A Model 728 Dilution Probe Controller is used in conjunction with a Dilution Probe to create a diluted sample. The dilution ratio an be increased or decreased by varying the dilution motive pressure with the dilution motive air regulator. The model 728 has a precision regulator with a double diaphragm to provide a stable dilution motive pressure to the dilution eductor located in the dilution probe for a stable dilution ratio. A gauge is supplied that indicates the pressure of dilution motive air. In similar fashion the instrument air for the fast-loop and calibration gas each have a pressure regulator and a gauge. Solenoid valves are installed to cut-off the fast- loop and dilution motive air in the event of a low temperature alarm or if the filter needs to be changed.