Process control instruments are used in a variety of manufacturing industries. Many types of companies, from dog food manufacturing, to oil producers to food and beverage companies must control their manufacturing process to ensure a quality and uniform product.

A control system uses a variety of instruments to control pressure, temperature, flow, level, viscosity and or density of the ingredients used to make a final product. Many variables must be measured or controlled to produce the final product.

Often water may be used to control the temperature of one of the ingredients. In which case the water is considered a manipulated variable and the process ingredient is considered to be the controlled variable. The water temperature is manipulated to keep the process ingredient temperature at a constant (controlled) temperature.

Obviously just controlling the process ingredients themselves is not sufficient. The process conditions themselves must be monitored and controlled to produce a final product.

Digital meters with LCD displays can be used to monitor and control industrials processes because they provide a fast, accurate easy to read display. Many other types of recorders and monitors are available. They can record things such as temperature and record the changes over time.

Recording and indicating instruments can be installed directly on the industrial equipment or remotely mounted in a control room.

4-20mA has long been the standard for industrial instrumentation. 4 mA represents a 0% signal and 20mA represents 100 percent signal. If 0mA were used it would be difficult to differentiate between a zero signal and a dead circuit. This is a one way analog communication system

Fieldbus became a standard in 2000 and is a digital technology that allows bi-directional communication. Fieldbus technology can reduce cost and increase efficiency through digital transmission. Fieldbus is much more accurate than older analogue technologies. It is like a local area network for process control devices.

Fieldbus technology reduces the amount of wiring required; this can significantly lower the cost of installation. The reduction of wiring should also increase reliability and reduce maintenance costs. With fieldbus technology all devices can be connected using a single cable and devices from different manufacturers can be used on the same network. Control system expansion is simple as new devices can easily be added to the existing bus cable.

There are currently 3 Fieldbus protocols which include Interbus, profibus and Foundation fieldbus.

More info on Fieldbus technology can be obtained at Fieldbus.org