In my previous blog post ‘A digital alternative to traditional VA-meters/purge meters’ I have written about the MASS-VIEW mass flow meter which is a digital alternative to traditional VA-meters/purge meters and the reasons why to use such a thermal mass flow meter instead of a traditional purge meter. This time I will answer the 5 most frequently asked questions about this type of thermal mass flow meter.
1) Can the MASS-VIEW be used for gas mixtures?
Since the introduction of the MASS-VIEW, I have regularly been asked whether the instrument is also suitable for gases or gas mixtures that are not stored in the instrument by default.
Despite the fact that the pre-installed gases might be the most common gases the MASS-VIEW is used for, the wetted parts of the instruments allow to use them for other gases and/or gas mixtures as well.
Traditionally it is possible to apply a fixed conversion factor, calculated with the free online calculation tool ‘FLUIDAT® on the Net’ , to the measurement of the MASS-VIEW. It’s a solution. However, Mass Flow ONLINE offers a more user-friendly solution, called the FluidAdd, which is actually an additional calculated fluid curve.
As a MASS-VIEW user, such an additional curve allows you to overwrite one of the default gases. The creation of a FluidAdd file requires the following information specified by the user:
- Conversion factor. The calculation of the gas conversion factor can be made via FLUIDAT® on the Net using the CFMassView module.
- Standard density. You may check Fluidat® on the Net for the correct data. The density is needed to show the flow not only in normalised volume flow units (like ln/min or ls/min) but also in mass flow units like g/h.
- Serial number of the instrument. This information is required to make sure that the FluidAdd file is adopted to the instrument.
- Custom gas name. The custom gas name will be shown in the list of selectable gases in the instrument.
The new calculated curve is delivered by e-mail. Using the FluidAdd software, the FluidAdd file can be easily uploaded into the instrument.
2) Can the MASS-VIEW be used at sub-atmospheric pressure conditions?
To answer this question properly, it is actually required to start with a closer look at the physical properties of gases. In physics and engineering, mass flow rate is the mass of a substance which passes per unit of time. Considering a sub-atmospheric flow rate, you can imagine that the gas flow rate need to be (significant) higher to transport a particular amount of gas (mass).
Since the MASS-VIEW series operate on the principle of direct thermal mass flow measurement, the combination of its structural design and the increased (volumetric) gas flow rate in sub-atmospheric conditions might have negative side-effects to ensure a proper measurement. Therefore the measurement output cannot be guaranteed in sub-atmospheric conditions.
3) Will the instrument (calibration) be affected by dust, humidity and/or oil mist in the process gas?
Humid air for instance can be seen as a mixture of water and air and additionally to this, dust and oil might be present in the process gas. The physical properties of those mixtures will differ from those of dry and clean air. As from a technical point of view, MASS-VIEW is able to deal with the humidity as long as there is no condensation inside the flow channel. However, the inaccuracy of a thermal mass flow meter calibrated for dry air could increase when humid air is applied instead of dry air.
As for the oil and dust, potential clogging of a thermal mass flow instrument in general is just around the corner. However, the thru-flow nature of MASS-VIEW’s working principle from Bronkhorst is relatively insensitive to possible clogging in potentially polluted industrial gas applications. However, the insensitiveness does not mean that clogging is impossible. It is highly recommended to filter those process gases before it enters the mass flow meter.
4) What is the recommended calibration interval?
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 built up over time (even very slight), plus other factors will all contribute to affecting the accuracy of an instrument.
Your instruments should regularly undergo a calibration check if not a recalibration. But how often? Because the nature of each application is different (conditions, running time, etc.) a calibration interval can last three years or three months.
Bronkhorst instruments do not have specified due dates for calibration. We suggest 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.
5) How to hook up the alarm settings?
MASS-VIEW instruments have built-in programmable alarm functions available to make the flow meters as versatile as possible. These functions enable the user to get warned for or in cases of:
- System errors
- System warnings
- Min/max alarms
- Response alarms
- Batch alarm
- Master slave alarms
When alarm settings are activated, the flow alarm will automatically open or close Alternating Current (AC) electrical circuits, activating warning lights, bells, pumps or other process control equipment. In fact, today’s highly flexible and versatile alarm trips can be found working in a wide range of applications, under an impressive list of pseudonyms.
As a standard feature, the MASS-VIEW flow meter has two alarms connected to a relay/switch.
One side of the switch is connected to ground (pin 4, 0 Vdc)
and the other side is connected to Pin 3 (alarm high).
The other relay is also with one side connected to ground (pin4, 0 Vdc) and the other side is connected to Pin 5 (alarm low).