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
 Enable. At 1 the mixer is enabled and the outputs are driven. At 0 the mixer closes for the run time and then switches off all outputs. If the input is not assigned, the mixer is automatically enabled.
SV
 Setpoint flow*
 Flow setpoint to which control is performed.
SR Setpoint return flow* Return flow limitation. If the return flow temperature exceeds this value, control is regulated back.
IV
 Actual value flow*
 Flow actual value.
IR Actual value return flow* Return flow actual value.

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 together with the enable.
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.

Parameters
Run time
 Run time of the mixer. If the enable is switched off, the mixer closes for 2x the mixer run time.
Gain
 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 With this parameter 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.




See also common parameters of all function blocks.