| Ever wanted to quickly and cheaply measure the | | | | conditions should be specified at the time of order, |
| flow rate of a gas flow or water flow, then one of | | | | as the manufacturer will configure the meter to suit. |
| the simplest and most economical flowmeters on the | | | | To improve the in-use accuracy of the meter it will |
| market is the variable area type flowmeter. Often | | | | be necessary to measure the temperature and |
| referred to as a rotameter or glass tube flowmeter, | | | | pressure of the flowing media and correct for the |
| this is one of the most economical and reliable | | | | difference in tube reference conditions. In applications |
| instruments for measuring flow. They are available in | | | | where the meter is operating close to the tube |
| a wide variety of configurations for different gases, | | | | reference conditions, it is often found that no |
| fluids, temperatures and pressures, all with different | | | | temperature or pressure measurements are taken, |
| styles of connections. The flowmeter requires no | | | | and the tube reading is read directly. |
| power and in its smallest form can be carried in your | | | | During use the meter will often accumulate foreign |
| pocket. | | | | material on the tube walls or on the outside of the |
| It consists of a simple measurement principle of a | | | | float, and will cause inaccurate readings, often |
| float moving up and down in a graduated tapered | | | | resulting in the float sticking in the tube. Even worse, |
| glass tube. As the flow enters the bottom of the | | | | if the float has been allowed to hit the end stops of |
| meter, which is positioned in a vertical position, the | | | | the meter this can permanently damage the meter, |
| flow pushes the float upwards until a sufficient gap | | | | and replacement parts will be required. It is essential |
| has grown between the tube wall and the float, at | | | | to maintain a regular calibration of the flow meter |
| this point the float is in equilibrium. Decreasing the | | | | when any errors and maintenance issues can be |
| flow causes the float to fall and increasing the flow | | | | rectified during the calibration process. When |
| causes the float to rise. With a calibrated graduated | | | | organising the calibration of your variable area |
| scale marked on the tube, the positioning of the float | | | | flowmeter, request the calibration is undertaken on |
| then determines the flow rate through the meter. | | | | the actual gas/fluid specified for the flowmeter, |
| The float is often a cone shaped slug in the larger | | | | although it is not always, it is the ideal calibration |
| meters and a ball in the smaller meters. | | | | method. Some calibration laboratories can only |
| The accuracy of the flowmeter varies from | | | | calibrate on air or water and then theoretically |
| manufacturer to manufacturer but typically ranges | | | | correct for density changes. This can often incur |
| between 1 and 5% FSD. Typical flowmeters on the | | | | large calibration errors especially on the smaller size |
| market include models from Omega, KDG flowmeter, | | | | meters. Specialist flow calibration laboratories will |
| Brooks, Platon, Fischer Porter, Yokogawa and | | | | often have facilities for flow calibrations on air, helium, |
| Krohne, to name a few. You will generally find the | | | | argon, propane, nitrox, oxygen, carbon dioxide and |
| variable area flowmeter is specified for use with a | | | | with the use a a gas divider can also undertake |
| specific air or gas, at a standard air density. To gain | | | | specific gas mixtures as required. |
| the best from your flowmeter your operating | | | | |