Beckhoff ELX3351, Руководство по эксплуатации

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Parameterization and programming
ELX3351 38 Version: 1.3.1
5.1.5 Calculating the weight
Each measurement of the analog inputs is followed by the calculation of the resulting weight or the resulting
force, which is made up of the ratio of the measuring signal to the reference signal and of several
calibrations.
Y
R
= (U
Diff
/ U
Ref
) x A
i
(1.0) Calculation of the raw value in mV/V
Y
L
= ( (Y
R
- C
ZB
) / (C
n
- C
ZB
) ) * E
max
(1.1) Calculation of the weight
Y
S
= Y
L *
A
S
(1.2) Scaling factor (e.g. factor 1000 for rescaling from kg to g)
Y
G
= Y
S *
(G / 9.80665) (1.3) Influence of acceleration of gravity
Y
AUS
= Y
G
x Gain - Tare (1.4) Gain and Tare
Name Description CoE Index
U
Diff
Bridge voltage/differential voltage of the sensor element, after filter
U
Ref
Bridge supply voltage/reference signal of the sensor element, after filter
A
i
Internal gain, not changeable. This factor accounts for the unit standardization
from mV to V and the different full-scale deflections of the input channels
C
n
Nominal characteristic value of the sensor element (unit mV/V, e.g. nominally
2 mV/V or 2.0234 mV/V according to calibration protocol)
0x8000:23 [
}
60]
C
ZB
Zero balance of the sensor element (unit mV/V, e.g. -0.0142 according to
calibration protocol)
0x8000:25 [
}
60]
E
max
Nominal load of the sensor element
0x8000:24 [
}
60]
A
S
Scaling factor (e.g. factor 1000 for rescaling from kg to g)
0x8000:27 [ } 60]
G Acceleration of gravity in m/s^2 (default: 9.80665 ms/s^2)
0x8000:26 [
}
60]
Gain
0x8000:21 [
}
60]
Tare
0x8000:22 [
}
60]
5.2 Application notes
5.2.1 Wiring fail indication
The ELX3351 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.
5.2.2 InputFreeze
If the terminal 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 realized by
the user in the PLC, they are not components of the ELX3351.
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.