Morehouse UCM - Tare Load

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 30
Rev. 3/2024
Cauon: Calibraon of a unit under test should not be aempted unl the personnel concerned are complete-
ly familiar with the operaon of the reference standard and the unit under test.
Detailed procedures for calibrang the various types of instruments are beyond the scope of this manual. In
general, such calibraon consists of applying a series of forces to the calibraon system (by means of the hand
pump and jack assemblies) and comparing the indicaon of the reference standard with that of the unit under
test.
Caution: When applying forces, always monitor the force applied by the reference standard. Never depend on
the indicated value of the unit under test to determine the applied force unless the accuracy of the unit under
test has been veried. There may be a signicant error in the unit under test, which could cause the reference
standard and the calibrang machine to be overloaded and damaged.
To apply a load to the reference system, open the reservoir vent and close the relief valve on the hand pump.
Apply the load to the test setup by working the pump handle unl the desired load is almost reached.
Note: The tension e bars should not touch the sides of the holes in the upper machine platen, as the resulng
fricon would reduce the accuracy of calibraon. If necessary, move the locking collars up the e bars so that
clearance between them and the upper machine platen can be observed.
Complete the loading to the exact force required by using the auxiliary screw piston (hand wheel). Read and
record the force indicaon of the reference standard and the unit under test. Repeat the procedure at as many
loading points as necessary to complete the calibraon. To apply forces in descending increments, open the
relief valve slightly to achieve the approximate load desired, and make ne adjustments as necessary by means
of the auxiliary screw piston.
4.7 Tare Weight
All instruments have dierent characteriscs that may or may not require correcon for the tare weight. The
tare weight is a “pre-load” on the reference standard. It is aributable to the weight of the moveable yoke, test
instrument, bearing plate(s), load ball(s), and adapter ngs.
Some load cells can withstand an overload of up to 150 % or more of rated capacity without damaging the load
cell, and others only 110 %. When evaluang an addional error due to tare, one would need to compare the
same force point with a tare load versus without.
In cases where the “pre-load” is over 5 % of the capacity of the load cell, ignoring the tare load eect may in-
troduce a signicant error in the calibraon. The error introduced can be determined by comparing two calcu-
laons.