Negative supply of Proximeters

Negative compared to what???

The supply voltage for proximitors are typically -18 VDC or -24 VDC, mainly because that is how Don Bently designed them way back when.... I have seen other brands that use a positive supply voltage, but the industry pretty much standardized on a negative supply.

Why is this a difficulty for you?

Can you please tell name of any brand that used positive power supply

Some of the very old IRD proximitors used a positive power supply, but the industry standards now specify negative supply.

I sincerely doubt that you will find any on the market today that take a positive supply...

Again I would be very interested to know why this is a problem for you...

Most proximiters I've used have an isolated input, so to me there is no fixed negative input?

But there are so many sorts, let's hope he returns to answer your question, Steve.

John.

I was asked this question to Mr. Mark Snyder of

Bently Nevada,his answer was

" the first reliable transistors that were commonly available for use were NPN, which required a negative supply ."

so may be ,from that time negative voltage became the standard of proximeter supply voltage.