Electrical Resistance Tomography - ERT (back)
The concept of ERT is that image conductivity distribution within vessels and pipelines is determined as a measurement of opposition to the passage of a steady current and is only applicable therefore to electrically conducting systems (for example, aqueous solutions, which have to be in constant contact with the electrodes). ERT has a relatively high temporal resolution compared to other tomographic modalities, therefore “chemical engineers used ERT from early on to measure flow patterns and material distribution in stirred vessels.” .
ERT measures amplitudes of voltage and current to produce images of resistivity (or impedivity) for variation with time or sine wave frequency. To determine resistivity/impedivity a current is introduced and resulting voltages measured (both known factors). The number of measurements made (determined by a Data Acquisition System (DAS)) determines the spatial resolution. As a rule of thumb, the higher the number of measurements the greater the spatial resolution will be (spatial resolution is proportional to sq. root of N, with N being the number of independent measurements).
The unknown factor will be the resistivity/impedivity as determined by the distribution of material contained within a vessel or pipe. Image reconstruction techniques are then utilised to produce a series of tomographic images, with reconstruction speeds a function of the total number of electrodes, n. EIT has been “used for measurement and modelling of multiphase flows in chemical reactors.
Early work shows it has promise in multiphase flow characterisation and velocity measurement of fast-flowing systems (both pipeline and tanks)” . Industrial Tomography Systems Ltd. provides the P2000/P2+ ERT system to a wide range of research and industry customers (www.itoms.com) which having being validated against criteria set out in the GAMP5® industry guide (21 CFR Part 11 technical compliance), is suitable for use in a wide range of applications.