Temperature Correction for new Nylon Coated Steel Tape?

jeffjohn 2Member

Here's a question that has evolved from the marvelous measurement workshop we had in Cuyahoga Falls on August 20.

One of the field exercises was to evaluate a unique calibration course that Mike Wickiser cleverly devised. One unexpected observation I had was that a lot of our top measurers were using nylon coated steel tapes. I've always avoided them.

I inquired... Even AIMS/IAAF Measurement Administrator Bernie Conway assured me that it is OK to use them.

I got to team up with Illinois IAAF "B" measurer Winston Rasmusson. He had a marvelous Keson 50 Meter nylon coated steel bladed tape. (Thanks Winston!) At 50 meters in length, we were done in no time!

The first thing I did upon my return was to order one myself!

The tape is unique in that the steel is coated with nylon and the blade is only 3/8 inch wide. Its durable and light.

There was an insert with some technical data. If I interpret it correctly, the Keson company suggests that the coefficient of thermal expansion for this type of coated steel tape differs from the industry standard for steel.

Most references, and the Procedures Manual, direct us to use 0.00000645 for degrees F and 0.0000116 for degrees C. But for these tapes I think Keson is advising that we should use 0.0000052 for degrees F and 0.0000093 for degrees C.

I tried some examples at 100 degrees F, and I think the variance is just enough to matter.

I wrote to Keson for clarification, but they just kindly sent me a PDF file with only the exact same technical blurb. No enlightenment.

I will try to post that PDF as an image:

If that does not work, then you can see the PDF file here: [url] http://BuffaloRunners.com/Meas...ion_Report.pdf/

If you use this type of tape, which numbers are you using? If you understand things like Young's Modulus of Elasticity how do you interpret this generalized calibration report? What is probably the most appropriate coefficient of thermal expansion to apply?

Jeff John
Buffalo NY

9/1/167:18 AM

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bobthurstonMember

Jeff,

That's some fascinating information-- I do wonder if some independent evaluator has checked this.

One thing I've noticed with tapes that are extremely light is that the wind will pick them up and make it hard to pull them straight-- this may not apply to this case, my experience was with a 300' very light tape. We were doing a track measurement, and we lost confidence in the tape when it continually sailed all over in the wind. Since we were measuring across a turf field I felt there was a danger the tape could get "stuck" between strands in the surface.

9/1/168:28 AM

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genenewmanRRTC Chairman

Interesting. I feel that most tapes vary and I am not sure how our adjustments were derived. Pete or Bob may be the ones to explain this.

First, I think the temperature of 100 is a very unusual. I think very few people would lay out a calibration course with that temperature. However, we are looking at about 6" for every 5k at that temperature. I don't see this as a big deal, because are measurements are not perfect.

To ask folks for the specifics of accuracy of their tapes would add another layer that could complicate the process.

David Katz says is steel tape is on of the most accurate in the world. I guess he uses our standards for an adjustment.

9/1/168:33 AM

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duanerussellMeasurer

Jeff, I am not a mathematician by trade, but when I multiply a 300 meter course by the .0000052 adjustment, I get 5 cm of adjustment. Since one click of the Jones counter is approx. 9 cm, unless you use half-clicks for your calibration calculations, the stretch in the tape is negligible. The difference between the .0000052 and .00000645 factors is even more negligible.

Seems like the use of either factor is going to give you a result that is much closer to one another than our Jones counters can discern.

9/1/168:31 PM

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AdminMember

The most important thing about temperature compensation is getting the sign right. Make sure not to subtract distance when you should be adding it.

When it's HOT, your final adjustment will be to SHORTEN your cal course (or not).
When it's COLD, your final adjustment will be to LENGTHEN your cal course.

9/2/164:20 AM

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jeffjohn 2Member

Thanks all for your input. It's reassuring that we may all agree that this revelation is academically fascinating, but not real troublesome.

I used the new Keson 50 meter tape for the first time yesterday to build a 300 m cal course.

Air temp = 79 deg F
Street Temp = 113 deg F
Tape Temp = 98 deg F

For the first time I have an open reel and could apply the Mike Wickiser technique to get a good average tape temp by shooting the reel with the infrared thermometer immediately after rewinding the tape. In this example the "whole reel tape temperature" value turned out to be the same as the average spot tape temps observed during the measures.

we examined both temp corrections (using 0.00000645 and 0.0000052 as the coefficients of thermal expansion) on the road. I must confess: viewing the two corrected course length marks on the road... the variance was not impressive! (we compared calculated adjustments of 0.0581 m and 0.0468 m)

If my arithmetic is not in error then Duane is certainly correct: The variance is only a little more than 12% of the distance of a single Jones count (at 11080 cnts /km) . When the 1.125 cm variance between the two coefficients is propagated over a marathon then the total impact is only about 1.58 meters.

I think Neal hit the nail on the head. It's way more important to make certain the temperature correction is applied in the right direction than to worry about which coefficient the measurer used.

JJ

9/6/166:18 AM

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