Applications of Analog Input Isolators
Yien offers a wide range of analog input isolators, categorized by the number of input channels into single‑channel and dual‑channel models, as well as versions that provide one‑input, two‑output signal distribution functionality.
2025-05-24
Yien offers a wide range of analog input isolators, categorized by the number of input channels—single‑channel and dual‑channel models—as well as versions with one input channel and two output channels for signal distribution. By power supply type, they are available in loop‑powered and independently powered configurations.
Loop-powered type
Both input and output are two-wire, making wiring convenient. The isolator supplies power from the DCS, PLC, or digital display meter, which is then isolated to provide power to the two-wire transmitter. Simultaneously, the two-wire transmitter generates a 4–20 mA signal that is isolated and fed into the DCS, PLC, or digital display meter. This solution is suitable for field‑mounted two‑wire transmitters that require isolated input to a DCS, PLC system, or display instrument, particularly when the input module of the receiving device provides its own internal power supply.
Shortcomings:
1. Generally, the transmitter should be able to operate with a 12 V power supply.
2. The transmission accuracy of isolators with independent power supplies is relatively lower; this should be taken into account when selecting them.
Independent power supply type
A commonly used power‑supply isolation barrier for two‑wire transmitters requires an independent power supply; its characteristics are:
1. High transmission accuracy, reaching 0.02%.
2. It can interface with two-wire transmitters, three-wire transmitters, or current-source signals, making it easy to use.
3. The power supply, input, and output are completely isolated from one another, providing excellent immunity to electromagnetic interference.
One-in, two-out signal distribution isolator
In practice, we often encounter situations where a transmitter signal needs to be connected to two or more receiving devices. If a series loop is used, an open circuit anywhere in the loop will result in no signal being delivered to any instrument on the loop. Moreover, the combined load resistance can easily exceed the transmitter’s maximum allowable load, and it is also essential to ensure that the reference points of the two loads are different.
This method is generally not used; instead, a resistor is connected in series within the circuit, and the load is connected in parallel across the resistor to obtain the voltage signal. For example, by inserting a 250 Ω resistor in series, a 4–20 mA current signal can be converted into a 1–5 V voltage signal. Although this approach avoids issues such as open circuits and limited load‑driving capability, it does have the following drawbacks:
1. The method of obtaining a voltage signal by means of a series resistor assumes that the receiving device has an infinite input impedance; consequently, the input impedance of the receiving device inevitably introduces measurement errors, and the greater the number of devices connected in parallel, the larger these errors become.
2. The longer the wire, the greater the voltage drop due to wire resistance, and the more significant its impact on the actual voltage signal; therefore, the signal transmission distance should not be excessively long.
3. Because RFI/EMI signals can easily superimpose on voltage signals, this connection is susceptible to radio-frequency and electromagnetic interference.
The optimal solution to the above issues is to use a signal splitter, which converts a single input into two isolated outputs, offering high precision and strong isolation.
1. The two output signals may be identical or different, and complete isolation is achieved between the transmitter and each receiving device.
2. A fault occurring in any one receiving device will not affect the entire loop or the other receiving device.
3. The Yi’en G-series signal distributor perfectly achieves a 1-to-2 signal split with opto-isolation, strong anti-interference capability, and stable signal output.
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