Messages

7381

Mach4 General Discussion / Re: Mach4 with ESS with C62 CNC4PC BOB

« on: September 28, 2016, 02:51:30 AM »

Hi Dean,
found the C62 docs, the internet is a marvellous thing....

Section 4.5 on page 5 and running on to page 6 show the jumpers I mean.

Are you using 5V or 24V? You have the option of the 'common' being either
5 or 24V or GND. Your description suggests that your BOB is currently set to
common=GND. Usual but not universal practice has common=5V. Try it and see.

Craig

7382

Mach4 General Discussion / Re: Mach4 with ESS with C62 CNC4PC BOB

« on: September 28, 2016, 02:33:27 AM »

Hi Dean,
I don't have an ESS yet, I've ordered one but likely a fortnight away yet.

A couple of things occur to me from your post.

Firstly the Estop is an input. So if that input goes active the expectation is that the BOB
LED will change state and the ESS will communicate back to Mach which should be visible
on the diagnostics page. If you hit 'disable' in Mach your BOB LED will not change state.

I suspect that your BOB is configured so that the input pin (port2 pin10) is low in idle state.
Therefore if you check 'active low' Mach considers it and enduring emergency condition
and you cannot simply re-enable Mach. You must clear the low state on the pin to do so.

Without documentation of your BOB I don't know but it is common that the input pins
have a jumper which allows a pull-up resistor to be enabled. Then port2 pin10
would be high at idle and would be pulled low by you activating the Estop switch, and
the active low setting that has been recommended would work fine.

Can you post the BOB docs or a link to them?

Craig

7383

Show"N"Tell ( What you have made with your CNC machine.) / Re: Linear Voltage Differential Transformer

« on: September 28, 2016, 02:08:14 AM »

Hi Roger,
the windings are reasonably neat but I suspect not particularly uniform.

The ferrite cores I bought of eBay, cheap and cheerful from a certain Asian
country! 10 cores for $15 so can't complain. Measured them out of the
packet and there is quite some variation, about 0.5mm length variation
on 25mm nominal and 0.25mm diametrical variation on 12mm nominal.
Given that they sintered after being pressed green about what I expected.
Sounds like I may have to take to them with a diamond wheel.

Craig

7384

Show"N"Tell ( What you have made with your CNC machine.) / Re: Linear Voltage Differential Transformer

« on: September 28, 2016, 01:42:12 AM »

Hi Roger,
some good info there. The current model I'm working on shows no tendency to
waver in phase and guess therefore not close to any resonant condition. If that
is the case then it was by happenstance rather than design!

I run the centre coil energised with the outer coils wired in phase opposition, almost
the exact opposite to your description, of  course being in the southern hemisphere
will mean that it works fine, lol!

Your comment about linearity being related to winding distribution fills me with dread
however. I used Mach to wind the coils but is FAR from optimal. I may be very disappointed
when I get myself setup to measure it accurately.

I was largely the ease or otherwise of winding coils in 0.2mm wire that induced me to go
for such a high excitation frequency. The prospect of winding in 0.05mm sounds maddening
to me but your insight suggests that commercial makers have done just that and  I can well
imagine it to be expensive.

Likely to be a few days before I can get some numbers, I have to borrow the boss's 3-4" micrometer
so I really really want to do something useful for him before I touch him up for it!

Craig

7385

Show"N"Tell ( What you have made with your CNC machine.) / Re: Linear Voltage Differential Transformer

« on: September 27, 2016, 06:29:10 AM »

Hi Roger,
hadn't thought of switches, they still require the phaseshift to make genuinely
synchronous. As it turns out the phaseshift tunes nicely to a repeatable peak
and once adjusted stays there unless the ldvt is altered. Do you think they offer
any advantage?. The noise floor of the existing design is pretty fair with potential
resolution in the region of 1um, about what I had hoped to achieve. Could I usefully
measure and use sub-micron resolution?

Don't have any reliable linearity measurements yet. The 'mental 'plot I had running
suggests good, but no hard evidence.

My development path is to get numerical data (zero crossing resolution, linearity vs stroke).
Next effort is about making it smaller and user friendly. After that thinking about suitable
outputs, probably zero crossing detector for straight probing and a 4 digit dual slope
integrating ADC similar to those used in multimeters and possibly 16bit digital output via
MODIO back to Mach.

