UPDATE 1-Cognex Q2 profit trails Street; sees weak Q3

(Recasts; adds details, share movement)

July 28 (Reuters) - Cognex Corp (CGNX.O), a maker of machine vision sensors, reported lower-than-expected second-quarter earnings, and forecast weak third-quarter results as it expects the U.S. economic slowdown to spread to other parts of the world in the current quarter, sending its shares down 27 percent.

The company, whose machine vision products are used to detect defects, monitor production lines, guide assembly robots, and track, sort and identify parts, earned $8.8 million, or 21 cents a share from continuing operations, in the latest second quarter.

Cognex earned $3.9 million, or 9 cents a share, a year earlier. Revenue for the latest second quarter rose to $67.1 million from $54.7 million.

Analysts expected earnings of 22 cents a share, excluding items, on revenue of $66.8 million, according to Reuters Estimates.

Cognex expects earnings for the third quarter to be 14 cents to 18 cents a share on revenue of $62 million to $65 million.

Analysts were expecting the company to earn 23 cents a share on revenue of $66.2 million.

Cognex shares fell to $16.00 in trading after the bell. Shares of the Natick, Massachusetts-based company closed down $1.88 at $21.94 Monday on Nasdaq. (Reporting by Anurag Kotoky in Bangalore; Editing by Pratish Narayanan)