laser measuring devices

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Do they work very well, or are they just for guesstimating?
Steve
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On Sat, 24 Dec 2005 21:38:21 -0800, "Steve B"

Don't know, but you could take some known distances and verify the one you buy. Seems to me one should do that anyhow, in case you get a bad one.
When I buy an egg-timer, the one with sand for example, I could have used a watch, but instead I flipped over several and compared them with each other. I bought one of the group that matched each other.
(although actually they were all very close. The worst might have been 5 seconds over two minutes, and almost all were within a second or two of each other, and these were cheap ones, 20 years ago.

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On Sat, 24 Dec 2005 21:38:21 -0800, "Steve B"

There are two types. One use the laser to actually make the measurement. They are quite accurate. The other type uses the laser as a visual aiming aid only, and uses ultrasound to make the measurement. They are a lot less accurate (say within a few inches at 50 feet distance or so) and are more prone to measuring the wrong distance, like to intermediate obstacles for example.
The first type run $350 and up, the second start under $100.
Paul
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wrote:

Then mine, probably some of the cheapest you can buy would be on a par technologically with a string and a tin can?
Probably.
But, I was going to go out and do some comparisons with a hard tape, and this thing. The major thing I can see is that it won't take a reading in bright sunshine. A problem here in Las Vegas, where it was 70 degrees here on Christmas Day. But cloudy.
Steve
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Steve B wrote:

Is that the LV version of a white Christmas? ;)
R
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I took a look at the Stanley level at HD and it says right on the box that the accuracy is limited to 1/2" over 10' which is not enough to comply with ANSI standards for ceramic tile installations. It would probably be visible to some people if say, a 5' shelf was 1/4" out of level. So these products are not any better than just eyeballing. But that's the level. My point is just that the cheap ones aren't accurate enough to be useful to anyone.
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Are you sure there are ones that measure by laser? Ultrasound ones use the bounced back wave to figure out the distance. To do this with a laser would require an extremely fast processor...we're talking supercomputer.
Mike
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It shines a little red dot at whatever you point it at. Is that an ultrasonic dot? Or a little laser pointer, and then the distancing device is ultrasonic?
Steve
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a big round hole that looks like a funnel and another smaller hole where the laser light comes out, it is the ultrasonic type with a laser pointer that gives the general direction of the aiming point. Also it may make a clicking sound.
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(Amazon.com product link shortened)"8013
This one states it measure with the laser (Amazon.com product link shortened)"8013#importantInformation
Product Description: The TLM 100 Tru-Laser distance measurer gives you Tru laser measuring at the press of a button just point, press the button and measure indoors, outdoors and hard-to-reach areas. Tru Laser technology actually measures the laser light travel distance.
Read about the technology here http://www.stanleytools.com/default.asp?TYPE=STATICLEFT&PAGE=PR_lasermeasuringLeica05.htm&LEFT=left_pr.htm
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wrote:

Very interesting. The funnel is much bigger than I thought was being talked about. I thought it was like a quarter inch at the top, instead of 2 or 3 inches.

very annoying. They won't tell you the price until you put it in the shooppping cart.
Amazon Visa discount:     - $30.00      Your new subtotal:     $64.94 Save $30 off your first purchase, earn up to 3% rewards, get a 0% initial APR, and pay no annual fee After just 2,500 points you'll get a $25 Amazon.com Reward Certificate.
Chuck Schumer, the senator, was talking about this in NYC a few weeks ago, about how store credit cards charge about TWICE the rate that bank credit cards do. He mentioned the ones like this one that give you a discount off your first payiment. Notice how many details this gives, but doesn't give the rate. Sleezy. Unbefitting a company like Amazon which is trying to establish a good reputation. Now it looks as sleezy as anyone else.
This is why I had all the questions about the telephone sservice advertized here earlier (spam.).
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Steve wrote:

Light travels 3.0 x 10^8 meters per second. Measuring 1 meter (3.3 feet) and ignoring the time taken to perform calculations would take 3.3 x 10^-9 seconds. Giving the benefit of the doubt and assuming it takes two processor instructions to recognize the returning light wave (that is, process two instructions in the given time) the speed of the processor is then 6.0 x 10^8 Hz, or 600 MHz. Microcontrollers don't run this fast and I doubt there's a Pentium in there. The laser is probably just a pointer so you know what your measuring to.
Mike
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That explains it. What I have is a POS toy, and not a really accurate measuring device.
Thanks to all.
Steve
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On Sun, 25 Dec 2005 20:22:41 -0800, "Steve B"
<snip>

(see the other posts) it's still pretty handy for quickly measuring room sizes for extimating materials, etc.
Can you use it to measure how long to cut that next pece of crown molding? No. But you can use it to know how much crown molding to buy, or carpet, or paint, etc...
So don't toss it yet...
Paul
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You might want to check out this link to Stanley Tools laser/ultra-sonic measuring device.
If the specs are correct, +/- 1/4 inch over 100 feet is not too bad.
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upand_at snipped-for-privacy@yahoo.com says...

software? That would truly be dumb. Time measurements in the 1ns range aren't difficult at all, though I agree this isn't what they're doing. Measuring even to 1ns is 1 foot accuracy; hardly useful.
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Keith Wiliams wrote:

No, what would truly be dumb is to reply when you don't know what you're talking about. The measurement IS being done in software. Where else is it going to be done? Do you think the light wave computes the distance itself and passes the data to the microcontroller to display it?
The microcontroller has an on-board timer and uses it to measure the phase difference, in time (T). But instead of measuring the time for the lightwave to bounce back, the phase shift is measured (in TIME). The transmitted frequency (R) is known so it then computes D, where D R x T.
Mike
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upand_at snipped-for-privacy@yahoo.com says...

Nice, but ignorant comment.

That would truly be dumb. Hardware can easily measure a nanosecond. Software can format the output of the hardware so a human can read it, but a software timing loop differentiating 1ns events? You're on drugs.

You really are ignorant. Have you ever considered a simple counter running at a GHz, or maybe interferometry to measure the phase relationship of the sent and received signal. The microcontroller certainly *not* going to be able to discern a 1ns signal, even it it does operate at a couple of GHz.

The timer would have to operate at a GHz, along with the I/O in question, just to get one *foot* resolution. Hardware can be used to measure the phase relationship without having to operate at 20GHz (1/2 inch).
--
Keith

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On 25 Dec 2005 18:06:18 -0800, upand_at snipped-for-privacy@yahoo.com wrote:

Sure, here's a link:
http://www.leica-geosystems.com/cpd/en/ndef/lgs_31658.htm
If you read the faq (there's a link on the above page), they go into a little detail about looking at the phase shift of the returned pulse train. Using a phase comparison of two pulse trains (emmitted and returned) avoids having to have a processor fast enough to measure the round trip time of a single pulse. Rather clever, actually...
Paul
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How soon people forget analog ;-) Or non-programmable digital for that matter. Custom ASIC running at a couple Ghz is easy, and very cheap in quantity. It's essentially a frequency counter.
--
Chris Lewis, Una confibula non set est
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