How can external conditions influence your flow meter?
Bronkhorst flow meters mentioned in the previous parts of this blog series, that are capable of measuring (ultra) low flows, are very sensitive. This implies that even the tiniest disruptions in a customer’s process or ambient conditions can be detected. So any disturbances that may have been present in the process now emerge, because the measurement accuracy is much better than before this sensitive flow meter was applied. A customer might then respond with “there is something wrong with the meter”. However, don’t shoot the messenger! Instead, use the information in this blog series to optimise your own process. Check external aspects such as the tubing to and from the flow meter, the influence of surrounding vibrating equipment or the presence of solid particles in the liquid flow.
To put the previous consideration in a practical context: when choosing a Coriolis-based mass flow meter or flow controller, a relatively high pre-pressure will be necessary to overcome the relatively high pressure drop over the device. This is mainly the case when Coriolis instruments are operating in their nominal flow range. However, because Coriolis instruments have a large turndown ratio down to 1%, the pressure drop in the lower region is usually negligible and comparable with thermal.
Although the measurement conducted with such a Coriolis flow meter is much more accurate than with a thermal-based flow meter, a high pre-pressure from a pressure vessel will allow more gas to be dissolved in the liquid. This is released as gas bubbles downstream in the process at a lower pressure, resulting in instability. These low-flow blog series are therefore intended to create awareness of all the things you can do to improve the setup of your process, each with their own pros and cons and possible effects.