The Altronic DTHO-1201/3201 series tachometers represent the third generation of Altronic digital speed sensing and indication devices. Designed for universal use, these high-quality, microprocessor-based devices can be powered from a C.D. ignition system or a magnetic pickup and are offered n two durable Lexan enclosures for use on natural gas engines and other critical rotating equipment. Overspeed trip and hour meter functions are resident in both devices. Setup of these highly accurate tachometers is accomplished through the front sealed-membrane keypad. They can be configured for use in monitoring engine RPM or higher speeds of interest such as turbocharger RPM. An advanced filtering algorithm assures a stable speed readout even during periods of speed fluctuation. The DTHO-1201/3201 devices are certified for use in Class I, Division 1 and 2, Groups C and D hazardous areas by Canadian Standards Association (CSA).