Achieving quick T90 times with extractive TDLS


Source: Axetris Ag

The Axetris LGD F200 is an extractive module designed for easy integration into gas analysis systems in a variety of applications – from environmental emissions monitoring (CEMS) to industrial process control.

For some applications, e.g. industrial process control, a short response time, usually expressed as T90 (time to reach 90% of applied concentration reading after a rapid concentration change), is a key requirement from the gas analyzer. For regulatory applications such as CEMS, a certain T90 reaction of the gas analyzer is defined by existing norms (e.g. EN14181/QAL1 testing requires an analyzer T90 < 400 seconds).

Achieving quick T90 times

The gas measurement cell volume of the LGD F200 is a miniscule 15 ml. This enables a quick exchange of sample gas through the extractive module. This product feature, combined with an intelligent design and material selection, helps the LGD F200 typically achieve a T90 time of a few seconds!

Relation of T90 to sampling flow rate

As every gas analyzer engineer would agree, there is a strong dependence between achieved T90 reaction time and the sampling flow rate. This dependence is especially strong for “sticky” molecules, such as ammonia (NH3) and hydrochloric acid (HCl) – two of the gases for which LGD F200 products are available. For such gases, molecule adsorption on all surfaces of the sampling system makes it extremely challenging to achieve quick T90 times. Recent internal tests, however, have shown that at suggested sampling flow rates of 2,000-3,000 sccm are used, the LGD F200-H NH3 achieves a T90 time of 3-6 seconds!

For more information on T90 test results, or to discuss the development of gas analysis systems based on the LGD F200, you can contact our dedicated application engineering group.

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