Actual Current Value Monitoring - Siemens SIMATIC S5 Manual

Special Functions for Plastic Machines

3.3.4 Actual Current Value Monitoring

An actual current value is measured per controlled temperature system. If heating bands are
connected in parallel (heating cartridges) the total current is measured. For the actual current value
measurement, a bridge-connected rectifier must be included so that both current half-waves can
be measured (see Fig. 3.3.4/1). The advantage of this compared with an actual current value
measurement in which only one half-wave is evaluated is that with inverse-parallel connected
thyristors it is possible to check whether the current flow in the negative direction is also OK. The
integration time of the ADC inputs must be set to 20 ms for a power supply frequency of 50 Hz and
to 16 2/3 ms at a frequency of 60 Hz. Frequency fluctuations are ignored, since they are not
detected by the module.
Fig. 3.3.4/1 Heating current monitoring
IP244
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C79000–B8576–C860–02