What is Process Tomography?

Tomography involves taking measurements around the periphery of an object (eg process vessel or patient) to determine what is going on inside.

The best known technique is CAT scanning in medicine, however process tomography instrumentation is cheaper, faster and more robust.

Industrial Tomography Systems (ITS) provides electrical tomography instrumentation, software, sensors and technical support. Process tomography is used to measure how and where materials behave during a process. Typically this will involve mixing separation or flow. It can be extended to visualization of reactions. The information it provides can be process end point, visualization of process conditions (such as the distribution of phases in a multiphase process and quality/consistency by measuring multiple points through a volume.

Measurement principles

Process tomography operates by taking data from an array of electrodes in contact with the process media. These are either mounted on a baffle / dip-pipe or around the circumference of the pipe or vessel.

For a standard 16-electrode sensor, 104 voltage measurements are taken every 20 milliseconds using an AC current and 4-electrode measurement technique. The images show the electrical field lines spreading out into the vessel from a single measurement. They are affected by the presence of conducting (red) and non-conducting (blue) regions.

Measurement Principles

From measurements to data

A reconstruction algorithm converts the peripheral measurements to vessel conditions. This is an "ill-posed" problem and there are many techniques of addressing it. ITS offers two techniques, one for on-line operation, and another (more accurate) which requires post-processing.

From data to process information

Typically, tomography data is presented as a colour coded image: red for conducting to blue for non-conducting. However each image (tomogram) is composed of an array of derived conductivity measurements.

Data can be analysed statistically (e.g. variance to determine extent of homogeneity or average to give representative data through a volume) and dynamically (e.g. to determine rate of change of a feature).

The process information Process Tomography provides can be the flow regime or the extent to which materials are mixed or have been separated. In the case of flow regimes typically tomograms are presented as cross sectional images where colors represent high and low concentrations of different phases. This can be extended by integrating a series of tomograms over time or space to provide a 3-d rendering of a flow feature (eg slug). In the case of mixing or separation tomogram of 200 or 300 data points can be analysed statically with a variance being used to show degree of mixing/homogeneity.