| 摘要 |
PROBLEM TO BE SOLVED: To suppress flow-out of bubble into a liquid by constituting a liquid level detector connected to a gas supply source to detect a liquid level according to a change in a back pressure of a porous material having predetermined gas permeability. SOLUTION: A liquid level detecting apparatus used for a liquid tank or the like in a semiconductor manufacturing system is constituted, for example, of a liquid level detector S having a porous material 8 including a mean pore size of 10 to 100μm and gas permeability of porosity of 20 to 80%. Gas from a gas supply source 1 is maintained to a predetermined pressure by a regulator 2, supplied to the detector S as a predetermined flow rate through an orifice 3, and a rise of the back pressure when the detector S is brought into contact with the liquid surface is, for example, detected by a pressure detector 4. As the material 8, a fluorocompound having a contact angle formed between the material 8 and the liquid is 90 degrees or above is adopted, and a check valve 5 or the like is adopted so that the back pressure may not rise above a predetermined pressure or above. Thus, gas is scarcely output into the liquid by an action of a surface tension or the like.
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