A non-invasive probe was used to measure and record potentials and currents at the terminal points. Such a probe (shown in Figure 2) was designed to minimize all the main error components that may influence the measurements and makes it possible to perform repeatable and reliable measures. A 2 mm diameter silver/silver-chloride electrode was used as biomedical sensor -. A pressure compensation system was studied to allow the operator to push the probe on the measurement point to a well defined and constant pressure. The presence of the pressure sensor allows the operator to work in a linear range of pressures in order to get the contact surface variation in a linear range too and to make the measurements almost insensitive to pressure changes for a wide span of values. Usually a span of 50-300g can be compensated. The status of the probe and of the pressure sensor can be checked anyway by the application software. It is also possible to modify the pressure compensation system parameters. Before performing any current acquisition the application software checks any possible residual pressure on the sensor.
Figure 2: The used probe.