Gas Sensor Temperature Modulation Equipment Based On DDS Technology

Aim to the semi-conductor gas sensor's shortcoming of poor selectivity, research the temperature modulation technology in system. To realize the temperature modulation of gas sensors, "gas sensor temperature modulation equipment based on DDS technology" is designed, which is able to modulate gas sensors with 4 normal kinds of modulation waveforms and arbitrary waveforms defined by user, while sampling the sensors' response signal in real time.At first, the paper analyses pieces of literatures and lists out the function requirements and design parameters of the equipment. Secondly, introduces the theory which the equipment uses to generate modulation waveforms, DDS technology, analyses its frequency spectrum and the influence of the DDS channel parameters to its noise. Later, emphatically describes the hardware design, includes "phase counter and ROM" design, "DAC and offset circuit" design, "low pass filter group" design and so on. During introduction, the paper not only describes the schematic circuit design, but also presents pictures which show the effect of the circuits.Testing gas sensor is a long time work, during the test, millions of data will be sampled. So the paper regards the equipment hardware as a part of a virtual instrument, develops data acquisition software by LabVIEW. The software communicates with the hardware through a RS-232 series port, controls the hardware to modulate gas sensors, receives data sampled by hardware, and displays data on screen while saving data as Excel files. Also, it can download waveforms defined by user to the hardware.With the equipment, the paper tests two typical kinds of gas sensor, TGS2442 for CO, TGS2611 for CH₄, and presents the results. With these kinds of sensors, the paper designs the "CO-CH₄ gas transducer used on domestic robot", which is a part of the national S863 program funded project, "MEMS Sensor Integration Application Research Used on Service Robot". The transducer transforms the concentrations of CO and CH4 indoor to a 0～3 linear voltage output.