OT: how does a laser tape measurer work?

[N_Cook]

A very basic one
https://www.screwfix.com/p/titan-mk715-laser-distance-measurer/5151p
Great having a reason to get inside (to extend the display hopefully by
about 1 metre, separate from the works.
4 back plane , 20 way ribbon including 2 for DC to the backlight.
In use you can feel something physically moving inside in operation.
This is a simple swinging gate flap that is closed or open, driven by a
little electromagnet. A crude white paint patch on this swing-arm
intercepts the laser to reflect into the receive section or back to the
dividing wall, otherwise all black inside.
So instead of pulse timing/phase difference if modulated, is it doing
something else, or or is some sort of calibration of the laser power
required ?

[Andy Burns]

N_Cook wrote:

> A very basic one

My Bosch one uses a phase shift rather than time-of-flight, this chap
did a tear-down and reverse engineering, in several parts

<https://www.youtube.com/watch?v=PsnzorA0WSs>

[peterw...@gmail.com]

https://home.howstuffworks.com/laser-tape-measure.htm

Yep. There are several types - with phase-shift devices typically limited to shorter distances than time-of-flight devices. Typically. Not Always!

And (also typically) much more accurate than a long metal tape, and easier to use than a cloth tape.

Peter Wieck
Melrose Park, PA

[peterw...@gmail.com]

On Friday, August 3, 2018 at 9:42:38 AM UTC-4, N_Cook wrote:
> A very basic one

> So instead of pulse timing/phase difference if modulated, is it doing
> something else, or or is some sort of calibration of the laser power
> required ?

Some professional laser devices used by surveyors and civil engineers do require calibration. As when two ends of a bridge meet in the middle, 1/8" (3.175 mm) does matter.

[N_Cook]

Admittedly I skipped thru most of that, but I did not see what the
function is of this close-coupled mechanical litteral gating .

[Andy Burns]

N_Cook wrote:

> Andy Burns wrote:
>
>> <https://www.youtube.com/watch?v=PsnzorA0WSs>
>
> Admittedly I skipped thru most of that, but I did not see what the
> function is of this close-coupled mechanical litteral gating .

Mine does give a mechanical 'clunk' when you press the measure button,
he describes this as a curtain that opens/closes to measure/calibrate.

Sounds a similar function to your gate, but mine doesn't rattle if you
waggle it.

[N_Cook]

There is not enough inertia in the mass of the gate itself, plastic
about 5x5x1mm, to be noticable in normal handling, it is totally free to
move though when unpowered.
It seems what you/I sense is the gate being suddenly stopped at either
end of its swing and the inertia of very fast movement is transfered to
the body of the unit.

[N_Cook]

My guess for the swing gate is, there is an optimmum power setting for a
given distance measured for accuracy, some middling setting initially
and then up or down the power of the laser after initial measured distance.