On Sat, 31 Jan 2015, Viesturs L?cis wrote: > Date: Sat, 31 Jan 2015 11:59:17 +0200 > From: "[UTF-8] Viesturs L?cis" <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Subject: [Emc-users] How to THC? > > Hello! > > I have Jasic 100 A plasma source and Mesa THCAD card (extended to 310V > measuring range). The thing is that there is no dedicated output > signal in plasma source that would provide a feedback of plasma arc > voltage. > > I thought that I might connect THCAD inputs directly to plasma torch > and ground leads, but THCAD manual convinced me not to do so - it says > something about "touch-start plasma only", which does not seem to be > the case here.
Do you have a THCAD-10 or THCAD-300? > > So far I have received 2 opposite suggestions: > 1) attach THCAD inputs to main transformer output _before_ rectifier > input - I was told that rectifier bridge will protect the board from > any HF (when arc is launched); > I would use very small and simple rectifier bridge (1000 V, 2A) to > make the signal from bipolar to unipolar and then try some HAL magic > to smooth out the fluctuations of the reading value; > 2) attach THC inputs _after_ rectifier input - I was told that main > transformer output frequency is in several kHz range and that would > bake my rectifier or some other electronics. > > I would appreciate any suggestions, where and how to attach THCAD > board to Jasic plasma source, which does not have dedicated output > signal for THC purpose. > > Viesturs > Unless you sense the arc voltage itself you will not get a meaningful reading This is because the plasma power source is really a big current source at its output (constant current VS voltage) so the voltage at the output varies widely depending on the arc length (and resistance) The problem with HF start is that it generates very nasty EMI with high voltage, fast rise time pulses. The THCAD-300 can tolerate 5KV transients So may be OK but its a bit of a risk. If you have a THCAD-10 you can add a string of external resistors to easily make the input tolerant of 20KV spikes or even more. You could also add some external resistors to a THCAD-300 if you dont mind losing some resolution These resistors are inexpensive and their 3700V rating makes it easy to build a HV divider string: http://www.vishay.com/resistors-linear/list/product-28733/ Note that any added divider string should be mounted in the plasma power supply itself for two reasons: 1. It will limit the radiation of HF noise (you dont want another transmitting antenna wire, especially one close to the control electronics) 2. The bare plasma power supply output make a handy arc welder/wire exploder in the middle of your control should you accidentaly short its output > ------------------------------------------------------------------------------ > Dive into the World of Parallel Programming. The Go Parallel Website, > sponsored by Intel and developed in partnership with Slashdot Media, is your > hub for all things parallel software development, from weekly thought > leadership blogs to news, videos, case studies, tutorials and more. Take a > look and join the conversation now. http://goparallel.sourceforge.net/ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Dive into the World of Parallel Programming. The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
