Rods "Spaceship" Scratch built Plasma Cutter build

Well, the last round of testing came to a sudden stop when the proximity sensor on the Z axis home switch failed. This is the second time its failed. Originally, I bought a swag of NPN connectors and I added some pullup resistors.

So this time I ordered some PNP sensors and thought it would be easy enough to unhook the relevant resistor. You can see it in the foreground with one leg waving in the air.



But I must have created a short when unsoldering the resistor and I let a lot of smoke out of the sensor. As per usual what should have been a 10 minute job took hours so I did not get any more tests done this weekend.

So I have a question for the brains trust. Should proximity sensors be protected with a current limiting resistor?

rodw wrote:
So I have a question for the brains trust. Should proximity sensors be protected with a current limiting resistor?

Yes... But like everything.... It depends.... On your breakout board circuit.

Am I reading the resistance correctly.... 11k ohm?

Thought that would be a bit high... What voltage are you running the limit switch circuit at?

Please bear in mind that proximity sensors have a leakage current.... They are not quite digital... If the resistors too high there will be a voltage across the resistor when it's off and it may be high enough to imply that the sensor is on. This is more of a problem if you have electrical noise or if you run the sensors in parallel....

www.google.co.uk/url?sa=t&source=web&rct...28UbibFqqS8tDHGudUFr

www.google.co.uk/url?sa=t&source=web&rct...a-5OKbX1-rnzI6FOHKTf

Some good info , just word search "leakage"

Also the recommended wiring arrangements for sensors (more an issue if you have multiple sensors on one input)

Another one

www.google.co.uk/url?sa=t&source=web&rct...hhJrQw376pMyRQOsmpAt

Hi Rod,

You have no luck. Why not try IFM sensors 24vdc in combination with Finder relais 24Vdc? Then you are also more protected to your Mesa equipment.

Thanks guys, I think its all fine. I did notice in Robert's second link that they used a 100 ohm resistor with a couple of diodes so I might try adding that to the new PNP sensor and worry about the others when they fail. Fortunately, I've left a fair bit of room for extra components on my distribution power board on top of the gantry.

Really, so many of my issues has been a lack of knowledge of electronics, crappy soldering skills and failing eyesight!

I have not really had any mechanical issues, its all been electronics.