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yes the circuit used pnp transistor which needs negetive signal for biasing butt its actual reason is that our harmonics and noise signals which are present every time in our medium are positve so it can not affect the vibration signal. so this is the main reason that our vibration signal is negetive and we precisely and accurately measure the vibration of rotating equipment.
Because the circuits used PNP transistors, a negative bias voltage was required rather than a positive bias voltage. Don chose -18V. This was later changed to -24V to allow more linear range from the transducer.
what differ between normal power supply and loop power supply
Please lakmuddian send me document simply describe how measure vibration and difference between radial and sismic and kay phasor
your answer is already hidden in your question that is PNP( positive-negative-positive). In PNP there is Emitter Base Junction and Emitter is at +2v. Then how you can give a +ve voltage???
Main funda of the NPN and PNP is electrons & holes. In PNP holes are majority careers. Since the Base Collector junction is always at reverse biased then the opposite polarity voltage (-ve) shoulde be for the Collector. That is why Base of the PNP transistor must be -ve with respect to Emitter. and Collector is also more -ve as compare to Base.
