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Signal isolators utilize electromagnetic isolation and optoelectronic isolation technologies to couple the received signals to the output through sampling/modulation, and then achieve isolated signal transmission via signal demodulation/conversion. In addition to suppressing interference through isolation, signal isolators also perform functions such as signal transmission, amplification, interface matching and bridging, as well as signal distribution. yunrun.com.cn/tech/3439.html Question 1: What is the difference between an isolator and a safety barrier? Isolated safety barriers can be used as a substitute for signal isolators, but their costs differ; it is recommended to choose based on actual usage requirements. Signal isolators cannot replace isolated safety barriers; they can be used in explosion-proof systems (Ex d). http://yunrun.com.cn/upload/202011/13/202011131549246454.png Question 2: How to distinguish between active signals and passive signals? First, it is necessary to understand the following basic concepts: current source (the output of a four-wire transmitter is usually a current source signal), three-wire transmitters, and two-wire transmitters. Current-type transmitters convert physical quantities into a standard 4-20mA current output, and therefore require an external power supply to function: 1. Four-wire transmitters – The most typical case is that such transmitters need two power lines plus two current output lines, for a total of 4 wires, which is why they are called four-wire transmitters. Typically, the output of a 4-wire transmitter is a current source ； 2. Three-wire transmitters: The current output can share the same ground wire as the power supply, which allows one wire to be saved; such transmitters are known as three-wire transmitters ； 3. Two-wire transmitters: Most 4-20MA transmitters are of the two-wire type; the 4-20MA current itself can supply power to the transmitter. In a circuit, the transmitter functions as a special type of load; in a two-wire system, the power supply and the load are connected in series, sharing a common point. Signal communication as well as power supply between the field transmitter and the instruments in the control room are accomplished using just two wires. The current consumption of the transmitter varies between 4-20mA depending on the sensor output. Taking Changhui Instruments’ high-performance YR9034A-0-GGNN-N type 1-input-2-output analog input signal isolator with 0.1% accuracy as an example: First, it is necessary to distinguish between the 4-20mA signal acquisition circuit and the power distribution circuit in different wiring systems. In a two-wire transmitter, the signal acquisition circuit and the power distribution circuit share the same circuit (5+, 3-) ； Three-wire transmitter: power distribution circuit (5+, 4-), signal acquisition circuit (3+, 4-) ； Current source (4-wire transmitter): Signal acquisition circuit (3+, 4-) ； The power supply is provided by other power devices. Question 4: For an analog input isolator with independent power supply, does it output an active signal? Conventional products output active signals, suitable for PLC/DCS IO ports that do not provide power. If the IO ports of PLC/DCS provide power, an isolator is required to output a passive 4-20mA signal. Question 5: How to distinguish between independently powered, loop-powered, and output-loop-powered analog input isolators? Independent power supply and circuit power supply generally refer to the power supply methods for isolator modules ； Power supply for the output circuit usually means that the signal circuit is passive and requires external power supply. ◆ Independent power supply: It means that the isolator requires a separate 24V power supply. ◆ Loop power supply: No separate power supply is required for the isolator; power and signal are on the same loop. It should be noted that: 1. The output accuracy of circuit-powered supply will be lower than that of independently powered supply ； 2. Pay attention to the formula Uo=Ue-0.02×RL-Ud; it is required that Uo≥the lowest operating voltage of the field transmitter ； For example: if the supply voltage on the safe side of the isolator is Ue=24V, the load resistance of the field two-wire transmitter is 300 ohms, and the voltage drop across the isolator is Ud=6V, then Uo=24-0.02×300-6=12V. If the minimum operating voltage of this 2-wire transmitter is 15V, the power supply will be insufficient and the transmitter will not be able to function properly. At this time, the problem can be solved by the following methods: ① Reduce Ud by selecting an isolator with a smaller voltage drop ； ②Reduce RL and select an isolator with a lower load resistance ； ③Choose a transmitter with a wider operating voltage range, so that it can function properly at 12V as well ； ④Increasing Ue means increasing the supply voltage to the isolator (the maximum operating voltage of the isolator is 35V).