Beckhoff ELX3351, Руководство по эксплуатации

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Parameterization and programming
ELX3351 33 Version: 1.3.1
5 Parameterization and programming
5.1 Basics of the measurement functions
The measuring functions of the ELX3351 can be described as follows:
• The ELX3356 Analog Input Terminal is used to acquire the supply voltage to a load cell as a reference
voltage, and the differential voltage that is proportional to the force acting on the cell.
• A full bridge must be connected. If only a quarter or half bridge is available, external auxiliary bridges
should be added. In this case, the nominal characteristic value should be modified accordingly.
• The reference and differential voltages are measured simultaneously.
• Since the two voltages are measured at the same time, there is basically no need for a high-precision
reference voltage with respect to the level.
The bridge supply and reference voltages are provided by the ELX3351 for the full bridge. A
connection of other, externally supplied circuits (e.g. an external bridge supply) is not permitted!
• The change of the quotient of the differential and reference voltages corresponds to the relative force
acting on the load cell.
• The quotient is converted into a weight and is output as process data.
• The data processing is subject to the following filtering procedures:
◦ software filter IIR/FIR (if activated)
• The ELX3351 has an automatic compensation/self-calibration function.
◦ Default state: self-calibration activated, execution every 3 minutes
◦ Errors in the analog input stages (temperature drift, long-term drift etc.) are checked by regular
automatic calibration, and compensated to bring the measurement within the permitted
tolerance range.
◦ The automatic function can be deactivated or activated in a controlled manner.
5.1.1 General notes
General notes
• The measuring ranges of both channels (supply voltage and bridge voltage) should always be used as
widely as possible in order to achieve a high measuring accuracy.
We recommended a load cell that has such a sensitivity (e.g. 2 mV/V) that the largest possible bridge
voltage (ideally ±20 mV) is generated.
Note the input voltages (see
Technical data [ } 12] ).
Fig. 25: Max. input voltages