Tyring to use NPN sensor in place of PNP

sonofthesouth8 · Apr 20, 2015

Ok guys I have a machine down because of a defective prox sensor. The defective prox is a PNP and I don't have a spare, lead time for a new one is 10 days. I have a few NPN sensors of the same style. Basically I'm wondering if there is a way I can connect the NPN to make it switch the positive since that's what my plc is looking for.

jdbrandt · Apr 20, 2015

sonofthesouth8 said:
Ok guys I have a machine down because of a defective prox sensor. The defective prox is a PNP and I don't have a spare, lead time for a new one is 10 days. I have a few NPN sensors of the same style. Basically I'm wondering if there is a way I can connect the NPN to make it switch the positive since that's what my plc is looking for.

Sure.
You cannot hook it up exactly as the old one.
You have to connect the output to a relay coil, and use the relay contacts for the PLC input.

Mickey provided this link a few years ago, and it still works.

http://www.theautomationstore.com/npn-pnp-devices-and-connections/

osmanmom · Apr 20, 2015

the machine design using PNP sensor

Doug-P · Apr 20, 2015

Maybe this will work for you

http://www.dot-as.dk/files/npn-pnp_new.pdf

sonofthesouth8 · Apr 20, 2015

Thanks for the information guys. I'm going to give it a try and let you know how it works out.

osmanmom · Apr 20, 2015

if this critical for safety then please get permission from your management for changing A to B

danatomega · Apr 20, 2015

Since the PNP is sinking, when the prox turns on it would pull your input low.
Your PNP prox sources and can only pull your input high.

Put a pull-down resistor on your input.
Attach your PNP prox to your input.
Invert the logic in the PLC.

You will need to calculate what size and wattage resistor to use to satisfy the input's requirements.

BTalbot · Apr 20, 2015

if the sensor has a M12 connector, Turck makes a NPN/PNP converter in their "Smart Plug" line

http://www.turck.us/Products/Sensors/Smart_Plugs/

shooter · Apr 20, 2015

use a resistor of about 2.5 kiloohm to get the input ON, then connect it normal way and the input should go off when active,
If you cant change program you will need an extra transistor or relay.

Doug-P · Apr 20, 2015

BTalbot said:
if the sensor has a M12 connector, Turck makes a NPN/PNP converter in their "Smart Plug" line

http://www.turck.us/Products/Sensors/Smart_Plugs/

Nice!

Tyring to use NPN sensor in place of PNP

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