Gas Sensors - Insights

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.

Due to development of Electronics, Response time, Output, Accuracy have improved. Spurious trips have reduced. Low Maintenance, Long Life , IR technology is influencing the gas sensor design.

I'm very interested to know more about this! Today, we use ultrasound which is maintenance free due to the fact that the detector is calibrated with ambient air.

Rae systems USA ( in portable gas monitors) , in fixed gas monitoring systems (wired) Dragger, MSA, industrial scientific are at par. In wire less systems RAE systems is far ahead.

The ones that use non conventional sensors, but unfortunately they are patented and still secret, I know they are using mass spectograph.

Would be nice to know. We from ASCO offer a good but not trendy detector. It's more on the "classical" side.

LDPE plant C2H4 leak detection (125 point) H2-CH4 compressor leak detection (24 point) O2 measurement automotive exhaust H2S mud pit monitor in off shore drilling operations NO measurement automotive exhaust

HART Enabled Detectors SIL2 Safety Instruments Low Power Advantages Phoenix Triple IR Ultraviolet/Infrared Single Ultraviolet Hydrogen (H2) & Silane FlameWatch II (flame/video)

CO/NO2 for parking garages, loading docks, warehouses Refrigerant monitors for mechanical rooms Hydrogen for battery rooms Many other toxic/combustible gas applications

Fumigation of air crafts to kill mice, rats etc.! There it was important to have a detector with a measuring range of 20% which the ASCO CO2 Gas Detector does. At that level of CO2 no life would have any chance any more!

Measuring the concentration of minor gases in biogas (SH2, NH3, H2, siloxanes...) Measuring the concentration of Methane / CO2 in biogas Measuring the concentration of alcohol vapor in fermenters

I use them for training. The ease in which it is used is important for officers who know little about contaminated atmospheres.

Early in the space program NASA ordered a bunch of Hydrazine detection instruments that used a caustic electrolyte. They tested great in the lab, but in the real world if people breathed near them it alarmed as if Hydrazing was present. Test your sensors in the real world.

Yes. An officer took the detector and put it beside a valve on a propane tank that was full of anhydrous ammonia at a meth lab. He cracked the valve which engulfed the air monitor. Say good bye to that sensor!

California BAR 97 NO measurement on loaded vehicles - specs were too demanding in chem cell sensors. NO measurements were unreliable, unrepeatable and sensor life of 6 months was too short.

A solid state sensor for each gas or vapor. High selectivity. If you have methanol and ethanol mixed together, the sensor can´t find the difference.

Sensitivity Specificity Portability Datalogging or interfacing with web data Remote start and stop via web interface On-board diagnostics

It should be visible at a glance - could be made of orange plastic? Users should always know where the detector/sensor is installed.

First is the range (it should be above the IDLH limit of the gas to be monitored i.e. for co its IDLH limit is 1200 ppm your gas monitor should be able to measure at least 1200 ppm or above) , resolution (go for the lowest as it is more accurate that way,a thumb rule), temp(depending your climatic conditions), ingress protection (at least IP 66 for single gas & IP 55 for multi gas).

Response time for gas detectors are more important, as it is a life and equipment saving instrument. Response time should be includes, fitting all the accessories like splash guards, gassing unit etc.

Beware of measuring buy difference, as is the case of CO2 measuring in flue gases. No solid state sensor can measure CO2, so its content is calculated indirectly. This leads to errors.

Know what you want them to do. The first question is how accurate and sensitive do you need to be. That determines how much money you need to spend. Also do you need to meet any specifications such as OSHA confined space entry. Second question are there power limitations? Some sensors are power hogs, some actually give power. Third, size limitations?

Check for the maintenance! Many companies offer cheap sensors that require a regular calibration using expensive calibration gas. A CO2 sensor should be placed approx. 30cm above floor level - CO2 is heavier than air!

Ask for 2 years replacement warranty on entire gas monitor including battery,sensors,electronics. Calibrate the instrument every 6 months.