Measuring air flow from centrifugal fans using pressure tap equipped inlet nozzles (or inlet “rings”) is discussed in the document “Airflow Measurement using Instrumented Inlet Rings”, which is available for download at http://www.ebmpapst.us/techarticles.asp. As an additional benefit, closed-loop flow control of centrifugal fans that use either the M3G112 or M3G150 motor can be achieved by using the free LISA fan programming software and taking advantage of the following capabilities of these motors;

- ability to accept any external sensor type and measurement range

- ability to accept a 0-10 vdc or 4-20 mA sensor output- internal PID controller which maintains fan speed

based upon a programmed set value

worlds in motion

CLOSED-LOOP FLOW CONTROL USING INSTRUMENTED INLET NOZZLES

100 Hyde Road, Farmington, CT 06034 USA • Internet: http://www.ebmpapst.usTel: 860 • 674 • 1515 • E-Mail: sales@us.ebmpapst.com • Fax: 860 • 674 • 8536

©ebm-papst Inc. 2005. ebm-papst Inc. reserves the right to change any specifications or data without notice 08/05

The available instrumented inlet nozzles allow the fan air flow to be determined indirectly by measuring the differential pressure across the inlet nozzle using a differential pressure transducer (DPT). If the output from the DPT is fed back to the integrated fan controller and the desired set point is entered into the fan using the LISA software, the fan speed will automatically adjust to changes in nozzle pressure to maintain the desired air flow.

Follow the recommendations for the inlet nozzle and DPT selection/setup discussed in the “Airflow Measurement using Instrumented Inlet Nozzles” document. Based on the DPT range chosen and entered into the LISA sensor selection screen, the differential pressure across the nozzle will be displayed on the main LISA fan screen. This differential pressure can be manually converted into air flow in CFM using the equation or chart provided in the cited document.

VVV

sensor

Voltage supplysensor

EC-Motor

Electronics

Voltage supply +set valueof control Centrifugal

impeller

Signal

INSTRUMENTED INLET NOZZLES

Setting Up Closed Loop Flow ControlThe following steps are needed to set up the closed loop flow control:

A. Set up LISA fan programming software for closed-loop sensor control Ref. Figure 1 In LISA in the “Actual Fan” screen under “Settings...Basic Settings...Control Mode”, make the following selections:

• Closed-loop sensor control • RS485 • Save set value to EEPROM

B. Enter sensor information

Ref. Figure 2

In LISA in the “Actual fan” screen and under “Settings...Basic Settings...Sensor Selection”, choose one of the preset pressure sensor ranges if they match the chosen DPT or select “customized” and enter the sensor range and units. For instance, if the DPT range is 0-5 inches H20 enter “0” in the box for the minimum value, “5” in the box for the maximum value and “inches H20”in the box for physical unit. In order to use the equation or chart provided in the “Airflow Measurement using Instrumented Inlet Rings” document, the sensor units should be in inches H20. If other units are used, the equation or chart must be adjusted accordingly.

Click on the “actual fan” button at the bottom of the screen to set these selections for the chosen fan.

(Figure 1)

Click on the “actual fan” button at the bottom of the screen to set these selections for the chosen fan.

INSTRUMENTED INLET NOZZLES

C. Control Parameters (PID control)

Ref. Figure 3

In LISA in the “Actual fan” screen and under “Settings...Basic Settings...Control Parameters”, the default values for the P-Factor (proportional control), I-Factor (integral control) and the D-Factor (derivative control) are “50”, “3.125” and “0”, respectively. These factors should be left at their default values or, if necessary, reset to these defaults. They can be individually reset in the “Control parameters” screen or as a group in the “Actual fan” screen under “Fan” by making sure the box to the left of “control range” is unchecked and then clicking on “set”.

Select the “positive (heating)” controller function in order to have the fan speed increase with decreasing sensor ouput, otherwise the fan will not run. This assumes that the DPT output signal is at its minimum (0vdc or 4mA) with no pressure differential across the inlet ring and at its maximum (10vdc or 20mA) when the pressure differential reaches the maximum value entered for the sensor in the sensor selection screen.

(Figure 2)

Click on the “actual fan” button at the bottom of the screen to set the selections for the chosen fan.

(Figure 3)

D. Set-value

Ref. Figure 4

The “set value” as shown in LISA in the “Actual fan” screen and under “Fan” is the nozzle differential pressure around which the fan speed will close loop. As discussed in section B, this differential pressure can be obtained from the chart by using the equation pro-vided in the cited document. Solving the equation for the differential pressure across the inlet nozzle at standard air density gives:

For example, if the required air flow from a 630mm diameter centrifugal fan is 6000 CFM, then the differential pressure to be entered into LISA as the set value equals:

Where the nozzle factor “k” equals 480

P = 1.78 inches H²0

Enter the desired “set value” in the provided box and confirm that the box to the left of “control range” is unchecked. Click on the “Set ” button appropriate to the fans being programmed.

The live fan speed nozzle differential pressure can be read in the boxes under “Actual values”.

INSTRUMENTED INLET NOZZLES

∆

Note: The system will reach the set value unless the targeted operating point is beyond the fan capability. In such a case, the fan will operate at maximum speed. The speed can be read via LISA, but an alarm is not provided for such a situation. If an alarm indicating that the fan has reached its maximum capacity is desired, the 0-10VDC signal on the “out” terminal of the wiring BUS can be measured. A signal above 9VDC indicates the fan is nearing or may have reached its maximum capacity.

(Figure 4)

∆P = ( )Q9.36k

2

∆P = ( )60009.36k

2