Closed Loop Brochure

8/3/2019 Closed Loop Brochure

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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 thatuse 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 USINGINSTRUMENTED INLET NOZZLES

100 Hyde Road, Farmington, CT 06034 USA Internet: http://www.ebmpapst.usTel: 860 674 1515 E-Mail: [email protected] 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


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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 H2

0 enter 0 in the box for the minimum value, 5 in the box for the maximum value and inches H2

0

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.


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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 contro

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)


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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 fanspeed 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 H0

Enter the desired set value in the provided box and confirm that the box to the left of control range is unchecked. Clickon 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.


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

(Figure 4)

P = ( )Q9.36k

2

P = ( )60009.36k

2

Documents

Closed Loop Brochure