【考案の詳細な説明】
本考案は、50℃近辺から約450℃に至る低温度
設定範囲を対象とする空気恒温槽型の低温域黒体
炉に関する。
放射温度計の検定または校正に使用する低温域
黒体炉の加熱手段としては、従来から球体の外周
面に絶縁体を介して電気抵抗加熱線を巻いた直接
加熱型の構造が多用されているが、近時、球形炉
体を間接加熱する空気恒温槽構造のものが昇温お
よび降温の迅速制御化に有効な点で注目されてい
る。通常、この種の黒体炉構造においては、球体
開口部附近に局部的な温度低下を生じるため、こ
の補償対策として直接加熱型構造では、開口部周
辺の電熱線発熱密度を大きくする方法または分割
して温度制御をする方法などが採られている。と
ころが、空気恒温槽型では有効な対応手段が知ら
れていない。
本出願人は、球体開口部に直結するサイテイン
グチユーブの先端部に外気との対流軽減により温
度分布を改善するエアバリア装置を設置した低温
域黒体炉をすでに提案（実願昭57−106356号）し
た。該構造は、球体と外気との温度差が小さいと
き（例えば、０〜50℃に設定可能な場合）には極
めて有効であるが、温度差が大きくなると、効果
が減少するため別の対策を必要とした。
このため、考案者らは空気恒温槽型黒体炉の球
体内面全域に亘る温度分布の状態を一層詳細に測
定した結果、以下の事項を解明した。
一般に、球体開口部からの熱の流出はサイテイ
ングチユーブを通しての熱伝導損と外気との空気
対流によるものであり、熱伝導損＞対流損の結果
として球体開口部全域にわたつて温度低下が生じ
るものと推定されがちであるが、実測によると50
〜450℃の広範囲において開口部の上部温度と球
体標的の温度偏差は僅少であつた。この理由は判
然としない点もあるが、サイテイングチユーブか
らの熱伝導損は球体外部の加熱風速を増大すれば
球体との熱伝達係数が大きくなるため、加熱装置
の容量に十分の余裕があるときは熱のバランスが
良好となるものと解釈される。しかし、外気との
対流は避けられない現象であり、球体開口部の下
部温度と標的温度との偏差は、設定温度50℃の際
に４〜６℃，450℃においては10℃以上に達する
事実が判つた。
本考案は、上記の知見に基づき、空気恒温槽型
黒体炉を構成する中空球体の開口部側を含む下部
外面に補助ヒーターを設けることによつて50〜
450℃の広温度範囲にわたる温度分布の有効均一
化を図つたものである。
以下、本考案を図示の実施例により説明する。
図において、１は加熱炉本体にサイテイングチ
ユーブ２を開口部Ｐに連結した中空球体３を中央
に配置し、この周辺を上下に網状板を備える恒温
内槽４、断熱材層５および外壁鋼板６で各被覆し
て構成されている。サイテイングチユーブ２およ
び中空球体３は、炭化けい素質、人造黒鉛質ある
いはステンレス鋼（SUS304，900℃５時間処理
品）などの材料で形成され、中軸心部に球体標的
７を有する。断熱材層５で区画された炉内底部に
は、電熱ヒーターなどの電気抵抗加熱源８および
空気循環用フアン９が内蔵設置されており、本構
造により炉内を50℃から450℃附近に至る温度範
囲内の所定温度に制御する機能が付与される。
１０は補助ヒーターで、中空球体３の下部外面
に沿つて少くともその開口部Ｐ側を含む部位を間
接的に被包する状態に適宜な固着手段を用いて介
設設される。該補助ヒーター１０の形状は特に限
定されるものではないが、例えばニクロム線をガ
ラス繊維布で被覆した面状発熱体あるいはリボン
ヒーターなど易変形性のものを用い、開口部Ｐ下
面を中心に球体と等間隔に設置することが望まし
い。また、補助ヒーター１０の電気的接続は、電
気抵抗加熱源８とは別個に、若しくはこれと直列
に接続することもできる。
本考案に係る低温域黒体炉は上記の構造を有す
るから、球体開口部下面に生ずる局部的温度低下
は補助ヒーターの加熱作用により常に補償され、
50〜450℃附近に至るあらゆる設定温度にわたつ
て大巾な温度分布の改善効果がもたらされる。
下表は、電気抵抗加熱源８に対し1/10容量をも
つ補助ヒーター１０を作動した例（本考案例）と
作動しない例（比較例）における球体開口部位の
下部と標的との温度偏差を60℃および400℃の設
定温度について測定したもので、本考案の高性能
が明瞭に確認される。
【表】[Detailed Description of the Invention] The present invention relates to an air constant temperature oven type low-temperature blackbody furnace that is intended for a low temperature setting range from around 50°C to about 450°C. As a heating means for low-temperature range blackbody furnaces used for verification or calibration of radiation thermometers, a direct heating structure in which electrical resistance heating wire is wound around the outer circumferential surface of a sphere via an insulator has traditionally been widely used. However, in recent years, an air constant temperature oven structure in which a spherical furnace body is indirectly heated has been attracting attention because it is effective in rapidly controlling temperature rise and fall. Normally, in this type of black body furnace structure, a local temperature drop occurs near the spherical opening, so as a compensation measure for this, in a direct heating type structure, the method of increasing the heating wire heating density around the opening or splitting the heating wire Methods such as temperature control are being adopted. However, there are no known effective countermeasures for the air temperature chamber type. The applicant has already proposed a low-temperature blackbody furnace in which an air barrier device is installed at the tip of the sighting tube directly connected to the opening of the sphere to improve temperature distribution by reducing convection with outside air (Utility Application No. 106356/1983). )did. This structure is extremely effective when the temperature difference between the sphere and the outside air is small (for example, when it can be set between 0 and 50 degrees Celsius), but when the temperature difference becomes large, the effectiveness decreases, so other measures are required. I needed it. For this reason, the inventors conducted more detailed measurements of the temperature distribution over the entire inner surface of the sphere of the air-controlled blackbody furnace, and as a result, the following findings were clarified. Generally, the outflow of heat from the sphere opening is due to heat conduction loss through the sighting tube and air convection with the outside air, and as a result of heat conduction loss > convection loss, a temperature drop occurs throughout the sphere opening. Although it is often estimated that the
