e2v has been leading the way in the design, development and manufacture of a wide range of reliable gas sensors for OEMs since developing the catalytic bead gas sensor (which became known as the Pellistor) in 1967.
As an independent OEM supplier of gas sensors, e2v pride themselves on providing customers with unrivalled product reliability and personal product support via specialist engineers.
e2v gas sensors are built to the highest standards with all pellistor and infrared gas sensors achieving ATEX and IECEx certification, e2v gas sensors are also UL and CSA approved.
e2v is ISO9001:2000 certified with the automotive semiconductor types also ISO/TS16949:2002 certified.
These include the following:
Pellistors are miniature calorimeters used to measure the energy liberated by the burning of a combustible (flammable) gas or vapour. A pellistor consists of a coil of small-diameter platinum wire supported in a refractory bead on which is deposited a layer of catalytic material, on which the gas is burnt. The coil serves two purposes. Firstly, it is used to heat the bead electrically to its operating temperature, about 500°C, and secondly it is used to detect changes in temperature produced by the oxidation of the flammable gas.
The earliest forms of catalytic gas sensors consisted solely of bare coils of platinum wire, operating at 800-1000°C. At such temperatures, platinum wire evaporates extremely quickly causing signal drifts resulting from a reduction in the wire diameter. The specification for such a sensor, which is still produced commercially, requires that the sensor has a life of 100 hours. The majority of present day devices, as stated earlier, have the coil cloaked in a porous ceramic onto which is deposited the precious metal catalyst.
The enhanced catalytic activity resulting from the much larger surface area of catalyst available permits much lower operating temperatures of around 500°C, resulting in lower power drain and longer device lifetime.
The concept of the pellistor is based on the fact that the most foolproof way to determine whether a flammable gas is present in air is to test a sample by trying to burn it!
A pellistor consists of a very fine coil of wire suspended between two posts. The coil is embedded in a pellet of a ceramic material, and on the surface of the pellet (or 'bead') there is a special catalyst layer.
In operation, a current is passed through the coil, which heats up the bead to a high temperature. When a flammable gas molecule comes into contact with the catalyst layer, the gas 'burns'. The reaction occurs without a flame since the level is below the Lower Explosive Limit (or LEL) of the gas. However, just as in a burning reaction, heat is released which increases the temperature of the bead. This rise in temperature causes the electrical resistance of the coil to rise.
There is another bead in the circuit which is identical to the detector bead, but does not contain any catalyst. This bead will react to changes in humidity, ambient temperature etc, but will not react to flammable gas. All that is required is a comparison of the resistance of one bead against another in a Wheatstone Bridge type circuit in order to obtain a meaningful signal.
Infrared Gas Sensors exploit the property that many gases absorb radiation in the 2-14 micron, infrared region of the spectrum. These spectral absorbances show features which may be regarded as 'fingerprints' to identify the gases and enable their concentrations to be deduced.
The sensor bodies contain an infrared source and infrared detectors inside a compact and combined gas cavity/ optical cell. The detectors have infrared bandpass filters placed in front, which tune them to the specific gases to be sensed.
When the specific gas enters the cavity it is registered as a change in detector signal. The magnitude of this change is related to the concentration of that gas via a simple exponential formula.
By utilising different infrared filters a range of gases can be sensed and discriminated with these devices. In cases where spectral lines overlap, then an individual sensor may show cross sensitivities to a gas range.
Infrared gas sensors are very robust devices not affected by contact with a harsh chemical environment. Any changes in ambient conditions such as temperature are compensated for in software.
Their dimensions and power requirements are compatible with and complementary to pellistor gas sensors.
After over thirty years of successful manufacture of pellistor-based flammable gas sensors, the range of Non-Dispersive Infra-red (NDIR) gas sensors represents the first of many diversifications into other areas of gas sensor technology by us.
sensors work on a different principle from the pellistor and IR
devices. With electrochemical sensors the target gas undergoes a
chemical reaction, producing a current that is directly proportional to
the concentration of gas present. The sensors use very little power and
show good responses to various gas concentrations over a wide range of
Two sizes of electrochemical
sensors are available for the measurement of Carbon Monoxide and
Hydrogen Sulfide. These sensors are drop-in replacements for the
current 20mm and 32mm diameter sensors.
Because pellistors measure the flammability of a gas, they cannot be used to measure levels of gas above the Lower Explosive Limit (LEL), since the reducing level of oxygen will result in a fall-off of signal. However, a similar device can be used to monitor these high levels of gas.
have a range of thermal conductivity sensors, which are designed to
complement the pellistor range in terms of electrical characteristics,
so that they can be used in the same Wheatstone Bridge circuits. They
are supplied with a compensator bead which is in a sealed enclosure of
air. This enclosure acts as the thermal conductivity reference in
exactly the same way as it acts as the reference for a pellistor.
Our pellistors and thermal conductivity sensors can be obtained already packaged as complete, flameproof gas detection heads for use in fixed gas detection systems. The VQ4250 gas detection head has CSA and BASEEFA approval and is just one example of our success in packaging sensors. The VQ600 is the latest product in this range and shows our commitment to continual development of device performance whilst reducing costs.
e2v is able to offer a range of semiconductor based gas sensors and sensing modules:
follow the link on the main left hand menu to access datasheets
Please contact us if you are looking for sensors to detect methane or hydrogen, or if your requirement does not match one of the gases listed above.
Sensor package options
Sensors can be supplied with different packaging:
-With hydrophobic teflon membrane
-With active charcoal filter
-TO or SMD packages
Ozone is used, because of its oxidizing properties, in a variety of applications to clean and decontaminate air and water. These applications include water treatment, air purification in smoky environments, and home air cleaners. Since ozone is hazardous to human health, its concentration needs to be monitored so that it does not exceed around 0.1 ppm in livable spaces. Mics 2610 is highly responsive to ozone and robust enough to be used in industrial devices.
Measurement of the blood alcohol content (BAC) by correlation with the alcohol in breath is common practice by the police to determine if a person is driving under the influence of alcohol. Using the 5135 alcohol sensor, a personal alcohol tester can be built at low cost, so that individuals can test their own approximate BAC level by simply blowing on the sensor. Such devices should not be used as a license to drive after drinking.
This sensor measures CO and hydrocarbons. Its SMD package makes integration on a PCB very cost-effective.