unit conversion 8

[tulum]

I don't know if I am in the right forum (just dropping in), however, need some help with a conversion.


I have a support (electrical insulator) that is good for a certain force in in.lbs (fron the data sheet). I have also calculated the force on the insulator for the given arrangement, only the result is in daN.

How do I get the units to equal?

Thanks.

 

[rmw]

gearguru,

There are 3 slide rules in my desk drawer. The beginners model that I probably had in high school, the 10" I used to get an engineering education, and the 5 incher that I carried in my pocket for several years as a service engineer for a large steam turbine mfg.

As I have contemplated them, recently, (part of throwing one of them up on the desk, and thinking about my roots,) I have also wondered what my children will do with them when I pass on. My son in law is a Civil Engineer, and I don't even think he has ever seen a real one.

Maybe I can stipulate that they bury them with me. The point is the contrast. My beginnings harken back to the slide rule, which was a mandatory piece of equipment for my profession, and now as I work in the world you describe, HP 28S, PC, Laptop, PDA, e mail, instant messaging, on line calculators, imperial units, metric, SI, etc, I wonder where it will all go even in my (and hopefully your) lifetime. These are challenging times for (old) engineers.

You deserved the star. I learned from your post. And, this site, with its fora is a real help to me in my professional development.

rmw

 

[mloew]

FYI,

I created a FAQ Unit Converters (faq404-901) consolidating links to on-line unit conversions.

Please also see The Metric Conversion Act of 1975 (

http://www.usaid.gov/policy/ads/300/metricact.pdf)

for information on the intended use of SI units in the US.

Best regards,

Matthew Ian Loew
"Luck is the residue of design."
Branch Rickey

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[PeterCharles]

Ah, the memories of sliderules! I've still got mine, two 10" (one which had a clip on magnifier to get more accurate results), and a 5" with a 'folded' 10" scale. All those different scales for trig functions and the log scales.

I've also got a copy of Inskips Combined Tables (log tables based on the foot). I have to say if there is one thing that increased efficiency and order of magnitude it was metrication combined with affordable electronic calculators. No way would I want to go back to using Inskips to calculate diagonal lengths to 1/16 th of an inch!!

By the way, did anyone buy and use a Sinclair Scientific electronic calculator?

 

[Skogsgurra]

rmw and all other people that I seem to have upset,

Decimal time? Oh, yes. Great idea. And as you probably know, the Swatch company introduced that idea sevel years ago. But it didn't seem to catch on.

Being such a jelly. I did buy one of their decimal watches, just to put it in a safe place. I kind of figured that there wouldn't be many after a couple of decades (see, decimal time again!).

Talking of jelly, PeterCharles. Of course I bought a Sinclair, but not a scentific calculator. I bought their first four-banger. Much for the same reason that I bought the Swatch.

And, you know what? I have a Reiss 3227 on my desk. And use it, too. It has got LL0 - LL3 as well as LL00 - LL03, and sinh1 and sinh2 to boot! My Sun-Hemmi pocket model does not serve me any more, eyes are getting a little too weak for those thin lines.

I really apologize if anyone thought that I was making fun of them - or their fathoms or grains. I just thougt that you needed some help to get into an EASIER world of engineering - and I did NOT say better world.

 

[gearguru]

skogsgurra,
yes, metric is easier - for the people who started with.
But please take into account that there are all the tools, gages, tool machines in this country based on inch system.
The fact, that the design is very often (at least in the auto industry, where it is mandatory for many years) made in mm does not change that inventory. And to run two sets of them (inch and mm) would create even more difficulties.
rmw,
thanks for the sincere, personal thoughts. And yes, these fora are excellent.
For your amusement - the unit for the force in metric evolved through the years 'till the N was finally established. I remember times, when we used kg*
(and kg for mass) then we used kp (kilopond, you can still find it in some German publications), then kgf... All of them meaning the same! And because its size is so familiar, the daN (=0.981 kgf) is sometimes used... I did not mention the "cgs" system what we also used long time ago - based on cm, gram and second. Isn't metric simple?
MLoew
Thanks, it was a good idea.