The temperature deviation between the upper part of the aperture and the spherical target was small over a wide range of ~450°C. The reason for this is not clear, but the heat conduction loss from the sighting tube increases by increasing the heating air velocity outside the sphere, which increases the heat transfer coefficient with the sphere, so there is sufficient capacity in the heating device. This is interpreted as a good thermal balance. However, convection with the outside air is an unavoidable phenomenon, and the deviation between the temperature at the bottom of the sphere opening and the target temperature reaches 4 to 6 degrees Celsius when the set temperature is 50 degrees Celsius, and more than 10 degrees Celsius at 450 degrees Celsius. I found out. Based on the above knowledge, the present invention has been developed by providing an auxiliary heater on the lower outer surface of the hollow sphere that constitutes the air-controlled blackbody furnace, including the opening side.
The aim is to effectively equalize the temperature distribution over a wide temperature range of 450°C. Hereinafter, the present invention will be explained with reference to illustrated embodiments. In the figure, 1 is a heating furnace main body with a hollow sphere 3 in which a sighting tube 2 is connected to an opening P arranged in the center, and around this is a constant temperature inner tank 4 with mesh plates above and below, a heat insulating material layer 5 and an outer wall steel plate. Each coating is made up of 6 coats. The sighting tube 2 and the hollow sphere 3 are made of a material such as silicon carbide, artificial graphite, or stainless steel (SUS304, treated at 900° C. for 5 hours), and have a spherical target 7 at the central axis. An electric resistance heating source 8 such as an electric heater and an air circulation fan 9 are built-in at the bottom of the furnace partitioned by a heat insulating layer 5, and this structure allows the inside of the furnace to be heated from 50°C to around 450°C. A function is provided to control the temperature to a predetermined temperature within a temperature range. Reference numeral 10 denotes an auxiliary heater, which is interposed along the lower outer surface of the hollow sphere 3 using appropriate fixing means so as to indirectly cover at least a portion including the opening P side thereof. The shape of the auxiliary heater 10 is not particularly limited, but for example, an easily deformable one such as a planar heating element made of nichrome wire covered with glass fiber cloth or a ribbon heater may be used, and a spherical shape centered on the lower surface of the opening P may be used. It is desirable to install them at equal intervals. The electrical connection of the auxiliary heater 10 can also be made separately from the electrical resistance heating source 8 or in series therewith. Since the low-temperature range blackbody furnace according to the present invention has the above-described structure, the local temperature drop that occurs on the lower surface of the spherical opening is always compensated for by the heating action of the auxiliary heater.
A wide temperature distribution improvement effect is brought about over all set temperatures ranging from 50 to 450 degrees Celsius. The table below shows the temperature deviation between the lower part of the sphere opening and the target in an example in which the auxiliary heater 10 having a capacity of 1/10 of the electric resistance heating source 8 is activated (example of the present invention) and an example in which it is not activated (comparative example). Measurements were taken at set temperatures of 60°C and 400°C, clearly confirming the high performance of the present invention. 【table】
【図面の簡単な説明】[Brief explanation of the drawing]
図は、本考案に係る低温域黒体炉を示す縦断面
図である。
１……加熱炉本体、２……サイテイングチユー
ブ、３……中空球体、４……恒温内槽、５……断
熱材層、６……外壁鋼板、７……球体標的、８…
…電気抵抗加熱源、９……空気循環フアン、１０
……補助ヒーター、Ｐ……開口部。
The figure is a longitudinal sectional view showing a low-temperature area blackbody furnace according to the present invention. DESCRIPTION OF SYMBOLS 1... Heating furnace main body, 2... Sighting tube, 3... Hollow sphere, 4... Constant temperature inner tank, 5... Insulating material layer, 6... Outer wall steel plate, 7... Spherical target, 8...
...Electric resistance heating source, 9... Air circulation fan, 10
...Auxiliary heater, P...Opening.