Semiconductor Gas Detector

Semiconductor gas sensors have a range of applications in safety, process control, environmental monitoring, indoor or cabin air quality and medical diagnosis. It is available with Height of (inch) : 2", 3".

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Detailed Description for Semiconductor Gas Detector

Semiconductor gas sensors (metal oxide sensors) are electrical conductivity sensors. The resistance of their active sensing layer changes due to contact with the gas to be detected. In the ideal case, the gas reacts with the sensor surface in a completely reversible reaction. Due to their chemical composition and properties, metal oxide gas sensors are well-suited for a wide range of applications and for the detection of all reactive gases. Depending on the material used and the gases that need to be detected, typical operating temperatures range between 300°C and 900°C. If required, catalysts such as Pt or Pd are used. The sensitive metal oxide layers are applied on customer-specific substrates using thin or thick film technology by sputter and evaporation systems or inkjet printers.

 

 FEATURES: 

  • -Measuring range: 30-300 ppm
  • -Linearity: linearized
  • -Response time t 90: max. 60 sec
  • -Operating temperature: -30 °C to +50 °C
  • -Start up after reconditioning: max. 1 hr

 

Electrical data sensor electronics

-Power connection: 3-core cable,

-shielded Supply voltage: 15...24 VDC

-Current consumption: maximum 110 mA

-Output signal: 4...20 mA/maximum 60 mA

-Operating temperature: -20 °C ... +60 °C 

 

Specification:

 

Working Voltage

AC 110-240V/50Hz, 60Hz

Rated Power

≤3W

Sensor

semiconductor gas sensor  

Warm-up Time

3-5 Minutes

Temperature

-10°c ~ +50 °

Humidity Range

 

10% ~ 95% Relative Humidity (RH)

Alarm Level

10%±5%LEL

Alarm Reset

 

Auto Reset after Gas Clears

Alarm Output

Sound & Flash Alarm

Alarm Sensitivity

<10% LEL

Indicator Information Power

Green LED ON

Alarm

Red LED Flashing

Fault

Yellow LED ON

 

Semiconductor sensors detect gases by a chemical reaction that takes place when the gas comes in direct contact with the sensor. Tin dioxide is the most common material used in semiconductor sensors, and the electrical resistance in the sensor is decreased when it comes in contact with the monitored gas. The resistance of the tin dioxide is typically around 50 kΩ in air but can drop to around 3.5 kΩ in the presence of 1% methane. This change in resistance is used to calculate the gas concentration. Semiconductor sensors are commonly used to detect hydrogen, oxygen, alcohol vapor, and harmful gases such as carbon monoxide. One of the most common uses for semiconductor sensors is in carbon monoxide sensors. They are also used in breathalyzers. Because the sensor must come in contact with the gas to detect it, semiconductor sensors work over a smaller distance than infrared point or ultrasonic detectors.

Semiconductor gas sensors can be used for a wide array of applications, ranging from safety equipment (explosion, leakage, fire, contamination and poisoning protection) up to emissions and air quality monitoring, quality assurance, process instrumentation and measurement technology. For example, gases such as carbon monoxide (CO), nitrogen oxide (NOx ), ammoniac (NH3 ), sulfurous gases (H2 S, SO2 ) and hydrocarbons (CxHy ) as well as volatile organic compounds (VOCs) can be detected. The measuring range depends on the gas being detected and covers from a few ppb into the percent range. The detection limit depends on the respective gas sensitive material.

Mode of operation

The gas/vapour/air mixture that occurs diffuses through the membrane to the active metal oxide surface. A temporary shortage of oxygen electrons arises on the indirectly heated surface during the presence of a gas concentration. This shortage of electrons produces a change in the conductivity, and thereby changes the voltage, which is evaluated as a signal. If the gas concentration reduces, the missing oxygen electrons will be replaced from the ambient air once again. The measurement reacts by oxidizing/reduction with oxygen. This characteristic leads to other gases being measured as well and triggering an alarm. By linearization of the initial signal this effect is minimized. The suitable application is to be implemented in "still" rooms; i.e. rooms in which no other gases are normally expected. 

Calibration

The gas measurement probe requires a longer stabilisation time when the gas measurement probe is first switched on. If the gas measurement probe has been put out of operation for more than 2 weeks, even after several years of use, the gas measurement element will require at least 48 hours to stabilise. If a calibration is carried out before the end of this stabilisation time, while the sensitivity of the measurement element is still increasing, faulty alarms could result. The calibration gas should be 75% of the measurement range, and must contain synthetic air as the carrier gas.

Maintenance

The measurement element with its associated electronics must be checked at least once or twice a year. The gas measurement probe must also be checked if the measurement element has been exposed to a gas concentration (gas alarm).

 


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