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.
AUTHOR
Rod Webster
LICENSE
GPL