August 2012 -- Since more than one year NIVUS is offering the sole certified flow rate meter (British MCERTS Standard) for open channel flows operating without additional primary equipment. Therefore we claim that this is the most accurate open channel flow rate meter available in the world. With the following investigations NIVUS extends the range of applications by another certified sensor, the POA correlation pipe sensor. This sensor operates with the same correlation technology, however is used for flow measurement in closed pipes exclusively. The sensor is driven by the same transmitter Type OCM Pro CF which has been certified before in connection with a wedge sensor. This sensor type is normally used in open channels.
The sensor can be mounted using various fastening systems for installation on any kinds of pipes. To prevent leakage when used with pressurized pipeslines, a retaining element is available. A piezo ceramic sensor determines the flow velocities with a spatial resolution in up to 16 scan layers. The sensor is designed to measure the flow rate of slight to heavy polluted media in part filled and full pipes. To determine the cross section of the flow in part filled pipes, the sensor additionally features a built-in ultrasonic level sensor. For this kind of applications the sensor must be mounted at the bottom. To minimize effects caused by fluid temperature an additional temperature sensor is integrated as well. During initial tests the mean error and repeatability have been checked.
Therefore several sensors were investigated under the same conditions and the tests were repeated several times. Different levels and velocities were applied for these tests. Additionally different pipe sizes have been used.
The average deviation was about 2 %. Considering all individual results a MCERTS class 3 (6.5 %) can be claimed. For the full filled applications the error was less and achieves a MCERTS class 2 (4 %). As a second investigation the influence of different fluid temperatures within a range of about 5 – 40°C was checked. During temperature changes, flow rate and velocity have been maintained at a constant level. The velocity was a typical one at about a 1.0 m/s. The effect of temperature on the reading was 0.03 % / °C and hence is negligible.
As a last point the response time has been investigated. This was necessary due to a significant change in values between part filled and full applications. For this test we changed the flow rate between 30 l/s and 75 l/s. For part filled applications this change causes waves and an accurate measurement is not possible for 1-2 minutes until the flow has smoothed. In full filled pipes the response time is much faster; it is definitely shorter than 15 seconds.
The certification of this pipe sensor allows to measure in a lot of additional applications which have not been possible before. Especially it must be mentioned, that there normally are much more applications in pipes than in channels of any other shape. More reliable measurements will be the result of these investigations and the certificate.
Department Technology Transfer