Vol. 4 No. 8
Subject: Flow Measurement News
Date: 8-14-02

From: McCrometer, "The Flow Measurement Specialists"
........ <<http://www.mccrometer.com>>

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This newsletter is e-mailed by McCrometer monthly to subscribers worldwide. It consists of flow measurement information of interest for professionals in this field.

For More information on our complete line of flowmeters go to: <<http://www.mccrometer.com>>

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McCrometer August 2002 Newsletter

What is the 'Master Meter' Calibration Method

Calibrating a flowmeter should be a well-defined procedure that can ultimately be related to a National Standard. Here, we look at the Master Meter method of calibration and how it achieves the traceability required to ensure accurate, reliable flow measurement.

Most meter calibration facilities use the method of calibrating a meter against a primary standard such as weight or volume. As well as producing low uncertainty, this method keeps the traceability chain to the National Standard short. Where this is not practical, the next level of calibration is what is called the 'Prover technique'. In this case, the meter is 'proved' against another device, which uses a fixed volume traceable to National Standards.

However, if neither of the above methods are available or practical, the Master Meter technique may be used. Simply put, the meter to be tested is placed in series with the Master Meter and the results compared. Although it adds one additional step to the calibration chain, it has the distinct advantage of speeding up the whole process and giving satisfactory results.

What type of meter would one use as a Master Meter? The meter must be compatible with the fluid being tested, be very reliable and repeatable, and give reproducible results. It is also an advantage if the meter does not adversely alter the flow profile. For example, positive displacement meters have been used for years as a Master Meter when checking gasoline pumps and other water and oil applications. Magnetic meters and ultrasonic meters are also attractive as Master Meters because they provide no pressure drop through the line.

Recently the V-Cone flowmeter was used very successfully as a Master Meter in a University’s steam lab. It provided a meter which was traceable to NIST, and met the criteria of being reliable, repeatable, and reproducible. In addition, the V-Cone conditioned the steam flow.

However, a word of caution from flow measurement 'guru', Loy Upp, about putting meters in series and comparing the results: "One flowmeter reading gives a result, two flowmeter readings give an argument and three flow meter readings result in litigation". So take care!

For more information about McCrometer's line of flowmeters, including the V-Cone, contact McCrometer at 951-652-6811 or visit our web-site at www.mccrometer.com <http://www.mccrometer.com>.
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Copyright 2002 McCrometer