Should you isolate sensors?

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Connecting a physical sensor to a data acquisition system is a serious undertaking. A laboratory connection may work well when connected with short wires in a benign environment. When mounted in the real world of electromagnetic signals and repetitive or one time emissions, several things should be considered. These topics are covered in much greater detail in Dataforth application note AN116, Why Use Isolated Signal Conditioners .

Overvoltage
Often overlooked is accidental connection to power line voltages. Inside a busy electronics cabinet this can easily happen either by an installation mistake or a dropped wire. Yes, some people have been known to work wiring hot. An isolation barrier will prevent a harmful voltage from getting into sensitive circuitry. Dataforth’s signal conditioning products provide a 1500V withstand barrier between the sensor and a user system. In addition they are designed to withstand connection to power line voltages without damage to themselves.

Crosstalk
Careless wiring and cabling can obviously cause problems. With good practices in the field, crosstalk still must be considered; because some sensors and long wire runs present a moderate to high impedance to a data collection point. Even active or smart sensors that present higher voltages and low output impedances need some consideration of possible crosstalk. Twisted wire pairs and shielding are the best practice. Remember that wiring capacitance adds to the output capacitance at the receiving end. Multiplexers allow one channel to interfere with another channel due to charging these capacitive effects. A signal conditioning amplifier presents a low resistance and small, uniform capacitance to the system multiplexer.

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