Carbon monoxide metering and alarm system - using thermistors to measure the temperature rise on oxidising the monoxide to dioxide

摘要

In a system for controlling the CO content of air or a measuring gas, comprising a pump for drawing in the gas to be tested via a filter and a cooler and delivering it to a thermostat for bringing it to a pre-determined temperature held within narrow limits and subsequently to a measuring chamber containing a catalyst for oxidising any CO present in the gas to CO2 and with a temperature measuring device for the determination and indication of the temperature rise in the measuring chamber caused by the oxidn., the improvement whereby (a) two thermistors are provided in a measuring bridge unit for determining these temperatures, one thermistore being installed before and the other in or directly after the catalyser (b) a measuring amplifier, an indicator and a control device are connected in series to the output of the measuring bridge. The use of thermistors with a bridge circuit gives the required sensitivity for small temperature differences as well as stable operation. The thermistors have the advantage of operating on a.c. voltage so that they can be used directly with standard a.c. amplifiers.