[stirling]

Still looking for an alternative to fitting a THC interface card inside the box. Why? Here in Europe - it's a health and safety nightmare and is certain to void the warranty of the plasma unit. How do you Stateside guys get round this?
Anyway - I'm thinking of an attachment containing a simple potential divider - two resisters - nothing else - attached between the torch tip and the torch mounting bracket to feed out the scaled down voltage. All ancilliary circuitry like TVS and rectification, conditioning etc. can then be placed inside or alongside the THC proper. This could even work with available THCs like THC300s and their ilk simply by tapping in after their onboard potential dividers (a feature I think is already provided on my THC300 - 2 jumpers marked "external divider"). Thoughts?

The current transformers for good arc detection can presumably go round the external work clamp lead rather than inside the box. Of course an electro-mechanical moustrap will have to be used for torch triggering to replace tapping into the torch switch contacts inside the box - again - thoughts?

[jimcolt]

The Hypertherm THC systems have a separate CE and CSA approved enclosure that usually is mounted on the outside of the plasma power supply. These systems use an isolated, filtered voltage divider that sends a rather pure DC signal devoid of the electrical noise created by the plasma arc....and also hand the ohmic contact connections for initial height sensing of the plate....as well as the arc transfer signal. The separate enclosure makes for a safer installation without violating safety and warranty issues.

jim Colt

[Normsthename]

It's a health and safety nightmare and is certain to void the warranty of the plasma unit

Hypertherms already have a terminal block inside the machine ready for wiring the THC into.
I asked the Hypertherm Rep before I purchased one, and he said that there was no problem voiding a warranty connecting a THC to there machines
Thermadyne were the dead opposite and warned me about voiding warranties etc.
So I bought a Hypertherm Powermax 1000

Andy

[stirling]

Just a thought - which may be completely wrong but...

given arc current is constant whilst arc voltage changes with arc length, then arc power changes. Given supply voltage is constant then supply current must change to maintain that changing power. So... instead of monitoring arc voltage can supply current not be monitored for THC?

[jimcolt]

I suppose it could, however due to filtration and capacitance and inductance....the responses in input current would be too sluggish to control torch height......the torch could crash into the plate before an adequate change in input current is detected.

Todays best THC's are rather complex....they have features that can tell the difference between a kerf crossing and a heiht variation in the plate, they can control torch to work distance withing a couple thousandths of an inch, and have the ability to work with CAM software to avoid collision with potential plate tipups.....as well as dozens of other features that were designed in since the first arc voltage THC was used in the early 1970's. Reaction and height adjustment needs to be very quick with todays close torch to work distance requirements.

Jim