INSTRUMENT FOR MEASUREMENT OF RADIANT TEMPERATURE ASYMMETRY

Abstract: The instrument consists of two parallel inter-insulated plate elements (1 and 2) on figure 1, between the two plates and in thermal contact with both two peltier-elements (3 and 4) have been affixed. This sensor is connected with a control and measuring device of known construction over the input terminals of which there is applied a voltage that is generate across the poles of one of the peltier-elements when, because of radiant asymmetry, a temperature difference arises between (1 and 2). In the control unit this voltage is transformed in a known way to a current proportional to the voltage which is led through the other peltier-element. The temperature difference thus occured between the two sides of the peltier-element will, when the element is rightly turned, neutralize the temperature difference between the two plate elements caused by the radiation so that these elements will adopt the same temperature. The required current is proportional to the radiant asymmetry perpendicularly at the sensor element.

Description: Instrument for measurement of radiant temperature asymmetry The present invention relates to an instrument for mea¬ surement of the radiant asymmetry in the thermal field. The instrument comprises a sensor device for heating, cooling and temperature measurements, and a control and measuring device for determination of the radiant exchange to the environment of the sensor. Both in the new ISO-norms for thermal indoor climate and the new Scandinavian directions for claims to the ther¬ mal indoor climate are given definite limits for the ex- tension of the radiant asymmetry in the thermal field. The radiant asymmetry is defined as the difference between the plane radiant temperature of two opposite sides of a small plane element. Instruments for measurement of the radiant temperature asymmetry are already known. In the U.S.patent no. 3 693447 an instrument consisting of two thermally insulating plates one on each side of a bigger highly thermally conductive and radiation reflective surface has been described. On top of each of the insulating surfaces a black, highly thermally conductive plate has been, affixed. The two last surfaces have been interconnected by one or more thermo -. elements. On top of that there are thin radiation permeable foils, between the foils and the black surfaces there are small cavities with stagnant air. When a radiant asymmetry arises perpendicularly to the black surfaces the two opposite surfaces will attain dif- ferent temperatures. The size of this difference, which can be measured by the thermoelements, is a measure for the radiant asymmetry. The disadvantage of this instrument is the thin transparant foils which - especially in undustry environments - quickly change their transmission ability for radiation and by that the sensitivity of the instrument. In the Danish patent 71112 a discription of a sensor is given; this sensor consists of two black and two polished square surfaces at the same level. The surfaces are inter¬ connected by a thermobattery which makes it possible with good accuracy to measure the temperature difference which arises between the polished and the black elements when the surface is exposed to a radiant temperature different from the air temperature. When using two of these sensors, one at each side of the insulating surface, it is possible to determine the radiant asymmetry. The disadvantage of this instrument is that the measured temperature difference is dependent on the air velocity around the sensor. In the Danish presentation document no. 141.673 an instrument formeasurement of the asymmetry in the thermal field is described. The instrument consists of two black surfaces with a good conductivity, each of which in con¬ tact with both an electric heating element and a tempera¬ ture sensor. The surfaces are located on each side of a third thermally insulating surface. The connected control- and measurement instrument assures a constant temperature of the two black surfaces and measures the necessary effect for maintaining the constant temperature. The difference of the two measured effects is an indication of the asymmetry in the thermal field. This instrument thus measures the asymmetry by the sum of the convection - and the radiant field perpendicularly on the plane of the sensor and not • the radiant asymmetry. The aim of the present invention is to create an instru- ment by which it is possible to measure the thermal radiant asymmetry without the disadvantages and sources of error mentioned above. According to the invention the problem has been solved as follows: The sensor consists of two parallel and from eachother thermally insulated plate elements the other sides of which are black. The elements are interconnected by a pel-: tier-element as well as by a thermo sensor which is able to measure the temperature difference between the two elements. The matching control and measuring instrument is adapted to keep the two elements at the same temperature as the peltier-element cools the warmer element and heats the cooler one until the thermo sensor indicates that the temperature difference between the two is 0. The effect per area unit of the elements needed to kee the two elements at the same temperature when exposed to an asymmetric radiation field can be measured, and it will equal the radiation flux perpendicularly on the plane of the elements and is thus equivalent to the radiation asymmetry at the place of the sensor. The invention is explained in detail below according to the following figures. Figure 1. shows a sensor for measurement of the radiant asymmetry. Figure 2. shows a sensor for measurement of the absolute radiant temperature. The two plate elements 1 and 2 have a surface with an emission figure as near as possible to 1 for the wavelength the asymmetry of which you want to measure. Between the two elements two peltier-elements 3 and 4 are located; the thickness of these peltier-elements are equal to the distance between the two plane elements. The space between 1 and 2 is filled with a good heat insulating material 5. The two peltier-elements work as follows: One is used for measurement of the temperature difference between 1 and 2 arisen because of the radiant x = asymmetry. A temperature difference between the two sides of a peltier- element will cause a potential difference between the two poles of the element. This potential difference is used, via a simple already known electronic control, to impose on the other peltier-element an electric current with an intensity and direction which reduces the temperature difference between 1 and 2 to 0. The electric current necessary to keep 1 and 2 at exactly the same temperature is a direct measure for the radiant asymmetry between the two half spaces limited by a plane through the middle of the sensor parallel with 1 and 2; or otherwise said this current is a measure for the radiation flux perpendicularly on 1 and 2. If the sensor, apart from an asymmetric thermal radiation field, is exposed to an air velocity the temperature of all the sensor can be changed but this will not influence the measurement because the radiation flux and thus the necessary flux through 4 is independent of the air velocity. A sensor according to fig. 1 can be used for measure¬ ment of the radiant asymmetry between the two half spaces but not for measurement of their absolute radiant tempera- ture. According to the invention this can be achieved by the sensor shown on the sketch fig. 2. This sensor consists of three parallel elements 6, 7 and 8 made of a heat conduc¬ tive material f.inst. aluminium. The space between the ele¬ ments equals the thickness of the peltier-elements. The space between the elements is filled by a heat insulating material 9. The element in the middle 6 has a diameter which is about 4 times bigger than the diameter of 7 and 8. 6 has a radiation reflecting surface which causes 6 to adapt the air temperature. This air temperature can in an already known way be determined f.inst. by a temperature dependent resistor 10 coupled in a bridge circuit. At the middle of each side of 6 two peltier-elements 11 and 12, and 13 and 14 have been located, all covered by the radiation absor- bing elements 7 and 8. By means of the two sets of peltier- elements as explained above 7 and 8 respectively will be kept at the same temperature, i.e. the air temperature. The intensity and the direction of the current through the peltier-elements 12 and 14 is a measure for the deviation of the two plane radiant temperatures from the air tempera¬ ture. The sum of the two currents is a measure of the radiant asymmetry. As all the sensor will adopt the air temperature because of the big surface of the middle ele¬ ment air movements as may arise will not influence the result of the measurement. The correlation between the current through the peltier-elements 12 and 14 and the deviation of the plane radiant temperatures from the air temperature can either be calculated on the basis of the physical data of each component or on the basis of the calibration of the known radiant asymmetric fields.

