| 摘要 |
Apparatus (1, 2) for measuring the permeability of sheet material, comprises: a chamber (4) for containing liquid and having an opening for the sheet material to be held across; means (5) for clamping the sheet material across said openings; means (6) for varying the volume of the chamber; a transducer (8) for measuring the pressure in the chamber and providing an electrical signal indicative of the measured pressure; means (36) for converting said electrical signal to a voltage proportional to said pressure; means (31) for generating a reference voltage which is an increasing function of time and is directly proportional to the desired pressure in the chamber; a comparator (32) for comparing the first-mentioned voltage with the reference voltage and, if the first mentioned voltage is less than the reference voltage, generating an electrical error signal; means (34) for receiving the electrical error signal and, when such a signal is received, operating the second-mentioned means to decrease the volume of the chamber thereby to increase the pressure therein. |
