87 and 118 according to rockwell r tensile strength yield of between 36 and 52 an electrical resistivity of 1 u00d7 10 16 ohms a dielectric constant of 2 9 a dielectric strength of between 15 and 35 kv mm and an arc resistance of 60 seconds materials having properties similar to abs and seaboard will be suitable for use as mounting panels enclosures and supports according to the invention for example seaboard has physical properties of density at 0 960 g cm 3 according to astm d 1505 hardness of 69 shore d according to d 2240 environmental stress crack of 25 hrs according to d 1693 and f50 resistance of greater than 55 hrs according to d2561 mechanical properties include tensile strength yield of 4 500 psi according to d 638 flexural modulus of 260 000 psi according to d 790 and flexural strength of 5 070 psi according to d 790 thermal properties include f50 low temperature brittleness of u2212 76 degrees c according to d 746 heat deflection temperature 66 psi of 82 degrees c according to d 648 and a vicat softening point of 130 degrees c according to d 1525 as shown in fig3 the entire assembly of fig2 may be enclosed within a housing 80 portions of housing 80 are also shown in fig2 in dashed line advantageously housing provides a rigid support structure for the sensor reflector and a second lower ionization nozzle fig4 shows an alternated embodiment of housing or frame 80 with one side panel removed the frame includes a mounting panel 80 a a partial enclosure 80 b and a support 80 c for safety or to meet regulatory requirements certain cleaning stations will use rigid pipe the electrical leads can.