Introduction
In order to make the system work, the first thing we need are sensor. I did some search and this is what I came up with. I need to fit sensors, parts and possibly some smd equipment into budget and that has made me fiddle with the design a LOT! Truthfully I am a bit ruffled up at this stage as to how I am going to make this work. People already have big workstations and workshops and I have been intimidated by all the "extra-electronic" craftsmanship in the past. I will do my best but it is easy to get scared at this point. 
Sensor research
So there are two types of sensors which can fit into budget. Here is a brief of both.
Semiconductor sensors
These are relatively inexpensive compared to other sensing technologies, robust, lightweight, long lasting and benefit from high material sensitivity and quick response times. They have been used extensively to measure and monitor trace amounts of environmentally important gases such as carbon monoxide and nitrogen dioxide. They are also sometimes called Metal oxide semiconductor gas sensors. These are relatively cheaper and good example is the MQ-x series which is popularly available. I am not sure about the advantages or disadvantages and hence I request anyone with the knowledge to contribute.
Electrochemical Sensors
According to wiki, "Electrochemical gas sensors are gas detectors that measure the concentration of a target gas by oxidizing or reducing the target gas at an electrode and measuring the resulting current." The gas diffuses into the sensor, through the back of the porous membrane to the working electrode where it is oxidized or reduced. This electrochemical reaction results in an electric current that passes through the external circuit. In addition to measuring, amplifying and performing other signal processing functions, the external circuit maintains the voltage across the sensor between the working and counter electrodes for a two electrode sensor or between the working and reference electrodes for a three electrode cell. At the counter electrode an equal and opposite reaction occurs, such that if the working electrode is an oxidation, then the counter electrode is a reduction.
Others
There are other types such as :
- Infrared sensors which use IR diffraction to measure gas levels. They are based upon the ability of some gases to absorb IR radiation. Many hydrocarbons absorb IR at approximately 3.4 micrometers and in this region H2O and CO2 are relatively transparent.
- Catalytic sensors which work on the fact that that when gas oxidizes it produces heat, and the sensor converts the temperature change via a standard Wheatstone Bridge-type circuit to a sensor signal that is proportional to the gas concentration.
- Flat surfaced ... sensors adopts advanced flat production technology. The heater and metal oxide semiconductor material on the ceramic substrate
- Solid Electrolyte Gas sensors... based on ceramic components for the quantitative detection.
- Other misc types
Manufacturers:
There is an array of manufacturers of these sensors and I list them out below:
- Winsensor 气体传感器_红外传感器_黑白元件--郑州炜盛电子科技有限公司
- Above in English 气体传感器|红外传感器|黑白元件-郑州炜盛电子科技有限公司
- Gas Sensors / FIGARO Engineering inc
- HW Sensor (The name on the datasheets) 气体探测器 - 河南汉威电子股份有限公司
- Ravi;s blog. http://www.figarosensor.com/,
- http://www.ccmoss.com/
Sensor Selection
I am selecting the following sensors for my application:
| Gas Detected | Type | Sensor Model |
|---|---|---|
| Carbon Monoxide | Semiconductor Sensor | MQ307A or ME2B-CO(INSIDE) MQ-7,(OUTSIDE) MQ309A or TGS3870( CO and Methane)(OUTSIDE) |
| Carbon Dioxide | Semiconductor Sensor | MQ135(OUTSIDE) |
| Carbon Dioxide | Electrolchemical Sensor | MG811(INSIDE) |
| Hydrogen Sulphide | Semiconductor Sensor | MQ136(INSIDE) |
| HydrogenSulphide and Air Quality | Semiconductor type | MQ135(OUTSIDE) |
| Oxygen | Electrochemical Sensor | ME3-O2(INSIDE) |
| Oxygen | Galvanic Cell Type | KE-25(OUTSIDE) |
| Ozone and Nitrous Oxide | Semiconductor Type | MQ131(OUTSIDE) |
| Nitrous Oxide | Electrochemical Type | ME3-NO2(INSIDE) |
| Hydrogen | Semiconductor Type | MQ137 |
| Volatile Hydrocarbons | MOS Type | TGS2602 |
| Temperature & Humidity | Semiconductor | HDC1000(INSIDE) |
| Temperature & Humidity | Semiconductor | HDC`1000(OUTSIDE), TMP008 |
| Particulate Matter | - | No IDEA |
I am still working on the Particulate Matter part of the Sensors. I hope these fit in budget. The system this time will have an extensive array of data on various gasses in the air which will be logger to sierra airvantage.
Help
I request anyone with knowledge to correct, ammend, remove, remake the above list. Please share your experience because I have none in this particular field.
Thanks
IP
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