Morehouse UCM - Page 31

Universal Calibrang Machine
(UCM) Manual
(PM-5201)
Morehouse Instrument Company, Inc.
1742 Sixth Ave., York, PA 17403-2675 USA
Phone: (717) 843-0081
www.mhforce.com
Page 31
Rev. 3/2024
First, calculate the load applied to the test instrument by treang the deecon of the calibraon standard
with the tare load applied as the “no-load” reading.
Next, calculate by taking into account the tare load. The tare load can be ascertained by weighing the items
(yoke, test instrument, etc.) on a suitable plaorm scale. However, it may be more convenient to determine
the tare load using a reference standard. The tare weight will have to be raised o of the load cell, and the
Indicator should be zeroed. Then the weight can be lowered, and the weight can be calculated.
Comparing the results of these two calculaons will readily show the error introduced. Once the weight is cal-
culated, the user can test to determine an addional error.
Unlike several load cells, proving rings do require a correcon for tare. This is due to the inherent non-lineari-
ty of the rings. For analog proving rings, the posion of the dial on the micrometer can be an addional error
source.
Below is an example of a formula used to correct tare loads. The formula corrects for tare and is applied to the
value of the applied load from the ed curve data provided with your calibraon report.
The tare load correcon formula is represented as follows: TCF = ((2 * A2) * L * T)) – A0
Where:
A2 = The value of the A2 constant found on the ring calibraon report
L = The force value applied
T = The force value of the tare applied
A0 = The value of the constant found on the ring calibraon report
Tare weight of less than 2 % is likely insignicant regarding the overall measurement uncertainty.
When the tare weight exceeds more than 2 % of the rated capacity of a load cell or proving ring, we urge more
tesng to capture error sources. If the tare weight is higher than 5 %, we recommend calibrang the device
to 105 to 110 % of the rated capacity to account for any of these errors. Correcon formulas must be used for
proving rings to obtain the correct deecon values.