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Section 7. Measurement Programming Examples
7-15
Connections
Figure 7-10 Wiring Diagram for Full Bridge Pressure Transducer
Program
01: Full Bridge (P6)
01:
1
Rep
02:
33
25mV 50Hz rejection Range
03:
1
DIFF Chan
04:
1
Excite all reps w/EXchan 1
05:
2500
mV Excitation
06:
1
Loc [:HTcm ]
07:
50.334
Mult
08:
7.48
Offset
7.13 Lysimeter — 6-Wire Full Bridge
When a long cable is required between a load cell and the CR10X, the resistance
of the wire can create a substantial error in the measurement if the 4-wire full
bridge (Instruction 6) is used to excite and measure the load cell. This error arises
because the excitation voltage is lower at the load cell than at the CR10X due to
voltage drop in the cable. The 6-wire full bridge (Instruction 9) avoids this
problem by measuring the excitation voltage at the load cell. This example shows
the errors you would encounter if the actual excitation voltage was not measured
and shows the use of a 6-wire full bridge to measure the output of a load cell on a
weighing lysimeter (a container buried in the ground, filled with plants and soil,
used for measuring evapotranspiration).
The lysimeter is 2m in diameter and 1.5m deep. The total weight of the lysimeter
with its container is approximately 8000kg. The lysimeter has a mechanically
adjustable counterbalance, and changes in weight are measured with a 113.6kg
capacity Sensotec Model 41 tension/compression load cell. The load cell has a 4:1
mechanical advantage on the lysimeter (i.e. a change of 4kg in the mass of the
lysimeter will change the force on the load cell by 1kg-force or 980N).
Figure 7-11 Lysimeter Weighing Mechanism
CR10X