Centroid Community CNC Support Forum

I cannot tell from your description, between what two points you are measuring voltages.

What I suggested was not to measure voltage anywhere, but instead to measure current flow through the probe.

You measure current by putting your current meter (milliamp meter), in series, between the probe and the PLC input.

cncsnw wrote: ↑Sat Feb 22, 2025 7:04 pm I cannot tell from your description, between what two points you are measuring voltages.

What I suggested was not to measure voltage anywhere, but instead to measure current flow through the probe.

You measure current by putting your current meter (milliamp meter), in series, between the probe and the PLC input.

Attached is a schematic of how the probe was re-tested. The detect component of the circuit is a switch and LED that when thrown signal the system that the tool touch off is in use.

In the untripped state the leg between the probe and input 7 was 4.31A and once tripped the leg had 3.68A. It seems like the untripped amperage should be zero since the switch in the probe is is normally open.

I see two probable causes. Either the probe is faulty or I've wired something wrong.

I am guessing you were measuring mA, not A. If the probe were conducting 4.31A full time when idle, it (or the Acorn input section) would quickly start to smoke.

You could try reversing your connections at the probe. Perhaps the probe has a "flyback" diode in it that is bypassing the switch in the current configuration.

Alternately, if the probe has an indicator LED that lights up when the probe is tripped, that could be the source of your problem.

This probe costs half as much and works REALLY well for what it is. It has a ground, VCC and a signal output. It also has a very low profile if you have limited Z travel.

https://www.amazon.com/V5-Waterproof-An ... r=1-5&th=1

cncsnw wrote: ↑Mon Feb 24, 2025 9:25 pm I am guessing you were measuring mA, not A. If the probe were conducting 4.31A full time when idle, it (or the Acorn input section) would quickly start to smoke.

You could try reversing your connections at the probe. Perhaps the probe has a "flyback" diode in it that is bypassing the switch in the current configuration.

Alternately, if the probe has an indicator LED that lights up when the probe is tripped, that could be the source of your problem.

There is a LED on the probe that lights up when the probe is tripped.

ShawnM wrote: ↑Mon Feb 24, 2025 10:20 pm This probe costs half as much and works REALLY well for what it is. It has a ground, VCC and a signal output. It also has a very low profile if you have limited Z travel.

https://www.amazon.com/V5-Waterproof-An ... r=1-5&th=1

I've spent too many hours trying to get the other probe to work so I've elected to cut my losses and get one of these probes. From other posts on this forum, it seems like several people are using them with good success.

On reflection, that (the indicator LED) is usually a problem with normally-closed probes. A normally-closed probe is supposed to cease conducting current when it is tripped, but if some current flows through the LED, then it will appear to remain closed (not tripped) as far as the PLC hardware is concerned.

Since you said this probe is supposed to be normally-open (close when tripped), the LED should not cause a problem.

However, if the probe conducts, for example, 4.3mA when idle and 3.6mA when tripped, then it is not going to be usable. That is not enough of a difference for the PLC to reliably tell tripped from not-tripped.

SMCNC wrote: ↑Wed Feb 26, 2025 12:50 am

ShawnM wrote: ↑Mon Feb 24, 2025 10:20 pm This probe costs half as much and works REALLY well for what it is. It has a ground, VCC and a signal output. It also has a very low profile if you have limited Z travel.

https://www.amazon.com/V5-Waterproof-An ... r=1-5&th=1

I've spent too many hours trying to get the other probe to work so I've elected to cut my losses and get one of these probes. From other posts on this forum, it seems like several people are using them with good success.

These come in both NO and NC flavors. Just pick which one you want. I have a NO probe because I use a single input for both of my tool touch offs (fixed and movable) and my probe. I prefer not to waste inputs.

It'll come with a flying lead cable so you'll need to purchase the connector of your choice to install and wire it to your machine. You'll have lots of options there as well and I'd definitely suggest you utilize the "probe detect" input to enable the safety features while probing. It may be only a $70 probe but you still don't want to destroy it on your first try. This can be done automatically with a 4 pin connector of your choice.

Update: I put the three wire probe suggested by ShawnM and it works like a champ. Thanks for your help!

SMCNC wrote: ↑Mon Apr 14, 2025 4:09 pm Update: I put the three wire probe suggested by ShawnM and it works like a champ. Thanks for your help!

Glad to help, it's a really good probe for the price.