Calibrating The Constant Flow Function; Constant Residual ∆P Regulation - Mitsubishi Electric s-MEXT-G00 006 Technical Manual

TM_s-MEXT_ME28relC_00_12_19_EN
When configuring the unit the project flow value and the number of fans in the unit are entered.
The programme also requires that the fan flow is never less than the set rated flow.
The parameters entry mask is under the "Fan" menu accessible through the "Service" password
The purpose of regulation is to keep the flow rate constant when there is an increase in the loss of load, with reference to the graph below.
Starting from nominal work point (A), the increase in load loss (due, for instance, to clogged filters) from P1 and P2 causes a shift in the fan work point along the curve
towards point B, with the ensuing capacity decrease. The logic tries to restore the work point by increasing the speed and move back towards work point C.
To avoid continuous speed adjustment without giving the fan time to adjust to the new speed value and consequently not allowing the pressure transducer to measure the
new differential pressure value, there is a "scan time" that sets the time between the two fan signal variations.
The EC control parameters are under the "Fan" menu, accessible through the "Service" password.
The default values are are the following:
•
Scan time = 60 sec
•
Step voltage = 10 (corresponds to a 0.1V
•
Hyst flow = 25
•
Fan modulation delay = 120 sec
The Fan modulation delay is used whenever the unit is started in order to allow the fan to start. Once this time elapses, speed adjustment begins.
This parameter is in the "Regulations" menu that can be accessed with the "Service" password.
10.5.2

Calibrating the constant flow function

To allow greater adjustment precision a calibration mask has been included, which evaluates the difference between the real value read by the transducer and the value to
reach. Calibration is performed during production testing using the following mask:
Once the value of "k" has been memorised correct, operation can be resumed.
This mask is under the "Function" menu accessible through the "Factory" password and only appears during the function configuration phase.
As soon as the offset is memorised, the mask is automatically hidden.
To re-calibrate, disable the function and enable it again.
10.5.3 Constant residual ∆P regulation
The pressure transducer is positioned according to the following figure.
Technical manual
Figure 10-5: Constant flow rate fan operation curve
signal increase / decrease).
DC
FLOW SENSOR ADJUSTMENT
Real Value
Current Value 0000
Set flow
Store K?
87
0000
0000
N
TRANSLATION OF THE ORIGINAL INSTRUCTIONS