| dc.description |
SUMMARYThe accuracy of a commercially available carbon dioxide meter can be increased from the generally quoted figure of ±0.1 to +0.01 per cent, by the procedures described. A number of modifications are needed, in particular the use of an accurate voltmeter to register the output of the instrument. The effect of changes in temperature and pressure were investigated and the largest cause of voltage drift under normal conditions was shown to be change in room temperature. This exerts at least two separate effects, one being a consequence of Charles's Law, whilst the other, equally large, factor is the temperature-sensitivity of one or more components in the amplifier assembly. The prevention of errors due to temperature changes is discussed in the light of these findings. A method of eliminating errors due to pressure changes is also described. When correcting for pressure changes, the need on occasion to make allowance for collision broadening is demonstrated. Errors due to changes in barometric pressure over periods of 3 hours are shown to be significant only on rare occasions. Corrections for non-linearity are shown to be crucial for high accuracy. The carbon dioxide concentration of cylinder gas, used for calibration, showed no change over 15 months. |
