NEW YORK (AP) — Emerson is going public with a $7.6 billion bid for National Instruments, saying the company has avoided serious buyout negotiations since early last year.

Emerson bumped up its cash offer for the maker of scientific measuring equipment and software to $53 per share in November, up from a per-share offer of $48 that it had made back in May.

Shares of National Instruments jumped 15% Tuesday before the market opened.

Emerson said that it's tried numerous times to initiate private discussions with National Instruments Corp. since May. The St. Louis company said that when it provided its increased bid in November, National Instruments said it had formed a group to look at the proposal and evaluate options. But Emerson said since that time National Instruments has resisted engaging.

Emerson Electric Co., which makes process controls systems, valves and analytical instruments, noted that it did meet with National Instruments earlier this month, but that National Instruments shared "limited, high-level" information about its business and was unwilling to provide more detailed information. Emerson said it was told by National Instruments that would be the extent of its engagement.

Last week National Instruments said that it was conducting a strategic review and put in place a "poison pill," a financial maneuver that companies use to ward off unwelcome suitors.

The elements of each poison pill vary, but they're all designed to give corporate boards an option to flood the market with so much newly created stock that a takeover becomes prohibitively expensive.

"Although Emerson would have preferred to reach an agreement privately, given National Instruments' announcement that it is undertaking a strategic review, and after refusing to work with us toward a premium cash transaction over the past eight months, we are making our interest public for the benefit of all National Instruments shareholders," Emerson President and CEO Lal Karsanbhai said in a prepared statement.

National Instruments, which is based in Austin, Texas, did not immediately respond to a request seeking comment Tuesday.

Emerson is interested in National Instruments' differentiated electronic test and measurement offerings and technology stack of intelligent devices, controls and software.

Emerson has purchased 2.3 million shares of National Instruments and says that it has approval to increase its stake.

Shares of Emerson fell 2% in premarket trading Tuesday.