Ohmic sensing trouble shooting

[Dan Turner]

I learned something yesterday that is so basic that I hesitate to admit, but if it helps someone else then here goes. I have upgraded my system to the Accumove 3, which is a great move. I have been trying to chase down and trouble shoot why my unit was not recognizing the Ohmic sensor. I replaced all of the grounding wires and built a new grounding block for he star ground. I sunk an 8' ground rod and rebuilt my water table to ensure that everything was attached properly. I used my multimeter to make sure that I had continuity everywhere and everything tested fine. I made long wires with alligator clips on the end so I could test more things, but I still could not get the Accumove to recognize the Ohmic circuit. When I tested attaching a wire from the end of mthe orange wire by the cap to the ground on the back of the VFC, the light on the dashboard of the Accumove software would then say there was a connection.

I was working on it again yesterday and had a friend testing the torch end while I was at the computer. I went into machine settings and turned the relay on. when he touched the shield, the light would come on saying that the Ohmic circuit was detected, but when he would touch the nozzle, the light would go off. I then went onto the Hypertherm website and learned that you have to have a special shield for the Ohmic sensing to go with Ohmic sensing retaining cap.

This is what I learned, the Ohmic sensing circuit goes through the Orange wire to the Ohmic sensing retaining cap through the Shield and not the nozzle. Therefore, the shield needs to touch the metal instead of the nozzle. this completely solved my problems.

On a side note, turn the relay off when finished because when you run a job, the relay will automatically turn on and off while running the job.

I hope that my learning helped others.

 

[bigjoe]

whats the difference between accumove 2 vs 3

 

[Matt]

The Accumove 3 is for the larger machines, has more powerful drive cards to run bigger motors to move bigger/heavier gantries.

 

[Dan Turner]

Thanks Matt, I just know that the Accumove 3 is used on larger tables.

 

[LECS Matt]

Matt is corrected. The main difference between the Accumove 2 and Accumove 3 is the power of the drive cards. Also the Accumove 3 has an additional 6 input slots that are used for Limit Switches on the bigger tables.

 

[Ray Avelino]

Thanks for sharing. I was having trouble yesterday with my Flexcut 125. When I start the job, the z axis goes down a bit then gets the limit exceeded error even without touching the plate. Thanks for the explanation I now sort of figured out the reason for error. Its all because of the busted retaining cap, which I ignored at first since the 4800 was running smoothly anyway with it.

I realized the moment I press start, the power supply fires a current for the ohmic sense, then retracts the torch. Now it made sense why "I'm getting limit exceeded at Z" error. The machine senses a current to the nozzle instantly the moment it fires, hence it retracts 2" away, but its already at its z limit, hence the z-limit error. Basically the connection to the nozzle is shorted.

I could probably still use the busted retaining cap, if I'm not gonna use ohmic sensing.

Here are the pictures of the busted retaining cap. I've been using this retaining cap for about 2 months plus with moderate use. Probably got busted due to high heat? I hope TM redesigns this to be more durable.