The volumetric measuring method is based on the measurement of partial quantities of a medium to be measured. The medium passing through a defined measuring chamber or via an analogous rotation of measuring blades is added up. This summation is described by the term "quantity transported through".
Volume meters are divided into two superordinate groups, "direct volume meters" and "indirect volume meters", according to their mode of operation.
(a) Indirect meters
With indirect meters, the volume is determined indirectly without a measuring chamber. There are various methods available here. For example, a measurement of the velocity of the flow or an integration of the flow values over a certain period of time can be carried out. In this procedure, density is usually an important variable to be taken into account, as it has an influence on the error curve of the flow meters.
(b) Direct volume meters
With the direct methods, small volumes of the medium to be measured are separated during the measuring process. The volumes are determined by the defined size of the measuring chamber or by the measuring chamber walls. With the aid of a counter, the partial quantities passing through can be recorded and output. The direct volume meters are further differentiated into outlet and displacement meters.
Outlet meters consist of a measuring vessel with fixed measuring chamber walls. The medium to be measured is filled into the measuring vessel by a slight overpressure. The meter is then emptied automatically by tilting or control devices. The fluid flows out of the measuring chamber without pressure (see Fig. 2 4). The method is not suitable for measuring gases. This method can also be used to measure polluted liquids, since the fluid always flows out through large drain openings or via tilting or rotating devices. The method can achieve accuracies of up to 0.1 %.
Displacement meters are characterized by movable measuring chamber walls which displace the medium to be measured. This principle, in contrast to outlet meters, allows the measurement of liquids and gases.
Due to the fact that outlet meters always delimit a certain volume, no continuous measurement can be performed. In addition, the measuring containers are relatively large, which makes implementation in a cooling circuit unattractive. Therefore, these outlet meters are not suitable for this task. For this reason, only individual displacement meters will be dealt with in the following.
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