On Tuesday 28 October 2014 08:25:25 Peter C. Wallace did opine And Gene did reply: > On Tue, 28 Oct 2014, Viesturs L?cis wrote: > > Date: Tue, 28 Oct 2014 14:18:30 +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] Question > > about Mesa THCAD-10 > > > > Hello! > > > > There is a plasma machine I built and I used THCAD-10 card for thc > > purposes, because the plasma source had such an output signal. > > Long story short - the machine has new owner and they want to use > > JasicCUT plasma source, which AFAIK does not have 0-10V signal output > > for thc, so I will have to connect directly to power leads of plasma > > cable. > > > > How do I calculate, what is the resistance of additional resistors > > needed to reduce max voltage from 300V to 10V? The unknown element > > here is the current that passes through THCAD card. > > > > Viesturs > > From the manual: > > EXTENDING INPUT RANGE > > The THCAD-10 can have its input range extended by adding > series resistance to its inputs. The input circuitry of the THCAD-10 > consists of a current to voltage converter with a 100 uA full scale > range. The THCAD-10 has 100K of total input resistance in its input > divider section giving it a full scale input range of 100K*100uA = > 10V. When external series resistors are used to extend the input > voltage range, the required resistance value is: (VFS - 10V)/100 uA > Where VFS is the new full scale input voltage and REXT is the new > external series resistor. For example, to extend the THCAD-10s input > range to a 500V a (500-10)/100uA = 4.9M resistor would be required.
Based on that Peter, and thanks for the info, he would then need a 2,940,000 ohm resistor for a 300 volt full scale. To do that for a 300 volt full scale, he would need to use a string of 9 each 33k resistors in metal film so that no one resistor sees more than its rated voltage, in this case 33.3 volts per resistor in an ideal world. Wattage doesn't count, its too low, but the voltage rating of the individual resistor does count. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
