Percostation is a system for continuous monitoring of dielectric constant, electrical conductivity and temperature of materials. It was developed in cooperation with the Finnish company Roadscanners OY for monitoring the critical bearing capacity of roads. The system consists of sensors installed in a problematic road section, at different depths in the road structure and subgrade soil; a data collecting unit installed roadside; and data transfer and analysing systems, which transfer the measurement results via gsm network or telephone cable to the pc screen of the road authority, for use in load restriction planning.
Technically, the Percostation deviates from the percometer in so far, as it enables measurements of dielectric constant, electrical conductivity, and temperature from eight channels. The probes are connected to Percometer via probe multiplexer unit. The measurement interval can be set to a minimum of 60 seconds (four channels). The measurement results are stored in the memory of the data-collection unit, where they can be read through a modem connection. The memory of the collection unit is sufficient enough to store 1300 measurements at once. The settings of the data-collection unit can also be modified through the modem connection. The Percostation operates on 12 V of electricity. A sufficient energy supply can be provided by a 260 Ah accu, which is recharged by a solar panel. Without recharging, 260 Ah provides sufficient energy to power the Percostation for approximately 1,5 months.
In operation, Percostation software connects to the measurement station(s), reads the last measurements from its memory and transfers them to a mainframe database where they are stored in files for each individual station. Each file also stores information on the structure, materials, and calculated critical tensions, dielectric values, and electrical conductivity values for the road structure being monitored. Based on this information, the Percostation software can warn the operator when conditions in different layers of the road structure and subgrade are approaching a critical state. The operator can use this information when deciding to impose or lift load restrictions, and for determining the maximum allowed axle weights and/or number of axles.
Up to now Percostations have been used mainly as a Tool for Monitoring Moisture and Bearing Capacity in Road Construction, and Optimising the Use of Load Restrictions but they can be used wherever there is a need to monitor materials electrical properties. Currently Percostations have been installed in Finland, Sweden and Scotland.
Sample of percostation data from road defrozing at Kittila, North Finland, 23.03.-05.07.2006