The SDT transmitter is designed for stand alone monitoring of hazardous gases and vapors. The gas level is indicated on the 4-digit, red LED display and transmitted with the linear 4-20 mA output for data loggers or recorders. Semiconductor sensors measure toxic gases in the low ppm ranges. They feature long sensor life and fast response time. Sensors are not affected by temperature and humidity changes — they can be used both indoors and outdoors. Catalytic sensors monitor flammable gases in the %LEL, or volume percent range. These sensors feature fast response, high accuracy, long life, and a high resistance to poisoning.