Requirements of the heating control
This example illustrates a heating control where the flow temperature of the heating is to be controlled at an inverse proportion to the outdoor temperature. This means that the lower the outdoor temperature, the greater the flow temperature.
PT100 sensors measure the outdoor and flow temperatures.
With an outdoor temperature of 0 °C, the flow temperature should be 50 °C (x).
If the outdoor temperature drops by more than 4 °C, the heating should switch on.
LOGO!Soft Comfort Solution
|
① |
A PT100 sensor is connected to AI1 which measures the flow temperature. |
|
② |
The parameters for the analog amplifier are as follows:
The amplifier causes the actual temperature that the sensor has measured to be issued as the output. |
|
③ |
A PT100 sensor is connected to AI2 which measures the outdoor temperature. |
|
④ |
The parameters for the analog amplifier are as follows:
The amplifier causes the actual temperature that the sensor has measured to be issued as the output. |
|
⑤ |
The parameters for the analog amplifier are as follows:
The parameters of the amplifier at B004 cause the difference of the compared temperatures of the comparator at B005 to be 0 if the sum of both temperatures is 50. |
|
⑥ |
The parameters for the analog comparator are as follows:
The analog comparator switches on the output Q2 if the difference between the flow temperature and the standardized outdoor temperature exceeds 4 °C. If the difference falls below 0 °C, the analog comparator switches the output Q2 off again. |
|
⑦ |
Output Q2 switches the heating on and off. |
Mode of operation
The outdoor temperature drops, which causes the value issued to the analog amplifier at B004 to increase to the same extent. The difference at the analog comparator between the flow and the outdoor temperature increases accordingly.
If the difference exceeds 4 °C the heating switches on.
By switching on the heating, the flow temperature increases. Because of this, the difference at the analog comparator between the flow and the outdoor temperature decreases (provided the outdoor temperature drops more slowly than the flow temperature increases).
If the difference falls below 0 °C, the heating switches off.
Changing parameters
The Offset parameter at the analog amplifier at B004 depends on your desired flow temperature at 0 °C outdoor temperature. Furthermore, the switch-on threshold and the switch-off threshold of the heating can change by means of the On and Off threshold values of the analog comparator at B005.
Try it out!
The example can be found as a circuit program on the LOGO!Soft Comfort DVD-ROM. Load the circuit program in LOGO!Soft Comfort and try out the instructions above in simulation mode.