Temperature compensation on field measurments

[clobo]

I am looking out for some info on usage of the temperature correction factors for field measurments. i work for a company that deal in the fabrication of offshore steel structures, like jackets and deck for oil platforms.

I was interested in getting some further understanding on the followings queries and would be happy if I got a few answers



“Measurements corrected to 20 degrees centigrade” - what does that mean and why is 20 degrees centigrade considered as a standard for basing the correction factors.
Is this correction to be applied while carrying out measurements with steel tapes only or is there any temperature correction to be applied while using EDM’s also.
How do you calculate temperature correction if the measurements are to be corrected to a non standard value, say 10 degrees centigrade.


Thank you



Claudius Lobo

[D Ryan]

20° Centigrade = 68° F which is the temperature at which steel tapes are standardized, and at a specified tension, usually 10, 12, or 15 lbs (manufacturer's specs). Under what scenario is this statement being made? I would surmise it only applies using a steel tape since corrections are automatically applied using an EDM if you are accounting for atmospheric corrections. Why 20°C? It falls somewhere between the extremes.

[bruce hall]

Most of the modern edm's have a way to enter the barometric pressure and temperature into the instrument prior to the operator taking measurements. You must enter the temperature or the values that are "returned" by your instrument may be in error. A "significant" error(and that can mean different things to different people) can occur when temperatures are very much above or below 68 deg. fahrenheit and you are measuring a long distance.

When I did a lot a measuring with a steel tape, circa 1968 to 1980, we factored in the temperature. As I remember the general "rule of thumb", for every 13 degrees F. change from 68 degrees F. the steel tape would "grow" or "shrink" 0.01' in a hundred feet. Or maybe it was 15 degrees. But it is something along those lines. My tapes were calibrated at 25 lbs. of pull. The temperature varied to get 100.00 feet. Some tapes were 100 feet long at 25 lbs at 62 degrees. Some were 100 feet long at 25 lbs at 72 degrees.
I still have a tape in my truck that when the temperature is 68 degress and I put a tension of 25 lbs on it, I can theoretically get a distance of 100.0005' in a hundred foot pull. I just have to keep the plumb bob still. Of course I haven't used it in a looooong while. It may need to be re-calibrated. I just don't know if time or age has anything to do with the expansion of this steel tape. Also I have a thermometer that can be affixed to the tape so that I can get a reading of the heat around the tape, instead of the temperature under the transit.

Now if your tape is calibrated to a different temperature, like a lot of mine were, that's okay too. You just have a different "base" from which to add or subtract the current temperature from. And this calibration is supposed to work with a tape that is subtended above the ground. If the tape is laying flat on the ground, all bets are off. Now like I say, this is how I remember it, and unlike my surveys, I didn't take any notes on this subject. I hope this helps. Good luck, Bruce Hall.