Instrumentation
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.
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:
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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.
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:
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Analog**
Pneumatics (Signal lines/tubes)
***3-15 PSI
***20-100 kPa
***6-30 PSI
**
voltage***1-5 V
***0-5 V
***0-10 V
**
Current ***
4-20 mA***8-40 mA
***10-50 mA
*
Digital**HART
Protocol**SMAR
Protocol**
Fieldbus**
Modbus**
Profibus**Industrial
Ethernet**Various wireless communications
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.
Measurement and controls, the two facets of
instrumentation, have brought
technology to an unprecedented degree of precision. Instrumentation enables the measurement of various variables such as
flow and
pressure.
Control works to keep these variables at a desired level of safe, economic and other constrained values. Instrument engineers usually have degrees in
chemical engineering,
electrical engineering, or
mechanical engineering and sometimes in the newer field of
control systems engineering.
Instrumentation Technologists,Technicians and Mechanics 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.
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Instrumentation News - a site for sensors, measurements, data acquisition, automatic control and related news.
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ISA.org*Lipták, Béla G. Instrumentation engineers' handbook. Process Measurement and Analysis. CRC Press. 2003. HB. ISBN 0-8493-1083-0
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History of ISA - The Technical Society for Instrument Engineers
