Heating Current Monitoring; Selecting The Heating Current Monitoring; Distribution Of The Controller Channels - Siemens SIMATIC S5 Manual

3.3 Heating Current Monitoring

The heating current monitoring is a function specifically intended for plastic. This function detects
whether the heating bands are supplied with the correct current at the correct time. This allows
errors/faults in the power supply of the heating bands to be detected. Such faults include line
breaks, short circuits, defect switching devices (relays, contactors) or failure of the power supply to
the heating bands. If a fault develops, the IP 244 generates a message to the S5 CPU, which can
then react accordingly.
The hardware required to measure the heating currents and the power supply must be implemented
in external devices.
This hardware is available as heating current measurement module 904, which generates voltage
values for the IP 244 proportional to the heating current or power supply voltage.
The heating current measurement module measures the heating currents via its six current
transformers and generates signals from the detected values for the IP 244. Thermocouples, power
supply voltage and Pt 100s are connected to the module and do not need to be connected to the
IP 244. The 904 module is connected to the IP 244 by means of the connecting cable supplied with
the 904 (length 2 m).
For monitoring 3-phase heating systems, three heating current measurement modules are required
per IP 244 (three current conducting cables per control loop).

3.3.1 Selecting the Heating Current Monitoring

If bit 1 of main control byte 1 is set to 1, the "heating current monitoring" mode of the IP is selected.
The module can then operate a maximum of six controllers with heating current monitoring. For hot
channel control, there is a fixed sampling time of 400 ms. In standard operation, the sampling time
depends on the time constants of the controlled system. For an ADC conversion time of 50 ms, this
is a multiple of 800 ms, for an ADC conversion time of 60 ms, it is a multiple of 960 ms. The sampling
time is entered manually or calculated by the self-tuning function. If heating current monitoring is
selected, the monitoring of the currents of each channel can be activated or deactivated individually.
If the heating current monitoring function has been selected, bits 4 and 5 in main control byte 2 (read
channel 13 or channel 14) are ignored, the special version can also not be selected. With Pt 100
operation, no heating current monitoring is possible.

3.3.2 Distribution of the Controller Channels

Channels 0 to 5 are used for temperature control as if no heating current monitoring had been
selected (see Figs. 3.3.2/1 and 3.3.2/2). Channels 6 to 11 are used for the heating current
monitoring of channels 0 to 5. Channel 13 is used for power supply voltage measurement.
Channel 15 is the compensation channel. All unused analog inputs must be short-circuited and
grounded.
IP244
C79000–B8576–C860–02
Special Functions for Plastic Machines
4–83