Beckhoff KL3356, Документация

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Product overview
KL3356 13 Version: 2.3.0
• In the first phase of the calibration, an input voltage of 0 mV is applied to both analog inputs ( zero
calibration [ } 11] ). The zero points of both analog input stages can be determined in this way. This
involves a system offset calibration of the A/D converter. In this measurement, both the respective
absolute values and the mutual deviation of the channels are of interest.
• An input voltage of approx. 24 mV is applied to both analog inputs in the second phase of the
calibration ( final calibration [ } 11] ). This is derived from the power supply to the load cell. At this point
the absolute value of the measurements is no longer an interest, only any possible deviation of the
values for the two analog inputs. The gain of the first channel is adjusted here to match that of the
second channel. The important point is that the calibrations are carried out using the same DC voltage
potential at the inputs to the operational amplifiers, as in a normal measuring operation.
Calibrating the input stages at both working points (the zero point and the final value) allows the straight lines
of the two measuring channels to be adjusted to one another so that they are congruent.
Fig. 2: Characteristic curves for calibration
If the terminal is carrying out a calibration, bit R0.2 [
}
44] is set in register 0 (the status word).
Testing the measuring amplifiers
In order to be able also to test the function of the analog input circuits and the source of the reference
voltage, it is also possible, in addition to the calibration described, to connect the internal reference voltage
signal of 2.5 V as the input signal. For this purpose, before measuring the reference voltage itself, a
difference voltage signal of 0 V with a DC voltage potential of 0 V is applied. Measurement of the 0 V
differential signal combined with a DC voltage potential of 2.5 V is then carried out. With the aid of the
measured values resulting from this, the CommonMode effect of the two input stages at an input voltage of
1.25 V can be calculated, and can be taken into account in the subsequent measurement of the reference
voltage. When measuring the source of the reference voltage, both operational amplifiers must deliver the
same measuring signal, in addition to which it must also be possible to predict the value to within a very tight
tolerance. If this tolerance is exceeded, the situation is classified as a hardware defect, and is indicated in bit
SW.8 [ } 44] of the status word.
If the terminal is carrying out a test, bit R0.2 [ } 44] is set in register 0 (the status word).