Basic Function Principles - Beckhoff EP3356-0022 Documentation

6.5

Basic function principles

EL/EP3356 and special versions
Unless stated otherwise, the designation „EL/EP3356"always refers also to special versions such as
the EL3356-0010 and EP3356-0022.
The measuring functions of the EL/EP3356 can be described as follows:
• The EL3356 Analog Input Terminal and the EP3356-0022 Analog Input Box are 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.
• It is compulsory to connect a full bridge. If there is only a quarter or half bridge available, you have to
add external auxiliary bridges. In this case you have to modify the nominal characteristic value.
• 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. On changing the reference voltage, the differential voltage
across the full bridge changes by the same degree. Therefore a stabilized reference voltage should be
used that is subject to only low fluctuations (e.g. the EL95xx supply terminal)
• 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:
◦ the analog converter (ADC) integrates over 76 samples
◦ calculation of mean values in the averager (if activated)
◦ software filter IIR/FIR (if activated)
• The EL/EP3356 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
• The EL/EP3356 can also be used as a 2-channel analog input terminal/box for voltage measurement
[} 89].
• The EL3356-0010/EP3356-0022 has a timestamp function that can be activated through Distributed
Clocks. The filter functionality is not available in Distributed Clocks mode.
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 supply voltage
of 12 V in connection with a load cell that has such a sensitivity (e.g. 2 mV/V) that the largest possible
bridge voltage – ideally ±25 mV – is generated. Please consider the max. input voltage (see technical
data).
EP3356-0022 Version: 1.1.0
Commissioning/Configuration
67