As is well known, the corrosion of embedded steel reinforced depends strongly of the concrete resistivity, which is related directly with the water contained into its porous network. Environment plays an important role on resistivity, due to have a direct correspondence with the relative humidity and temperature. In these terms, ingress or output of water is favored or hampered by the environmental parameters, as well as its fluctuations. This work presents a proposal of instrumented system to generate a map of electrical resistivity at concrete samples by using superficial and embedded electrodes. Mathematical analysis of equivalent circuit revealed the importance of the impedance of electrodes utilized, to simplify measures. Concrete samples were exposed to different relative humidity focused to try to obtain the relation between relative humidity and resistivity. An array of two electrodes distributed in a matrix was manufactured to apply a signal of direct current at first electrode and measure the resultant current at second electrode. The system applies a programmed sequence of switch to turn on and turn off to realize measurements over established zone and, in this form, allows identify zones with potentials gradients. Also, do easy the monitoring of concrete resistivity evolution in function of time and humidity conditions.