# Laser distance measurement

#### jpanhalt

Joined Jan 18, 2008
10,068
At a big box store I saw the Stanley The FatMax TLM100. It is sold as a "true laser" measuring device. The package and user's manual were uninformative, and the accuracy claimed on the package (+/- 1/8") seemed too good to be true.

I cannot find much on how it actually works; although, accuracy of +/- 1/4" at 100 feet seems to be a more common claim. Lowest price I have seen was $50 USD. Does anyone know how it actually works? That is, is it TOF, triangulation, or something else? John #### studiot Joined Nov 9, 2007 4,998 Early EDM (Electromagnetic Distance Measuring) equipment measured phase difference for the single (one way) journey. Examples of this were the Tellurometer. and Decca Navigator. Advances in electronic timing systems in the 1970s brought in various TOF (Time of Flight) systems such as the Trisponder (microwave) and Wild Distomat (infra red). The Trisponder measured one way distances, from a mobile to a fixed base station. The Distomat measured two way distances from a fixed base station to a reflector and back. The last 20 years have seen improvements in infra red sources such that 'point and shoot' TOF distancers have become possible, relying on picking up some of the reflected radiation from the base station, eliminating the need for a roving reflector. However it can be very difficult to be certain what you are bouncing the signal off on these. The most accurate types use light or laser interferometry and can measure down to a few wavelengths. Hope this helps Thread Starter #### jpanhalt Joined Jan 18, 2008 10,068 I am familiar with the techniques you mention. The question is what has Stanley done in this device that sells for as low as$50 new?

Interferometry would be tough, as the measurement is an absolute, not relative distance from less than 2 feet up to 100 feet. It does include a red laser for spotting. Don't know if that is the only laser. The manual makes reference to reflective properties and temperature effects, but claims it is not sound based. I almost bought one just to find out, but thought I would ask here first.

This forum often has questions about "final year projects" for which the questioner proposes some sort of radio or light TOF method to measure distances. Timing issues and detection sensitivity for the reflected laser are the greatest stumbling blocks. Wouldn't it be great to just have the Stanley solution available?

John

#### jpanhalt

Joined Jan 18, 2008
10,068
Update:

I just heard back from Stanley Tool Works technical department. They confirmed that the TLM100 series is time of flight.

So for \$50, you can get a TOF distance measurement tool that is accurate to <1/4". I couldn't wait for the answer, so I went ahead and bought one last week and can confirm it does in fact work. I can set it on a table, get a reading of say 11ft, move it 1/8" and the reading shows the change. The measuring pulse is rated to be <=1nS. More expensive units (TLM200 and TLM300) have even tighter specifications.

I am amazed by that degree of technology in a tool that is so cheap.
There has to be some other uses for them. Any ideas?

John

#### SgtWookie

Joined Jul 17, 2007
22,210
I am amazed by that degree of technology in a tool that is so cheap.
There has to be some other uses for them. Any ideas?
Ballistics.

Of course, range is only one input. Elevation delta angle is even more important, along with wind speed, spin drift, altitude, humidity, etc. But having exact range is a really good start.