Analog signals entering and leaving the PLC system are isolated using signal isolators
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Analog signals entering and leaving the PLC system pass through signal isolators, which seem to come in active and passive types – which one is generally used?
A signal isolator is a device for signal isolation that takes in single or dual-channel current or voltage signals, converts them into isolated single or dual-channel linear current or voltage signals, and enhances the electrical isolation between the input, output, and power supply. 1. Isolator with independent power supply: It requires a separate DC power supply of 20~35VDC. The advantage of this method is high isolation transmission accuracy ； There is complete isolation between the power supply, input, and output; multiple system power supplies do not require isolation, which ensures high interference resistance, and the input signal can be converted into other types. 2. Isolators for loop-powered systems: In actual industrial monitoring systems, the use of DCS, PLCs, or other display instruments that are powered internally by cards is becoming increasingly common. Loop-powered isolators often fail to meet the high requirements of such cards for signal isolation and transmission accuracy, as well as the high voltage requirements for powering two-wire transmitters. Therefore, the isolator with power supply from the output circuit retains the superior performance of the isolator with independent power supply, while also meeting the requirements of the output circuit power supply interface. Instructions for use: Input circuit – Default is single circuit. D: Dual circuits (isolated from each other). Input signals (both inputs are the same): 1: 4-20mA; 2: 1-5V; 3: 0-10mA; 4: 0-5V; 5: 0-10V. First output: 1: 4-20mA; 2: 1-5V; 3: 0-10mA; 4: 0-5V; 5: 0-10V. Second output: 0 – Default is no second output. 1: 4-20mA; 2: 1-5V; 3: 0-10mA; 4: 0-5V; 5: 0-10V. Power supply method: Default is 220V AC. D: 24V DC
Building on the reply from the second floor, I would like to share my opinion. The use of loop power supply is not common; in fact, the power supply method for isolators is quite similar to that of safety barriers – both rely on an external power supply circuit to ensure reliable and stable operation of the circuit. If isolators are used in control circuits, such as for electrical frequency conversion control, it is recommended to use an external power supply circuit. As for display isolation, could the loop power supply method be considered? Let’s discuss it before implementing it.
Which specific type to use depends on the type of signal wiring used in your PLC card