Answer / naveed iqbal

actually in proximaty probes inside used PNP tanasistor.so
transistor baising supply need - dc voltage.

Answer / chandrakant sahu

There is PNP type transistor used in ocsilator and also ti keep minimum interference negative voltage is suitable for this

Answer / waleedmahmoud

The basic reason is that the power supply is -24 VDC. So
since the supply voltage is negative the output voltage
will be as well.

IRD at one time made prox probes with a positive supply and
as a result a positive output.

Way back in the 50's uncle Don Bently made a design
decision to use a negative supply voltage (back then it
was -18 VDC rather than -24 VDc in the modern device) in
his circuit. This decision has stuck and is now even
included in the API standards

Positive are also there for example.

Metrix 5465F is -ve gap voltage

Metrix 5465E is +ve gap volatge

It does not make much of a difference wether you use
positive or negetive voltages. It is -ve because Bently
started with the design of -ve and now we stick to -ve.

Answer / md. rizwan

Because we measure the negative voltage in vibration system.

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