NAME

       ohmic - LinuxCNC HAL component that uses a Mesa THCAD for ohmic sensing

SYNOPSIS

       loadrt ohmic [count=N|names=name1[,name2...]]

DESCRIPTION

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

       Output pins are provided for:
       ohmic-volts -the voltage sensed on ohmic sensing.
       thcad-volts -the actual voltage measured by the THCAD.
       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 390 kΩ series resistor resulting in a voltage divider of 4.9.
       This  would  result  in a full scale reading of 24.5 Volts which is above the power supply
       output voltage.
       The circuit will remain protected by the THCAD's ability to  tolerate  a  500  Volt  over-
       voltage indefinitely.
       It  is  optional that power to the ohmic sensing circuit be disconnected unless probing is
       in progress.

FUNCTIONS

       ohmic.N (requires a floating-point thread)

PINS

       ohmic.N.is-probing bit in
              True if probing

       ohmic.N.ohmic-low float in (default: 21)
              The threshold volts below which ohmic sensing is set to be false

       ohmic.N.ohmic-threshold float in (default: 22)
              The threshold volts above which ohmic sensing is set to be true

       ohmic.N.thcad-0-volt-freq float in
              0 volt calibration data for THCAD card in Hz

       ohmic.N.thcad-divide float in (default: 32)
              THCAD divider set by links on THCAD board (1, 32, 64, or 128)

       ohmic.N.thcad-fullscale float in (default: 5)
              THCAD full scale in Volt (5, 10, or 300 Volt)

       ohmic.N.thcad-max-volt-freq float in
              Full scale calibration data for THCAD Card in Hz

       ohmic.N.velocity-in float in
              The velocity returned from the THCAD and read by the Mesa encoder input

       ohmic.N.volt-divider float in (default: 4.9)
              The divide ratio

       ohmic.N.ohmic-on bit out
              True if ohmic circuit is closed (material is sensed)

       ohmic.N.ohmic-volts float out
              Calculated ohmic voltage

EXAMPLES

       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.
       Example  Calibration Data: 0V = 122.9 kHz, 10V = 925.7 kHz should be entered as 122900 and
       925700.

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

AUTHOR

       Rod Webster

LICENSE

       GPL