Frequently Asked Questions

Process Tomography

What is ERT?

ERT stands for electrical resistance tomography. This measurement technique measures the distribution of electrical resistance (or conductivity) in a cross-sectional plane of a pipe or vessel. Measurements can be taken rapidly allowing real time viewing of data. The information is shown on a tomogram where the values are scaled from low conductivity (blue) to high conductivity (red). Conductivity measurements are useful as the different phases of a multi-phase process have very different values. This makes ERT a powerful technique for observing processes such as mixing, flow and separation. It is also useful for reactions where the reactants or products have different conductivities such as crystallisation.

What is ECT?

ECT stands for Electrical Capacitance Tomography. ECT is used where the bulk medium does not conduct electricity. In ECT the tomogram has red for high dielectric (eg oil) blue for low dielectric (eg air).

What is EIT?

ERT and EIT are often confused and used interchangeably. EIT stands for Electrical Impedance Tomography and these measure both resistive and capacitive components of materials. This allows discrimination of conducting materials to be differentiated based on their properties. For example organic material in suspension has a significant capacitive component and can be differentiated from ionic nutrients.

It should be noted that EIT still requires a conductive medium.

Ultrasound

What is Acoustics?

Acoustics is the general science of sound and its interaction with matter. Sound is a microscopic oscillation of the molecules of a material to create a propagating mechanical wave.

What is Ultrasound?

Ultrasound is high frequency sound (above the audible range) which is taken to be greater 20kHz

What is USS?

USS stands for Ultrasound Spectroscopy. USS measures the change in a ultrasound signal per unit distance as it propagates through a material. The interaction of the ultrasound and the material causes a energy loss in the wave which is characteristic of the material.

What can USS be used for?

USS can be used to characterise the density and viscosity of the material. With additional analysis it can determine solids loading and particle size distribution.

What type of materials can be measured?

USS is currently only used on liquid and colloidal materials. Hence can be used on pure liquids, mixtures of liquids, emulsions, slurries and soft solids.

Measurement Systems

Should I use ERT/ECT in my process?

ERT should be used where the continuous material is electrically conducting (eg water acids bases and ionic solutions).

ECT should be used where the continuous material does not conduct electricity eg air/oil. If the process moves to from conducting to no-conducting or visa versa then a combined ECT/ERT system is recommended. Example of this might be polymerization, drying or multiphase flow.

What is a tomogram?

A tomogram is a 2-dimensional representation of a cross-section through a pipe or vessel. It is derived from the Greek “tomos” – slice and “graph” – picture.

In electrical tomography, tomograms are shown using a colour spectrum for values of conductivity (ERT), capacitance (ECT) where red is high conductivity / dielectric and blue is low.

Tomograms can also be used to show concentrations (again with red = high and blue = low).

What does a tomography system consist of?

A tomography system consists of a sensor (in contact with the process), a data acquisition system (such as p2000, m3000 or z8000) and software to reconstruct the acquired data.

Electrical Tomography System
Electrical Resistance Tomography System (Laptop not included)

What information do the measurements provide?

The key to applying tomography is to relate the instrument’s measurements to process conditions.

Electrical process tomography measurements are taken from a sensor using an array of electrodes mounted on a substrate (the sensor). The measurements are initially presented as raw voltages.

These raw voltages can be used in their own right, either for bulk trend data, exporting for research into different tomography algorithms, direct input into MVSP (multivariate statistical processing) packages for analysis alongside other process measurements.

Typically the voltage measurements are converted into conductivity data for ERT and capacitance date fore ECT. [In the case of EIT, data is also available on phase angle and reactance which is of more specialised interest.] Both ERT and ECT data are usually converted into concentration data and displayed as tomograms.

Mixing

starting point of process
end point of process
mixing time
level of homogeneity
Determine mixing efficiency

Flow

flow patterns/regimes visualisation, real time, online, high speed
cross correlation , velocity profiles
phase distribution / volume fraction
visualisation of solids transportation : speed, settlement, understanding of potential corrosion effects

Separation

start and end point
interface detection
quality of separation - validation of equipment such as separator for example
volume fraction
phase inversion

Reaction Engineering

end and start point
visualisation of additions
crystallisation - information from nucleation stage, start of crystals formation, crystals homogeneity and dispersion = quality status

Will it work with my process?

Scale:

Sensors can be made with diameters from 5mm up to 2m and lengths from 5cm to 4m.

Materials:

Electrical tomography systems can work with a very wide range of materials ranging from air and non-conducting fluids (using capacitance techniques) to water and polar organic solvents (using resistance techniques). The most common materials which present significant challenges to the current technology are very highly conducting systems (such as molten steel). Resistance tomography systems for use in food and pharmaceutical environments are available and intrinsically safe systems are also available.

