simple photo eye problems!

Wow today i am having a big problem and felling pretty dumb! I am trying to use a banner vs1 photoeye as an imput into my slc 500. You can wire it up using pnp and npn but i can not get it to work npn(pos. switching) For anything! I have 3 wires blue, brown, and black. The black wire on the print is showing load and i am using it as my signal.

I can get it to work as neg. switching(but dont want to use a relay), but not pos. switching. What kind of a load do i need on this thing?

Thanks!

What type of input card are you connected to?

According to the VS1 datasheet
http://info.bannersalesforce.com/xpedio/groups/public/documents/literature/56465.pdf
you have to purchase the sensor with the logic you want (PNP or NPN). One sensor will not do both. From your description I'm guessing that you have the NPN version.

I am not familiar with this type of photoeye but with photoeyes i've used before there has been a switch on the photoeye to choose npn or pnp.

Just change the logic from XIO to XIC or vice versa......In the old days of relay logic this was a problem PLCs make it easy. :site:

On this particular model you ONLY have NPN switching mode.
Usually 4 wire sensors have the switch or by selecting the wire (Black or white) you select your switching mode (PNP or NPN).
If you do not want to purchase a new sensor and your application (detection time) isn't a fast one, use an optocoupler to do the NPN switching for you so you can interface it to the existing PLC.

tacm said:

Just change the logic from XIO to XIC or vice versa......In the old days of relay logic this was a problem PLCs make it easy.

Click to expand...

PNP/NPN is not the same as normally open/normally closed.
PNP and NPN devices can both function as normally open or nomrally closed switches.

A PNP device applies a voltage potential to an input terminal.

An NPN device is connected to an input terminal which sources a voltage potential and swtiches that potential to ground or neutral.

            PNP_sensor          PLC

+24VDC--------] [-------------[Input]----0VDC

 

 

 

             PLC              NPN_sensor

+24VDC------[INPUT]--------------] [-----0VDC

 

However, an NPN device could be wired to sink the voltage applied at an input and then the logic would be inverted with respect to the PLC input, which may be what you were thinking, there is just more to it than software logic. It must be wired differently and an upstream load must limit the current.

 CURRENT_LIMITING_LOAD       PLC

+24VDC----/\/\/----------+-------[INPUT]-----0VDC

                         |

                         |      NPN_SENSOR

                         +---------] [-------0VDC

In this instance, the PLC input sees voltage potential when the NPN sensor is OFF.

A better solution is to match the PLC input type and the sensor type, even if that means buying another sensor, ie, the correct sensor.

I agree with Alaric. It's not really a question about PNP or NPN sensors.

I think it may be more of a question on light operated or dark operated photoeye modes.

I prefer dark operated mode photoeyes in case a wire gets cut I'd rather have the input default to being blocked than clear in most situations.