INSTRUMENTATION, MEASUREMENT AND SENSORS

Instrumentation is of prime importance for automation activities since it provides the informations needed to control an automated plant.

Actually, instrumentation is like the set of the senses of a human as it provides eyes, ears, feeling and even smelling to the programmable controllers through the sensors. By extension, the term « instrumentation » reassembles any device associated with control, command, measurement and detection, including output devices with embedded capabilities too, such as frequency inverters or control valves for instance.

Instrumentation is a very wide area using a big amount of technologies, sometimes sophisticated enough ( such as image processing or programmable controllers for instance ). It can also be in association with other domains such as automatic control for example. According to the context, instrumentation can be operated over a well adapted instruments network. The exploitation of the delivered data can be made easier with some signal treatment, analysis or visualization software.

National Instruments provides a huge collection of didactic and technical papers related to instrumentation, data acquisition, signal processing and numerous measurement technologies.

General informations.

• Understanding Instrument Specifications.

Fundamentals in measurement, instrumentation, sensors, data acquisition

• Analogical Fundamentals.

• Sensor Fundamentals.
• Instrument Control Fundamentals.

www.ni.com.

• Fundamentals about instrumentation, measuring devices, and PID control. ( )

  CSNC technical training group

  The first part of this document explains different measurement techniques and devices to get temperature, pressure, flow and level values.

  For each physical value, it presents the theory, the most common detector technologies and implementations, the data treatment, the effect of the environment on the measurement, which errors could occur and how to detect them.

  The second part reports on control techniques, especially on the PID control loop.

  Beginning with an introduction to the basic control principles, this section teaches us on / off control and proportional control, in theory and from a practical point of view. Then it presents the multiple control modes and some other considerations.

This educational folder provided by National Instruments is a wide collection of technical resources related to sensor technology only.

• Sensors terminology.
• Measuring strain with Strain gauges.

• Measuring pressure with pressure sensors.
• Accelerometers principles.

www.ni.com

« Flow meter directory » is a commercial directory dedicated to flow measurement.

This specialized web site delivers a well-stocked set of interactive calculators tools to convert physical units associated with flow measures.

For clarity, these tools are often displayed with a technical drawing, the applied formula, and the definition of the parameters.

• Units converters ( speed, flow, weight, etc ).
• Flow computing in a pipe.
• Viscosity computing.
• Reynolds number computing.

• Computing the flow rate in a Pitot tube.

  ( For compressible and incompressible fluids )

• Energy consumption computing.
• Mass flow computing.

www.flowmeterdirectory.com [ Archive ]

The KROHNE company provides a very interesting didactic document about the ultrasonic technology applied to flow measurement.

Its designer tackles here the following :

• The acoustic properties of liquids and gases.
• The ultrasonic Doppler flow meters basic technology.

• The principles of the ultrasonic flow-meters operating by the transit time method.
• The presentation of the different types of ultrasonic flow meters operating by this technology.

Friedrich HOFMANN - www.krohne.com.

In a very detailed didactic document, the Krohne company presents the radar technologies and the different method used to measure a level - continuous wave ( CW ) radar, pulse radar, Time Domain Reflectometry ( TDR ) radar and more.

Its author tackles here the following items :

• An introduction to the radar systems.
• The microwaves main features and their fields of application.
• The different kinds of radar level measurement systems.

• The components used for radar systems.
• The various types of antennas.
• The waves propagation and how they reflect.

• The various methods to evaluate the measuring signal.

Detlef BRUMBI - www.krohne.com

The RFID ( Radio Frequency IDentification ) technology has been used for tens of years in the industry, particularly in the automotive industry. Nevertheless, it is told more and more in public about the RFID technology as a new one.

Why ? How does RFID technology work ? Will the RFID technology be replacing bar codes ? What about the news, what about the trends and what are the stakes ?

See also : Wireless communications and wireless networks

• An introduction to Radio Frequency Identification.
• What is RFID ?.
• Some good introductions and overviews to RFID.

[ Archives ]

• RFID technology overview. ( )

  Steve HEAP

  These slides present quickly what is the RFID technology, and what can be the benefits while using it.

  It shows the tag attributes, the active and passive tag mechanisms, the EPC ( product manufacturer ) network - building block - and the EPC ( product manufacturer ) code.

  At least, it shows how the EPC network will automate the supply chain, in order to get a global vision.

  ---

• RFID white papers.

  [ Archives ]

• RFID news.
• RFID opinion.
• RFID case studies.
• RFID white papers.

www.rfidjournal.com

• Understanding Radio Frequency Identification ( RFID ).

  www.rfidcanada.com

  ---

• Transponder news.

  [ Archives ]

Mitchell COTTRELL publishes a very nice, very well detailed and very well illustrated document about the temperature measurement and control technologies.

Following a short introduction and a short summary about temperature measurements, he presents the glass tubes and bimetallic thermometers, with different probe and sensor technologies using techniques such as thermistor, RTD, thermopiles, thermocouples, semiconductors and non contact devices such as cameras.

Next, Mitchell describes some different control techniques such as ON/OFF control, PWM control, DC pulses outputs, SSR outputs, PID loop control.

At last, the author presents what are analogical and digital transmitters, Ethernet devices and analogical / current transmitters.

