Important Factors to consider when choosing a Process Gauge

 A process gauge is an instrument that is important for many industrial applications. Buyers of process gauges are often motivated by low cost while others are more concerned of reliability and safety as well durability. Process gauges are not created equal and while those that are cheap can be interesting, they usually end up being more expensive since they have to be replaced more often. In selecting a process gauge for an application, it is important to understand the product and how it performs.

Important characteristics of a process gauge

·         Improves safety and efficiency

·         Produces most precise measurements

·         Exceeds process gauge standards based on ASME B 40.100and EN 837-1 (mandatory testing of performance)

·         Meets fire resistant case with flammability rating according to UL 94, V-0 testing procedures

·         Reduces downtime from regularly replacing worn-out instruments

It is clear that in most cases a process gauge is a crucial part of the processing systems and they need to be reliable, accurate and readily available however, some processes gauges have proved that at certain conditions such as extreme system pulsations and vibration, wear begins to show on some parts like the Bourbon tube and gauge movements which will eventually result into failure. Worn out process gauges may release hazardous process media which are a safety concern in refining, petroleum, petrochemical and chemical manufacturing industries. It is therefore important to select a process gauge that can withstand extreme environments including system pulsation, vibration and shock.

Factors to consider in the selection of pressure gauge

Accuracy – when the process gauge is used for mechanical applications, accuracy is defined as a percentage of a full-scale range. While requirements may differ among industries it is important to refer to the guidelines of ASME B40.100 or the DIN specifications for accuracy.

-        Test gauges and standards – 0.25% through 0.10 full scale accuracies

-        Critical processes – 0.5% full scale accuracy

-        General industrial processes – 1.0% accuracy

-        Less critical commercial uses – 2.0% accuracy

Dial size – in process gauges range from 1 1/2” to 16” diameter for readability requirements. Space limitations and required gauge accuracy will determine gauge size but generally accuracies of 0.25% or 0.5% have dial sizes of 4 ½” or larger.

Case style/material – gauge performance is affected by environmental considerations such as ambient temperature, air-borne particulate, condensation, humidity, water and chemicals. Ambient conditions may require the process gauge to be isolated from temperature extremes. When ambient conditions are corrosive or contain a large number of particulates or if the process gauge will be exposed to wet or humid environment, the gauge must be weatherproof/hermetically sealed or liquid filled.

Media/wetted parts – of the process gauge including the Bourbon tube and socket must be compatible with process media. Once it is not compatible, corrosion is likely to occur which will cause the gauge to fail with possible safety issues.

Connection size – gauges are available with a variety of connections that includes NPT, DIN, JIS, BSP and SAE. Process gauges with 4 ½“dial size or larger are often supplied with ½” NPT connection for best support. Factors to consider in the choice for connection include process pressure, gauge size and weight, space limitations, leak integrity and past experience.