We used to run through this exercise all the time, back in the (highway) chaining days.
If recording distance (hot), it measures short, add.
If staking (hot), it measures long, subtract.
:coffee:
What if I use a fiberglass rod?;-)
Lay it end to end.
Count how many times and multiply it by the rod height.
Then go out and buy an EDM.
:coffee:
WOW!!
My initial response was going to be "Insignificant", but I decided to wait and see what happened here. Half of us can't even figure this issue out, yet we are also dealing with SPC's! Do you suppose that half of us apply scale factors incorrectly? I do...
WOW!!
sorry left out mili in front of meter
AS3
A quick way to check H.I.'s:
Measure in feet (I'm assuming a US survey foot job but this can be reversed) and write it down-measure in meters and write it down-then input into the data collector the H.I. in meters with a m behind it (using a trimble data collector; other data collectors might not have this feature) and it will automatically convert it to US survey feet. Then you have a check on your HI measurment before you start. Best to use two tapes and not the kind with feet and meters on opposite edges of the same tape.
WOW!!
I'm at elevation 50...wgy do I need to apply scale factors to my SPC's?;-) 😛 😉
Joe
I might understand if there was a slight nonlinearity versus temperature. But what you seem to be suggesting is nonlinear versus length, and I have no clue how that could be.
Martin F said it right and explained it well.
Slightly differently said:
+10 deg. is 10 deg. colder than standard temp.
The rod has shrunk by 0.33mm in the cold (Hey, it happens)
The rod is therefore reading too long a measurement.
"-0.33mm" must be added to the reading to get the temp. corrected height.
The lesson is ...
IF YOU NEED TO APPLY TEMP. CORRECTIONS TO YOUR H.I. TO YOUR TOTAL STATION, YOU'RE USING THE WRONG EQUIPMENT OR AT LEAST THE WRONG TECHNIQUE. TAKE YOUR ELEVATION OFF A BENCHMARK.
Adam Salazar observed:
>the coefficient of thermal expansion of the Leica measuring tape is not constant
That's an interesting observation. Converting Adam's thermal expansion coefficients* to ppm per degree C, they vary from [tex]alpha[/tex] = 19 to [tex]alpha[/tex] = 21, which is clearly more of a difference than can be explained from two-decimal-place rounding error in the chart.
As Bill93 noted, the variability of [tex]alpha[/tex] is primarily relative to the length, not relative to the temperature change. This fact suggests a possible explanation for the variability: the object in question is made of two separate parts with different expansion coefficients.
I haven't used the GHM007, so I located a Leica newsletter which provides some discussion and a sketch of the Leica GHM007 (in the context of adapting it for use with GPS). The article shows that the modified tape is not measuring the entire height, but instead only measuring up to a point on the tribrach which is nominally 196 mm below the tilting axis of the reflector.
If the tape has a coefficient of expansion which is different from that of the 196-mm base portion of the reflector, then that would explain the apparent variability of the [tex]alpha[/tex] values that Adam derived from the table. This is because a different amount of tape is unspooled and contributing to the combined height for each different h.t. (and is therefore also contributing a different percentage amount to the combined thermal expansion).
There are enough correction values listed in the original table to set up a least squares model to compute separate values of [tex]alpha[/tex] for the tape and for the 196-mm base portion of the reflector, relying on the (questionable) assumption that these two parts each have their own constant expansion coefficients.
Solving this model provides an estimate of [tex]alpha[/tex] = 23.0 for the tape, and [tex]alpha[/tex] = 2.7 for the 196-mm base portion of the reflector.
These values don't make a lot of sense when you try to use them to determine what materials they might represent (an aluminum tape?), so maybe the height should be modeled using three or four separate sections with their own individual values of [tex]alpha[/tex].
However, the two-part model described above provides "perfect" agreement (two decimal places) with correction values listed in the table, using the two computed values of [tex]alpha[/tex] in the following equation for the combined expansion correction:
[tex]correction (mm)quad=quad1000(L-0.196)(frac{23.0}{10^6})(T-20)quad+quad1000(0.196)(frac{2.7}{10^6})(T-20)[/tex]
- Doug
* original units in Adam's listing were mm/m per degree C.
Great detective work!