Performance assessment of EIT measurement systems

EIT acquisition systems, when regarded as measuring instruments, can be characterized by their inherent characteristics: reproducibility, repeatability and discrimination. The ultimate limit to all three is noise, whether long-term or short-term noise. In addition, for some applications accuracy can also play a role, although accuracy is not an inherent characteristic and requires a known test object to be defined. Because EIT systems are multichannel instruments and the information of all channels is being combined to produce an image, a procedure to standardize the performance assessment must be set up in order to allow for meaningful comparison of different systems or different settings in the same system. We propose the use of three parameters defined long ago but scarcely used among EIT systems designers: SER (Systematic Error Ratio), NER (Noise Error Ratio) and RER (Reciprocity Error Ratio). We applied these definitions to our latest EIT instruments, TIE5-sys, in a wide frequency range and with different settings in configurable acquisition parameters and provide the interpretation of the results obtained in terms of reproducibility, repeatability and discrimination. We also comment on the tradeoffs that show up when using the usual definition for these figures.