On Sat, 31 Jan 2015, Viesturs L?cis wrote: > Date: Sat, 31 Jan 2015 19:26:49 +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: Re: [Emc-users] How to THC? > > 2015-01-31 17:22 GMT+02:00 Peter C. Wallace <[email protected]>: >> >> Do you have a THCAD-10 or THCAD-300? >> > > It is THCAD-10 with additional 3 MOhm resistence added on input to > extend the range to 310V. > >> >> 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) >> > > I am sorry, but I am not sure that I understand, how to interpret your > reply. Yes, my target is to sense arc voltage. > >> >> 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 >> > > Ok, thanks for the tips, I actually have the resistors in the control > box, but will definitely move them to the plasma source. > So how do I calculate, how much more should I add to my resistor > string to make it safe? > That link you shared - are those resistors special about something or > can I use usual 0,25W 1MOhm resistors (with 100uA max current they > should tolerate 2500V each, I have 3 in series, so that totals to 7500 > V for the resistors).
Those resistor are special high voltage resistors, normal 1/4 W resistors are typically only rated for 300V or so > And where to connect the wires - right on the torch and earth leads or > somewhere in the middle - transformer output etc? It seems that with > enough additional resistors I can connect to torch leads... > I would connect to the torch lead (inslde the plasma power supply box) Note that you are working with lethal voltages here so be very careful! > Viesturs > > ------------------------------------------------------------------------------ > 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
