Touch Probe Will Not Change State <Resolved>

[SMCNC]

I'm in the process of setting up a new touch probe following the procedure 'Acorn Probe Setup' manual. The probe is a generic Normally Open model with two wires. The red probe wire is connected to input 7 and the black wire is attached to the common via a common bus.

The problem: When I invoke the Diagnostics tab to verify it is a normally open probe, the led in the diagnostics tab shows that it is closed. When the probe is tripped using my finger, it does not change states in the diagnostics tab.

I tested the probe outside the router and it functions properly (it will switch a 1V circuit on and off by manually moving the stylus) and it operates as a normally open switch. I went ahead and populated the input tab and probe tab and got a "8040 Warning: Probe Tripped" error. I tried a variety of option combinations with no success.

A bit about the machine, there is a manual tool touch off detect switch (input 6) for a normally closed tool touch off located on input 4.

Any ideas would be greatly appreciated (an a huge learning experience)

[ShawnM]

Is the input inverted? I don't see a input for "probe detect" either.

[cncsnw]

Try bench testing it with: a 24VDC supply; a resistor somewhere between 2K and 3K (to limit the current to somewhere between 8 and 12 mA); optionally an LED for easy viewing; and an Amp meter (or rather, milliamp meter).

What you want to find out is, when it is "off" (not tripped), does it leak some current? It may only take a couple mA to keep a PLC input active.

[SMCNC]

What you want to find out is, when it is "off" (not tripped), does it leak some current? It may only take a couple mA to keep a PLC input active.

Interesting thought. I'm going to do that experiment.

[SMCNC]

Is the input inverted? I don't see a input for "probe detect" either.

I might be wrong, but a Normally Open touch probe can be used with and without a Probe Detection circuit. I opted to not use one because the probe is a two wire variety and I wanted to keep the wiring as simple as possible by not putting in a manual switch.

The tool touch off circuit uses a manual switch, and the TT device is normally closed. Two inputs are used to make the circuit work. One is for the TT signal (ToolTouchOffTriggered) and the other is for the manual switch (ToolTouchOffDetect). That circuit works perfectly.

Does anyone know of a way to make the "ToolTouchOffDetect" switch and the "ProbeDetect" use the same input so only one manual switch has to be used? Also, I'm out of inputs on the Acorn board if I needed to add a manual probe detect switch.

[ShawnM]

Neither the probe or the tool touch off need the "detect" circuit. They are there to offer "protection" when using them. If it were me I'd want the probe detect circuit wired up to protect my probe when I'm using it. I don't bother with the tool touch off detect because mine is always wired to the machine for semi-automatic tool changes.

I also don't use manual switches for my probe detect circuit. I have the circuit wired into the 4 pin connector I use for my probe. When I plug it in it automatically detects the probe and enable the safety probing features. When I unplug the probe it opens that input.

[SMCNC]

I also don't use manual switches for my probe detect circuit. I have the circuit wired into the 4 pin connector I use for my probe. When I plug it in it automatically detects the probe and enable the safety probing features. When I unplug the probe it opens that input.

Hey that is pretty cool. I'm going to figure out how to wire up a four pin plug with a detect circuit in the plug.

When you pull the plug out you open the circuit. My first guess is that two pins are for the probe or TT circuit and the other pins are jumped together?

[SMCNC]

Try bench testing it with: a 24VDC supply; a resistor somewhere between 2K and 3K (to limit the current to somewhere between 8 and 12 mA); optionally an LED for easy viewing; and an Amp meter (or rather, milliamp meter).

What you want to find out is, when it is "off" (not tripped), does it leak some current? It may only take a couple mA to keep a PLC input active.

I built a simple circuit using a bench power supply and ran the voltage to somewhere above 12 volts (I forgot to record the actual power supply voltage) but did get a result from the touch probe. Untriggered, it recorded 12.52V and triggered it recorded 12.87 volts. That's a huge leak. If I'm not mistaken, the voltage should start at zero with a normally open probe that is untripped and go up to the voltage supplied. I think the probe itself is the problem.

[suntravel]

What if you change the polarity?

Uwe

[SMCNC]

Try bench testing it with: a 24VDC supply; a resistor somewhere between 2K and 3K (to limit the current to somewhere between 8 and 12 mA); optionally an LED for easy viewing; and an Amp meter (or rather, milliamp meter).

What you want to find out is, when it is "off" (not tripped), does it leak some current? It may only take a couple mA to keep a PLC input active.

I've carefully taken most of the probe apart to look at the circuit board and see if there were any shavings in the probe contacts or corrupted components and didn't see anything, but got very different results when bench testing the touch probe again.

I ran exactly 12V through the probe and recorded between 2 and up to 3 mV when untripped and 12V when tripped.

Are 2 or so millivolts enough to trick the system into thinking the probe is tripped? If so, is there anything to be done about it?

I would say the probe is now functioning properly but the probe still won't change state in the diagnostics tab on re-installation in the machine.