thc − Torch Height Control


loadrt thc


Torch Height Control Mesa THC > Mesa 5i20 Encoder > EMC THC The Mesa THC sends a frequency based on the voltage detected to the encoder. The velocity from the encoder is converted to volts with the velocity scale parameter. The THCAD card sends a frequency at 0 volts so the scale offset parameter is used to correct this.

Component Functions If enabled and torch is on and X + Y velocity is within tolerance of set speed allow the THC to offset the Z axis as needed to maintain voltage.

If enabled and torch is off and the Z axis is moving up remove any correction at a rate not to exceed the rate of movement of the Z axis.

If enabled and torch is off and there is no correction pass the Z position and feed back untouched.

If not enabled pass the Z position and feed back untouched.

Physical Connections Plasma Torch Arc Voltage Signal => 6 x 487k 1% resistors => THC Arc Voltage In THC Frequency Signal => Encoder #0, pin A (Input) Plasma Torch Arc OK Signal => => Plasma Torch Start Arc Contacts

HAL Plasma Connections hm2_5i20.0.encoder.00.velocity => thc.encoder-vel (tip voltage) motion.spindle-on => (start the arc) thc.arc-ok <= <= (arc ok signal)

HAL Motion Connections thc.requested-vel <= motion.requested-vel thc.current-vel <= motion.current-vel


thc (requires a floating-point thread)


thc.encoder-vel float in

Connect to hm2_5i20.0.encoder.00.velocity

thc.current-vel float in

Connect to motion.current-vel

thc.requested-vel float in

Connect to motion.requested-vel

thc.volts-requested float in

Tip Volts current_vel >= min_velocityequested (SP)

thc.vel-tol float in

Velocity Tolerance (Corner Lock)

thc.torch-on bit in

Connect to motion.spindle-on

thc.arc-ok bit in

Arc OK from Plasma Torch

thc.enable bit in

Enable the THC, if not enabled Z position is passed through

thc.z-pos-in float in

Z Motor Position Command in from axis.n.motor-pos-cmd

thc.z-pos-out float out

Z Motor Position Command Out

thc.z-fb-out float out

Z Position Feedback to Axis

thc.volts float out

The Calculated Volts

thc.vel-status bit out

When the THC thinks we are at requested speed


thc.vel-scale float rw

The scale to convert the Velocity signal to Volts

thc.scale-offset float rw

The offset of the velocity input at 0 volts

thc.velocity-tol float rw

The deviation percent from planned velocity

thc.voltage-tol float rw

The deviation of Tip Voltage before correction takes place

thc.correction-vel float rw

The amount of change in user units per period to move Z to correct


John Thornton


GPLv2 or greater