I'm trying to retrofit a sensor to a piece of machinery. The machine is a plasma table and what I'm doing is integrating (what the industry refers to as) an "ohmic sensor". It basically uses the machines torch as a work locating probe. There's a lead on the torch and a lead attached to the work piece and when the torch touches the work, a circuit is made and a signal is sent to the controller.

The sensor's logic circuit requires a COM in which I provide +5VDC and this is switched to the output whenever the probe circuit is closed and open (probe's circuit uses 12VDC). I managed to figure out the sensor and get it to find the work piece (via the LED on the sensor) but on the logic circuit side, the output is outputting ~4.6V, but there's no measurable current. I assume the 0.4V drop is due to the thirty feet of cable the voltage runs through from the sensor the the controller. I tested this sensor on the bench beforehand and it produced 5V when the wires were only a few inches.

I've read the forums that it's possible to have voltage without current but how do I make use of this?

I'm sending the signal to a microcontroller breakout board which has 5V l/O but since there isn't any current, the controller does't recognize that the input is HIGH.

Thanks

 

Why are you connecting +5V to the COM terminal? Does your documentation recommend that connection? The COM, ofter common, terminal usually suggests the reference point to which other voltages are referenced throughout the circuit, in some circuits this is GROUND.

More details would need to be provided to really give any sort of answer to the question. Do you have a schematic/drawing of the circuit? Part numbers or datasheet for parts that are interfaced?

 

That's what I thought too. When I had the leads switched, I wasn't getting anything. Not sure if it's protected. I can't really look inside to see how the circuits are laid out because it's been painted.

 

Just thinking out loud; table is grounded, LED with current limiting R is connected to + 5 V & torch. When torch touches table the circuit is completed, LED lights ? Take the signal from torch & invert, giving 5V output when torch touches the table ?
A sketch would help.

 

The only issue is the probe side needs to handle upwards of 300VDC while the machine is cutting.

Here's a crude sketch I found online:

Ignore the hashed blue and red lines. Essentially this is it in a nutshell. Instead of 12V going to the "Neuron THC Module", I have 5V going to the controller I/O BOB.

 

Just to be clear, you have the negative terminal of a +5V supply going to the OHMIC sensor and to the COM input on the NEURON THC module. You are feeding both the positive and negative leads of the +5V supply into the OHMIC sensor.

When you measure the output voltage, ~4.6 volts, are you measuring it on the OHMIC and COM terminals of the NEURON THC module?

 

No, I have a +5V supply going to the COM (yes, I know it's common that this port is the negative). The "Neuron THC module" has an onboard 5V supply going to the ohmic sensor (sorry, not shown in this pic) which is supplying the sensors COM. Then the sensors output (when switch on the probe side, 12VDC) is turned HIGH (5V) when the probe/torch touches the material. That 5V (4.6V) signal goes back to the "Neuron THC module" to a respective input where that port is configured to do something when HIGH.

 

What is the voltage between the OHMIC and COM pins on the Neuron THC module when the sensor is LOW and when it is HIGH?

 

Typically if you are going to set a stand off height then you would also have a pilot arc H.F. & high voltage to contend with.
Max.

 

Did you follow the user manual to set it up for your torch and controls?
hhttp/neuroncnc.com/assets/docs/NeuronSimplicityUserManual.pdf

 

I'm not using the Neuron brand but the unit is similar. That was the only pic I could find on explaining ohmic sensing.

Figured it out. I guess the labels are swapped, lol. I just said screw it and started swapping wires at risk of destroying the unit but one of the other ports was the COM. It all works now.