Electro Rent Corp. has been acquired by private investment firm Platinum Equity in a deal valued at more than $323 million. Shareholders in the Van Nuys company, which rents electrical testing equipment, will receive $13.12 a share, or more than 24 percent over the closing price on Friday. The transaction is expected to close in the next three to four months. The news of the acquisition comes less than three weeks after Daniel Greenberg announced he was retiring as chief executive in early July after 35 years. Greenberg and a member of his family own 29 percent of the outstanding shares and are in support of the sale. Steven Markheim, president and chief operating officer, will become the new chief executive officer after Greenberg steps down. The company looks forward to partnering with Platinum on meeting the needs of global customers and manufacturing partners, Markheim said. “The transaction presents an outstanding opportunity for all of our stakeholders, as we should greatly benefit from additional resources and experience to further enhance our already high inventory, service and support standards,” Markheim said in a prepared statement. Platinum Equity, in Beverly Hills, has more than $6 billion in assets and has a portfolio of companies in the hospitality, manufacturing, entertainment, information technology and telecom industries. Its founder, Tom Gores, recently appeared at No. 21 on the Los Angeles Business Journal’s list of Wealthiest Angelenos with $3.43 billion in estimated net worth. Shares closed up $2.55, or more than 24 percent, to $13.10 on the Nasdaq.