Hello Guest it is January 18, 2020, 06:41:17 PM

Author Topic: Does this product exist?  (Read 3811 times)

0 Members and 1 Guest are viewing this topic.

Offline Davek0974

*
  •  2,580 2,580
    • View Profile
    • DD Metal Products Ltd
Re: Does this product exist?
« Reply #10 on: September 22, 2016, 02:30:55 AM »
This was the routine that comes with the 2010 screen set, it was most likely just crap under the tip or an intermittent ground connection - i was relying on the circuit through the spindle and motion bearings, slides etc.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives
Re: Does this product exist?
« Reply #11 on: September 22, 2016, 02:56:06 AM »
Hi Davek0974,
I've had a look at Tweaky's probe and its really nice, his workmanship is superb.
I've not seen anything like it for sale and can only guess that whomever bought
his design went no further with it, a shame.
Except for a few operator bungles I've never had a problem with probing. Nonetheless
I have considered no 'overrun' to be less than desirable.
A good microswitch is not a bad idea. Both Ormron and Honeywell make a competitive
line of switches with good repeatability, hysteresis and overrun. I achieve .01mm repeatability
with 2.5mm overrun with one such switch, I also use the same series of switches for home switches.

More recently I became a bit more ambitious and started making a linear voltage differential transformer.
Project not finished yet but testing shows .002mm absolute accuracy with +-2mm stroke. The example
I'm working on has an overall height of 110mm so not compact. Subsequent designs will be about 50mm
height 4mm stroke and 1um accuracy.

Given that probing works as well as it does this is probably a waste of time but I'm having fun!

Craig
My wife left with my best friend...
     and I miss him!

Offline Davek0974

*
  •  2,580 2,580
    • View Profile
    • DD Metal Products Ltd
Re: Does this product exist?
« Reply #12 on: September 22, 2016, 03:04:46 AM »
Its the fun that counts :)

Sounds good, no idea what a linear voltage differential transformer is though, but i'm sure i need one ;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives
Re: Does this product exist?
« Reply #13 on: September 22, 2016, 04:39:05 AM »
Hi Davek0974,
some good vid's on youtube about them. Reamarkably simple tho, three coils side by side
with the centre one energised by some AC voltage, few kHz is common, mine is 160kHz.
A magnetic core slips down the middle of the coils, if nearer one end than tother the outer coil
gets energised by transformer action, shift the core to the other end and that coil becomes energised.
Little bit of electronics and you have an infinite resolution linear gage with core in the centre
equal zero V.
They are available comercically as rugged contact free transducers. One with 1mm stroke but centre
accuracy of 100nm right through to 200mm and more stroke with centre accuracy of 20um.
I can't afford to buy one but I can make one! My current one offers 38mV/mm sensitivity and a linear
range of plus/minus 2mm. Not great but getting better.

Craig
My wife left with my best friend...
     and I miss him!

Offline Davek0974

*
  •  2,580 2,580
    • View Profile
    • DD Metal Products Ltd
Re: Does this product exist?
« Reply #14 on: September 22, 2016, 04:40:44 AM »
Learn something every day, nice:)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline rcaffin

*
  •  1,019 1,019
    • View Profile
Re: Does this product exist?
« Reply #15 on: September 25, 2016, 05:42:01 AM »
I LIKE LVDTs, but the commercial ones tend to be $$$ (and these days it's my wallet, not someone else's).
What are you using as a core? Round lump of ferrite?
Any more details?

Cheers
Roger
Re: Does this product exist?
« Reply #16 on: September 26, 2016, 06:33:59 AM »
Hi rcaffin,
yes that is exactly what I'm using.
I considered using a soft nickel-iron but eddy loss limits frequency which requires
multi thousand turn coils in VERY fine wire which I deemed to be beyond reasonable
means at home.
Ferrites on the other hand while being lower permabilty behave well loss-wise in the
100's of kHz and I can wind multi hundred turn coils in 0.2mm wire without undue
difficulty.
The current example offers 38mV/mm/Vexcitation and best measurement to date with
passive de-mod a noise floor of 200uV at 4.5V excitation for resolution of 1.2um.
If I can shrink future examples to 50mm overall height I might end up with something
useful at a fraction of the cost of existing commercial designs.

Craig
My wife left with my best friend...
     and I miss him!

Offline rcaffin

*
  •  1,019 1,019
    • View Profile
Re: Does this product exist?
« Reply #17 on: September 26, 2016, 07:22:21 AM »
All understood.
How about going to active demod? Could seriously improve the resolution. There's an AD chip, but pricey, or you could improvise.

Cheers
Roger
Re: Does this product exist?
« Reply #18 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
My wife left with my best friend...
     and I miss him!

Offline rcaffin

*
  •  1,019 1,019
    • View Profile
Re: Does this product exist?
« Reply #19 on: September 27, 2016, 02:59:07 AM »
Sure I would be interested.
Fwiiw, I am a retired research scientist (physics, metrology) and used to supervise several electronics engineers at the full technical level. So blaze away.
Cheers
Roger
PS: yeah, I reckon the AD chip is too $$ as well.