Analysis of on-site calibration
and testing
of crane scales- and the need for an accurate calibration system.
For a quality system to be effective, it must
analyze accurate data.
Crane scales, both legal for trade and non-legal for
trade, have inherent use problems. Loads are often jerked or snatched, which exerts a
shock load onto the sensitive weighing element. Likewise, off center loads exert a side
load factor into the scale.
Crane scales often exhibit non linear calibration
curves. This means that the scale might be accurate at some weights and inaccurate at
other weights. The ONLY way to know, is to do a calibration check at several load points,
(for example, 25% - 50% - 75% and 100% of rated load capacity). Often times, it is not
readily feasible to load more than 20,000 lbs. of certified class F test weights onto a
scale. This guarantees accuracy at 20,000 pounds, but leaves all weights above 20K in
doubt, and is expensive and time consuming.
A common practice is to weigh something heavy (i.e.,
a coil of steel) on a truck scale and them use it as a transfer standard on the crane
scale. Again, this is a relatively accurate check at the reference weight only. Truck
scales have an acceptable maintenance tolerance of plus or minus .2% of applied load plus
or minus one graduation, typically 20 pounds. This equals plus or minus two pounds per
thousand pounds. Therefore, a 60,000 pound coil of steel ( or other substitute test
weight) could be plus or minus 140 pounds, giving a band of uncertainty of 280 pounds.
National Scales' National Crane Scale
Calibration Kits are guaranteed accurate, with direct NIST traceability, to 0.1%
of applied load from 10% of capacity to 100% of the rated kit capacity. Normal crane
scales have a maximum scale count resolution of one part in 10,000 counts. The National
Crane Scale Calibration Kit displays one part in 50,000 counts - over FOUR times
GREATER ACCURACY resolution than a crane scale or eight times the accuracy resolution of a
truck scale!
| For example, a 25 ton crane scale would
count by 5 pound graduations. A typical truck scale would count by 20 pound graduations.
The National Crane Scale Calibration Kit would count by 1 pound
graduations. The finer the count resolution, the more accurate the test. |
 |
| The TL2000
is the revolutionary tension link load cell used in the
National Crane Scale
Calibration Kit.
National Crane Scale
Calibration Kit
|
The National Crane Scale Calibration
Kit is both quick and easy to use. A typical test time is under 10 minutes. To
use, merely hang the calibration kit load cell (using the optional Crosby safety rated 5
to1 shackles) onto a hook. Any object lifted becomes a known weight within one pound per
thousand lbs. weight. Several loads of differing weights can be used to check the
linearity of the crane scale. QA can quickly and accurately verify the calibration
accuracy of any in plant crane scale as often as desired.
The National Crane Scale Calibration Kit
is absolutely ideal for all ISO9000 quality assurance systems. Weights can be read in
pounds or kilograms at the touch of a button. An optional printer can record the time, the
date, and weight(s) of your calibration checks.
National Crane Scale Calibration Kits
carry a two year warranty on the load cell and digital indicator. The optional printer
carries a six month warranty.
Periodic NIST traceable recalibrations can be done
as often as your QA procedure dictates. Emergency recalibrations can be done on a priority
basis with a one day turnaround.
Sounds like a win/win situation? It is! The National
Scale Crane Scale Calibration Kit will not only give you accurate test data, it will save
you both time and money.
For full Pricing and specifications, please call:
Larry Eagan or Thomas Robusto at:
800-899-9988
sales@measurespec.com
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