Kgf/cm2 vs Kg/cm2 7

[Terrass604]

We are getting inquires for pressure transmitters to be calibrated in Kgf/cm2 instead of our usual Kg/cm2. They seem to be exactly the same, but why are there diffent designators? How did it come about and why?

Thanks for any info.

 

[saxon]

Terrass604, It's the same reason why there are Pounds force (lbF) and Pounds mass (lbm). Both known as Pounds. The pound mass designation is strictly a weight. In pressure gages the designation is PSI, (pounds per sq. in); if one wanted to be super accurate, the designation would be, PFSI (pounds force per sq. in.)

Hope this helps.
saxon

 

[lubes]

1 Kgf is the weight of an object that has a mass of 1Kg and is accelerated at 9.8 m/s2 (acceleration of gravity at 45 deg of latitude and sea level). Strictly speaking, a pressure transmister should be calibrated in "Kgf/cm2", not in "Kg/cm2". Pressure should always be expressed as force applied per unit area. People use Kgf and Kg indistinctly, but the former is a measure of force -or weight- whereas the latter is a measure of mass. Note that force and mass are not the same thing. When people use "Kg/cm2" (instead of Kgf/cm2) they are just probably being lazy and dropping the "f"; they most probably mean "Kgf/cm2" in the first place.

 

[Terrass604]

Thanks, and that clears that up for me and will relay this on to our quotations group as well.

 

[25362]

To avoid confussions and reach an international consensus the trend now is to use N/m² = Pa.

1 bar = 100 000 Pa = 100 kPa
1 torr = 1 mm Hg = 133.32 Pa
1 psi = 6894.8 Pa
1 atm = 101.325 kPa
1 in Hg = 3386.6 Pa

 

[saxon]

25362, The pascal-newton/meter unit system has always been a curve ball to me.

Have a better one.
saxon

 

[25362]

saxon, what is your preferred nomenclature ?

 

[pmureiko]

Why use metric if your going to confuse and abuse it with units like kgf? Sounds like a case of English system envy.

 

[TD2K]

Maybe we can come up with a metric slug ;-)

 

[hacksaw]

kgf/cm2 (the so called kilopond) units predate the Pa and are still in use, like the bar, atm, psi, mmHg, mmWC, etc.

really we should get way from pressure and use elevation measurements. that would really "clear things up".

 

[quark]

Actually as mass per unit area doesn't have any significance, kg/cm² is used for kgf/cm² for ease.

Adding to the confusion, we generally use the following pressure units.

Steam and water - kg(f)/cm²

Compressed air - psi

Vacuum - mm of hg, ultra low vacuum - Torr

ventillation system - mm of wc (regulatory authorities are asking for Pa now):-(

Just give us 100 more years after all you people start to use common system of units.

huh..I don't think any unit is left behind

By the way I am very good at conversion of units. Unit conversion is the first chapter in our text books always.



Believe it or not : Goldbach's conjecture says any even number can be written as a sum of two prime numbers. Postulated in 16th century, nobody could, so far, prove it nor disproove it.

 

[patrickraj]

To all,

It is actually Kgf/Cm2 or Lbf/In2.
In practice we use KG/Cm2 or Lb/In2.
The derivation follows:

Pressure = FORCE / AREA
Force = Mass x Acceleration
= Lbm x g/gc
= Lbm x (ft/Sec2) x ((Lbf x Sec2/(Ft-Lbm))
Pressure =Lbm x (ft/Sec2) x ((Lbf x Sec2/(Ft-Lbm))/(ft2)
=Lbf/ft2 (OR)
=Lbf/In2

We say One Atm = 34 ft of WC,but it is 34 ft(f) only, derivation follows:
Head = Press/Density
= Lbf/In2/Lbm x In3
= Lbf x In/Lbm (OR)
= Lbf x ft/Lbm
= ft (as we say)

 

[jsummerfield]

The gram is a unit of mass not a unit of force. Other international projects use kPa but we use kg/cm2 on my project. The British engineers substitute Bar for kg/cm2. Consider proposing Bar instead of kg/cm2.

John

 

[alomaritrq]

Gentlemen,

The fact is that the metric system has a separate unit for force, called the Newton (kg.m/s^2) while the, apparently revered, English system does not; so a unit of force in the English system is called a pound force (lbf) and is equivalent to lbm.ft/s^2. Simply to differntiate the two pounds.

There is an lbf and an lbm, while only 1 Kg.

In the Metric system, if you want to talk force, you use Newton - no confusion.

 

[zdas04]

alomaritrq,
Oh would that it be so. If Newton's (and their companion Pascals) were universal, then we wouldn't be having this thread. I firmly believe that "kgf" is just a stupid as "slug" and I wish that instrument manufacturers would not accept orders for instruments calibrated in this abortion of a unit - except that instrument makers are not cops, and if one of us engineers ask for it and the first maker ssys "no" then the next will say "yes" and the first maker will have lost a sale and possibly a customer.

Engineers have to stop asking for stupid things before manufacturer's will stop making the stupid things.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

 

[clun]

In US, NIST have 2 very useful publicatin for unit conversion and definition. #1 SP330 & SP811. You could download from NIST website.
In UK, NPL also have paper to describe the relationship between kg and kgf.

 

[hacksaw]

kgf and slugs are no more stupid than shoes on mules or something to that effect.

the standard measure of weight and force was a platinum mass in a day when gravity was thought to be a constant,having no really precise way to measure force.

as a result the kgf and a related lbf, poundals, and slugs became common place.

just remember both cm mm as metric units do not comply with SI either. it is a matter of dogma or engineering, but at the end of the day it has to fit and work

 

[TD2K]

cm is not an SI unit but mm is most definitely is an SI unit.