Charlotte will be one of the first three cities in the nation to test a new TV ratings system, the marketing-measurement firm Nielsen announced Friday.

This winter, installation of a new device called the Nielsen Code Reader will begin in Charlotte, Dallas and St. Louis. Code readers will help Nielsen quadruple the number of households sampled to compile local TV ratings, a move welcomed by stations and ad agencies eager for more reliable ratings information.

Charlotte is the nation’s 25th largest television market and incorporates 2.8 million people in 1.1 million households in 22 counties from the Virginia line to Chester, S.C.

Now, Nielsen measures TV-watching habits person-by-person in about 600 sample households in the region with so-called Local People Meters. These are used to project overall demographic viewer data used by the advertising industry in determining where to buy commercial time.

In major markets like Charlotte, this information is transmitted to Nielsen through monitoring devices attached to TVs. Code readers and additional set top boxes are to be placed in about 1,800 additional households in the region.

Code reader boxes sense inaudible watermarks that identify which station is being watched and when. After accumulating information, the box dials into a Nielsen computer and downloads its ratings data.

While code readers would not provide demographic information on who was sitting in front of the screen like the people meters, it would provide household numbers of viewing habits to give the ratings company a bigger sample and better information for its ratings service.

Broadcasters have complained that Nielsen’s sample is too small to give highly-accurate demographic information, particularly in measuring limited subsets of viewers like people aged 18-24, and Nielsen has not yet made clear to stations how the new devices will improve those numbers.

“We are thrilled they are doing this and we are one of the first markets,” said Jim White, station manager for Fox Charlotte (WCCB, Channel 18). “We expect it will make the survey more robust and give a more stable reading of the market.”

After installation of the code readers, local stations will examine the data for several months to evaluate its effectiveness and to comment to Nielsen. “We’ve always wanted a larger sample size and but we want to make sure it’s done thoughtfully and is representative of the market,” said Robert Wendt, research director for sister stations WSOC (Channel 9) and WAXN (Channel 64).