All that with charts, curves, technical features, parameters, tables, diagrams, cabling schemes and the fundamental knowledge to get in each measurement technique.

Mitchell S. COTTRELL - University of Missouri

web.mst.edu/

Systems of non contact temperature measurement based on infrared radiations are largely used in industry and building areas.

• A first objective can be controlling the temperature of surfaces, of products, of vessels, of pipes or of pumps for instance.
• A second objective - independently of the activity's area - is to control how well an electrical installation ( cabinets and devices ) is working, and how well cabling junctions remain correct ( no bad connections, no overheating for relays, motors, contactors, isolating switches etc ).
• A third objective is particular to the building area and consists to control the loss of heat through the roofs and the walls, among other things.

The non-contact temperature sensors are divided in two major families : the thermical sensors ( the pyrometers ) and the quantum sensors ( the thermopiles and the bolometers ). These two sensors families operate infrared radiations by using totally different physical principles.

The pyrometers can be very small, they can be portable and mobile, and they can be easily integrated inside the manufacturing process. As for the quantum sensors, they offer a very faster response time than the thermical sensors, that is why such quantum devices are mainly operated in infrared vision systems and in infrared scanners, while such systems need high data acquisition speed.

To know more about infrared temperature measurement, one of the « FLUKE » company's website offers a well interesting introduction to such technologies ( please, see the presentation of this site below ).

Inside its knowledge centre, the « FLUKE » company presents a collection of papers about the basics and on the principles of non contact sensors infrared temperature measurement technologies, and more about the basic knowledge carrying on the infrared radiations.

After having written a short reminder about infrared radiation discovery by William HERSCHEL, this website presents the basic knowledge to acquire in order to use correctly the technologies operated by the infrared ( IR ) measurement systems.

In one section, the editor defines the parameters to take in account in order to operate an accurate infrared temperature measurement, namely the features of the target to be measured ( emissivity ), the nature of these targets ( metal, plastic, glass ), the influence of the ambient conditions, as well as the importance of optics and of their resolution.

To go a little bit further, we can study into what the emissivity consists in, then we can consult the metal emissivity table and the non-metal emissivity table, which will allow us to refine the choice of our measurement devices according to a well defined application.

Inside other pages, we are discovering how do the infrared measurement systems work and what are infrared radiations, in term of matter characteristics and in term of electromagnetic spectrum.

Another section describes how do the ratio pyrometers work ( these pyrometers use simultaneously two different wavelengths selected inside the infrared range ), what are the problems they solve, and what is their usage.

From these pages, you will be able to download an interesting paper in pdf format of about 25 pages, about the « principles of noncontact temperature measurement ».

Fluke - www.flukeprocessinstruments.com/en-us/

See also in this page : National Instruments.

« Scilab is a scientific software package for numerical computations providing a powerful open computing environment for engineering and scientific applications ».

It is the direct rival of Mathlab and Mathematica in computing software, data processing and display, but it is opened and free to use. The Scilab project is developed by INRIA.

SCILAB is composed of hundreds of mathematical function, and provides 2D and 3D graphical functions.

Among its functionalities, we can find mathematics and simulation, 2D and 3D visualization, optimization, statistics, control system design, analysis, signal processing and more.

Plus, you can benefit of many modules developed by the Scilab team and by the community.

On the official site of SCILAB

• Supports, publications, documentation and books.
• Tutorials.
• The SCILAB history.
• SCILAB news.

www.scilab.org

The MUSTIG ( Multidimensional Signals Tools for Interactive and Graphics ) software is a data processing software developed and published freely by the Images and Signal Laboratory ( LIS ) within the ( french ) National Scientific Research Centre ( CNRS ), intended to industrials, engineers, scientifics and researchers.

This system is interactive, entirely graphic, and what does its strength is its high simplicity of usage.

It allows analysing, simulating, displaying and filtering multidimensional signals and matrix.

Input signals come from dedicated input modules, disk files or «copy-paste» operations.

http://mustig.free.fr/en/

FDT is a standard interface to exchange data between measuring devices, communication channels and systems.

The devices manufacturer provides « device DTM » - a file which describes the equipment - which is approximatively a software driver allowing a « FDT application » to exchange data through a communication network.

For instance, the application could be a software used to setup an instrumentation device or a software used to get diagnostic data such as Pactware.

This application must be FDT compliant to recognize the data exchanged.

The field bus manufacturer provides a « communication DTM » which describes the protocol, the data structure and how to exchange the data.

The main advantage to use a standard interface is to let the user free to choose the devices he wants, that is measuring devices, communication interfaces and the system to use. Thus, the user is independent according to the suppliers.

• FDT technical documentation, FDT specifications and FDT standards.

www.fdtgroup.org

PACTWARE is a software used to set up field measuring devices and to get diagnostic data from them.

It is manufacturer independent and FDT technology compliant, thus it can work with various devices and field networks used in instrumentation through the « device DTM » and the « communication DTM » provided by the suppliers.

This software offers to diagnose a remote sensor just by setting its communication port with the number and the parameters of a virtual serial port over Ethernet, which will allow you to connect to the HART interface of the remote instrument when the latter is supplied with an HART modem.

www.pactware.org