DC-DC chip is not isolated, are common ground.
Buy an isolated power module, there are 5V-5V, should meet your needs.
This power module is not large, and the size of the 14-pin integrated circuit is about the same. The two DC power supplies are truly isolated, and the 5V and GDN are definitely isolated. The signal isolator is a signal isolation device, which converts the input single or double current or voltage signal to the output isolated single or double current or voltage signal, and improves the electrical isolation performance between the input, output and power supply.
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In a complex industrial site environment, there are quite a number of signal interference sources will harm the normal work of sensors, instruments and meters the most serious is the grid peak pulse interference, the signal in the transmission process will encounter a variety of interference, in order to ensure signal stability, the use of signal isolation transmitter is particularly important, signal isolator is the input single or double current or voltage signal, Transmit isolated single - or dual-route current or voltage signals and improve electrical isolation between input, output, and power supply.
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First of all, the PLC accepted signal, through the semiconductor device modulation transformation, and then through the light or magnetic sensing device isolation conversion, and then demodulation transformation back to the isolation of the original signal or different signals, while isolating the power supply of the isolated signal, signal isolation transmitter can ensure that the transformed signal, the power supply, the absolute independence between the ground; Accept temperature signals from thermal resistors, thermocouples, temperature transmitters, etc., for isolation processing, that is, isolation temperature transmitters; The working energy of the passive signal isolator can be taken from the isolator output (conventional\/i.e. not specified by the user) or from the isolator output (specially customized).