Instrumentation & Measurement Magazine 23-6 - 36

Fig. 7. Plot of load cell data and calculated position on a platform segment for a human subject.

Peak indicates whether a new peak weight has occurred or not.
A 'P' is written to indicate a new peak occurred; otherwise an
'o' is written to the file.
A script was created that plotted the data from the text file,
displaying the four load cell signals, total weight and the location of that force in the same graph. Fig. 7 shows an example
of the plotted data; the signal signature seen is that of a human
subject's natural walking pattern.

Testing and Results
Tests were conducted to evaluate the measurement accuracy
of the position coordinates and weight. This test involved
determining how accurately the system could measure the
weight of an object placed anywhere within a platform section and whether the center of pressure could be calculated
correctly. A 20 kg calibration weight and a 25 mm circular
point load stand were used as the test weight (Fig. 8). A laser
cut test jig was made with 25 mm cut outs at 50 mm spacings
so the point load stand could be placed accurately across the
entire segment. The weight and positional coordinates were
recorded at each test point location. The overall X-position
accuracy was calculated to be within 1.0 ± 2.2 mm and the Yposition accuracy was 0.8 ± 1.8 mm. The weight accuracy was
calculated to be 20.08 ± 0.03 kg, with the mean weight error

to be 0.44% of the 20 kg weight. The slight variation in weight
is attributed to the RMS noise of the ADC, the load cell scaling variance (2 mV/V ± 0.1%) and the voltage reference drift
(4.096 V ± 0.05%).

Capturing and Plotting Data from Cows
To test the system in the field, it was deployed on a farm and
cows were made to walk over it on the way out from the milking shed. Data was captured and processed in real time. Fig. 9
shows the data captured for a cow weighing approximately
500 kg. It shows the signals from each section of the platform
and the location where the feet landed on the platform.

Dynamic Weighing of Cows
Ten walkover trials were done with ten cows with body
weights varying from 388 to 616 kg. The cows were weighed
statically before dynamic weighing. Table 3 displays the static
weights, average dynamic weights calculated from each of
the trials and the average error. Taking an overall average of
all the cows' trials combined, the mean error and standard deviation were: Section AB: -20.14 ± 13.78 kg; Section BC: -10.69
± 10.57 kg; Section CD: -10.15 ± 12.36 kg; and Combined Sections: -13.66 ± 7.52 kg. Section AB performed the worst out of
the four arrangements with an average error of 20 kg less than
the static weight. The main reason for this is that the cow had
to step up 100 mm onto the platform which slightly altered her
weight distribution; more weight was spread to the hind legs
which are placed on the ground. Section BC and CD produced
similar results as the cow was walking on a level surface.

Detecting Lameness from Weight Distribution
Parameters
Fig. 8. Calibration weight on point load stand and test jig with 25 mm cut
outs at 5 mm spacing.
36	

When a cow has an infected hoof, it hurts when walking. To
alleviate the discomfort, the cow naturally distributes weight
to other limbs which are not infected and thus not hurting.

IEEE Instrumentation & Measurement Magazine	

September 2020



Instrumentation & Measurement Magazine 23-6

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 23-6

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