The Rense DM-509 series of portable, battery operated, thermo-hygrometers are designed for portability and easy use. Units ensure long term accuracy and reliability, and feature a large easy-to-read, high contrast LCD display, with low battery indication. The DM509 will provide up to 200 hours of continuous operation on a 9V alkaline battery, and includes automatic power-off function and options such as dust filters and a leather carrying case. The DM-509 offers several different probe/display options to suit almost any application, and three models are available. Versions include one with a fixed sensor head and an M-type humidity sensor element for 10-95% RH; a high accuracy version with a replaceable sensor for accuracy with ±2% RH, without recalibration; and a rugged industrial version equipped with T-sensor elements, available in various probe configurations. Probe designs include a stainless steel sword probe for measurement between layers of paper and a high temperature stainless steel probe for operation up to 150ºC.