The function block Mixing Valve Controller can be used to control common mixing valve types.
This makes it possible to control the flow temperature in heating systems or similar applications in ventilation and air conditioning systems.
Mixing valves or actuators can be controlled with two digital outputs for opening and closing, or with an analogue value of 0-10.
The setpoint and actual temperature are connected to the block's inputs.
The PI controller of the block calculates the necessary mixing position based on the deviation between the setpoint and actual value, and controls the outputs accordingly.
For applications where cooling is required, the block can be switched to an inverted mode.
Table of Contents
|T||Target temperature||Analogue Input - Target Flow Temperature||°||∞|
|AI||Temperature||Analogue input current flow temperature||°||∞|
|Dis||Disable||Disables input (T) (child lock)||-||-|
|AQ||Analogue Output - Provides signal for 0-10V mixing valve||V||0...10|
|Qo||Digital output open mixing valve||-||-|
|Qc||Digital output close mixing valve||-||-|
|Qe||Digital error output (invalid values)||-||-|
|Abbreviation||Summary||Description||Unit||Value Range||Default Value|
|R||Mixing valve run-time||Parameter - Mixing Valve run-time in seconds||s||0...∞||150|
|S||Scanning time||Sampling period of controller in seconds. New values for AQ, Qo and Qc are calculated by the controller at this time interval.||s||0...∞||60|
|Kp%||Gain||Controller gain in %, where Kp% = Kp * 100.||%||0...100||2|
|Ki%||Integral part||Integral part of the controller in %, where Ki% = Ki * 100.||%||0...100||0,03|
|Sm||Stop mode||Mixing behaviour if mixing is stopped - (St) enabled
0 = unchanged, 1 = open, 2 = close
0 = normal, 1 = inverted (for cooling: mixer opens as the temperature rises)
|Min||Minimum Position||Minimum position for mixing valve in % (except calibration runs)||%||0...100||0|
|Max||Maximum Position||Maximum position for mixing valve in % (except calibration runs)||%||0...100||100|
0 = normal, 1 = analogue output is inverted (0V = 100%, 10V = 0%)
|Use for System Status Messages||If this box is ticked, an error message will be sent from this input via the mailer and the system status.||-|
The following example shows the basic programming of the block:
The block is provided with the setpoint value at input T and the actual value for the flow temperature at input AI. Relay outputs for controlling the mixing valve are connected to the outputs.
In addition, the block can be stopped via the St input when it is not in use.
Usually the block is used in combination with other blocks and logic, and further devices like pumps have to be controlled.
The following picture shows an example:
In this example, the Intelligent Temperature Controller determines and transmits the setpoint value for the flow temperature, and switches the Mixing Valve Controller and circulation pump on and off together. The St input of the mixing block is inverted for this purpose.
Please note that further logic must be added here if mixing valves or pumps may only operate under certain conditions.
Whenever the mixing valve is moved to an end positions (0 or 100%), the respective digital output is activated for 1.2 times the mixing valve runtime.
This calibration run ensures that the end position is definitely reached and that the calculated position corresponds to the actual position.