Still a power of work/fun/learning to be had yet!

Craig

7386

Show"N"Tell ( What you have made with your CNC machine.) / Re: Linear Voltage Differential Transformer

« on: September 27, 2016, 04:01:49 AM »

Hi All,
will post some pics and diagrams of the transformer itself, as per usual I have to
make plans after I've made it!

The two circuit diagrams above are first the circuit I'm using currently and the second
is the next evolution, as yet unbuilt.

Refering to the first circuit the amp IC3A, biasing, gain setting and voltage limiting
components feeback into the LC tank C1,C2,L1 and R3.

R3 is a current sense and is amplified by IC3B by a gain of 50 to drive the lvdt primary
and the all-pass phaseshift amp IC3D.

The double balanced modulator is driven by the phaseshift amp via R16 and keeps the
ring diode currents to a few mA.

R15 and C13 lowpass the DC while damping out the LO+RF signal and IC3C is DC buffer.

The osc amp, gain amp and phaseshift amp all require a fast opamps, I chose OPA1654AIPW
with gainbandwidth of 20MHz. I ordered these only to realise that they are TSSOP with .6mm
pitch. Real sods to hand solder!

The net evolution will use similar amps but probably duals rather than a quad and SOIC being a lot
easier to handle. The only other difference is using two amps each with a gain of 7 rather than one with
a gain of 50. If I'm using two amps why not introduce some filtering.... hence the extra resistors/caps
as 4 pole Butterworth. Most if not all components on the 'evo' board will be SMD.

I'll draw some diagrams and be back when done.

Craig

7387

General Mach Discussion / Re: Does this product exist?

« on: September 27, 2016, 03:31:46 AM »

Hi All,
rather than further hijack this thread I've posted in 'show'n'tell' board as Linear Voltage Differential Transformer.

Craig

7388

Show"N"Tell ( What you have made with your CNC machine.) / Linear Voltage Differential Transformer

« on: September 27, 2016, 03:27:10 AM »

Hi All,
I've been fooling around making a lvdt for a tool height setter. Very amateurish
at present but coming along.

7389

General Mach Discussion / Re: Does this product exist?

« on: September 27, 2016, 02:02:13 AM »

Hi rcaffin,
when I say passive demod what I actually mean is a double balanced modualtor
based on two transformers with centre tapped secondaries and four diodes
in a ring. Such devices are used a lot at RF frequencies and some manufacturers
have models with input bandwidth down to tens of kHz. They are rugged/reliable/
simple and broadband. They all suffer some loss of RF to IF conversion in the
region of 5-7dB. They are commonly quoted with noise figures of 7-8dB which is
dominated by the loss. They are in fact quiet devices excluding the loss.

The actual voltage loss is about 2.5. I can readily amplifiy the output to whatever
level I desire and provided I use decent opamps used properly insignificant signal to
noise degradation. Active demodulation achieves the same result but all I end up
with is more signal not increased sensitivity.

The Analog Devices chip uses a different demod technique based on a ratio method
so avoids the requirement for a synchrous local oscillator. Great idea. The chip is
limited to 20kHz and so way lower than my device. Additionally see that they sell
for around $50US The handful of components I use cost less than $20 and in all
other respects the match for the AD device.

Sensitivity of an lvdt is related to it magnetic properties rather than signal processing
electronics. The higher the effective permability of the core at the frequency of interest
the greater the change in output voltage for a given distance of core shift. At low
frequencies nickel-iron or soft silicon irons outperform ferrites but become too lossy
beyond a few kHz.

If you're interested I could post a few pics and diagrams. I would be (already am!) guilty of dragging
this thread way off topic so not sure where to post.

Craig

7390

General Mach Discussion / Re: Help Please: Computer upgrade causes no communication with controller

« on: September 26, 2016, 07:05:51 AM »

Hi All,
I think this is the identical unit:

http://www.ebay.com/itm/One-Port-Parallel-IEEE-1284-PCI-Host-Controller-Card-Chipset-MCS9865-for-Moschip-/142065138484?hash=item2113bdfb34

Certainly the chip is the same. I seem to recall having to go to the MOSCHIP site and experiment with the different
drivers until I found one that played nice.

Craig