SL-186-type spark sparks on-line detection of metal surface insulation coating is too thin, leakage iron and leakage micro-hole at the resistance value and the air gap density is very small, when there is high pressure through the formation of air gap breakdown spark discharge, To the alarm circuit to produce a pulse signal, the alarm sound and light alarm, according to this principle to achieve the purpose of anti-corrosion coating.SL-186-type EDM line detector is based on Canadian standards for online detection of spark, combined with the actual situation in the country Developed, it is used to detect the metal pipe in the production process in the quality of its surface anti-corrosion insulation layer of a special testing equipment.