The ST420 from Electro-Sensors Inc., Minnetonka, MN, is a loop-powered, SS, analog shaft tachometer that reliably detects magnetic pulses from a rotating shaft-mounted pulser disc or wrap. The device converts the pulses to a 4–20 mA analog signal directly proportional to the pulse frequency. The 18 mm dia. device has been tested to UL913 and is rated intrinsically safe for Class 1, Groups C and D and Class II, Groups E, F, and G environments when used with an approved IS barrier. Applications include shaft speed monitoring for grain and bulk materials handling, mining, power generation and water utilities, packaging, food processing, and textile production.