Lesson 4 - Process Instrumentation

Welcome back. So, what were your thoughts? There are a number of factors to consider. Examples are given below, which we have grouped as either process requirements or financial factors. You may have thought of some of the following:

Process Requirements

• The range of the variable to be measured (minimum and maximum values)

• The resolution required (what increment of the variable must be measured)

• The accuracy and precision required (how critical is this parameter for the process?)

• The process conditions both internally (conditions inside the pipe or vessel such as temperature, pressure, and fluids/gases) and externally (the environment where the instrument will be located)

• Special process requirements such as its level of hygiene (can it be cleaned in place and is it safe to use with food?) and whether it could be a source of ignition for fires or explosions (for use in areas where explosive atmospheres exist)

• The installation space (the space and configuration required – should it be mounted on a vessel or installed in a pipe with a given diameter that requires a certain length before and after, without bends?)

• The level of reliability required (whether it is only for indication or whether it controls a critical variable)

Financial Factors

• The cost of the instrument

• The cost of maintenance and spares, including servicing and calibration

• Special cleaning requirements

• Control system requirements

• Power source requirements for the instrument

• The communication protocol used