Direct and Indirect Methods of Level Measurement

Effective level measurement plays a critical role in a broad range of industries like ethanol production, oil and gas production, pulp and paper mills, waste water management, mining, and biochemical plants. It enables organizations to determine the precise amount of liquids, solids or gases within their equipment, therefore ensuring safety and optimal performance.

There are direct and indirect methods of level measurement and an isolation valve helps ensure working efficiency within the measuring process.

Direct Method of Level Measurement

The direct method of level measurement involves the use of physical properties, like fluid motion, as well as thermal, optical and electrical properties. This direct measurement is often simple because measuring the level is just a matter of measuring the height of the substance in a vessel. A leading advantage  of all direct methods is that they don’t require the operator to compensate for changes in level caused by temperature. While liquids and gases might expand or contract due to temperature changes, direct methods of level measurement will show the amount of the product.

Oftentimes, when measuring the level of the object directly, an operator may monitor the object’s position visually, through a site glass, a float, or dip sticks. Alongside isolation valves, a number of other products are utilized within direct methods of level measurement, including displacers, air bubble systems and diaphragm boxes.

Indirect Method of Level Measurement

When there is not an easy direct method of measuring a liquid, gas or solid within the system equipment operators must use an indirect method. The indirect method of level measurement involves converting readouts and data of a known quantity, such as pressure ratio to the volume.  Because all known substances have some weight and therefore exert a measureable force over a specific area within the equipment, this force can be measured in pounds per square inch.

When technicians have determined how much pressure is exerted at a specific area per square inch, the height of the substance in relation to that measuring point can then also be determined. However, it’s important for operators to note that indirect level measurement is sensitive to the specific gravity of the substance, as well as the substance’s temperature. It is vital to consider these factors during all indirect level measurement work because they can affect the accuracy of the calculations and measurements. For example, kerosene has a different specific gravity from water. Therefore any indirect measurement of the level of kerosene within an application must factor in kerosene’s specific gravity of .82.

Both direct and indirect methods of level measurement are applicable to a range of industrial level analysis applications. By utilizing an isolation valve in each of these methods, companies can provide ease of field calibration, improve safety conditions, and obtain more accurate measurements of their inventory.

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