- A diaphragm meter is physically composed of a pressure container which forms a part of chambers that measure gas. These chambers are filled & emptied periodically & the diaphragm separates the chamber so that the gas pressure fluctuates on either sides. The third component which is important is the valve & seats that controls the flow of gas into the side of the diaphragm. The valve & the index register the revolution of the entire mechanism.
- A diaphragm meter is like a double acting piston where there are two phase systems. If the piston is in phase then in next operation it will be 90 degree out of phase.
- Each stroke of diaphragm displaces a fixed volume of gas, so that at one full stroke a fixed volume of gas is displaced & the meter will record the amount of displacement. When the demand for gas is made on the downstream side of the meter, a pressure drop is created across the meter & its diaphragms. The differential provides the force to drive the meter. In addition to the capacity of the meters the body must be physically constructed to withstand the internal pressure of the gas. Modern diaphragm meters have sufficient structural integrity to withstand a minimum shell test of 10 psi. The meter should always be shipped, stored & installed in an upright position. Dust caps on the inlet & outlet connections should be left in place until the meter is installed. Caution should be used with meters while maintenance, as gas may be present within the diaphragm chambers.
- Diaphragm meter is the most widely used for domestic & commercial gas metering & is usually installed at the customer premises. When the meter is used in the areas like domestic & commercial, ventilation should be provided & meter should be accessible for examination, reading, replacement or maintenance.
- Coriolis meters work on the concept of Coriolis effect. Coriolis effect is described as the deflection of moving objects when the motion is described relative to a rotating reference frame. Coriolis meters measure the force resulting from the acceleration caused by mass moving toward a centre of rotation. These meter measure the mass flow rate of gas directly.
- In Coriolis flow meter, no compensation is needed for temperature, pressure & density variation. A U-shaped flow tube with inlet on one side & outlet on the other enclosed in sensor housing is connected to an electronic unit. The gas flows through one or more oscillating tubes. The flow rate of gas affects the oscillation of the tubes, which can be used to determine the gas flow rate.
- These meter have higher accuracy than most flow meter & can be used in a wide range of flow conditions. These meters are also suitable for bi-directional flow.