frequency and temperature so that the beginning of operation of the communications system may have as alternatives the startup with parameters at room temperature last parameters used in measurement or automatic adjustment according to a table of parameters stored in previous measurement or calibration runs the control and processing block 90 shown in fig1 is composed of the plc receiving digital block 340 the plc transmitting digital block 330 the measurement digital block 320 the storage digital block 350 the uart universal asynchronous transceiver transceiver digital block 310 and the central processing digital block 300 the analog signal coming from the receiving module 60 is shown at the input of the plc receiving digital block which is connected to the central processing digital block to process the command messages coming from the surface module 11 the central processing digital block 300 connects to the measurement digital block 320 to capture the physical parameters of the measurement block 66 it is connected to the uart transceiver digital block 310 to transmit commands and receive responses from the tractor 17 by means of the rs 485 module 125 it is also connected to a plc transmitting digital block to communicate the results to the surface module the plc receiving digital block from fig1 is composed of an analogue to digital converter adc 400 a digital filter block 410 a demodulating block 420 a data link and message detection block 430 the adc 400 receives the analog signal coming from the plc receiving module 60 the adc 400 converts such analog signal to a digital representation which.