The April Technology Evening was kindly sponsored by Endress+Hauser and Alwin Lutchman gave the meeting an interesting and entertaining presentation entitled ‘Understanding automatic tank gauging’. Alwin has been employed with Endress+Hauser for 12 years and is the business driver for Inventory Management Solutions.
He showed the audience various techniques for measuring the level of liquids and solids in tanks, and then concentrated on two high accuracy types: servo and radar. Their accuracy of measurement was covered and examples of the potential cost of measurement errors in large storage tanks was highlighted, showing the justification for installing accurate and repeatable measuring systems on such tanks. Operation of a servo gauge was demonstrated using a working model, and its ability to measure not only a liquid surface level, but also a liquid/liquid interface and the tank floor level were covered, as were its limitations in applications where the level in a tank changes relatively slowly and the fluid does not suffer from significant surface disturbance. Where disturbances could exist, Alwin mentioned the use of stilling wells to minimise their influence on the displacer.
The topic then moved on to radar gauges and their operating principle. As with the servo gauge, Alwin had a working model set up for demonstration and for inspection after his talk was finished.
During his presentation there were many questions from the audience, ranging from the reference method used to verify tank level gauges, to details of the principles used to sense the level and convert this to a signal. Much discussion centred around the sensing and conversion of the magnetically coupled drum position of servo gauges to a level measurement with an accuracy of less than 1 mm. Alwin noted that, at present, the reference method is the use of a manual dip, where an operator uses a dip tape through a hatch and the average of three consecutive dips is taken to be the true level. Many of his audience shared his concern that this method is prone to human error, and also that in many cases the dip tape accuracy has not been verified.
The talk was both interesting and informative as shown by the large number of questions, all of which were answered very capably with projections and examples to assist understanding. Alwin was thanked for his presentation, and the meeting adjourned to some networking over a good hot meal and drinks.
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| Email: | ina@saimc.co.za |
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