Explaining the process of calibration and the adjustment of flow meters
For us, as suppliers of flow meters and flow controllers for low flow rates of gases and liquids, supplying a proper working measuring device of high quality to our customers is incredibly important. Therefore quality control becomes very important. As a final step in production, we calibrate all our flow meters to provide accurate flow measurements.
Calibration can be easily confused with concepts such as re-calibration and adjustment. This article written by the folks at Bronkhorst is meant to bring some clarity about these concepts.
What is the difference between calibration and re-calibration of flow meters?
Calibration is comparing the output of a measuring device with a reference. When using Bronkhorst devices this can be done by a Bronkhorst service office, Calibration centre, or by the end user if they have the right equipment.
What is Re-calibration?
Re-calibration is a popular word for doing a re-check and is often referred to like this when a purchased flow meter has been sent back to the factory for a periodic calibration check.
What is an adjustment and when are they necessary?
It is of the utmost importance that the customer has a proper working measuring device, therefore, subjecting a meter to a periodic calibration check. If the meter shows a deviation outside its specification limit, adjustment is recommended. The instrument will be adjusted to indicate the proper value. After the adjustment is applied, the instrument will be subjected to calibration, and that comes with the calibration certificate.
Why is calibration necessary?
Every instrument is subject to aging, wear and dirt. In order to ensure the instruments are offering measured values representing the proper value, a periodic check is often recommended. For some applications a periodic check is required due to legislation, norms or directives. Minor deviations can be caused by aging of mechanical and analog electric components, this is almost unavoidable. If the deviation is more than a few percent, this is usually caused by dirt or wear. In this case full service, repair, and new adjustments are recommended for the instrument.
Frequently asked questions:
How often should I perform a calibration check on my mass flow devices?
Mass flow instruments, in fact all process instruments, experience wear from the conditions of the process in which they are installed. Temperature, electronic component tolerance shift, contamination build up over time, plus all the other factors that contribute to affecting the accuracy of the instrument. Your instruments should regularly undergo, at a minimum, a calibration check if not a re-calibration.
But how often?
Because the nature of each application is different (conditions, running time, etc.) a calibration can last three years or three months. Bronkhorst® instruments do not have specified due dates for calibration. Bronkhorst suggests that our instruments be calibrated every year. However, based on the application conditions, and perhaps company quality procedures, each customer must determine when they need to send in an instrument for recalibration. Properly calibrated instruments will be more accurate, more reliable, help ensure consistency, and help improve production yields.
How to interpret the data and terminology on Bronkhorst calibration certificates?
By clicking the link below you can open a fake certificate with the explanation of the different fields in calibration certificates.
In case of emergency, can I repair, clean and calibrate the instruments myself?
It is possible to calibrate an instrument by checking its measured value with an accurate reference yourself.
Repair and cleaning;
It is possible to restore the function of the instruments if no parts are irreversibly damaged. However, it can affect the accuracy of the device. Please note that if the device has been opened, the calibration as well as the pressure and leakage test carried out at the factory is no longer valid. Bronkhorst cannot accept any warranty for any instruments opened by other than Bronkhorst certified service offices.
In general, we recommend returning contaminated or defecting devices to our Bronkhorst certified service offices for repair, cleaning and calibration services.
Is it possible to use a thermal mass flow meter/ flow controller for other fluids?
In general, a thermal mass flow meter/controller can be used for other fluids. However, it is important that the sustainability of the sealing material used for the new gas or liquid is ensured beforehand. In addition, when using a thermal mass flow meter a conversion factor must be used, as the media differ in their thermodynamic properties.
Another influencing factor is the Kv value of the valve. Using another medium affects the flow range for which the instrument was originally suited, this can change significantly.
Unlike thermal mass flow meters, flow instruments using the Coriolis or ultrasonic measuring principle, are medium independent and do not require a conversion when using other media. However, when switched over to another medium with a liquid flow instrument, the pressure drop can be different.
To clarify the suitability of the sealing materials, please contact the local Bronkhorst office or distributor. We will gladly inform you about the conversion factors that apply to the thermal flow instruments, or you can register on our database Fluidat on the Net, which is free of charge, to set up the required calculations yourself. The database offers the user extensive calculation tools for conversion factors.
Bronkhorst Global Service Offices & Calibration Centre
At bronkhorst Global Service Offices and at our Calibration Centre in Ruurlo (NL) we are capable of calibrating and adjusting Bronkhorst flow devices and also third party instruments within our scope.
Besides that, Bronkhorst Calibration Centre has been accredited as ISO 17025 compliant by the Dutch Accreditation Council (RvA), providing international recognition of its technical competency and qualification.