Psychrometer sensors type FEPto measure the psychrometric difference and air temperatureto determine relative air humidity.

FEP

1 2 3 4 5 6

Psychrometer-sensor type FEP2

Pt100 Pt100 Pt100

1.dry temperature wet temperature2.dry temperature

Connection diagram

DescriptionThe FEP psychrometer sensor unit consists of two or threePt100 temperature sensors connected to a water tank and ahumidifying wick. The sensors are arranged horizontally abovethe water tank filled with water. A cotton wick which covers thelowest temperature sensor rises up with its free end into thewater tank, constantly absorbs water, and produces themoistening important for psychrometric measuring.

Psychrometric measuring is based on the principle that thesurface of the temperature sensor (wet-bulb temperature) -which is kept moist - cools down by evaporation. Using the airtemperature which is measured simultaneously (dry-bulbtemperature), the partial pressure of the water vapour in the aircan be calculated by applying the Sprung formula (see separatedescription).Psychrometer tables or diagrams give information on therelative humidity.

Psychrometer wickThe quality of the psychrometer wick is equally asimportant for a good measuring result. Ideally, distilledwater should be used for the humidifying process. In apractical application, and particularly duringcontinuous measuring or regulation, water is takenmainly from the mains using the flow-and-rinseprinciple. It should be noted, however, that calcareouswater causes the wick to become incrusted, so that itloses its absorbent property and the measuring resultbecomes distorted.

VentilationAdequate ventilation of the humidity temperaturesensor is an essential requirement for flawlesspsychrometric measuring. Ventilation at an air speedof more than 2 m/sec is sufficient.A higher air speed does not have any appreciableinfluence on the measuring result. An air speed below2 m/sec can have a decisive influence on themeasuring result as there is insufficient evaporationand therefore no latent heat at this air speed. The wet-bulb temperature is too great and the relative humidityis too high.

Output

Input

Technical datasensor ...................................... resistance thermometer Pt100

in accordance with1/3DIN EN 60751 cl.Bdry-temperature sensor ............................................. 1(2) x Pt100wet-temperature sensor ................................................. 1 x Pt100max. allowable power............................................................. 3mAconnection .................. screw terminals in the connection headtype of protection ..................................................................... IP54housing ......................... complete fitting made of highgrade steel,

item no. 1.4571allowable ambient temperature ............................. -10...+100 °Cworking temperature ............................................... -10...+100 °C

! from 0°C to -10°C employ the psychrometric constant of ice, see description psychrometer

mounting position ......................................................... horizontalinstallation depth type FEP1 .............................................130mm type FEP2 ........................................... 210mmwick ..................................................................... absorbent cottonweight ..................................................................................... 0.8 kgelectromagnetic compatibility EMC

resistance to interference ......................... ref. EN 50 082-2interference emission ............................... ref. EN 50 081-2

"subject to technical modifications"

GallGallGallGallGalltectectectectec Mess- und Regeltechnik GmbH MELAMELAMELAMELAMELA Sensortechnik GmbHD-71145 Bondorf . Germany D-07987 Mohlsdorf (Thüringen) . GermanyTel. +49 (0)7457-9453-0 . Fax +49 (0)7457-3758 Tel. +49(0)3661-62704-0 . Fax +49(0)3661-62704-20E-Mail: sensoren@galltec.de . Internet:www.galltec.de E-mail:mela@melasensor.de . Internet: www.melasensor.de

This information is based on current knowledge and is intended to provide details of our products and their possible applications. It does not, therefore, act as a guarantee of specific properties ofthe products described or of their suitability for a particular application. It is our experience that the equipment may be used across a broad spectrum of applications under the most varied conditionsand loads. We cannot appraise every individual case. Purchasers and/or users are responsible for checking the equipment for suitability for any particular application. Any existing industrial rightsof protection must be observed. The perfect quality of our products is guaranteed under our General Conditions of Sale. Issue : May 2001 valid until 31.12.2006 FEP_E. Subject to modifications,current version available at www.galltec.de. This issue supersedes all previous technical leaflets.

Dimension diagramFEP_E page 2

Mounting drawing

Front view Back view

Side view

Connection

screw terminals in the connection head