Hardware probe setting up ohmic sensor

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Hardware probe setting up ohmic sensor

Postby Greolt » Thu Dec 31, 2020 10:26 pm

Because I use a pilot arc plasma with no shield. See this post for explanation. viewtopic.php?f=16&t=2021&start=10#p16102

I have two relays in series to disconnect the ohmic sensor from the pilot arc circuit when not used. Trying to avoid it being blown to bits by the pilot arc.

Trouble is that when the relays turn on (just before G31 probe move) the ohmic sensor triggers. This of course ends the G31 and the macro moves on to the next item.

Once triggered even momentarily the ohmic stays on for a couple seconds. Probably a design feature to ensure a stable signal response.

If I turn the sensitivity up to the point where this does not happen then the tip touching the plate also does not trip the sensor.

So I am struggling to work out how to stop the sensor being triggered by the relay turning on.

Any ideas?
Greolt
 
Posts: 174
Joined: Sun Sep 04, 2016 6:22 am

Re: Hardware probe setting up ohmic sensor

Postby Greolt » Fri Jan 01, 2021 12:20 am

Bit more fiddling and discovered it is not the act of the relay turning on that is triggering the sensor.

The relay connects the sensor to the circuit that is supposedly open until the torch tip touches the material.

But there is some sort of residual connection further down the line. In the plasma cutter? Which expires after time.

Capacitance or something. I am no electronics tech. No idea what it is actually
Greolt
 
Posts: 174
Joined: Sun Sep 04, 2016 6:22 am

Re: Hardware probe setting up ohmic sensor

Postby Greolt » Fri Jan 01, 2021 4:45 am

Persisted as best an old carpenter can.

Got it going on the test board at least.

Put another relay to interrupt the connection between the nozzle and the plasma unit.

Double pole relay rated at 240v AC 5amp, so used both NC poles in parallel. Does not need to make or break while pilot arc is active.

So the NO relays isolating the ohmic and the NC one above turn on just before G31 and off straight after.

Next is to get it all mounted in a proper enclosure and tidy.
Greolt
 
Posts: 174
Joined: Sun Sep 04, 2016 6:22 am


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