View Full Version : Digital Caliper Technology
09-26-2010, 06:09 PM
Digital calipers utilize capacative sensor technology. Considering the low cost of digital calipers, the parts must be pretty cheap. I would like to purchase lengths of the ruled (or unruled) tape that is used for these so I can make my own measuring devices of different lengths and shapes. Does anyone know of an inexpensive source? The Chinese shops that make these have to obtain them from a manufacturer. I've been searching the Internet but have not found a source.
09-26-2010, 08:41 PM
You can go to the ShumaTech group at Yahoo and find out all about Chinese scales.
09-26-2010, 10:16 PM
One issue with capacitive calipers is that the sensing head and the "scale" has to be flat and held at a precise distance apart to work properly.
It's essentially an air gap capacitor and the gap has to be held constant.
The only easy way to make your own sensors would be to buy a long scale and reader unit and cut it to your application.
Now if you really want to make your own scales you might want to try to etch some circuit board. One of my old Mitutoyo scales looks like copper circuit board etched at 5mm pitch. 2.5mm wide copper bar followed by 2.5mm gap. Repeat, rinse and wipe hands on pants.
The reader head from any caliper could be made to work as long as its guided to maintain the gap. I have no idea on the tolerance of the gap, you might want to experiment to see how much tolerance there is.
Flexible magnetic scales are available from Siko and others, not cheap though...
09-27-2010, 03:34 AM
US Digital do them as well.
They have prices on their web site.
10-01-2010, 04:23 PM
Judging from all the mitutoyo patents on the use of inductive sensing, I think this is what they might be using for their calipers. It is far less sensitive to gap size and fluids.
Still don't know where you could buy separate components though.
There is very cheap magnetic tape here
but the read head does cost a bit.
10-03-2010, 04:27 PM
You can get a self adhesive "digital tape" (works just like the calipers) that can be stuck onto anything and then mount a small reader on your movable part. I don't have a company name but they are in the US.
10-04-2010, 03:27 AM
They are magnetic strip encoders. I have one mounted in the frame of my laser cutter.