PlasmaC Fiber laser 1Kw head height control + auto focuas

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11 Apr 2020 14:54 - 11 Apr 2020 14:56 #163621 by PCW

there is no much noise from the system,, 10 bit is good for me
but how can the low pass filtering effect the resolution


Because the THCAD is a V-F converter. It has an output frequency range of
about 100 KHz to about 1 MHz. LinuxCNC reads this frequency by measuring
counts per servo thread period, so if the servo thread period is 1 ms , full scale
volts will read about 1000 counts per servo period (roughly 10 bits of resolution)
If you chose a longer servo period you would have more counts and higher resolution
A low pass filter has a similar effect, that is, the more the frequency output is averaged,
the higher the resolution.

I would try the 9V battery, you should not see 1% of full scale noise, only about 0.12%
(at 1 ms servo thread)
Last edit: 11 Apr 2020 14:56 by PCW.
The following user(s) said Thank You: taloot

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11 Apr 2020 15:11 #163622 by taloot

there is no much noise from the system,, 10 bit is good for me
but how can the low pass filtering effect the resolution


Because the THCAD is a V-F converter. It has an output frequency range of
about 100 KHz to about 1 MHz. LinuxCNC reads this frequency by measuring
counts per servo thread period, so if the servo thread period is 1 ms , full scale
volts will read about 1000 counts per servo period (roughly 10 bits of resolution)
If you chose a longer servo period you would have more counts and higher resolution
A low pass filter has a similar effect, that is, the more the frequency output is averaged,
the higher the resolution.

I would try the 9V battery, you should not see 1% of full scale noise, only about 0.12%
(at 1 ms servo thread)

with or without lowpass?
with lowpass im having 0.12%

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11 Apr 2020 15:19 #163625 by PCW
Without lowpass

At 1 ms servo thread and full scale input from a noiseless source
(9V battery or just inputs shorted) you should have about 0.12%
( of full scale value ) noise, that is, if you have your
scaling set so that you are reading volts (10V full scale)
you should expect about +- 12 mv of noise

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12 Apr 2020 02:14 - 12 Apr 2020 02:21 #163705 by taloot

Without lowpass

At 1 ms servo thread and full scale input from a noiseless source
(9V battery or just inputs shorted) you should have about 0.12%
( of full scale value ) noise, that is, if you have your
scaling set so that you are reading volts (10V full scale)
you should expect about +- 12 mv of noise


whats the maximum frequency that can be read with mesa 7i92 and 7i96 encoder input. THCAD makes 100khz ~1MHZ... if its 1MHZ ~10MHZ is it will give better performance... am i right?
because i will build capacitance to frequency converter and i will build it based on maximum mesa count rate

im using 3 axis (and 4th is focus) step/pulse and 1 encoder
Last edit: 12 Apr 2020 02:21 by taloot.

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12 Apr 2020 03:04 #163727 by PCW
Depending on the input circuitry most Mesa non-multiplexed encoder inputs are
capable of reading to 5-10 MHz. Note that if you have that high a frequency, you pretty much need differential data transmission.

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12 Apr 2020 12:10 #163745 by taloot
cutting speed about 27m/min and the space between the head and workpeace is about 0.8mm
do you think its enough to use THCAD?

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12 Apr 2020 15:00 #163766 by PCW
I guess that depends on height measurement scaling
(what distance range scales to 0 --> 10V) and what precision
you need

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12 Apr 2020 15:11 #163769 by tommylight
The slowest thing in your setup is the RS485 interface, everything else is much faster.

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12 Apr 2020 23:01 - 12 Apr 2020 23:24 #163816 by taloot

The slowest thing in your setup is the RS485 interface, everything else is much faster.


i change the head no more rs485
now i have RF cable for capacitance measuring,, and i make capacitance to frequency converter to be connected directly to mesa encoder pin,, similar to THCAD but convert the capacitance to frequency
500khz to 5mhz i will squeeze the fpga performance
Last edit: 12 Apr 2020 23:24 by taloot.

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12 Apr 2020 23:04 - 12 Apr 2020 23:15 #163817 by taloot

I guess that depends on height measurement scaling
(what distance range scales to 0 --> 10V) and what precision
you need

about 5cm will be scaled 0-10, precision the maximum i can reach with this setup.. i just want to keep up with head high while cutting at 27m/min

also encoder cable will be 15m+-,,, whats the suggestion for this
Last edit: 12 Apr 2020 23:15 by taloot.

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