Abstract: An improved remote calibration is disclosed for calibrating a gas sensing device. A housing is provided which receives the gas sensor in an open end and a valve/diaphragm assembly in a receiving end. A plurality of openings are formed in the housing adjacent the open end to allow the ambient gas to communicate with the gas sensor. A cap is provided to define a gas chamber between the cap and the rolling diaphragm. The valve is carried by the diaphragm. A gas inlet in the cap admits pressurized gas, driving the diaphragm and the valve toward the open end of the housing to obstruct the ambient gas from the gas sensing device. An orifice is provided in the diaphragm and communicates with a bore in the valve. Calibration gas passes through the orifice and the bore in the valve and floods the region around the gas sensor.