Demands on the heating control
The example illustrates the counter rotational nature of lead temperature and outdoor temperature with a heating control.
The lead temperature of the heating should be controlled inversely proportional to the outdoor temperature. This means: The lower the outdoor temperature, the greater the lead temperature.
Outdoor and lead temperatures are measured using PT100 sensors.
With an outdoor temperature of 0 °C, the lead temperature (x) should be 50 °C.
If the outdoor temperature drops by more than 4 °C, the heating should switch on.
LOGO!Soft Comfort solution
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A PT100 sensor is connected to an AI1, and this measures the lead temperature.
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The analog amplifier is parameterized as follows:
The amplifier causes the actual temperature that has been measured by the sensor to be issued on its output.
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A PT100 sensor is connected to an AI2, and this measures the outside temperature.
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The analog amplifier is parameterized as follows:
The amplifier causes a value that is inversely proportional to the temperature measured by the sensor to be issued on its output. Hence: The greater the outside temperature, the lower the issued value.
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The analog amplifier is parameterized as follows:
The value issued by
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The analog comparator is parameterized as follows:
The analog comparator switches on the output Q2 If the difference falls short of 0 °C, the analog comparator switches the output Q2 back off again.
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Output Q2 switches the heating on and off.
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Mode of operation
The outside temperature drops; this causes the value issued on the analog amplifier to increase to the same extent. The difference on the analog comparator between the lead and the outside temperature increases.
If the difference exceeds 4 °C the heating is switched on.
By switching on the heating the lead temperature increases. Because of this, the difference on the analog comparator between the lead and the outside temperature lowers (provided the outside temperature drops more slowly than the lead temperature increases).
If the difference falls short of 0 °C, the heating is switched off.
Changing parameters
The Offset (y) parameter with the analog amplifier depends on your desired lead temperature (x) with 0 °C outside temperature. The parameter is calculated as follows:
y = x -150
Furthermore, the switch-on threshold and the switch-off threshold of the heating can change by means of the threshold value of the analog comparator .
Note
You can save block if you adapt the threshold value in the analog comparator accordingly.
Try it out!
The example can be found as a circuit program on the LOGO!Soft Comfort CD-ROM. Load the circuit program in LOGO!Soft Comfort and try out the instructions above in simulation mode.