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Puzzler

Hi All,

I recently acquired an inductive proximity sensor designed for industrial applications.

The unit has two terminals and runs on 10..55V DC.

All you need to do to connect it up is place a load (relay etc) in seres then apply power.

The interesting property is that wired one way around the unit is normally open (apply a metal plate to the sensor and it switches on). Wired the other way around and the unit is normally closed (apply a metal plate to the sensor and it switches off).

The unit claims a maximum dropout of 4.6V.

This poses some interesting design issues:

My first inclination was that the terminals of the unit went through a full wave bridge before the drive electronics. This will be tricky as you have just lost 1.2V across the bridge and leaves 3.4V for the electronics.

Second thought was that there are two complete systems within the unit. One for the 'positive' polarity (NPN) another for the 'negative' polarity (PNP). Each system is designed with opposite output drive sense.

Anyone have any other thoughts about topology of this device ?

See

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Regards,

Mark

Reply to
MarkAren
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3V @ 800uA should be plenty for the electronics.

Reply to
Spehro Pefhany

Even with the original spec of 2V dropout, Schottky diodes would leave about 1.2 volts for the electronics. But an electromechanical relay that will work from 1.2 volts to 55 volts would need some special circuitry. A SSR would not be much problem.

Paul

Reply to
Paul E. Schoen

3.4V is probably plenty....

suppose they use schottky diodes for the bridge then they'd have 4v for the electronics - which is heaps.

.---------. .---------. ___ | | | |-----' 3 sensor o--------|~ +|-----| | 3 | | | |------___3 | bridge | | out|---. |rectifier| | | | o-----+--|~ -|-----| | | | | | | | | | `---------' `---------' | `-----------ZZ-------------' 2x4.2v zener that's probably not how they do it though. bye.

Reply to
Jasen Betts

I can think of several ways to accomplish this, but ....

...having one device that can be wired up backwards and invert its logic seems to be an invitation for trouble. In the event that the commissioning test isn't thorough or a unit needs field replacement and the technician isn't aware of the system operations, this could get put in backwards and appear to work.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
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If your only tool is a hammer then every problem looks like a thumb.
Reply to
Paul Hovnanian P.E.

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