LINK Systems System 1100 Tonnage Monitor - Manual (Page 42)

THEORY OF OPERATION
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3-5
Figure 7.
The peak tonnage on the left side of the press was 60 tons at time
t1. The peak tonnage on the right side of the press was 60 tons
at time t2. But the peak total tonnage never exceeded 100 tons.
Thus, the correct readings on the tonnage monitor display are 60
tons on the left channel, 60 tons on the right channel, and 100
tons for the total peak tonnage.
3.4 Limits of Measurement Accuracy
Several factors influence the absolute accuracy of tonnage
measurements on machines that use forces in production processes.
Although inherent instrument accuracy can be within 1% of total
machine rating, there are machine and load dependent factors which
can affect tonnage readings.
3.4.1 Machine Vibration
On mechanically driven machines with flywheels and crankshafts,
harmonic vibratory forces induce low level tensile and compressive
stresses and strains in the machine frame. The induced strain on
large machines, and particularly large gear driven machines with
clutch engaged, can be as large as a few percent of strains induced
in the frame due to loading the machine to rated tonnage. This
results in a "wiggly" baseline electrical signal from strain gauge