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.TH OHMIC "9" "2024-03-13" "LinuxCNC Documentation" "HAL Component"
.SH NAME

ohmic \- LinuxCNC HAL component that uses a Mesa THCAD for ohmic sensing
.SH SYNOPSIS
.HP
.B loadrt ohmic [count=\fIN\fB|names=\fIname1\fB[,\fIname2...\fB]]
.SH 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:
.br
ohmic-volts -the voltage sensed on ohmic sensing.
.br
thcad-volts -the actual voltage measured by the THCAD.
.br
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.
.br
This would result in a full scale reading of 24.5 Volts which is above the power supply output voltage.
.br
The circuit will remain protected by the THCAD's ability to tolerate a 500 Volt over-voltage indefinitely.
.br
It is optional that power to the ohmic sensing circuit be disconnected unless probing is in progress.

.SH FUNCTIONS
.TP
\fBohmic.\fIN\fB\fR (requires a floating-point thread)

.SH PINS
.TP
.B ohmic.\fIN\fB.is-probing\fR bit in \fR
True if probing
.TP
.B ohmic.\fIN\fB.ohmic-low\fR float in \fR(default: \fI21\fR)
The threshold volts below which ohmic sensing is set to be false
.TP
.B ohmic.\fIN\fB.ohmic-threshold\fR float in \fR(default: \fI22\fR)
The threshold volts above which ohmic sensing is set to be true
.TP
.B ohmic.\fIN\fB.thcad-0-volt-freq\fR float in \fR
0 volt calibration data for THCAD card in Hz
.TP
.B ohmic.\fIN\fB.thcad-divide\fR float in \fR(default: \fI32\fR)
THCAD divider set by links on THCAD board (1, 32, 64, or 128)
.TP
.B ohmic.\fIN\fB.thcad-fullscale\fR float in \fR(default: \fI5\fR)
THCAD full scale in Volt (5, 10, or 300 Volt)
.TP
.B ohmic.\fIN\fB.thcad-max-volt-freq\fR float in \fR
Full scale calibration data for THCAD Card in Hz
.TP
.B ohmic.\fIN\fB.velocity-in\fR float in \fR
The velocity returned from the THCAD and read by the Mesa encoder input
.TP
.B ohmic.\fIN\fB.volt-divider\fR float in \fR(default: \fI4.9\fR)
The divide ratio
.TP
.B ohmic.\fIN\fB.ohmic-on\fR bit out \fR
True if ohmic circuit is closed (material is sensed)
.TP
.B ohmic.\fIN\fB.ohmic-volts\fR float out \fR
Calculated ohmic voltage
.SH EXAMPLES


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

loadrt ohmic names=ohmicsense
.br
addf ohmicsense servo-thread
.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         4.9
.br
setp ohmicsense.threshold            22
.br
setp ohmicsense.ohmic-low            21
.br
net ohmic-vel    ohmicsense.velocity-in <= hm2_7i76e.0.encoder.00.velocity
.br
net ohmic-enable ohmicsense.is_probing  <= plasmac.ohmic-enable
.br
net ohmic-true   ohmicsense.ohmic-on    => plasmac.ohmic-probe

.SH AUTHOR

Rod Webster
.SH LICENSE

GPL