controlengineeringinformation varycontrol vavunits

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Control engineering informationVARYCONTROL® VAV UnitsDiaphragm pressure transducer

VFP ...

Intended Use 1

Area of application 2

Functional description2

Requirements for the measurement location 3

Zero point adjustment 4

1

VFP ...

Electronic controller

Diaphragm pressure transducer VFP Intended UseThe diaphragm pressure transducer VFP is part of the airterminal unit and in conjunction with an electronic controllerand actuator provide a control loop for flow rate or pressurecontrol.

The air terminal units are suitable for use in ventilation andair conditioning systems. Particular conditions can restrictthe functional capacity and must be taken into accountduring the design stage:

• Installation should only be carried out by specialists. Thenormal rules of site working, in particular the health andsafety regulations must be complied with.

• For aggressive air, only air terminal units made of plasticmaterials should be used after extensive tests forsuitability.

• Galvanised sheet steel units must not be installed incontaminated environments (e.g. acetic acid).

Dependency of orientationThe diaphragm pressure transducer operates based on thestatic measurement priciple and comprises a diaphragm.The weight of the diaphragm means that the orientation ofthe transducer affects the measured signal. The transduceris factory fitted and adjusted with the diaphragm in avertical position. The tube connection points can be on topor bottom also on either side but with the diaphragm stillvertical. Other installation orientations must be specifiedon order.

MaterialsPlease note that in critical cases, material compatibilitytesting should be carried out on the air terminal unit and thediaphragm pressure transducer, taking into considerationthe harmful substances involved and the concentrations inwhich they occur.

Maintenance• The mechanical components are maintenance-free

• A yearly adjustment of the zero-point of the transduceris recommended.

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1) Control components according to order code

Air terminal unitswith diaphragm pressure transducer VFP

Code 1) Controller

Diaphragm pressuretransducer

TypeTROX-part No.

Range inPa

BR.. VRP-MVFP 100 M546EJ6 100

BG.. VRP-STP

BP.. VRP-M

VFP 300 M546EJ1 300BB.. VRP

BJ.. VRP-STP

BS.. VRP-MVFP 600 M546EJ7 600

BH.. VRP-STP

2


VFP ...

2

VFP ...

Area of applicationThe electronic diaphragm pressure transducer VFP… isdesigned for use in VAV systems. Combined with anelectronic controller, it is used for measuring actual valuesof flow rate and for room or duct pressure control.

The mounting, wiring and tube connections for flow ratecontrol are factory fitted. The tube connections for room orduct pressure control must be made by others.

The orientation dependency must be taken into accountduring installation. The correct installation orientation isshown by an arrow.

The VFP… is supplied with voltage from the controllerVRP-M. Because of the static measurement principle, theVFP… is suitable for systems with contaminated airand/or aggressive media.

Functional descriptionThe pressure differential is measured using the static diffe-rential pressure principle. The pressure differential causesthe diaphragm in the differential pressure transducer todeflect, the movement is detected by induction and conver-ted into a linear pressure/voltage signal.

The measurement range is factory set. For parameters ofthe flow rate or pressure control see control engineeringinformation on the controller being used.

VFP 100

1

3

2

2

Diaphragm pressure transducer

Positive pressure point

Negative pressure point

Connecting cable with plug4

00

Characteristic of actual value signal

∆pNom

(100%)

Pre

ssur

ed

iffer

entia

l

Actual value signal *

* Actual value signal from VFP is not identical to the actual valuesignal of controller VRP-M

Connecting plug

12

3

VFP 300, VFP 600

1

1

3

243

4

1 Supply voltage2 Ground/earth3 Actual value signal

(0 to 10 VDC)

3


VFP ...

Measurement locations for static pressure

Pressure tapping> 2 D

> 2 D

90°

Pressure tapping

Pressure tapping

Room

Duct

Ød

ØD

ØD

1

2

3

4

Requirements for the measurement location• The centre line of the pressure tapping must intersect theduct axis at right angles.

• The hole diameter (d) should be as small as possiblebut sufficiently large to minimise risks of blocking andinsufficient dynamic response.

In example 1:• Connecting nipple of pressure tappingping must be 90°to the direction of air flow

In example 2 and 3:• Minimum distance of 2D must be maintained downstreamfrom a damper blade, elbow or bend.

In example 4:• Room pressure tappingpings must not be located inareas influenced by room air movement.

Measurement locations for staticpressure

1 Circular or rectangular duct2 Circular duct3 Bend upstream of the pressure tapping4 Pressure tapping into the false ceiling

4


VFP ...

Zero point adjustmentThe supply voltage must be connected for at least an hourbefore carrying out measurements. With the tubing dis-connected if the value shown is not zero then adjustment isrequired. More recent controllers provide an indicator lightto carry out this function.

• VRP-M:The zero indicator light indicates a non zero value.

• VRP and VRP-STP (new design)The V+ light indicates a non zero value.

• VRP and VRP-STP (old design)The U5 signal of VRP... is > 2,5 or < 1,7 VDC.

To adjust the zero point proceed as follows:

• Disconnect both (!) measuring tubes from VFP...

• Remove cover from VFP casing

• Turn zero point potentiometer clockwise until indicatorlight at VRP-M comes on

• Turn zero point potentiometer slowly counterclockwisebackwards until indicator light goes off

• Replace tubing

• Replace cover

Zero point adjustment

VRP-M

Zero point potentiometer

Zero point potentiometer

Zero point indicatorlight

VFP 100

VFP 300, VFP 600

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