| 摘要 |
<p>PURPOSE:To perform accurate calibration without using span gas all the time by varying the gain of an amplifying circuit for a measurement signal and making a span adjustment. CONSTITUTION:A common-use switch 84 is opened to flow zero glass to a cell, infrared rays are projected thereupon from a light source 30, and modulation is imposed by a chopper 40, so that a comparison signal VS and a measurement signal VR are obtained from a comparative wavelength detector 31 and a measured wavelength detector 32. The signals VS and VR are equalized in level by variable resistances 105 and 106 and zero calibration is so performed so that the output of a subtracter 60 is zero. Then, th gas whose thickness is known is flowed and a variable resistor 101 is so controlled that a meter output corresponds to the thickness of the gas. The zero glass is flowed while zero and span calibration is performed completely, and the normally-open switch 84 is closed to store the current indication value. When a periodic check is made afterward, the switch 84 is closed after the zero calibration and the resistor 101 is adjusted so as to obtain said stored value, so that span drift is checked without using the span gas all the time.</p> |
