Beckhoff EP3356-0022, Документация

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Commissioning/Configuration
EP3356-0022 40 Version: 1.4
Fig. 29: Impulses on a load cell with and without InputFreeze
Explanation: The weight (A) is shown in blue; the state of the InputFreeze variable, which can be controlled
by the PLC program and can be TRUE/FALSE, is shown in red (B). The first two impulses (C) lead to large
peak deflections in the signal. After that the following is activated in the PLC program (see
example program
[
}
75] ):
• if the measured value for the last cycle (cycle time 100 µs) has changed by more than 10 g (indicating
a sudden load), bInputFreeze is set to TRUE for 50 ms by a TOF block on the EP3356
The effect can be seen in (D): The peak load is no longer acknowledged by the EP3356. If it is optimally
adapted to the expected force impulse, the EP3356 can measure the current load value without overshoot.
Gravity adaption
The calculation of the weight depends on the gravitation/the Earth's gravitational force/acceleration due to
gravity at the place of installation of the scales. In general, acceleration due to the gravitational pull of the
earth at the place of installation is not equal to the defined standard value of g = 9.80665 m/s². For example,
4 zones of acceleration due to gravity are defined in Germany, in which a local acceleration due to gravity of
9.807 m/s² to 9.813 m/s² is to be assumed. Hence, within Germany alone there is a clear dispersion of the
order of parts per thousand for acceleration due to gravity, which has a direct effect on the measured weight
in accordance with the equation F
G
= m*g!
If
• load cells are used in the theoretical calibration with characteristic values according to the sensor
certificate
• calibration weights are used whose weight at the place of installation of the scales is by nature different
to that at the place of origin
• scales of the accuracy class I to III are to be realized
• scales that are generally independent of acceleration due to gravity are to be realized
then one should check whether the gravity correction needs to be adapted via object 0x8000:26 [
}
66] .