With THC mode, is the common negative ?


I may have got this wrong, does Masso work with a common voltage thru any THC application ? So this common is negative ? So the up down signals are assessed by a negative before the up /down is seen.
Hi Lilow,

Masso input work only with a positive voltage referenced to the Masso -ve of the power supply. It needs to turn on an optocouler LED and any voltage from 4 to 24 volts will do

The input needs to change to High for the Up, Down and ARC to be acknowledged. I imagine if you are looking at the Proma Setup you see the THC switching ground. This is because of the recomendation in the Proma Manual .
COM terminal is a common input terminal connected to the ARC, UP and DOWN relay contacts inside the device, according to the diagram located on the cover (above picture).

Suggested route is to GND at driver/pc end. Do not jumper this connection to the 7-35V negative.

To do this the input is taken high by pull up resistors and as the Proma turns on the Masso inputs change to Low. The 3 THC inputs should be inverted to reverse their state, though now I look at the page I see they are shown as not inverted which is incorrect. Because the inputs are held high normally they should be inverted to change them back to Low in the normal state.

It will depend on your THC how you will connect it.

I hope this helps





Thank you for the reply.

I've attached 2 documents with the circuit layout.

First page is the THC standalone setup I'm using with the Masso / Plasma 5 axis v3.39.

I have read that there maybe another THC version by request.

The 2nd page is how I would like to go by using another axis on the Z, Z would be programmed in 3D.

The 4th or 5th axis would be floating with up / down signal delivered to and driven by Masso.

Is this feasible ?

Cheers, Ian.


  • Standalone-mode-for-plasma.pdf
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