GB/T 44065-2024Thermometer screen (English PDF)

3 Terms and definitions

3.1 Thermometer screen is defined as the white louvred box in which temperature, humidity and similar instruments are installed so as to be protected from direct solar radiation and from radiation reflected off the ground while still being suitably ventilated.

4 Technical requirements

4.1 Function. The screen is to be usable in the open air under natural conditions; to keep solar radiation and radiation reflected off the ground from falling directly on the instruments inside; to have a path by which inside and outside air exchange; and to protect the instruments inside from strong wind, rain and snow.

4.2 Performance. The radiation error is not to exceed one half of the half-width of the permitted error of the temperature sensor, and the ratio of the wind speed inside the box to the wind speed outside is to be about 1:3.

4.3 Structure and parameters. The screen is made up of the box and the top board, as Figure A.1 shows, and the box itself of the door, the door lock, the base, the walls and the ventilating partitions. The space inside is to suit the instruments to be installed, and the dimensions of Table 1 are preferred, the structural dimensions being drawn in Figures A.2 to A.7. Table 1 covers three kinds, the small wooden screen, the large wooden screen and the glass fibre reinforced plastic screen, and gives a basic dimension and a tolerance for each. The internal width is 460 mm plus or minus 2 mm for the small wooden screen, 460 mm plus or minus 2 mm for the large wooden screen and 466 mm plus or minus 3 mm for the plastic screen. The internal depth is 290 mm plus or minus 2 mm, 460 mm plus or minus 2 mm and 462 mm plus or minus 3 mm respectively. The internal height is 537 mm plus or minus 5 mm, 612 mm plus or minus 5 mm and 618 mm plus or minus 5 mm. The top board is 720 mm by 610 mm by 24 mm plus or minus 3 mm for the small wooden screen, 720 mm by 780 mm by 24 mm plus or minus 3 mm for the large wooden screen and 720 mm by 780 mm by 21 mm plus or minus 2 mm for the plastic screen. The vertical spacing of the louvres is 11 mm with a tolerance of plus 1 mm for both wooden screens and 45 mm with a tolerance of plus 2 mm for the plastic screen. The flatness of the outer edges is less than 2 mm for the wooden screens and less than 3 mm for the plastic screen, with no tolerance given. The ventilating partition thickness is 12 mm plus or minus 2 mm for all three. The top board makes an angle of 3 degrees plus or minus 0.5 degrees with the upper face of the box, sloping so that the door side is raised and the opposite side lowered. The ventilating partitions of the upper and lower faces of the box are both of the double-layer, five-board overlapping kind.

4.4 Materials. A material may be chosen that is hard, low in thermal conductivity, resistant to high and low temperature and does not readily take up water, such as glass fibre reinforced plastic or wood. Components may be of a strong, corrosion-resistant material; the stays inside the box may be metal with the surface treated against corrosion; and the door hinges and the door lock are to be of stainless steel.

4.5 Appearance. The surface of the box material is to be white, even in shade and without obvious colour difference. There are to be no knocks, no deformation and no areas of rubbing damage. There are to be no areas of small particles, foreign matter or protruding marks, no areas of pitting, bubbles or blowholes, no delamination and no cracks. Metal parts are to be given an effective anti-corrosion treatment.

4.6 Environmental adaptability. For transport shock the screen, in its packaging, is to withstand the shock transport test of GB/T 25480-2010 at a peak acceleration of 100 metres per second squared with a pulse duration of 16 ms. For free fall the screen, in its packaging, is to withstand the free fall test of GB/T 25480-2010. For salt spray corrosion the screen is placed in a salt spray chamber and subjected, under GB/T 2423.17-2008, to a continuous 48 h salt spray corrosion test at a temperature of 35 °C plus or minus 2 °C with a sodium chloride solution of 5 % plus or minus 1 % by mass; after the test it stands for 1 h and its appearance is observed within 2 h.

5 Test methods

5.1 Function is checked by eye, to see whether the space inside the box will take the instruments needed and whether the door opens and closes normally.

5.2 Performance. Radiation protection is tested under natural atmospheric conditions, using as the reference either the World Meteorological Organization reference ventilated psychrometer or a platinum resistance digital ventilated psychrometer that can serve as a second-order standard. The result is expressed as the systematic error variable obtained by comparing the temperature sensor dynamically with the reference by day and by night; the screen passes if the radiation error does not exceed one half of the half-width of the permitted error of the temperature sensor. The dynamic comparison test follows Annex B. Ventilation performance is tested in the natural state by comparing the natural wind speed outside the box with the wind speed inside, both measured with wind speed sensors. For the inside measurement the sensor is placed inside the box and the door closed. The instantaneous wind speeds inside and outside are to be read from the data logger at the same moment, generally not fewer than 60 pairs of readings; the inside and the outside values are averaged separately and the ratio of the inside mean to the outside mean is calculated.

