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Keys to Successful Flow Measurement: Tubing Sensor Calibration Adjustments at the Benchtop

By Nick Glover26 Jul 2022

Inspired by our ‘Questions from the Field’ blog series, which focusses on pressure and pressure-volume technology, I plan to shed light on a few common workflow questions for our 400-Series Research Flowmeters over my next blog installments. In today’s article, we’ll take a closer look at Tubing Flowsensor calibration and the user’s ability to both verify and make small calibration adjustments at the benchtop.Double PXL

As a Research Sales Representative of Transonic Tubing Flowsensors, I have the pleasure of connecting with users to discuss a wide range of flow applications and measurement goals. This allows our knowledgeable team to provide feedback and suggestions as your ‘Trusted Partner in Research’, while working with the user to define the application conditions that are dictating sensor calibration. Calibration parameters are an essential part of accurate flow measurement with transit-time ultrasound technology. For more information on calibration factors and optimizing flow measurements, please see the following article from my colleague, Astrid Haegens, PhD, published earlier this year: Keys to Successful Flow Measurement: Flow to Perfection.

Research Tubing Flowsensors (PXN – inline and PXL – clamp-on) can contain up to 4 unique calibration slots (combinations), made up of the following use conditions: fluid type, temperature, flow range and for clamp-on sensors, tubing material. This information is stored directly on the sensor EPROM, and each calibration slot is selectable during use on the TS410 Tubing Module hardware. By confirming the calibration requirements at the time of purchase, the sensors are delivered ready to use and come with a NIST traceable calibration certificate which covers all calibration conditions for our stated accuracy specification.

We pride ourselves on making this calibration process as streamlined and informed as possible, however, the question of ‘what happens if I use the sensor outside of the calibrated conditions?’ is valid and expected in the research world. The good news is that we have a few different ways to approach this and have provided users with the ability to modify a calibration slot to a certain extent at the benchtop if needed.

User Adjusted Gain

The User Adjusted Gain feature is valuable in that it can provide versatility in situations where you need to measure flow and do not have the exact fluid or temperature condition on the existing sensor calibration slots. In this case, you can adjust the calibration gain by percent (%) of any existing calibration slot and that adjustment will be saved on the flowsensor until reset to the factory default of 100%.

The image below shows the menu structure for accessing this feature while the sensor is connected to a TS410 Tubing Flow Module. There are visual identifiers within the menu when user adjusted gains are applied (%, *). The complete guide for adjusting sensor calibration gains can be found in the user manual.

TS410 Gain Controls*Note that this is specific to the TS410 Tubing Flow Module and PXN/PXL Tubing Flowsensors.

Syringe Calibration

To get started, we need to determine the actual flow rate of the new fluid type or temperature, to calculate the appropriate % gain adjustment for the existing calibration slot that we want to change.

This process requires a secondary measurement in which a known volume of fluid is passed through the tubing at a measured time. We describe this process in detail on Technical Note: Syringe Calibration of Tubing Flowsensors, where a syringe with two switch points is used in best practice. However, a beaker and stopwatch can be effective using the same principle and we would suggest taking multiple measurements across your anticipated flow range and calculating an average.

Using the secondary measurement, the average volume flow of the syringe (volume flow = volume/time) is known. At the same time, the tubing flowsensor’s instantaneous flow output is collected and can be averaged over time. Use the formula below to then determine the % gain correction required (+ or -). Data points are ideally taken at intervals near the typical flow range and the corresponding slopes are averaged together.

Syringe Calibration EquationIt is worth noting that this secondary method of flow measurement and comparison to the flow rate provided by the flowsensor can also be used to periodically confirm that your existing calibrations are accurate in situations where use conditions have not changed.

Sensor Recalibration

While the User Adjusted Gain feature is effective and valuable in providing flexibility, it is not suitable in all scenarios and therefore can be limited in scope. In cases where the calibration conditions/experimental design has changed significantly – entirely different fluid composition, different tubing material, dramatic change in temperature – we suggest considering our recalibration service. Specific to tubing flowsensors, this recalibration option can update/revise the calibration slots (up to 4) and would certify each use condition before being returned to the user.

All new Transonic research flow equipment (meters and sensors) come with a calibration certificate that is valid for 12 months. As many users have a requirement to maintain certificate validity for their internal audit and tracking purposes, all recalibrated equipment is returned to the user with an updated calibration certificate, valid for 12 months. The calibration certificate itself has different ‘Tiers’ that report different levels of detail, but this is a topic for another blog.

Should you have any questions related to Transonic equipment calibration and optimizing your flow measurement in the lab, please contact a member of our Team.