NEW GENERATION OF LIQUID FLOW SENSORS FOR THE NANOLITER THROUGH MILLILITER PER MINUTE RANGE WITH EXTREMELY SMALL INTERNAL VOLUME

摘要

In this paper, a new generation of liquid flow sensors has been presented that is capable of meeting the requirements as imposed by the life science, analysis, biotech and other markets. The actual flow sensor consists of a straight flow tube with two active elements around it. The internal diameter of the flow tube may vary between 20 and 200 μm. The corresponding internal volume is 15 nanoliter and 1.5 microliter, respectively, which is extremely small. Several instruments have been built in which the wetted material of the flow tube was either stainless steel, fused silica or PEEK. The feasibility of other materials suitable for the above mentioned markets will be further investigated. The flow sensors have been driven with two different measurement principles, namely the constant power (CP) and the constant temperature (CT) method. The CP measurement principle proved to be useful for flow ranges below circa 100 microliter/min, the CT measurement principle was suited for flow ranges above circa 100 microliter/min. The tested instruments were capable of measuring flow ranges between 25 .. 500 nanoliter/min. (smallest flow range) and 100 .. 2000 microliter/min. (largest flow range) water. These flow ranges will be further extended, both downwards and upwards. Moreover, measurements on other liquids will be performed. The measured response time of the flow sensors is of the order of t_(98%) ≈ 2 seconds. The feasibility of the new measurement concept for low liquid flows has been proven. In due time, products based upon this new technology will be commercially available.