 

[JoeTank]

A Canadian friend of mine once noted that inch-by-inch they are getting closer to the metric system in their daily operations at the the refinery.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[IRstuff]

I found out once that my Dodge Charger used metric threaded lug nuts with a metal sleeve to convert to English socket.

Took the car in for service and several months later was stuck on the road with a flat, had 3 lug nuts off but found the remaining one was a real metric nut...ARRRGGHH!!

TTFN

 

[rmw]

Skogsgurra,

No apology needed. I mentioned in an eariler post, that I have to deal with a metric product, and in another post that is of spanish origin. Gearguru helped me with his post, because I really did not know what drove the change, after I was comfortable in the m-kgf world.

When I can get into a situation where I have to draw something up, and fabricate it myself (hobby stuff), I much prefer the metric system rather than 1/16, 1/32, 1/64, etc.

The part I hate is going back and forth, having to do all the converting. I still can't think in metric, as in have a point of reference. 10 feet is about the height of one story of a building, 50 ft, then would be a 5 story building. And, 150 ft is about half the length of a US football field. But 1910mm, is that as tall as the empire state building, or the height of a basketball goal, or a real tall glass of tea?? I have no mental point of reference. I have to stop and convert it for it to have any meaning for me.

Gearguru said it best, metric is easier for those who started with it. The hard part is knowing that metric is easier, but being thrust into a project like I was recently, where the drawings are 30 years old, and everything is in imperial units. I started with that system, but it is becoming more difficult for me to endure.

I enjoyed the discourse, and your input. Keep 'em coming.

rmw

 

[IRstuff]

rmw,

Time to move up to Mathcad. I use it nearly daily and the beauty is that you can do the unit conversions in situ.

You enter the values in whatever units you want, do the calculations and output the result in the desired units. The real beauty is that since the equations are live, you can change input values and the result is recalculated, again with the desired units.

The big disadvantage of unit converters is that you still have to run the resulting values into a separate converter; change a value and you have to re-convert.

Additionally, most converters do not deal well with converting BTU/hr/ft^2/ºF into W/m^2/ºC in a single operation like you can do in Mathcad.

TTFN

 

[sacem1]

gearguru:

There are two systems in the metric world: cgs (centimeter-gram-second) and mks (meter-kilogram-second) both are systems not units the units are:
length: meter
mass: gram
time: second
The beautty of the metric system is that most units are related to one another and not all arbitrary in their starting point so in most cases one can convert or move from one unit to the other in a very aproximate way with out crunching numbers or looking at tables. i,e,:

length x length = area unit = square meter
length x length x length = volume = cubic meter = 1000liters

Sounds like square feet and cubic feet right but lets get more elaborate: when you go up or down in english units you divide by 144 to move from square feet to square inches and by 1728 from cubic feet to cubic inches in metric from cubic meter to go to a lower unit you just move the decimal point 3 places to get liters and another 3 places to get cubic centimeters no calculator or slide rule needed and no memory or table to look up

The same logic applies to other units: a gram is the mass of 1 cc (cubic centimeter) of pure water at 4ºC at sea level barometric pressure so if you want to know how much does a 4.5 cubic meter tank of water weights you can say very aproximatly that it has 4,500 kg, because there are 4,500 liters in the tank and each liter weights 1 kilogram (right kg is a mass unit but weight is still done in kg-f not Newtons or decaNewtons, by the way 1000 kg is a Metric Ton.

Ever tried to do that with out a slide rule/calc in english units?

By the way temp is based in something we have all around: water, it freezes at 0ºC and boils at 100ºC (at atmosferic pressure and pure water but usually differences are not requiered for normal use) not 32ºF or 212ºF and why did you made 180º in between?

This is not intended to be a units class but just to make a point, metric is more logic and intuitive to use once you get a grab on it, but for the time being we are stuck with two systems and the change is going to be slow and for some painfull, here we use both systems (english/metric) every single day and it's sometimes confusing but in the end metric will prevail because its simply more logical.

