Overview Mixer basic with return flow limitation


With this function block a mixer control is implemented. In addition to a standard mixer, the return flow can be limited here. This is needed for network mixers in order to limit the losses caused by an excessive return flow temperature.



Inputs

FG
 Enable
 Optional. Not equal to 0 enables the mixer, the outputs are driven. 0 closes the mixer for twice the run time and then switches off all outputs. Not assigned: the mixer counts as enabled.
SV
 Setpoint flow*
 Flow setpoint to which control is performed. A setpoint of 0 switches the mixer off like a missing enable.
SR Setpoint return flow* Return flow limitation. If the return flow actual value exceeds this value, two measures take effect: the mixer is not opened any further, and the flow setpoint is lowered slowly (0.01 degrees per second) until the return flow is below its setpoint again. When the return flow drops, the reduction is taken back in the same steps.
IV
 Actual value flow*
 Flow actual value.
IR Actual value return flow* Return flow actual value.
RA Feedback open Optional. Feedback of the actuator for the output open. If it does not take on the value of the output within the monitoring time for feedback, the output is sent again and a fault is reported. Not assigned: no monitoring.
RZ Feedback close Optional. Feedback of the actuator for the output close, otherwise as feedback open. Not assigned: no monitoring.

Outputs
AU
 Open
 Output mixer open.
ZU
 Close
 Output mixer close.
PR
 Percent
 0-100% output. For mixers with analog input. The manipulated variable of the internal controller IY is added to or subtracted from this value depending on the operating mode. The accumulation is performed at every rising edge at the open/close outputs; using the gain parameter and the PWM settings the control time can thus be influenced. If the percent output is used, the P component must be set significantly smaller than the default value.
PU
 Pump
 Pump. A heating circuit pump can be connected here. It is switched on when the enable is given and the setpoint is not equal to 0.
ST
 Info Status
 Output is set to 1 when the mixer is active.
IY
 Info Y
 Output of the internal controller for diagnostic purposes. The output ranges from -255 (whole PWM time close) to +255 (whole PWM time open).
IP
 Info PWM
 Output of the internal PWM timer - time until next open/close  cycle.
SR Fault Is set to 1 as soon as a feedback does not match the corresponding output. If the feedback follows, the output returns to 0 by itself. The mixer keeps controlling unchanged while a fault is present.
FZ Error counter Counts every detected monitoring error, including every repetition. After a restart of the controller the counter starts at 0 again.

Parameters
Run time
 Run time of the mixer. If the enable is switched off, the mixer closes for 2x the mixer run time.
Gain P
 Gain for the internal controller. With a higher value the mixer reacts faster. Important: With too high a value the mixer starts to oscillate (constant open/close control).
PWM time
 Time for one open/close cycle. The manipulated variable from 0-255 is mapped to this time. On time is PWM time/255 * manipulated variable. This time also determines when the manipulated variable is integrated (time +/- percent output).
PWM min. pause
 In this parameter a minimal pause time can optionally be set (both outputs remain off). This pause is observed at minimum, even if the calculated off time would be shorter. After an open cycle the pause should be at least as long as the flow sensor needs to report back the current temperature.
PWM max. pulse
 In this parameter a maximal pulse time can be set. The internal controller is limited to this maximum (maximal time for open), even if the calculated on time would be larger.
Hysteresis
 Within this hysteresis the temperature is considered reached and the mixer remains in its current position. The hysteresis acts in both directions, for example with a hysteresis of 1 the temperature is considered reached within +/- 1 degree.
Anti-blocking function If this parameter is set, the mixer is started 1x per week when the enable is 0. This is intended to prevent the mixer from blocking when it is not in operation for too long. The function is started on Sunday at 0:00h. The mixer travels the mixer run time open/close, or the analog output is set to 0/100 percent, and the pump output is switched on.

When the anti-blocking function is active, 100 + step is output at the Status output.
  • 101: Outputs off
  • 102: Mixer open
  • 103: Wait time mixer run time
  • 104: Mixer close
  • 105: Wait time mixer run time
  • 106: Pump on
  • 107: Wait time mixer run time
  • 108: Outputs off, cycle finished.
Monitoring time feedback Time within which the feedback must take on the value of the output. If the output changes again before that, the time starts over - during short PWM cycles there is therefore no monitoring, but there is during the pauses and while switched off. The time should be longer than the reaction time of the actuator and shorter than the PWM min. pause.
Repeat send time Interval at which the output is sent again after a fault.
Max. repetitions Number of repetitions per fault. After that nothing is sent any more, the fault remains until the feedback matches again. 0 = unlimited.




See also common parameters of all function blocks.