Instrumentation [2]

This article is about instrumentation, the physical science. There is an article on musical instrumentation.

There is also an article on the instrumentation amplifier, an integrated circuit sometimes used in measurement instruments.

Instrumentation is defined as "the art and science of measurement and control". Instrumentation can be used to refer to the field in which Instrument technicians and engineers work, or it can refer to the available methods of measurement and control and the instruments which facillitate this.

Measurement

Instruments are devices which are used to measure attributes of physical systems. The variable measured can include practically any measurable variable related to the physical sciences. These variables commonly include:

• pressure
• flow
• temperature
• level
• density
• viscosity
• radiation
• current
• voltage
• inductance
• capacitance
• frequency
• chemical composition
• chemical properties
• various physical properties
• etc.

Instruments can often be viewed in terms of a simple input-output device. For example, if we "input" some temperature into a thermocouple, it "outputs" some sort of signal. (Which can later be translated into data.) In the case of this thermocouple, it will "output" a signal in millivoltage.

SCADA is the term used to denote large-scale, distributed measurement systems.

Output

Instruments communicate with some sort of signal, often adhering to a standard. This signal may be defined by standards associations, or it may be a proprietary standard. Some standards include:

• Analog
  • Pneumatics (Signal lines/tubes)
    • 3-15PSI
    • 20-100 kPa
    • 6-30PSI
  • voltage
    • 1-5V
    • 0-5V
    • 0-10V
  • Current
    • 4-20mA
    • 8-40 mA
    • 10-50 mA
• Digital
  • HART Protocol
  • SMAR Protocol
  • Fieldbus
  • Modbus
  • Profibus
  • Industrial Ethernet
  • Various wireless communications

Control

These devices are generally connected to some sort of control system which responds to the instrument's measurement. The response programmed into the control system manipulates control devices attached to the process. This cycle of changing of manipulated variables, measurement of controlled variables, and proper response is the basic concept behind process control. The control systems used are often considered part of the field of instrumentation, and can include simple Programmable Logic Controllers(PLCs) or Remote Terminal Units (RTUs), to more advanced Distributed Control Systems (DCSs). Inputs can vary from a few measured variables, to thousands of measured variables.

Related professions

Instrumentation Engineers largely design control and measurement systems primarily for industrial processes, although instruments are present in almost any modern technology today including vehicles, computers, appliances etc.

Instrumentation Technologists largely troubleshoot, repair, and install instruments and instrumention systems. This trade is so intertwined with electricians, pipefitters, power engineers, and engineering companies, that one can find him/herself in extremely diverse working situations.

External links

• Instrumentation News - a site for sensors, measurements, data acquisition, automatic cotrol and related news.
• Pressure Regulators

Further reading

• ISA.org
• Lipták, Béla G. Instrumentation engineers' handbook. Process Measurement and Analysis. CRC Press. 2003. HB. ISBN 0-8493-1083-0