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A Historical Perspective
From Aristotle to Hawking
Force & Its Effects
Measurement Limitations
 
The Strain Gage
Sensor Designs
Measuring Circuits
Application & Installation
 
Process Pressure Measurement
From Mechanical to Electronic
Transducer Types
Practical Considerations
 
High Pressure & Vacuum
High Pressure Designs
Very High Pressures
Vacuum Instrumentation
 
Pressure Gauges
& Switches
Pressure Gauge Designs
Protective Accessories
Pressure Switches
 
Force, Acceleration,
& Torque
Force Sensors
Acceleration & Vibration
Torque Measurement
 
Load Cell Designs
Operating Principles
New Sensor Developments
Strain Gage Configurations
 
Weighing Applications
Weighing System Design
Installation & Calibration
Specialized Installations
 
Information Resources
Glossary
Index
List of Figures
Data Tables
 
Technical Learning Home

Pressure gauges and switches are among the most often used instruments in a plant. But because of their great numbers, attention to maintenance--and reliability--can be compromised. As a consequence, it is not uncommon in older plants to see many gauges and switches out of service. This is unfortunate because, if a plant is operated with a failed pressure switch, the safety of the plant may be compromised. Conversely, if a plant can operate safely while a gauge is defective, it shows that the gauge was not needed in the first place. Therefore, one goal of good process instrumentation design is to install fewer but more useful and more reliable pressure gauges and switches.

Figure 5-1: Pressure Gauge Designs

  One way to reduce the number of gauges in a plant is to stop installing them on the basis of habit (such as placing a pressure gauge on the discharge of every pump). Instead, review the need for each device individually. During the review one should ask: "What will I do with the reading of this gauge?" and install one only if there is a logical answer to the question. If a gauge only indicates that a pump is running, it is not needed, since one can hear and see that. If the gauge indicates the pressure (or pressure drop) in the process, that information is valuable only if one can do something about it (like cleaning a filter); otherwise it is useless. If one approaches the specification of pressure gauges with this mentality, the number of gauges used will be reduced. If a plant uses fewer, better gauges, reliability will increase.

Pressure switches with adjustable setpoints.

       
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