Hypersensing questions

component ohmic3 "LinuxCNC HAL component that uses a Mes THCAD for Ohmic sensing"; description """ Mesa THCAD Card component to scale input and outputs from the Mesa THCAD5, THCAD10 and THCAD300 cards. Which is designed to allow user configurable voltage threshold for ohmic sensing. Scaling of the Plasma arc voltage by a voltage divider is supported. .br Output pins are provided for: .br ohmic-volts (the voltage sensed on ohmic sensing) .br ohmic-on (true if ohmic-volts >= ohmic-threshold) .br arc-on (true if arc voltage is received eg. full scale reached or exceeded) .br Actual voltage as read from the THCAD card (0-300V, 0-10V or 0-5V depending on the THCAD version used. .br Normally, we would use a THCAD-5 for ohmic sensing in conjunction with a 24 volt isolated power supply and a 390K resistor. This would result in a full scale reading of 24.5 volts which is above the power supply output voltage. So if full scale is reached, it can be assumed that the THCAD-5 is sensing an arc voltage. In this case, the circuit will remain protected by the THCAD's ability to tolerate a 500V overvoltage indefinitely. It is recommended that power to the Ohmic sensing circuit be disconnected unless probing is in progress to prevent corrosion in consmables where a water table is in use. .br \\fBEXAMPLE:\\fR .br THCAD5 card using a 1/32 frequency setting and a voltage divider internal to the plasma cutter with range extended to 24.5 volts with a 390K external resistor as per the manual. Additional information and wiring diagram is contained in the Plasma Primer in hte main Linuxcnc documents. .br .br loadrt ohmic names=ohmicsense .br addf ohmicsense servo-thread .br .br setp ohmicsense.thcad-0-volt-freq 122900 .br setp ohmicsense.thcad-max-volt-freq 925700 .br setp ohmicsense.thcad-divide 32 .br setp ohmicsense.thcad-fullscale 5 .br setp ohmicsense.volt-divider 32 .br setp ohmicsense.threshold 18 .br setp ohmicsense.ohmic-low 5 .br net ohmic-vel ohmicsense.velocity-in <= hm2_7i76e.0.encoder.00.velocity .br net ohmic-true ohmicsense.ohmic-on => plasmac.ohmic-probe """; author "Rod Webster"; // Example Calibration Data: 0v = 122.9 kHz, 10v = 925.7 Khz should be entered as 122900 and 925700 pin in float thcad_0_volt_freq "0 volt calibration data for THCAD card in Hz"; pin in float thcad_max_volt_freq "Full scale calibration data for THCAD Card in Hz"; pin in float thcad_divide = 32 "THCAD Divider set by links on THCAD board (1,32,64 or 128"; pin in float thcad_fullscale = 5 "THCAD Fullscale (5, 10 or 300)"; pin in float velocity_in "The velocity returned from the THCAD and read by the Mesa encoder input"; pin in float volt_divider = 4.9 "The divide ratio (default 1:1)"; pin in float ohmic_threshold = 18 "The threshold volts above which Ohmic sensing is set to be true"; pin in float ohmic_low = 5 "The threshold volts below which Ohmic sensing is set to be false"; pin out bit arc_on "True if full scale (eg arc is on)"; pin out float thcad_volts "Measured thcad voltage"; pin out float ohmic_volts "Calculated Ohmic voltage"; pin out bit ohmic_on "Threshold plasma torch voltage"; pin in bit is_probing "True if probing"; pin in s32 motion_type_in "Connect motion.motion-type here"; pin out bit power_on "Turn relay on with this pin"; pin in s32 mode = 0 "0 = use low threshold, 1 = use trend"; pin in s32 num_readings = 5 "number of servo cycles to stay on trend"; pin out float dbg_avgv "average arc volts"; function _; license "GPL"; ;; #include <rtapi_math.h> #define BUFSIZE 1000 // maximum number of readings to average torch volts float avgarcvolts(double tvolts, int iscutting, int buffersize); static int cycles = 0; double buf[BUFSIZE]; int reading_count; float avgarcvolts(double tvolts, int iscutting, int buffersize) { // Calculates the moving average of buffersize readings static double *b = &buf[0], *p = &buf[0]; // pointers for beginning of buffer and current position static double *e; // pointer for end of buffer static int wascutting = 0; // cutting state last time static double sumvolts = 0.0; // Sum of readings in buffer static int numreadings = 0; // number of readings in buffer e = &buf[buffersize]; // Initialise end pointer if(!iscutting && wascutting){ // Torch just turned off, so reset the variables p = b; sumvolts = 0.0; numreadings = 0; wascutting = iscutting; //and save the state return(0.0); } if(iscutting){ // Arc_OK is on so lets start gathering data to average *p++ = tvolts; // Save volts to the buffer and increment pointer if(numreadings < buffersize) numreadings++; if(p > e) // if we've gone past the end of the buffer, wrap to the beginning p = b; sumvolts += tvolts; // add the new reading if(numreadings >= buffersize) sumvolts -= *p; // subtract the oldest reading (which is the one we are pointing at now) } wascutting = iscutting; //and save the state if(numreadings) return(sumvolts/(double)numreadings); // return Average volts else return (0.0); // catch divide by zero errors } FUNCTION(_) { double thcad_vel_scale = 1/((thcad_max_volt_freq - thcad_0_volt_freq)/thcad_fullscale/thcad_divide); double thcad_scale_offset = thcad_0_volt_freq/thcad_divide; double avgvolts = 0.0; // average volts thcad_volts = (velocity_in - thcad_scale_offset) * thcad_vel_scale; ohmic_volts = thcad_volts * volt_divider; // Calculated torch volts from THCAD static int first_pass = 0; if(num_readings > 1000) //enforce number of readings limits reading_count = 1000; else if(num_readings < 3) reading_count = 3; else reading_count = num_readings; if(is_probing){ if(!first_pass){ first_pass = 1; if(! power_on) power_on = 1; } } power_on = !motion_type_in ? 0 : 1; avgvolts = avgarcvolts(ohmic_volts, (int)1, (int)reading_count); switch(mode){ case 0: if(is_probing) ohmic_on = (ohmic_volts > (ohmic_threshold && is_probing) ? 1 : 0); else if( ohmic_volts < ohmic_low) ohmic_on = 0; break; case 1: if(is_probing){ dbg_avgv = avgvolts; if(!ohmic_on){ if(ohmic_volts > ohmic_threshold){ ohmic_on = 1; } } else{ if(avgvolts < ohmic_threshold || ohmic_volts < ohmic_low){ ohmic_on = 0; first_pass = 0; } } } else{ ohmic_on = 0; } break; default: // Report error invalid mode break; } arc_on = (thcad_volts >= thcad_fullscale ? 1 : 0); if(!is_probing) first_pass = 0; }