Universal Calibrating 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 25
Rev. 11/2021
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 until the desired load is almost reached.
Note: Be sure that the tension tie bars do not touch the sides of the holes in the upper machine platen, be
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cause the resulting friction would reduce the accuracy of calibration. If necessary, move the locking collars up
the tie bars so that clearance between the tie bars 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 indication of the reference standard and the test instrument. Repeat the procedure at as
many loading points as necessary to complete the calibration. To apply forces in descending increments, open
the relief valve slightly to achieve the approximate load desired, and make fine adjustments as necessary by
means of the auxiliary screw piston.
4.7 Tare Load
The tare weight is a “pre-load” on the reference standard. It is attributable to the weight of the moveable yoke,
test instrument, bearing plate(s), load ball(s), and adapter fittings. When calibrating a test instrument whose
capacity is approximately equal to that of the calibrating machine, the reading of the calibrating instrument
with no force applied to the test instrument may be considered a “no - load” reading with negligible error. In
cases where the rated capacity of the test instrument is substantially less than that of the calibrating machine
or where it is necessary to obtain the highest possible degree of accuracy, ignoring the tare load effect may
introduce significant error into the calibration.
The error introduced by not allowing for the tare load can be determined by treating the deflection of the cali
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bration standard with the tare load applied as the “no - load” reading when calculating the load applied to the
test instrument. Comparing the results of this calculation with the results of a calculation taking into account
the tare load (as outlined below) will readily show the error introduced.
The tare load can be ascertained by weighing the items (yoke, test instrument, etc.) on a suitable platform
scale. However, it may be more convenient to determine the tare load by means of a reference standard. This
is done as follows:
a) Use the motor to raise the upper yoke platen to obtain approximately 1/8” (3 mm) clearance between the
load ball (or bearing plate) that is used with the reference standard and the upper yoke.
b) Remove the load ball (or bearing plate) from the top of the reference standard, and read the no - load de
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flection of the reference standard.
