Maplin Digital Caliper

Maplin have a good offer on Digital Caliper Electronic Digital Caliper • Electronic 25mm LCD display caliper • Resets the zero point of instrument
Order Code N48AA http://www.maplin.co.uk/Module.aspx?C=Newsletter&U P3-1&ModuleNo2198&T058695   was £29.99   Save 50%  £14.99 This one has a power-off button and auto power-off
Mike
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But they all just switch off the display.
Nick
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Nick Mόller wrote:
> >

>

Otherwise you'd have to re-zero the caliper every time you turned it on.
I was given one of these a while ago: accurate as a regular vernier caliper & very good value for money. Just without that nice expensive-tool feel to it...
cheers Guy
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wrote:

And watch out for the battery cover falling off........
Cheers Tim
Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
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Yours as well ?.. :-(
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Regards Jonathan

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wrote:

My Mitutoyo one has an off button and an on/zero button. As the batteries last a couple of years or so I'd hazard a guess that they turn off more than just the display.
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This is in reply to message of Fri, 24 Feb 2006 20:54:37 +0000, Martin

Both right - how long does your digi watch battery last - that's on all the time? They both use electrically erasable programmable read-only memory (EEPROM) to store data in but then switch off - quoting gemplus.com, "The current Flash-EEPROM memories are guaranteed for a data retention time of at least 10 years". But you will notice that even if switched off with the caliper closed and zeroed then open the caliper and switch on, the display is correct so the only part totally powering down is the display. The sensor remains active to update the EEPROM. If you are using batteries at a rate try those cards of "watch"batteries from markets for a quid; they seem to work admirably. Mike
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My understanding is that these devices work by capacitance and not by a traversing-generated series of impulses.
So, when switched back on again - just measure the capacitance to give you the present position.
Mike wrote:

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On 25 Feb 2006 00:39:22 -0800, "Plod's Conscience"

The scales use a pattern of small capacitors on the "track", sensed by the traversing read head, to generate a series of pulses corresponding to an incremental distance moved, so there is no absolute measure of position in these devices other than starting at a reference point and counting pulses.
Consequently, on models that maintain position regardless of "power down", the only way this can work is if the sensing and position recording circuitry never actually powers down.
Regards, Tony
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>

Interesting. What is caliper made of and how are the "capacitors" constructed?
I've just looked at my digital calipers (one of the cheap "Chinese Copies" from Aldi) and there is no visible mechanism to sense the position or movement of jaws. No "track" to be read, at least not that I can see. Mine display the current setting when turned on, no need to close and zero before use (other than to check for zero).
-- 73 Brian www.g8osn.org.uk
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wrote:

Basically copper pads on a PCB. They are covered by a protective/decorative plastic layer.
Regards, Tony
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Tony Jeffree wrote:

Sounds like a cheap flashing Christmas decoration.....
Joules
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wrote:

Many thanks for posting the link - fascinating stuff.
Wasn't the idea invented (& patented) by a Swiss ?
--
M Stewart
Milton Keynes, UK
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You're welcome!

To my knowledge yes. It was Sylvac. Anybody knowing better, please correct me.
Nick
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wrote:

Indeed, an excellent bit of info.
Thank you.
-- 73 Brian www.g8osn.org.uk
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On Sat, 25 Feb 2006 00:00:09 +0000 (UTC), Mike

That is not possible to do on the Mitutoyo model I have, the "on" is also as mentioned in my original posting also the "zero" so if I move the caliper to mechanical zero and power off, then open up to another setting and then turn it on the reading is automatically zeroed to the mechanical offset by the switch on action.
But out of interest I just measured the current and it's around 10 micro amps when turned on and zero when turned off. (Mitutoyo CD6P measured with a Fluke 8060A multimeter)
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Mike wrote:

I doubt eeprom is used in these things - no need. The calipers use micro-power ICs like those used in watches, that are on all the time. Only when the caliper is being used (opened or closed) is any major current required (charging/discharging the capacitive sensor & the capacitive LCD display if it is 'on' on!). When the caliper is static and the display isn't active, it's as good as off.
Guy
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There are two types (disregarding some inductive working Mitutoyos): The capacitive ones: They have to run all the time, because they only see when they are moved by comparing the voltages the coupling caps transmit. They only switch off the display. The ones with a rotary decoder (quadrature encoder): They have a slotted wheel that looks like the ones in the ball-type PC-mice. These can nearly completely switch off. They do have a LED (to be precise: 2 LEDs) that is emitting light that is either shielded or not. On the receiver-IC side it is quite easy to send the micro-controller to sleep and wake it up when a signal is changing on an input pin.
Nick
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I think the micro-power my venier uses is so little the batteries shelf life is probably shorter. My battery has been in since new 4 years ago.
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