Flir Systems Inc. in Portland, Ore., has signed an agreement to acquire Inframetrics Inc., a privately held infrared imaging company in Billerica, Mass. The deal will involve an exchange of stock. The planned acquisition could strengthen Flir's sales of commercial IR imaging systems, while enabling the company to maintain its work on large government contracts, according to a company statement. Flir Systems posted sales of $91.8 million in 1997 and $104 million for the first nine months of 1998. Inframetrics had sales of $53.5 million in 1997.