Industry instrumentation : Units and conversion tables for process control - Instrumentación industrial : Unidades y tablas de conversión para el control de procesos

Table 1- Approximate Pressure Ranges for Pressure-Sensing Devices

Pressure-sensing devices are chosen for pressure range, overload requirements, accuracy, temperature operating range, line-of-sight reading, or electrical signal, and response time. In some applications there are other special requirements. Parameters, such as hystersis and stability, should be obtained from the manufacturers’ specifications. For most industrial applications reading positive pressures, the Bourdon tube is a good choice for direct visual readings and the silicon pressure sensor for the generation of electrical signals. Both types of devices have commercially available sensors to measure from a few pounds per square inch pressure FSD up to 10,000 psi (700 MPa) FSD. Table 2 gives a comparison of the two types of devices. Table 1 lists the operating range for several types of pressure sensors.

Table 2- Comparison of Bourdon Tube Sensor and Silicon Sensor

The following should be taken into consideration when installing pressure- sensing devices.

1. Distance between sensor and source should be kept to a minimum.

2. Sensors should be connected via valves for ease of replacement.

3. Overrange protection devices should be included at the sensor.

4. To eliminate errors due to trapped gas in sensing liquid pressures, the sensor should be located below the source.

5. To eliminate errors due to trapped liquid in sensing gas pressures, the sensor should be located above the source.

6. When measuring pressures in corrosive fluids and gases, an inert medium is necessary between the sensor and the source or the sensor must be corro- sion resistant.

7. The weight of the liquid in the connection line of a liquid pressure sensing device located above or below the source will cause errors in the zero, and a correction must be made by the zero adjustment, or otherwise compensated for in measurement systems.

8. Resistance and capacitance can be added to electron circuits to reduce pressure fluctuations and unstable readings.

Tags : U-tube manometer, Bellows, Bourdon tube, Helical bourdon, Strain gauge, Stainless steel diaphragm, Diaphragm, Capsule, Spiral bourdon, Piezoelectric, Solid state diaphragm