Calibration: Why is the standard kilogram losing weight?

10/18/2007


If you think you have calibration problems, consider this: The world standard kilogram, a cylinder of platinum and iridium alloy which was cast in 1889, is apparently losing weight. There are reports that its weight has decreased by about 50 micrograms when compared with other copies kept around the world. The standard kilogram is kept in a vault at the International Bureau of Weights and Measures in Sevres, France, southwest of Paris. Regardless of what is or isn’t happening with the other references around the world, this one is THE kilogram and it’s the one that seems to be changing.

Scientists are baffled. They can’t really tell if the others are getting heavier or the master one is lighter. Nor can they figure out why the weight has changed at all. Of course, let’s be practical: 50 micrograms is described as the weight of a fingerprint.

The larger issue is the nature of standards. The kilogram is one of the last to depend on an actual artifact. Most others have been redefined. For example, the idea of defining a meter with a marked stick went out in 1983 when it was changed to the distance that light travels in 1/299,792,458 of a second. Keep that in mind the next time you have to calibrate a tank level sensor. Ask your boss if you can borrow a stopwatch.

Along the same lines, Ron Fox, a retired physicist, and Ted Hill, a mathematician, both from Georgia Tech, have suggested the gram be redefined as the mass of exactly 18 x 14074481 (cubed) carbon-12 atoms. I find that much more helpful. Go ahead and start counting. Let me know when you’re done.

—Peter Welander, process industries editor, PWelander@cfemedia.com ,
Control Engineering Weekly News





No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Big Data and IIoT value; Monitoring Big Data; Robotics safety standards and programming; Learning about PID
Motor specification guidelines; Understanding multivariable control; Improving a safety instrumented system; 2017 Engineers' Choice Award Winners
Selecting the best controller from several viewpoints; System integrator advice for the IIoT; TSN and real-time Ethernet; Questions to ask when selecting a VFD; Action items for an aging PLC/DCS
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Motion control advances and solutions can help with machine control, automated control on assembly lines, integration of robotics and automation, and machine safety.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Big Data and bigger solutions; Tablet technologies; SCADA developments
SCADA at the junction, Managing risk through maintenance, Moving at the speed of data
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
click me