component ohmic "LinuxCNC HAL component that uses a Mesa THCAD for ohmic sensing";

description
"""
Mesa THCAD Card component to scale input and outputs from the Mesa THCAD2, THCAD5, THCAD10, and THCAD300 cards.
.br
Allows user configurable voltage thresholds for ohmic sensing.

Output pins are provided for:
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ohmic-volts -the voltage sensed on ohmic sensing.
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thcad-volts -the actual voltage measured by the THCAD.
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ohmic-on    -true if ohmic-volts >= ohmic-threshold, false if ohmic-volts <= ohmic-low.

A THCAD-5 would often be used for ohmic sensing in conjunction with a 24 volt isolated power supply
and a 390K series resistor resulting in a voltage divider of 4.9.
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This would result in a full scale reading of 24.5 volts which is above the power supply output voltage.
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The circuit will remain protected by the THCAD's ability to tolerate a 500V over-voltage indefinitely.
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It is optional that power to the ohmic sensing circuit be disconnected unless probing is in progress.
""";

examples """
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The below HAL example assumes a THCAD5 card using a 1/32 frequency setting and a voltage divider internal to the plasma cutter with range extended
to 24.5 volts by a series 390K external resistor as per the manual.
Additional information and wiring diagram is contained in the Plasma Primer in the LinuxCNC documentation.
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Example Calibration Data: 0v = 122.9 kHz, 10v = 925.7 kHz should be entered as 122900 and 925700

loadrt ohmic names=ohmicsense
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addf ohmicsense servo-thread
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setp ohmicsense.thcad-0-volt-freq    122900
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setp ohmicsense.thcad-max-volt-freq  925700
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setp ohmicsense.thcad-divide         32
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setp ohmicsense.thcad-fullscale      5
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setp ohmicsense.volt-divider         4.9
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setp ohmicsense.threshold            22
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setp ohmicsense.ohmic-low            21
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net ohmic-vel    ohmicsense.velocity-in <= hm2_7i76e.0.encoder.00.velocity
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net ohmic-enable ohmicsense.is_probing  <= plasmac.ohmic-enable
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net ohmic-true   ohmicsense.ohmic-on    => plasmac.ohmic-probe
""";

author "Rod Webster";

pin in  bit   is_probing                 "True if probing";
pin in  float ohmic_low = 21             "The threshold volts below which ohmic sensing is set to be false";
pin in  float ohmic_threshold = 22       "The threshold volts above which ohmic sensing is set to be true";
pin in  float thcad_0_volt_freq          "0 volt 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 full scale (5v, 10v, or 300v)";
pin in  float thcad_max_volt_freq        "Full scale calibration data for THCAD Card in Hz";
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";
pin out bit   ohmic_on                   "True if ohmic circuit is closed (material is sensed)";
pin out float ohmic_volts                "Calculated ohmic voltage";

function _;
license "GPL";
;;
#include <rtapi_math.h>

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;

    ohmic_volts = (velocity_in - thcad_scale_offset) * thcad_vel_scale * volt_divider;
    if(is_probing)
        ohmic_on = (ohmic_volts >= ohmic_threshold ? 1 : 0);
    else
        if(ohmic_volts <= ohmic_low)
            ohmic_on = 0;
}