Beckhoff EP3356-0022, Документация

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Commissioning/Configuration
EP3356-0022 39 Version: 1.4
5.4 Application notes
Symmetric reference potential
The EP3356 measures the two voltages U
supply
und U
bridge
independently of each other. The measuring
accuracy can be increased still further if an internal coupling is employed to prevent the internal measuring
circuits from drifting apart. To this end the EP3356 has an internal switch that is closed in the default state
and establishes a potential reference between the internal electronics and the bridge point.
Fig. 28: Internal switch for increasing the measuring accuracy
If several strain gauges are supplied by the same power supply and equalising currents flow that falsify the
measurement, the switch can be opened via CoE
0x8000:05 [
}
66] . Alternatively, electrically isolated strain
gauge supplies are to be installed.
Open-circuit recognition
The EP3356 has no express open-circuit recognition facility. If one of the bridge wires is broken, however,
the voltage measured there generally moves towards the final value, thus displaying an error in the status
word. Over/underrange of the supply voltage is likewise indicated.
Input freeze
If the box is placed in the freeze state by InputFreeze in the control word, no further analog measured values
are relayed to the internal filter. This function is usable, for example, if a filling surge is expected from the
application that would unnecessarily overdrive the filters due to the force load. This would result in a certain
amount of time elapsing until the filter had settled again. The user himself must determine a sensible
InputFreeze time for his filling procedure.
For clarification: temporal control of the InputFreeze and the decision regarding its use must be realised by
the user in the PLC, they are not components of the EP3356.
In the following example (recorded with Scope2) impulses on a 15 kg load cell are recorded; the filter is wide
open at IIR1 so that steep edges occur in the signal.