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- Elbow-Mounted Measuring Device
- SECONDARY DEVICES
| Target Meter In target meter the fluid flows around a disk (target) suspended in the tubular section of the meter. The orifice, then, is the annular space between the target and the walls of the tube. It does not measure a pressure differential. Instead, it measures the force of the fluid flow against the target. This force is converted to an output of 3 to 15 psi or 4 to 20 mA. The target meter is mostly used for measuring viscous, dirty, or hot fluids. Its use is limited to pipe with a diameter of 4 inches or less. 64 Field Instrumentation GEN Rev) Elbow-Mounted Measuring Device It measures pressure differential without creating a restriction in the flow. It measures the DP across a 90° elbow. The DP is created by the acceleration of the fluid flowing through the elbow. This kind of measurement is not as accurate as that obtained with a thin sharp-edged orifice plate, but its repeatability is good. Therefore, if a system can be calibrated against a known flow, the accuracy of this arrangement is quite acceptable. 65 Field Instrumentation GEN Rev) SECONDARY DEVICES Secondary instruments measure the differential produced at the primary devices and convert it into a signal for transmission. Secondary instruments include mercury manometer and various types of force balance and motion balance pneumatic and electronic transmitters. Accuracy: It is the overall degree to which the measurement system can determine the actual value of the measured variable. Precision: It refers to the ability of the measuring instrument to agree with itself repeatedly in response to the same input. In other words, precision is the degree of repeatability in a series of successive measurements. Lack of precision or accuracy causes measurement errors. Download 3.37 Mb. Share with your friends:
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