Well after looking at Televue prices of there digital indicator for there focuses i was shock at the cost. The indicator and cable would set me back a shocking price of $1300. The data cable itself is $369 for a cable. Now i think this is a bloody rip off. So i got online and work out i could do the same thing for get this about $200. I found these guys really good http://www.tresnainstrument.com/digi...FQsQagod7gTkJA
So i now have a digital read out on my focuser and comuter for allot less then it would cost from the shops that sell these things for televue. The resolution is 0.001mm/0.00005"
Excellent work.
And definitely NO to ripoffs :-)
However, do you really need 0.001mm resolution?
Electronic caliper with 0.05mm costs around $50 or so. And it has RS232 (interface must be added though but I think this is just low-voltage RS232 level converter)
Also I saw mechanical gauges (looks similar but no electronics, just gears inside and round dial with pointer under the transparent cover), for similar price.
Electronic caliper with 0.05mm costs around $50 or so. And it has RS232 (interface must be added though but I think this is just low-voltage RS232 level converter)
Most of the cheap calipers with RS232 out use a funny Chinese protocol and arent "simple" RS232 at set bauds ( which is a pain ) ie http://www.shumatech.com/support/chinese_scales.htm
I have hacked into a std vernier caliper, and can read it with my PC via a parallel port logic analyser, but its not real practical for a focusser. A dial unit with RS232 out may be the go if it uses the same protocols.
Andrew, fair enough :-) and thanks for the very interesting link, I did not know about this.
Anyway, even $200 is excellent compared to k$ "normally" asked for...
Here is the link to schematic and code to implement RS232 connection to cheep Chinese digital calipers http://www.compendiumarcana.com/caliper/
I did not try to build it myself yet.
I've got a few old Mitutoyo micrometer heads lying around but never thought of connecting them to an RS232.
Do you know the part# of the small 4 pin(?) connector used, also what's the software to display the readings?
Last edited by Merlin66; 11-12-2008 at 09:51 PM.
Reason: spelling!
Bojan,
I found most of these references but they require additonal $$$$$ hardware/ software to talk to PC.
Does anyone/ has anyone found a source of cheap connectors which will allow the Mitutoyo verniers to plug directly into a PC? ie 4pin to 9pin serial? and associated fread-out freeware software???
I did find www.windmill.co.uk interesting?!!!
Accuracy and resolution are two different beasts..
Accuracy means how far away you are from REAL value (compared to etalon or standard).
There is a third parameter which should be listed but is not, and that is repeatability of reading, because people mix it with accuracy.
Basically, if repeatability is good (that means, always the same reading whenever you measure the same thing) it can be calibrated if you have a standard.. then accuracy becomes the same as resolution
Accuracy and resolution are two different beasts..
Accuracy means how far away you are from REAL value (compared to etalon or standard).
There is a third parameter which should be listed but is not, and that is repeatability of reading, because people mix it with accuracy.
Basically, if repeatability is good (that means, always the same reading whenever you measure the same thing) it can be calibrated if you have a standard.. then accuracy becomes the same as resolution
thanks, bojan.
I am familiar with precision versus accuracy, which is what you refer to as the "third parameter", I think.
however, i guess i had the thought experiment:
reading = 10.001
but accuracy states that true value could be anywhere from 9.996 to 10.006. Therefore, a precision of 0.001 is not helpful. In this case I am equating Acccuracy to error, which may not be strictly correct.
reading = 10.001
but accuracy states that true value could be anywhere from 9.996 to 10.006. Therefore, a precision of 0.001 is not helpful. In this case I am equating Acccuracy to error, which may not be strictly correct.
You are quite right, in your way of thinking.
But if you have a standard (or something you know it is exactly 10.000) then you can determine what the error or gauge is, and account for it in any future measurement. Then, a precision (I would rather use term "resolution") of 0.001 will become useful.
However, in our case, I believe the stated resolution (number of digits) is more a marketing thing.. so not very useful in reality.
I just love it when people "stick it to the man"
