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PID Cascade

If temperature of heating element is measured, it is possible to increase stability of the heating system using two PID Smart Rules linked together (a.k.a. PID cascade).

Comparison with simple hysteresis regulation:

PID Cascade

Hysteresis

(tick) 

(/) smooth continuous regulation

(error) 

(X) slow start

(tick) 

(/) fast start

(error) 

(X) oscillating regulation


Example of using PID cascade in regulation of floor heating, measuring both - under-floor and ambient room temperature.

Parameter

Zone PID Smart Rule

Floor PID Smart Rule

Output actuator

Thermostat for heating element
0% ... 19 ºC
100% ... 28 ºC

Switch (relay)
15 minute switching period

Limit temperature

Optional: By default is set to 10 ºC - 30 ºC.
This can be changed in service settings of zone thermostat

Optional: Floor temperature sensor
Max. temperature 28º C

Max. floor temperature allowed by hygienic standards is 28 ºC, however for heating purposes it is possible to use a few degrees higher temperature (e.g. 36 ºC), because temperature sensor is measuring temperature below surface.