOEMU-POM series, is equipped with input signal interference suppression filter circuit and output interference harmonic absorption circuit inside the IC to enhance anti-EMC electromagnetic interference and high-frequency signal spatial interference. . It is especially suitable for occasions where there are frequency conversion control equipment, high-power electromagnetic starting, and GPS high-frequency signal wireless transceiver.

2. Spatial interference of high frequency signal radiation

Each control system and equipment are respectively equipped with a metal shielding box (the metal components used in different frequency segments are different) and the housing is reliably grounded, and the signal communication transmission line is a twisted pair shielded cable.

3, RS232/RS485 remote communication line interference

The DC-DC isolation module power supply is installed on the RS232/RS485 communication interface to directly isolate the communication power supply from other power sources. The signal communication transmission line also uses a twisted pair shielded cable (shielded grounding).

4, the interference in the system power supply circuit

There are large current thyristors, frequency conversion control devices, and high-power electromagnetic starting devices on the site, which will have distortion effects on the power supply parameters of the power supply system. Through the power circuit, the interference signal will enter the various control devices in the field. Therefore, first make sure that the devices in the field are well grounded, and the power supply of each device should be equipped with a matching power supply filter (low-pass EMI filter or suppression reactor).

Analog signal isolation amplifier isolation transmitter bandwidth and frequency response industrial field technical indicators selection application reference:

1. When the analog signal is slow (<50Hz) (such as measuring temperature, pressure, displacement, flow, etc.), an isolation amplifier with small bandwidth and low frequency response can be selected: ISOEMU(A)-POM series products (M: Indicates low frequency sound). Therefore, in the inverter control system, in order to suppress and isolate the EMC interference, the isolation amplifier of the ISOEMU-POM series is often used.

2. When the analog signal is high (>2KHz) (such as measuring the speed, adjusting the high-speed electronic switch, PWM control of the switching power supply, etc.), in order to ensure the integrity and reliability of the collected data, high bandwidth and high and low frequency are often used. Isolation Amplifier: ISOEMU(A)-POH series products (H: indicates high frequency response).

3. Most systems other than high-frequency and low-frequency environments choose conventional frequency response (2K) products: ISOEMA-PO or ISOEMU-PO series.

4. Opto-isolated amplifiers can be used for strong magnetic space interference (high-frequency electromagnetic high-current load) in the field environment: ISOU(A)-POM series.

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Label: Analog Isolation Transmitter and Drive Technology

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