A TERMPAPER

ON

STEVENSON’S SCREEN:

USES, DETAIL AND LIMITATIONS

Presented by:

GROUP FOUR

Adetunji Olufemi Samson ARC/06/8481

Adegbola Adewale Oladeji ARC/06/8475

Adeyinka Adeniran Progress ARC/06/8483

Course:

ENVIRONMENTAL CONTROL: CLIMATE

(ARC309)

Lecturers-in-charge:

Prof. O.O. Ogunsote mnia

Arc. J.J. Adam

In partial fulfillment of the requirements of the award of bachelors’ degree of Technology in Architecture.

MARCH, 2008.

TABLE OF CONTENT.

LIST OF PLATES.

LIST OF TABLE.

1.0INTRODUCTION.

1.1Background history of Stevenson’s screen.

1.2Aim of the study.

1.3Objectives of the study.

2.0DESIGN OF STEVENSON’S SCREEN.

2.1Functional Qualities

2.2Contents

2.3Constructional Details

3.0USES OF STEVENSON’S SCREEN.

4.0LIMITATIONS OF STEVENSON’S SCREEN.

5.0RECOMMENDATIONS.

6.0CONCLUSIONS.

7.0REFERENCES.

1.0INTRODUCTION.

Stevenson’s screen has developed to be an important instrument that has even used for decades in metrology. Even, it has been improved upon to make it more functional and to have a higher degree of accuracy in the climatic data.

1.1Background history of Stevenson’s screen.

Stevenson’s screen is the standard housing for meteorological thermometer. It was designed by Thomas Stevenson (1818-1887), a Britishcivil engineer and father of the author Robert Louis Stevenson.A temperature sensor must be shaded but with good airflow to be accurate. One way to do this is with a Stevenson screen, named after its inventor Thomas Stevenson. Not finding any I liked on the web, I opted to design my own as shown here. My friend Bob Paauwe helped me refine the design and actually cut all the pieces in his wood shop.

1.2Aim of the study.

The aims of studying the instrument are to know its functional qualities and the following, viz:

  1. to know the composition of Stevenson screen.
  2. to know what and where it is used.
  3. To know how the instrument is been constructed.

1.3Objectives of the study.

The ways in which the study is carried out are follows:

  1. Electronic research on the instrument through the internet.
  2. Searching through the books on metrology in FUTA library.

2.0DESIGN OF STEVENSON SCREEN.

The traditional Stevenson’s screen is a box shape, constructed of wood, in a double-louvereddesign. It consists of a wooden cupboard, with hinged door, mounted on a steel or timber stand, so that its base is about 3 ft 6 in (1.05 metres) above the ground, the whole painted white. Indirect ventilation is provided through the bottom, double roof and louvered sides, and instruments placed within it give a close approximation to the true air conditions, undisturbed by the effects of direct solar or terrestrial radiation.

2.1Functional Qualities

The top of the screen was originally composed of two asbestos boards with an air space between them. These asbestos boards have generally been replaced by a laminate due to health and safety reasons. The whole screen is painted with several coats of whitewash to reflect radiation and will usually require repainting every two years. The functional qualities are as follows:

  1. The white painted wall of the screen helps to restrain the screen in absorbing radiant heat from the sun i.e. to reduce the effect of heating of solar radiation.
  2. The leg of the screen helps to reduce the heat gain through conduction from the earth.
  3. The louvered hinged door helps to shade the interior from direct radiation from the sun.
  4. The screen serves as shield instruments against precipitation and direct heat radiation from outside sources on the content instruments.
  5. Contents

A Stevenson screen or Instrument shelter isusually designed to hold various instruments including: viz

  1. Thermometers (ordinary, maximum and minimum),
  2. Hygrometer,
  3. Dew cell,
  4. Psychrometer,
  5. Barometer
  6. Thermograph

The two basic instruments that are mostly present in some Stevenson screen are the thermometer and hygrometer. These two instruments are used for various purposes in determination of climatic data

2.3Constructional Details

The louvers are 1/8" white tile board cut to 1-1/2" wide strips. The ends are cut at 45 degrees while sitting on a jig that holds the face at 45 degrees from the table saw surface. This forms the compound angle where the ends meet. The length to the tips must be 13" for the outer louvers and 10-1/4" for the inside ones.

The louvers are held in place by 1-1/2" square posts. The outside and inside of the posts have 5/8" deep slots cut at 45 degrees leaving 1/4" of uncut material up the center of the post. The slots are one inch apart with the inside set staggered 1/2" from the outside set to get the alternating louver positions. 8" posts are shown but the height can be extended easily by just adding more louvers.

Four posts are used, one in the center of each side. The posts are permanently fixed to the ceiling, as shown by the screw. The floor remains removable and is how the sensor is installed. The floor has a board sticking up inside for mounting the sensor. Square screw hooks go up into the bottom of the posts and extend down through slots in the floor. Turn them 180 degrees to secure or open the floor.


Plate1 - Plan of Stevenson Screen constructed by Brian Burley, Worthington, Ohio. Source:

Plate2- drawing showing the back of the Stevenson’s screen

source: screen

PLATE3- drawing showing the louvered hinged door of the Stevenson’s screen source:screen

PLATE4- drawing showing the louvered hinged door of the Stevenson’s screen source:screen

SIZES: / Height: / Width: / Depth:
EXTERNAL: / 26"
660mm / 23"
580mm / 15¾"
400mm
INTERNAL: / 15"
380mm / 16"
405mm / 9"
225mm
All sizes are approximate.

TABLE 1 Showing the height, width and the depth dimensions of Stevenson's screen.

3.0USES OF STEVENSON’S SCREEN.

The Stevenson’s screen can be used in various forms due to its content instruments

  1. Collection of raw climatic data for further processing, analysis, and interpretation into tables, figures and diagram.
  2. It allows temperature to be compared accurately at different places..
  3. Protection of the internal instruments from solar radiation to avoid damages and wrong data collection.

PLATE 6- THE INTEROIR OF STEVENSON'S SCREEN.

  1. It shields instruments against precipitation.
  2. It creates a uniform environment in relation to the air outside.

PLATE 6- THE SITTING OF STEVENSON'S SCREEN IN A METERIOLOGICAL STATION.

  1. The sitting affects orientation of buildings and trees.

4.0LIMITATIONS OF STEVENSON SCREEN.

The limitations to the use of Stevenson’s screen are;

  1. It can cannot be sited anywhere because of the climatic criteria needed to be satisfied in sitting the instrument.
  2. The wooden materials used in constructing the instrument may affect the reading of the content instruments.
  3. Interference of both the internal and external air while taken the readings.
  4. It’s immobile.
  5. The readings cannot be taking automatically.

5.0RECOMMENDATIONS.

The followings are recommended concerning the instruments for it to meet up with the pace of developments in the related fields, viz:

  1. There should be a means of reducing heat gain into the instrument to a negligible level to have a high accuracy value.
  2. There should be an invention of installing climatic sensors in the instrument to automatically take the reading.
  3. It should be installed in many areas in our environment for meteorologist to study temperature changes between and within our environment.

6.0CONCLUSIONS.

Stevenson’s screen has been in use in determination of climatic variables for time long, it needs to be modified and upgraded to suite the ever-changing climate. This has to be done because of its peculiar qualities and characteristics. Furthermore, its work cannot be neglected in the field of meteorology and other climatic-related field.

7.0REFERENCES.

of meteorology

Stevenson Screen. Environment Canada. Retrieved on 2007-12-04.

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