SACEM1

 

[cb68]

If we're talking SI units I thought according to thermodynamic temperature water froze at 273.15 kelvin and boiled at 373.15 kelvin.

 

[MintJulep]

Ok Metric guys. Figure this one out!

I have an inspector working for my company that is resident at a Japanese manufacturer's facility.

He has a tape measure that is graduated in meters/centimeters/millimeters along one edge and 1/33 meter increments along the other edge.

Anybody car to venture a guess on the significance of the thirty-third of a meter?

 

[Skogsgurra]

I do not know about the 1/33, but I know about tape measures that are graduated in 3,1416 cm increments, which is quite close to 1/33 m. They are used to measure diameters of large cylinders by measuring the circumference and reading the diameter. Are you sure it is thirty-thirds?

 

[gearguru]

sacem1,
as I mentione above, I am an old metric man transplanted in inch based world, so I know what you are talking about.
It was pain for me to learn the fractions, and I still can not visualize the small distances, thousandths of an inch, for example. My colleagues have the same problem with mm, We use them all the time, but they first convert to inch and then they know what approx. it is in size.
Yes, metric is more logical. But I learned that to change to it is not that simple. And to convince the inch people that it is better, it should be used more uniformly in metric countries (see rmw's Spaniards). Somewhere I read a question - why the liter is not 1 cubic meter? Why cubic decimeter? And why the unit of pressure "bar" is still legal and used in some countries? (we both know that it is almost the same as 1kgf/cm2, the old good "atmosphere")
I promise that this is my last entry in this neverending topic.

 

[rmw]

IRstuff,

I work with heat transfer a lot, (heat transfer equipment produced in Germany, customers in USA, with a lot of the technical data from South Africa, and I have to be the interface between those two metric systems, and the end users. Hence my comments earlier about the fun of having to convert back and forth in order to function as the liason.

I like a conversion program available from the sugartech site,

http://www.sugartech.co.za,

called Uconeer, by Katmar. It has the OHTC conversions, as well as a volumetric to mass flow rate converter, if you have the sp. gr. to input.

If you work with heat transfer, I recommend it.

I also use a conversion program that is part of a vacuum equipment sizing software that Graham,

http://www.graham-mfg.com

distrubutes. I use the mollier and conversion functions much more than I use it to size jets and pumps.

I thought others involved in this thread might be interested in these converters, so I followed up on your post.

sacem1,

I am giving you a star. Your post was educational for those of us who are still struggling to correlate the two, especially when it involves more than just converting inches to mm.

SteveBraune,

I thought your post was poignent, but in the case of those that I work with, I think the word "getting" would be best substituted with "being drug kicking and screaming"

To all contributors to this post, it is obvious by the comments submitted that this is an "up front and personal" issue with many in the engineering profession. Thanks for all the valuable input.

 

[IRstuff]

Most of my thermal calculations are rather lightweight, but I've gotten a lot of mileage from Mathcad. So long as the physics is properly entered in the equations, I can mix essentially any unit with any other unit.

This allows me to use h's in BTU/hr/m^2/ºF with areas in ft^2 and power in Watts completely with the equations. This is all done completely on the fly by Mathcad. Since everything is live, I can immediately change the area to something in m^2 without changing anything else in the calcuation and the results will come out correctly.

TTFN

 

[MintJulep]

Skogs,

Yes, 1/33 of a meter. 3.03 cm.

 

[chicopee]

Going back to the rating of 1200 in-lbs for your insulators, is that rating for end moment exerted by the bus on the supporting insulators; if so than you are dealing with beam formulae;for a bus simply supported by two insulator theoretically you would have no end moments; for a bus with ends fully constrained by the insulators, you would have end moments. Any strength of material book would have the formulae you need to evaluated the bus end loading on the insulators.

 

[unclesyd]

rmw.

Check this out

http://www.raenbo.com/pages/base12-3.html

 

[rmw]

unklesid, that is great. I have a few math teacher friends that are going to have that forwarded to them. Thanks.

rmw