OHMIC(9)

💖 OHMIC(9) — HAL Component 💖

okay bestie, welcome to the ohmic glow-up ✨ it's a LinuxCNC HAL component that uses a Mesa THCAD for ohmic sensing. that's the whole vibe. let's get into it 🫶

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🌸 NAME 🌸

ohmic — a LinuxCNC HAL component that uses a Mesa THCAD for ohmic sensing 💅

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✨ SYNOPSIS ✨

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

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🦋 DESCRIPTION 🦋

so this is the Mesa THCAD Card component, and what it does is scale the input and output from the Mesa THCAD2, THCAD5, THCAD10, and THCAD300 cards. it also lets you (yes, you, main character) configure the voltage thresholds for ohmic sensing. iconic behavior honestly 👑

the output pins you get are:

• 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

ngl a THCAD-5 would often be used for ohmic sensing alongside a 24 Volt isolated power supply and a 390 kΩ series resistor, and that combo gives you a voltage divider of 4.9. the way that math works out, your full scale reading lands at 24.5 Volts — which is above the power supply output voltage, so slay 🌈

and don't worry about frying it: the circuit stays protected because the THCAD can tolerate a 500 Volt over-voltage indefinitely. periodt 💪

also, it's optional to disconnect power to the ohmic sensing circuit unless probing is in progress. lowkey a nice touch 💅

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🔥 FUNCTIONS 🔥

• ohmic.N (requires a floating-point thread)

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👑 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

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💜 EXAMPLES 💜

okay so this HAL example below assumes a THCAD5 card using a 1/32 frequency setting, plus 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, bestie. additional info and a wiring diagram live in the Plasma Primer in the LinuxCNC documentation, iykyk 📖✨

Example Calibration Data: 0V = 122.9 kHz, 10V = 925.7 kHz — those should be entered as 122900 and 925700. no cap.

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

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🌟 AUTHOR 🌟

Rod Webster 💖

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🎀 LICENSE 🎀

GPL

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and that's the whole page, babe 🦋 this one's from the LinuxCNC Documentation, dated 2026-03-17, and the manual section is OHMIC(9) — go forth and sense some ohmic, you've got this bestie 🫶💅✨