5.3 Structure and parameters. The dimensions of 4.3.2 are generally checked or judged with ordinary gauges such as a steel rule, a steel tape, vernier callipers and feeler gauges, or with purpose-made gauges, the items and methods being set in Table 2. The internal dimensions of the box are measured with a steel rule, steel tape or purpose-made gauge, the width as the distance between the outer edges of the left and right louvres, the depth as the distance from the outer edge of the rear louvre to the inner frame of the door, and the height as the distance between the upper and lower wooden partitions inside the box. The top board is measured with a steel rule, steel tape or purpose-made gauge. The vertical spacing of the louvres is measured with a steel rule, steel tape or similar gauge at three points and the mean recorded. The flatness of the outer edges is checked on the three outer faces of the box by holding a steel rule against the outer edges of the louvres in three positions in an asterisk pattern and observing and measuring with a feeler gauge the gap by which each louvre edge stands away from the rule, which is to be not more than 3 mm. The partition thickness is measured with a steel rule, steel tape or similar gauge at three points and the mean recorded. The slope of the top board is measured with a protractor as the angle between the sloping edge of the board and the horizontal edge of the box.

5.4 Materials and appearance are checked by eye.

5.5 Environmental adaptability. The transport shock test follows 4.5 of GB/T 25480-2010, the free fall transport test follows 4.7 of GB/T 25480-2010, and the salt spray corrosion test follows the requirements of Clause 6 of GB/T 2423.17-2008.

6 Inspection rules

6.1 Inspection is divided into type inspection and delivery inspection.

6.2 Type inspection is carried out on first production; when the structure, the material or the process changes enough to affect the performance of the product; when production restarts after being stopped for a year; when the delivery inspection result differs appreciably from the last type inspection; and when the quality inspection department asks for it. The items and test methods are listed in Table 3, which sets out six items with the clause that states the requirement and the clause that states the test method: function, 4.1 and 5.1; performance, 4.2 and 5.2; structure and parameters, 4.3 and 5.3; materials, 4.4 and 5.4; appearance, 4.5 and 5.4; and environmental adaptability, 4.6 and 5.5. In the same table a filled circle marks an item to be inspected and an open circle an item not inspected: type inspection covers all six items, while delivery inspection covers structure and parameters, materials and appearance only. Type inspection samples are drawn from products that have passed delivery inspection, the sampling plan and decision rules following 6.4.

6.3 Delivery inspection. Each screen is to pass inspection and be issued with a certificate of conformity before it leaves the works, and the items are those of Table 3.

6.4 Sampling plan and decision rules. Sampling inspection follows GB/T 2829, using a single sampling plan at discrimination level I, as set in Table 4. For class A non-conformities the unacceptable quality level is 30, the sample size 3 and the decision pair, acceptance number and rejection number, 0 and 1; for class B, 65, 3, and 1 and 2; for class C, 120, 3, and 3 and 4. A note explains that the two figures of the pair are the acceptance number and the rejection number. Non-conformities are classed as follows: class A means a failure in an important respect such as the performance test, the main structure or the material performance test, which destroys the usefulness of the product; class B means a more serious dimensional non-conformity, for instance one exceeding the tolerance by more than 50 %, or a more serious appearance or workmanship non-conformity, which has some effect on the usefulness of the product; and class C means a slight dimensional deviation, for instance one exceeding the tolerance by less than 50 %, or a slight appearance non-conformity, which has almost no effect on use. The batch passes only if every sample passes. A batch that fails periodic inspection is dealt with as GB/T 2829 requires.

7 Marking, packaging, transport and storage

7.1 Marking. The nameplate is made of a corrosion-resistant material, preferably 316 stainless steel, and is to state clearly the maker's name and mark, the model and name of the product and the works serial number. It is to be fitted in the middle of the lower part of the door side of the box.

7.2 Packaging. The markings on the outside of the packing case take in the model and name of the product, the number of the document, the case dimensions in millimetres given as length by width by height, the gross mass of the case in kilograms, the destination station or port and the consignee, the dispatch station or port and the consignor, and any safety marking needed during transport. The case should be economical and strong; dry, soft cushioning material is to be put inside so that the screen does not shift in transit; and the case is to be strapped. The complete product takes in one box, one top board, one set of accessories with its list, one set of installation and operating instructions and one certificate of conformity.

7.3 Transport. In its packaging the screen is to suit carriage by any means of transport.

7.4 Storage. The screen is to be stored indoors in a dry, ventilated place free of chemical attack, and is to withstand storage at temperatures from -40 °C to 60 °C and a relative humidity below 90 %.

A Annex A (informative) Structural drawings of the thermometer screen

A.1 Figure A.1 shows the structure of the screen, with six numbered parts: the base, the door lock, the door, the top board, the walls and the ventilating partitions. The column height of the glass fibre reinforced plastic screen should be 1 060 mm plus or minus 3 mm.

