ohmic - LinuxCNC HAL component that uses a Mesa THCAD for Ohmic sensing
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loadrt ohmic [count=N|names=name1[,name2...]] |
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.
Output pins are provided for:
ohmic-volts (the voltage sensed on ohmic sensing)
ohmic-on (true if ohmic-volts >= ohmic-threshold)
arc-on (true if arc voltage is received eg. full scale
reached or exceeded)
Actual voltage as read from the THCAD card (0-300V, 0-10V or
0-5V depending on the THCAD version used.
Normally, we
would use a THCAD-5 for ohmic sensing in conjunction with a
24 volt isolated power supply and a 390K resistor. (voltage
divider = 4.9) 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 optional that power to the Ohmic sensing circuit be
disconnected unless probing is in progress ut this adds
additional complexity.
EXAMPLE:
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 the main Linuxcnc documents.
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 32
setp ohmicsense.threshold 22
setp ohmicsense.ohmic-low 1
net ohmic-vel ohmicsense.velocity-in <=
hm2_7i76e.0.encoder.00.velocity
net ohmic-true ohmicsense.ohmic-on =>
plasmac.ohmic-probe
ohmic.N (requires a floating-point thread)
ohmic.N.thcad-0-volt-freq float in
0 volt calibration data for THCAD card in Hz
ohmic.N.thcad-max-volt-freq float in
Full scale 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 Fullscale (5, 10 or 300)
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 (default 1:1)
ohmic.N.ohmic-threshold float in (default: 18)
The threshold volts above which Ohmic sensing is set to be true
ohmic.N.ohmic-low float in (default: 5)
The threshold volts below which Ohmic sensing is set to be false
ohmic.N.arc-on bit out
True if full scale (eg arc is on)
ohmic.N.thcad-volts float out
Measured thcad voltage
ohmic.N.ohmic-volts float out
Calculated Ohmic voltage
ohmic.N.ohmic-on bit out
Threshold plasma torch voltage
ohmic.N.is-probing bit in
True if probing
Rod Webster
GPL