Rockwell Automation 937CU-AISTR-DC1 Strain Gauge Converter Installation Instructions - Manual (Page 44)

Sensor data
Because the truck scale rests on 4 measuring cells the parameters of each individual measuring
cell must be combined: The following entries must be made in the menu Sensor:
• Supply voltage:
Here the resulting total resistance of the parallel connection of the 4 sensors must be taken into
account. If the resulting resistance of the sensors connected in parallel falls below 100
Ω, a lower
supply voltage must be selected due to the maximum available current. The maximum permitted
supply voltage is calculated as follows:
Total resistance x 49 mA = maximum supply voltage
− 4 measuring cells with each 350 Ω = 87.5 Ω
− 87.5 Ω x 49 mA = 4.2875 V
Set the supply voltage to 4 V.
The maximum permitted total resistance of the sensors is 10 k
Ω.
• Sensitivity:
The sensitivity of the individual cells can be accepted 1:1.
Example:
4 cells with 2 mV/V each, entry in Sensitivity = 2 mV/V
• Cell data:
Max. cell load: The cell load of the individual sensor must be multiplied by the number of sensors.
Example:
4 sensors with 15 t each, entry in Cell load = 60 tons).
Explanation:
If e.
g. only one cell is loaded at its individual maximum load it will output its maximum voltage. The
other 3 sensors are connected to this voltage and become consumers; this puts a load on the
voltage source and results in a voltage drop. Only if all 4 cells are loaded at their respective
maximum loads will they output their respective maximum voltages equally which is then measured
in parallel by the
Strain Gauge Converter. All uneven loads between those two extremes behave
linear, therefore the parallel connection can be considered as a single measuring cell.
Bul. 937
C Strain Gauge Converter Installation Instructions
42