The InterTech Group Inc. has exited its decade-long investment in a video surveillance technology firm in exchange for shares in another business. The North Charleston-based company had been a stockholder in Vicon Industries Inc. since 2008, but the investment never quite hit pay dirt. This week, two InterTech affiliates traded their combined 46 percent stake for slightly more than 1 million shares of Cemtrex Inc. that were valued at about $2.96 million as of Tuesday. Robert Johnston, chief strategy officer at InterTech, said the Jenkins Avenue conglomerate plans to give up its seat on Vicon’s board.