Pneumatic system for a gas sensor

A pneumatic system for controlling admission of a gas sample to a gas sensor comprising:

• a. a series loop cicuit including a gas sensor, a flow meter, a pump, a first manifold valve operably connected in the series circuit downstream from said pump to regulate gas flow between it and the sensor, a second manifold valve operably connected downstream from the sensor between it and the pump to regulate gas flow to said flow meter,
• b. a vented gas sample input chamber including an overflow gas input orifice connected to receive gas from a point in said series loop circuit between said pump and a first flow restricting needle valve in said first manifold valve, an outlet orifice connected to deliver gas to the first manifold valve, and a sample gas inlet orifice disposed between said overflow input orifice and said outlet orifice and operable to deliver a gas sample into said input chamber, and
• c. a bleeder line operably connected between the first and second manifold valves to bypass some gas received from the gas sample input chamber around said sensor, whereby said pump is effective when operated in said series loop circuit to force gas through said manifold valves, flow meter and sensor and to cause gas to flow continuously through the bleeder line and said manifold valves both during intervals when a sample gas is being introduced to the series loop and during intervals when sample gas is not being fed into the loop.