THC with Beckhoff EL5101 and THCAD2 => encoder signal loss

Yes, it consistently appears to be around 10ms.

However, I believe I’ve found a workaround. I have noticed, that the EL5101 outputs the encoder period which is an absolutely stable signal. So I wrote a custom component to calculate the frequency based on it, which in turn can be used in PlasmaC. In the attached Halscope screenshot, you can see the troublesome frequency signal with drops from the EL5101 in red, the encoder period in cyan, and the calculated frequency in green.

I looked through the EL5101 docs and - did I get it right? - it measures frequency by counting number of edge rises during a 10 ms window? Could be where 10 ms comes from. Seems low resolution also, frequency will be in steps of 100 Hz.

Yes, indeed. However since the drops seem to be random, I am not sure if it is related.

The manual also states that no frequency measurement is possible if the counter is blocked by the gate, but that in this case the period can be measured regardless.

And further: If an encoder signal is only present at input A/A and the frequency/period is to be measured, the terminal must be set to “Enable FWD count” in CoE 0x8000:03 [} 155].

   

If the pulse length method works for you it is even better. 100 ns resolution between two rising edges gives 0.1 Hz resolution and seems to be updated every cycle.
 

I had a quick look at the manual and I saw something that indicated the drop to zero was an index mark. My guess is that one of the PDOs needs to be set to remove it.

As I said earlier in the Ethercat world, a 0-10 volt analog input is probably a better choice but I have not tried one (assuming the plasma cutter has a voltage divider).. The EL3061 for example offers 500 volt isolation which is similar to the Mesa THCAD. To scale the voltage you would just need to use a mult2 component, send the output to QTplasmac and set the Qtplasmac offset to zero and the scale to 1.

I think one can not take for granted that EL3061's signal ground is the same potential as the workpiece ground. If you are lucky it might work, but to be on the safe side the torch signals should be isolated and free to float.