> Hi,
>
> If a staff expands due to temperature, then the reading will be smaller, therefore the expansion value should be added to the initial reading. Is this correct?
>
> Thanks in advance.
>
> ss
Pretty much, all the posts are right. However, for the student surveyor, the answer to your question is yes....that's correct. You are envisioning exactly right.
A lot of people get it backwards. (ie: It's too long therefore you need to subtract...)
You need to picture it correctly (like you did). You will have the same dilemma when thinking about measuring with a tape/chain. If you are measuring between existing points and the chain is too long, you will read a smaller number than "true" and need to correct by adding your factor. If you are setting out a point, you are going to far, because the chain is to long, so you would need to subtract. Think it through before answering. you will get that kind of question on tests, including licensing tests, etc.
A lot of people get it backwards. (ie: It's too long therefore you need to subtract...)
You need to picture it correctly (like you did). You will have the same dilemma when thinking about measuring with a tape/chain. If you are measuring between existing points and the chain is too long, you will read a smaller number than "true" and need to correct by adding your factor. If you are setting out a point, you are going to far, because the chain is to long, so you would need to subtract. Think it through before answering. you will get that kind of question on tests, including licensing tests, etc.
That is a very good point. When I was doing hi-rise building consulting work in the 80's. The company I worked for issued us tapes which had the temperature scribed on them. Some were 65, 68, 66, 69 etc. We carried both offset tapes and layout tapes. Although we did both layout and measuring everyday, there wasn't a day that went by that we weren't second guessing ourselves. It just goes against intuition.
Ralph
Seems like I remember a rough estimate of a hundredth */-per 100 feet per 10 degree change, tape calibrated at 68 degrees F..
jud
> Seems like I remember a rough estimate of a hundredth */-per 100 feet per 10 degree change, tape calibrated at 68 degrees F..
> jud
Off the top of my head I believe we used .01 per 15 deg Fahrenheit. I don't think the 68 temperature has anything to do with expansion. All tapes are different. The reason your calibration certificate would come back using 68 deg as a basis was because the basement at NIST, where they conducted the tests had an ambient temperature of 68 degrees.
Ralph
The temperature of 68 Fahrenheit is also 20 Centigrade, which is the reference standard temperature used outside the USA. As noted, most calibration laboratories would use a controlled environment held at the standard temperature.
I'm not sure when 20 C was adopted, but certainly it has been used on European tapes since mid-1950s and UK tapes used it long before metrication took over. Most tapes have the standard temperature and tension values marked on them: a calibrated tape should have the temperature of the calibration shown on the certificate.
> The temperature of 68 Fahrenheit is also 20 Centigrade, which is the reference standard temperature used outside the USA. As noted, most calibration laboratories would use a controlled environment held at the standard temperature.
>
> I'm not sure when 20 C was adopted, but certainly it has been used on European tapes since mid-1950s and UK tapes used it long before metrication took over. Most tapes have the standard temperature and tension values marked on them: a calibrated tape should have the temperature of the calibration shown on the certificate.
Thank You Chris, that is a big misconception that many have.
Cheers,
Ralph