A.2 Figures A.2 to A.7 give the box dimensions and structure in millimetres: a front view and a side sectional view with reference structural dimensions for the small wooden screen, the same pair for the large wooden screen, and the same pair for the glass fibre reinforced plastic screen.

B Annex B (normative) Dynamic comparison test method

B.1 Reference instruments, reference apparatus and comparison references. The reference instruments, reference apparatus and comparison references used are to hold a valid verification certificate from the metrology authority, and the test equipment is to be checked before the test, its main technical performance being sound. Where the object of the measurement is to obtain the systematic error of the item under test, the additional error caused by the reference instrument, test equipment or reference apparatus used in the static test is not to exceed one tenth of the measurement result; where it is to obtain the random error, that additional error is not to exceed one quarter. Every reference instrument, item of test equipment and reference apparatus used in static testing is to have a test and demonstration report of its expanded uncertainty giving a definite value, and that expanded uncertainty may be treated as the additional error of the measurement result of the item under test; the testing, evaluation, estimation and calculation of measurement uncertainty are to meet JJF 1059.1. Where the item under test supplies statistical or analytical material for meteorology or climatology, the comparison reference is to be an observing instrument of the same kind as prescribed for the meteorological observing network, and where the sensor under test is to be put into service in that network the World Meteorological Organization reference ventilated psychrometer is also to be used, preferably a platinum resistance ventilated psychrometer or an Assmann ventilated psychrometer. A temperature measuring instrument used as a comparison reference is to be checked at the ice point within a week before use and shown to be sound.

B.2.1 Purpose. The dynamic comparison test is run to obtain, from real observing data, the dynamic measurement error of the item under test and how comparable it is with the instruments used in the meteorological observing network; to verify that the item handles the dynamic variation of the measured quantity soundly in real measurement and meets the relevant requirements of the World Meteorological Organization or of the national meteorological authority; to establish whether the item can be brought into the observing network or used to form a new observing network, and how the data of such a new network would differ from those of the existing one; and to establish whether there is a systematic error or an obvious difference between the dynamic use of the item and its static measurement result, so as to settle how far metrological verification of the sensor under test is valid.

B.2.2 Test method. There are normally two comparison references and two items under test in the test, installed or erected in the same observing enclosure or room. The distance between the sensing parts of any two instruments being compared is to be more than 1.5 m and less than 5 m. The sensor under test is installed as its operating instructions require; where its technical specification does not call for installation in a standard thermometer screen, a purpose-made screen or a radiation shield is to be provided. The sensing parts of the item under test and of the comparison reference are to be erected at the same height, and the erection and observation of any one instrument is not to disturb the natural airflow near any other. The measuring part of a platinum resistance or Assmann ventilated psychrometer used as a comparison reference is to be installed outside the standard screen and is not to receive direct solar radiation during observation; the temperature sensing element of the World Meteorological Organization reference ventilated psychrometer is to face the sky background and its ventilation opening is to face away from the wind. Nothing is to be put inside a screen other than the measuring instruments, the sensors and the purpose-made supports belonging to the test, and each screen is to hold one set of instruments or sensors only. Where the sensor under test has no ventilating device, or where the ventilation rate is found on testing the ventilator to be less than 2 metres per second, the effect of different natural wind speeds on the measurement error of the sensor is to be verified during the test.

B.2.2 (continued) Comparison data are to be obtained under a range of temperature conditions and are normally grouped by whether the air temperature is rising, falling or fairly steady. For an electrically measuring temperature sensor the data are also grouped by the outside wind speed, normally in three groups: calm or below 1 metre per second; 1 to 5 metres per second; and above 5 metres per second. The test is to be run separately above 0 °C and at or below 0 °C, the difference between the two being more than 25 °C, each carrying the two groupings just described. The comparison reference and the item under test are to take their data at the same time and the terminal output value of each is taken as its measurement result; one independent group of data normally has not fewer than 60 readings. Where an obvious systematic error appears between the observing results of the sensor under test and the comparison reference, the two are to be swapped over in position to establish whether a temperature gradient between the two positions is responsible. Pressure, temperature, humidity, wind direction and wind speed are to be recorded continuously through the dynamic comparison test, together with the main weather phenomena. To establish the dynamic performance of the sensor under test near the upper and lower limits of its measuring range, the test may where necessary be combined with the natural environment test of the item and run in a tropical and in a cold region.

B.2.3 Data handling and evaluation. The difference in time constant and hysteresis between the sensor under test and the comparison reference is explained from the comparison results under the different trends of temperature change. The relation between the self-heating effect of an electrically measuring temperature sensor and the wind speed is explained from the difference in systematic error under the different wind speed conditions, the systematic error in calm air being compared with that at wind speeds above 5 metres per second to show the size of the self-heating effect. Where the dynamic comparison and the static test results do not agree, the cause is to be analysed and, where necessary, the static test repeated, with fewer test points and fewer readings if appropriate.