Claims: Patent Claims. Claim 1. Instrument for measurement of radiant asymmetry containing a sensor with two parallel and from eachother thermally insulated plate elements (1 and 2) , the two opposite sides of which are black, as well as a control unit and a temperature sensor which keeps the two surfaces at the same temperature and a measuring device to measure the necessary effect c h a r a c t e r i z e d in that the two elements are connected with a peltier-element (4) , which by means of the temperature sensor (3) and the con¬ trol unit is able to keep the two surfaces at the same temperature during the measurement as it cools the warmer surface as well as there are means to measure the direction and intensity of the required current. Claim 2. Instrument in accordance with Claim 1 c h a r a c- t e r i z e d in that the temperature measurement device in the sensor element is an extra peltier-element (3) , located next to the peltier-element (4) mentioned above. Claim 3. Instrument in accordance with Claim 1 or 2 c h a r a c t e r i z e d in that there is, between the black surfaces, a much bigger polished surface which, be¬ cause of the radiation reflecting surface, will adopt the air temperature and there are two peltier-elements with matching control units one between each of the black sur- faces and the polished plate. OMPI Claim 4. Instrument in accordance with Claim 1 or 2 for measurement of considerable radiation fluxes, c h a r a c- t e r i z e d in that the two surfaces will each have a peltier-element affixed, the free side of the peltier- element will be kept at the air temperature by forced cooling for inst. by an electric ventilator.

Inventors: MADSEN THOMAS LUND, MADSEN, THOMAS, LUND
Applicants: NIMATIC APS
Application year: 1982
Main classification: G01J5
IPC codes: G01J5