Westinghouse Electric Corp., citing improved results from its industry products unit, said yesterday its net income in the second quarter rose 7 1/2 percent from the same quarter of 1980.

Earnings for the quarter amounted to $111.8 million ($1.31 a share) on sales of $2.4 billion. In 1980, second quarter earnings were $104 million ($1.22) on sales of $2.1 billion, the company said.

In the first six months, net income totaled $230 million ($2.69) on sales of $4.6 billion, compared with income of $205 million ($2.40) on sales of $4.2 billion for the same period last year.

International Business Machines Corp., citing increased sales of data processing equipment, reported yesterday that second-quarter earnings rose to $804 million, up 5.3 percent from the same period a year ago.

Earnings for the three months ending June 30 came to $1.37 a share on revenues of $6.9 billion, compared with earnings of $764 million ($1.31) on revenues of $6.2 billion in the same 1980 period.

For the first six months of the year, IBM said it earned $1.5 billion ($2.62) on revenues of $13.4 billion, compared with profits of $1.4 billion ($2.48) on revenues of $11.9 billion in the same period a year ago.

Control Data Corp. said improved operating margins and a lower tax rate helped it post a 10 percent gain in second-quarter earnings, compared with the same quarter last year.

Control Data, with interests in computer services and systems and financial services, said its profit in the second quarter ended June 30 was $43.3 million ($2.27), compared with $39 million ($2.25) in the same period last year. Revenue in the quarter rose to $1.01 billion, compared with $934.2 million in the second quarter of 1980.

During the first six months of 1981, Control Data's earnings rose to $83.6 million ($4.39) on revenues of $1.98 billion, compared with $74.2 million ($4.28) on revenues of $1.81 billion in the first half of 1980.

NCR Corp. whose operations outside the United States account for more than half of its business, yesterday blamed the reduced dollar value of foreign currencies for an 8 percent decline in earnings and "limited revenue gains" in the second quarter.

The company, which manufactures and markets business information processing systems, said its worldwide revenues rose 8 percent in the second quarter to $853.8 million, compared with $788.2 million a year earlier. That brought six-month revenues to $1.59 billion, up 10 percent from $1.45 billion in the same period last year. Net income for the quarter was $52.3 million ($1.94 a share), down 8 percent from 1980 second-quarter earnings of $56.7 million ($2.12 a share), the company said.

For the six-month period ending June 30, net income declined 3 percent to $79.8 million ($2.96), compared with $82.2 million ($3.08) a year earlier.