possible or not?

bigrthanur · Aug 30, 2008

Does anyone know of a situation where a 24VDC photo eye would power up in reverse polarity. not talking signal wires just pos. and neg. being reversed.

CeCo3 · Aug 30, 2008

not talking signal wires just pos. and neg. being reversed.

What ARE you talking about? Please elaborate.

ndzied1 · Aug 30, 2008

bigrthanur said:
Does anyone know of a situation where a 24VDC photo eye would power up in reverse polarity. not talking signal wires just pos. and neg. being reversed.

Is this something you want to do or something you saw and are trying to explain?

If it relates to a specific product what is the manufacturer and part number?

If you want to make something so that it can't be hooked up with reversed polarity, how about a keyed connector?

MasterBlaster · Aug 30, 2008

I suppose one could wire a small relay in such a way that if the incoming voltage polarity is "corect", the relay does nothing but pass the voltage to the circuit board. But if polarity is reversed, the relay energizes, and the contacts are wired to reverse the polarity at the output of the relay so the circuit board never knows the difference.

I've not sketched it out, but my mind's eye can see it working.

Bill

keithkyll · Aug 30, 2008

Some devices are universal AC/DC. They have an internal full wave bridge. This is typical of 2 wire devices.

bigrthanur · Aug 30, 2008

Why i am asking is our plant manager asked the question to a mechanic about a photo eye being wired correctly. Pos. to Pos, and neg. to neg. He stated that he has seen before a photoeye wired backwards and still worked but had wrong voltage and would not give an output.

I disagree with him and was thinking he was talking about NPN vs. PNP. He said NO it is possible to wire a 24VDC eye backwards and eye will still show lights as "working" but will give wrong voltage on output.

milldrone · Aug 30, 2008

bigrthanur,

I do not know what your manager saw, but perhaps this is a possibility.

Banner makes a photo eye series (ez beam) that has two diferent configuations depending on how it is hooked up. One configureation is with a NC and a NO output. But if you reverse the polarity on the wires (blue to positive, brown to negative) then one of the outputs is an alarm output to warn you if the excess gain goes below 1.5 . The other output will be NO.

So if he connected to the alarm output the photo eye would appear to work (by looking at the indicator lights) but there would be no change of state on the alarm output if the excess gain were outside of the .9999999 to 1.5 excess gain area.

panic mode · Aug 30, 2008

what is the part number of the sensor?

milldrone · Aug 30, 2008

panic mode,

Were you asking me or bigrthanur?

brucechase · Aug 30, 2008

If it was me, I would just wire one up in front of the boss and see what it does.

bigrthanur · Aug 31, 2008

brucechase said:
If it was me, I would just wire one up in front of the boss and see what it does.

Thought about it but He would just make another excuse to how he was right.

Anyway i am putting my 2 weeks in on tuesday. I GOT THE JOB I HAVE BEEN WAITING FOR. I am now officially a robotics engineer!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

panic mode · Aug 31, 2008

hi mildrone,

sorry i wasn't clear, i was asking bigrthanur. there is plenty of products on the market and they may behave differently. it would be good to know what product we are talking about.

for example reverse wired reed switches may work but not lit the indicator.

in this case we are talking about photo eye, chances are the boss is recalling case where the output configuration of the sensor didn't match the plc input so even if the sensor is working, plc sees no change (PNP/NPN mismatch)

Cameltoe Fancier · Aug 31, 2008

I believe this is what milldrone is speaking of

http://info.bannersalesforce.com/xpedio/groups/public/documents/literature/116157.pdf

As you can see from the connection diagram the power polarity is reversed in relation to the blue and brown wires when the alarm configuration is desired.

If the PLC input was connected to the NC (white output wire) and the polarity was switched on the blue and brown wires. Then this output would only turn on when the alarm condition exsits.

The sensor would appear to function according to the led indicator lights but the PLC input would not change because the was connected to the alarm input. Then if the plant manager switched the power leads to 24V+ on the brown and 24V- to the blue, the output would change just like the indicator lights on the photo eye.

bigrthanur · Sep 3, 2008

cameltoe: The drawings you have there, I believe that thoes are two different part numbers one part for an alarm and one with out an alarm. Am i correct?

Cameltoe Fancier · Sep 3, 2008

bigrthanur,

No, all of the EZ-Beam series, (DC only) have this feature

The S18 series (DC)
http://www.bannerengineering.com/en-US/products/16/Industries/660/c/157/S18-DC
The T30 series (DC)
http://www.bannerengineering.com/en-US/products/16/Industries/660/Food-Beverage/176/T30-DC

T30SN6LP

T30SN6LPQ

T30SP6LPQ

S30 series
http://www.bannerengineering.com/en-US/products/sub/171/S30-DC

S30SN6R

S30SN6RQ

S30SP6R

S30SP6RQ

Q40 series (DC)

http://www.bannerengineering.com/en-US/products/industry/17/660/Food-Beverage/88/Q40-Series

T18 series

http://www.bannerengineering.com/en-US/products/industry/17/660/Food-Beverage/125/T18-Series

.

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