Operating Conditions:

Tomography systems can be used in a wider range of temperatures, atmospheres and processes. Resistance tomography can be used in metal walled pipes and vessels in the presence of metal internals (such as down pipes and impeller shafts). However a substantial quantity of metal internals (such as metallic packaging) or highly conducting systems (such as concentrated acids and molten metals) can present a challenge.

Is the system an AC or charge / discharge principal?

Our electrical tomography systems are an AC princial

Sensors

What sensor is right for my application?

In considering the best sensor for your application the first thing to think about is whether to use ERT or ECT. You would use ERT for processes where the bulk medium is a conductor, ECT is the bulk material not a conductor and dual modality where the process moves between the two.

ERT sensors consist of an array of electrodes supported by a substrate. The electrodes need to be in contact with the process fluid and can be made out of a wide range of materials. (stainless steel etc). The substrate is typically an engineering plastic eg PVDF although other materials such as ceramics and metals can also be used. Providing they are insulated from the electrode.

Can sensors be removed from the process?

Sensors can easily be fitted on a temporary or permanent basis.

Do the electrodes get dirty?

Electrodes can get dirty. There is an electrode check function built into ITS’s software which allow users to determine if there has been any significant signal deterioration.

How often do sensors need to be replaced/cleaned?

Sensors are manufactured from metal (electrodes) and a supporting substrate and are typically as robust as the pipes / process vessels they are fitted into.

Is the technology intrusive?

ECT and ERT sensors can be designed so that there are not intrusive to process conditions. Where surface affects are important (such as chromatography) or if there are significant constraints for retrofitting sensors into an established vessel this can be challenging.

Is the technology invasive?

ECT sensors can be mounted on the outside of pipes and process vessels so do not intrude in the flow of materials. To do this, the pipe / process vessel needs to be made of Perspex, glass, plastic, ceramic or other non-conducting material. For metal vessels, ECT sensors need to be in contact with the process (similar to ERT described below).

ERT sensors need to make contact with the process and so will intrude into the process vessel. ITS have had many years experience in engineering sensors so that any affect is minimised and that the integrity of seals etc are maintained.

Resolution

What is the temporal resolution?

The most rapid tomography system supplied by ITS is the z8000 which takes a complete set of measurements from 2 x 16-electrode planes in less than 1 millisecond. These rapid frame rates are important for fast processes or getting a statistically significant number of measurements for flow velocity analysis. More typically the m3000 and p2000 have frame rates of around 30 frames per plane per second.

What is the spatial resolution?

Typical on-line resolution is approx 5% of the diameter of a circular sensor around the edge of a pipe or vessel.

How can I improve the resolution?

Resolution can be improved by using off-line reconstruction techniques. Examples of such techniques are SCG (sensitivity conjugate gradient) or parametric (model-based) techniques. On a practical level, resolution can be also be improved by taking a good reference (stable measurements at values close to those of the process under observation). It should be noted that on and off line references can be used.

What is LBP?

LBP stands for “linear back projection” which is a single step reconstruction technique. It is computationally simpler than SCG and other iterative techniques and can be operated in real time when tomography data is acquired. LBP tends to smooth boundaries and hence is good where there is a concentration gradient (such as liquid-liquid mixing).

What is SCG?

SCG stands for “sensitivity conjugate gradient” which is an iterative reconstruction technique. It uses better field modelling (for example taking account of electrode size and shape) and repeatedly runs until an optimum value is reached. It is particularly strong for resolving sharp boundaries (such as gas / liquid interfaces).

What is parametric reconstruction?

Parametric reconstruction is based on rules (parameters) that are known about a process. The process is modelled using these rules and raw tomography data is processed to provide the best fit of the data to possible process conditions.

Find out more

How can I see a demonstration?

Our application engineers are able to carry live demonstrations of our p2000 ERT, m3000c ECT and m3000 Dual Modality ERT/ECT instruments. The lab is equipped with various circular and linear sensors, a lab-scale bubble column as well as an integrated tomography test rig. An ERT/ECT Dual Modality sensor is also available for 3-phase flow air-oil-water demonstrations. Our application engineers are also available for demonstrations at your site. Please contact us to arrange an appointment.

Is there equipment available for rental/trials?

ITS equipment is available for rental on a short term basis to best suit your research needs, this includes instruments and sensors. ITS also offers trials and feasibility studies, these can last from a few days to a few months using our on-site laboratory or on-site trials can also be run.

How do I get in contact?

The simplest way to get in contact is via our website using our online contact form

Alternatively, our full contact details are as follows:

Do you have representatives where I am?

ITS has representatives around the world, full details can be found here:

http://www.itoms.com/distributors

If there is no representative in your region, then please direct your enquiry to Industrial Tomography Systems

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WHAT IS PROCESS TOMOGRAPHY?