| 摘要 |
<p>749,147. Electric tests. MINE SAFETY APPLIANCES CO. Feb. 11, 1954 [Feb. 27, 1953], No. 4025/54. Class 37. [Also in Group XXXVII] Apparatus for determining the oxygen content of a gas mixture by means of an electrochemical cell through which the gas mixture or a mixture containing a known oxygen concentration may be sent comprises a control circuit actuated by predetermined values of concentration, and is characterized in that the valve controlling the entry of the test gas to the cell is mechanically interlocked with switches in the control circuit to prevent automatic operation of the control circuit during or immediately after the test gas has been replaced by a standard gas for calibration and zeroizing of the equipment. The electrochemical cell 1 (Fig. 1) comprises a zinc electrode 7 and carbon electrode 3 in an insulating container 2 together with a liquid dielectric 6, the test gas being passed through a central bore in the carbon electrode 3 to diffuse through windowed recesses 5 for chemical reaction with the electrolyte 6, producing a voltage or current indicative of the oxygen content of the test gas. The test gas is supplied by pipe line 12 through a two-way valve 18, and may be replaced by a gas containing zero oxygen content via pipe 20, or a gas having a known oxygen content via pipe 24. In order to calibrate or zeroize the electrical equipment, the valve 18 is operated by a handle 36 (Figs. 3, 4) to release operating button 37 of a switch 38, thereby short-circuiting contacts 39, 40 (Fig. 2), disconnecting an audible alarm 46 and visual alarm 47. Access to the calibration controls is effected by opening a door 33 which breaks switch 50, further disconnectng the alarm devices 46, 47. After calibration the door 33 is closed, thereby closing switch 50, and the handle 36 is operated to admit the test gas to the cell 1, the alarm circuits being completed after a delay produced by a thermal, bimetallic switch 51, and a timer 54.</p> |
