Johnson Controls offers a complete line of Carbon Dioxide (CO2) transmitters for measuring and transmitting CO2 levels, ranging from 0 to 2,000 parts per million (ppm), within Heating, Ventilating, and Air Conditioning (HVAC) applications. These compact, duct mounted devices offer a choice of 0 to 10 V or 0 to 20 mA output signals and feature an optional relay output with or without a digital display. Johnson Controls® CO2 transmitters are easy to install and to operate. The silicon-based CARBOCAP® sensor delivers high accuracy and long-term measurement stability (±100 ppm) over a five-year period without calibration. The diffusion-aspirated, single-beam, dual-wavelength sensor structure is remarkably simple. It consists of an infrared (IR) source, a sample cell, an IR detector, and a tunable interference filter that enables measurements at two wavelengths. Reference measurements made using a tunable interference filter eliminate the typical weakness of dual-beam sensors and permits shifting the optical pass band electronically. This innovative design provides precise reference readings that eliminate the typically broad deviation expected from a traditional CO2 sensor.