17
Rev. 2 – 10
th
November2015
Constant Airflow
The constant airflow mode is available when the INPUT TYPE register 34 is set both at 0 or at 4. In the first
case the constant airflow is set through the Modbus by changing the Holding register parameter number 39
“CONSTANT AIRFLOW”. In the second case the constant airflow is proportional to the analog signal present
at driver terminals.
In figure 21 it is shown the relationship between the signal and the constant airflows.
Fig. 21 – Analog Signal-Constant Airflow relationship
The max resolution from on constant airflow to another is +/-50m3/h.
The max precision guaranteed is SET AIRFLOW +/- 100 m3/h
In the instability areas typical of some fan sizes the constant airflow precision can’t be
guaranteed. It’s anyway suggested to work outside these areas.
MASTER/SLAVE functioning
A master and slave configuration is possible by setting the MASTER both in Constant Airflow mode or Speed
Control and the SLAVE in Speed Control mode only.
The SLAVE Modbus Holding Register number 34 “INPUT TYPE” must be set at value= 3 (see Modbus
communication paragraph) and in figure 22 is shown the connection diagram.
The Holding Register 46 = configuration of the OUTPUT as Tachometric or Alarm must be set at 0.
Fig. 22 – MASTER/SLAVE connection
This function is recommended when two fans work in the same plenum and in constant
airflow mode.
If the fans are set both in constant airflow driven by the same analog signal the two close
control loops interfere each other.
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