THCAD-10

In order that my brother and I not forget the processes we followed to get the THCAD-10 to function on his plasma table, in case we ever needed to do it in the future, I wrote an instruction manual for us...Although there is quite a lot of information that others have written and shared I have attempted to consolidate the methods which seem at present to be working for us...I am quite sure that some of the descriptions and nomenclature used in my writing may not coincide with actual descriptions that others would use, but for us I tried to keep it simple and understandable...
Mike

Torch Height Control

Description: The following describes the processes I used to set up a
functional THC.

Plasma Table: 50" x 50" with four stepper motors (2X; 1Y; 1Z)
Plasma Torch: HyperTherm PowerMax 45 with 50:1 voltage divider
Electronics: Mesa 5i25/7i76/THCAD-10 divide by 32 mode
Control: LinuxCNC ver 2.7; THC-PID component (by John thornton)

PROCESS: Using the equation provided in the THCAD-10 manual as a guide
for calibration of the THCAD-10 as follows:

V= VFS * (FOUT - FZERO) / (FFS - FZERO)

Both FZERO and FFS values are obtained from sticker on rear of THCAD-10 card.
where: FZERO = 118000 (frequency output at 0.0 volts input)
FFS = 924800 (frequency output at 10.0 volts maximum input)
FOUT = 806800 (difference by subtracting FZERO from FFS)
VFS = 10 (Maximum allowable volts through THCAD-10 card.

NOTE: FOUT is the total frequency range.

Substituting values in above equation provides:
V = 10 * (806800 - 118000) / (924800 - 118000)
V = 10 * (688800) / (806800)
V = 10 * 0.8537431
V = 8.5374318 (Estimation of THCAD-10 voltage at maximum range.)

Calculate an offset/scale which converts frequencies to voltages using
the following equation:

Scale = Divide By Mode * VFS / (FOUT - FZERO)
Scale = 32 * 10 / 688800
Scale = 0.0004645

Actual calibration was done using 9 volt battery and multimeter. The battery
provided 9.5 volts. Disconnecting the PM45 Plasma power supply cable
from the input side connector (right side) of the THCAD-10. The battery
provided the 9.5 volts input. Using the LinuxCNC HAL Meter function and
selecting the pin thc-pid.volts, the Hal Meter showed approximately 11+ volts.

This suggested that the existing Scale had to be reduced to be equivalent to
the input voltage of 9.5 volts...To provide an approximation, the Scale was
changed to 0.0004 and the Hal Meter was again read and was very close to the
actual input voltage of 9.5 volts.

Scale = 0.0004

To factor in the 50:1 voltage divider built in to the HyperTherm PM45, the new
scale (0.0004) was multiplied by 50 providing a new scale factor of 0.02. This
was tested by actual cutting and was found to perform well with the foregoing
approximate values.

Scale = 50 * 0.0004
Scale = 0.02

It should also be noted that further testing needs to be done with to obtain
more accurate measurements and values. Also, using the Correction Velocity
(thc-pid.p-gain) of 0.00002 as suggested by John Thornton seems to be a good
value to start with.

While we don't have the up/down indicator LED's working as yet, and I don't
yet have an understanding of what "Velocity Tolerance"; "Volts Tolerance";
and "Volts Limit" actually do and/or control, I am presently satisfied with
leaving the default settings of each until I understand more. The other
features seem to work properly and the cutting voltage setting is imported
from Gcode into the display screen "Volts Requested" and when cutting the
"Volt Meter" (actual volts) seems to function properly.

I've been following along in this thread and have been able to achieve decent functionality with a similar setup (THCAD-300 instead of -10). However, I think I'm running into corner lock issues. After looking into THC_PID.comp, I'm a little stumped by this line:
where velocity_tol is a number between 0.1 and 1 (as per JT's shared config).
Taking requested_vel as say, 1.0, min_velocity works out to be [1.0 - (1.0*(1/0.2))] = -4. This forces min_velocity to always be less than current_vel, and
always having vel_status = 1. Therefore, correction is always performed even while going into corners. Am I incorrect here?

I looked at the original THC.comp and the above line was a little different:

I am guessing that the velocity_tol in this one assumed a number between 1 and 100?

Not meaning to sidetrack the current topic but it’s kinda related. Where is everyone connecting their THCAD to the plasma cutter. Are you connecting stright to the inside of the plasma or inside the torch it’s self?

It depends:
Mine is in the control box beside the 7i76e but I have both divided and raw arc voltage coming from the CPC port on the plasma cutter. If you use raw arc voltage, make sure you count the existing resistors as part of the scaling resistance. I'm using divided voltage.

Islander has his in a metal box mounted on the plasma cutter itself. The advantage of this approach is the frequency output is more immune to noise so would be good in a High Frequency start environment or if you don't have a CPC port to start with.

Right now I’m using a hypertherm 30XP but will be upgrading to a 45xp next year. I will then sell the 30XP as I’m getting a machine and hand torch with the 45xp. So that being said not sure about drilling and mounting things to the 30XP if I’m going to sell it later.