Penril Corp., a high-technology company with headquarters in Rockville, said yesterday it has acquired Network Products Inc., which manufactures data communication products for computer networking.

Penril paid $1.9 million in cash for Network Products and will pay additional sums pegged to its sales annually for the next three years for the company, the 15th electronics firm Penril has bought in the last 12 years. The companies did not disclose the estimated amount of the additional payments.

Robert H. Nichols, the president of Network Products, which is based in Research Triangle Park, N.C., said that his company will be able to provide data multiplexers, devices that allow many users to share one communication line. The new product is expected to complement another Penril product, modems. Modems are devices that enable computers to communicate over phone lines.

Network Products also produces a modular data communications system that allows users to build data communications products for their own networks. The company, which is privately held, currently has projected annual sales of $3 million, according to Penril, and has 45 employes.

Network Products becomes a part of the Penril Data Communications Division, based in Gaithersburg, Md. Nichols will continue to manage Network Products, according to Kenneth M. Miller, Penril's president and chief executive officer.

Over the nine months ended April 30, Penril earned $56.9 million, with a profit of $1.9 million (87 cents a share). In April, Penril purchased Alltest Inc. of Palatine, Ill.