3 wire PNP N/C proximity switch (Resolved)

[Growls]

Is it possible to use this type of switch with Acorn as inputs for homing? How would they be wired? The voltage range is between 10 and 30 vdc. I have searched the forum and most references are for two wire limit switches or possibly 3 wire NPN switches.

[Richards]

A PNP sensor SOURCES current (or provides positive voltage). The inputs on the Acorn require the attached device to SINK current (or pull down the Acorn's input voltage from +24VDC to near 0 volts). A PNP device does not SINK current. In order to make a PNP device compatible with an Acorn input, you need to change the polarity of the sensor's output, such as using a relay. The PNP sensor would control the coil on the relay. The contacts of the relay would be wired to provide a SINKING circuit for the Acorn's input. An external PLC, such as the $69 CLICK from AutomationDirect can also be used. If the complexity or the final cost of your design makes a PLC a practical way to solve the problem, then it might be the best solution. At one point, I had homing sensors, limit sensors, servo fault signals (from two different manufacturers that had opposite polarities, and I had the need to control the servo enable signal. A PLC was the simplest solution.

If you decide to use a relay board, be sure to buy one that works with PNP signals. That means that it will have common GND signal on its input side and individual inputs for each relay. With a PNP N/C sensor, a relay connected to the sensor will always be on unless the sensor senses the homing target. You can buy six or eight relay boards on EBay for about $20. Just be sure that you buy one that works with PNP sensors.

[Growls]

Mike, thanks for the reply.

It was less expensive to just order NPN normally closed sensors. I got 5 of them for $18.00.

[cxagent]

The forum is AWESOME! I was about to post a similar question but a search showed it had recently been answered!

[martyscncgarage]

The forum is AWESOME! I was about to post a similar question but a search showed it had recently been answered!

This is exactly why I send all users here to ask their questions. They remain archived and searchable for the next user!