The level of the adsorption inclination of the moisture depends on the raw material of the measurement tubing. The lower the dewpoint temperature, the more significant is the effect of this influence. Unsuitable materials for the measurement tubing are, particularly, rubber or plastics with the exception of PTFE. Above the dewpoint temperature of -25°C, copper, aluminium or brass are suitable. For dewpoints below -50°C, nickel or stainless steel form the best choice as an ideal material. In order to keep the storage or delaying effect of the sample extraction system as low as possible, relatively high flow velocities are necessary. The higher the flow velocity of the gas being monitored, the more rapidly a change in moisture is detected. The maximum flow velocities for the flow of gas at the measurement value recorder must, however, be within the tolerance range.
Diagram 8.5.2.1
In principle, flow does not affect the accuracy of the reading, only the response time.
