International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Caterpillar has for many years used telemetry as a key component in the data acquisition and analysis systems used to test and develop heavy equipment. The testing of construction and mining equipment at Caterpillar presents several unique challenges, such as the operating environment of the test machine, the large number of models in the product line, the need to change test machines on a daily basis, and the need to test machines at job sites throughout North America. These challenges have resulted in the development of telemetry, data acquisition and data analysis systems that have been highly customized to meet all of our requirements for construction equipment testing. This paper describes the past history of telemetry use at Caterpillar, from early FM/FM systems to our current PC/Unix based PCM/FM system, the criteria used to develop these systems, and how our current telemetry system is being used today to help develop and test product.