Gas Sensors

© Brooke Clarke 2017 - 2020



Looking into Oxygen sensors.  It turns out that these are often part of Lower Explosive Limit (LEL) (Wiki) sensors.  This is related to Miner's Safety Lamps, which are really methane detectors.

State rep Nino Vitale (R-Ohio) (YouTube channel, Facebook, ) put up a video claiming that face masks deplete oxygen.  But what he really was doing is measuring the O2 in exhaled air.  Later he cheated and claimed to be breathing out onto the sensors on the front and top of the CX-2009 showing no alarm(but the sensors are on the bottom. (he may have put his thumb on the O2 sensor, hard to tell in the video).
Ohio Rep. Nino Vitale Tests Mask Use, Which Shows Oxygen Levels Drop Into Danger Zone 5 Seconds
 • DC Dirty Laundry
His testing was done using the RKI GX-2009 gas monitor.
Thunderf00t posted a Busted Nino Vitale video that was itself pulled by YouTube as was the one by Vitale.

It turns out that all the chemical type sensors, including CO for home protection, work using chemistry that runs out of reagent over time and so needs to be replaced.  That applies to the GasTesh unit on this web page as well as the GC-2009.  So in order to get a unit that works and that you can trust you need to get one where the sensors have been replaced and hopefully calibrated.

Figaro makes many sensors.  Their O2 sensors come in 5 and 10 year life versions.  The KE-50 may be the most economical 10 year life model.  But takes about 100 seconds to respond.
The GX-2009 responds very fast so my be using a sensor like the KE-12 (maybe the dash number is the seconds to 50% response?).
KE-12 life: 2.5 to 10 years.  Trying to get data sheet for the KE-12.
The Amphenol SGX-40X O2 sensor is in stock at Digi-key.  0V bias. Linearity S = K*Loge(1/(1-C), 5 year life.
 SGX sensor Tech - AN-2 EC sensor design -


While the first sensor on this page is the GasTech 1214S GasTechTor (Wiki: Explosimeter) the manual for the 1238ME is on line and that unit looks very similar.

The bottom contains the sensors and pump and the top contains the meter, alarm sounder, control panel and electronics.

The metal fitting is the input which goes directly to the sensor housing/combustible gas sensor.  Its output goes to to the air pump, its output goes to the GasTech Oxygen sensor and its output goes to the  plastic exhaust tube.

Sensor Technologies

Wiki: Gas Detector -
Wiki: Catalytic bead sensor - platinum wire each embedded in a bead of alumina
Wiki: Pellistor - Catalytic and Thermal Conductivity types
3092799 Apparatus for detecting combustible gases having an electrically conductive member enveloped in a refractory material,

Wiki: Electrochemical gas sensor -

Oxygen Sensor

Electrochemical oxygen cell - gold and lead electrodes immersed in gel-type electrolyte, covered by a permeable fluorocarbon membrane. Current output.

Combustible Gas Sensor

Heated platinum catalytic element and matching reference element.


Fig 1 Connector at right is to charge the internal 8.4V Ni-Cad battery.
Fig 2 Terminal strip at left, top to bottom
Black Pump Wire
Red Pump Wire
Red Combustible Gas Sensor sensor wire
Green Combustible Gas Sensor sensor wire
White Combustible Gas Sensor sensor wire
The PCB is marked P2, P1, R, G, W
Fig 3 Oxygen Cell, Gastech No. 65-0601, Code 9514
hand written: 12 May 95
The pin (3) to the right of the white dot is the Black sensor wire
and to the left ( 4) of the white dot is the White sensor wire.
Connector is SATO parts, Japan
Fig 4
Fig 5 Oxygen Cell  White crud growing out  of sensor.
Does that mean it's dead? let me know.
Fig 6 Combustible Gas Sensor






PRC68, Alphanumeric Index of Web pages, Contact, Products for Sale
Page Created 20 July 2017