Protection against high currents and voltages is a very important requirement for signal processing circuits. A high current can be protected against by the incorporation in the input line of a series resistor to limit the amount of current flowing to an acceptable level and a fuse to break if the current exceeds a safe level. This arrangement is illustrated in the figure 1(a) below:
It is also crucial that high currents or voltages are not transmitted from the sensor to a microprocessor hence it may be required to completely isolate the circuits so that there are no electrical connections between them. This can be accomplished by using an optoisolator as illustrated below:
The optoisolator converts electrical signal into an optical signal (infrared radiation), transmits this optical signal to a detector which then converts it back into an electrical signal. The input signal passes through an infrared light-emitting diode (LED) which produces a beam of infrared radiation that is detected by a phototransistor.
Related: Optoelectronics
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