How to extend the service life of gas alarm

Code for installation and acceptance of fire alarm systems. Welcome to post your country's code of it here.
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How to extend the service life of gas alarm

Unread post by vedard »

Do not store the instrument in high temperature or cold (lower than -40℃ and higher than 70℃) to avoid shortening the service life of electronic components.

Do not use harsh chemicals, detergents or concentrated cleaning agents to clean the instrument. Dab the instrument with a clean soft cotton cloth dipped in a little water or soapy water without harmful substances, and dry it in time.

Do not make the dust block the instrument detection hole, to avoid liquid into the detection hole, once the liquid into the instrument detection hole is placed downward, so that the liquid flow out, do not violently shake the instrument.

Do not drop, knock or shake the instrument violently. Rough use may damage the instrument.

Try to avoid using and storing instruments in dusty, dirty places.

Keep the surface clean and dry, away from rain, moisture and corrosive gases and liquids.

Protects gas sensors from exposure to lead mixtures, silicon and chlorinated hydrocarbons. Because the sensor in these gases will cause sensor poisoning, thus affecting the service life of the sensor.

In the detection of combustible gas alarm strict requirements can not use lighter gas to detect, because the concentration of lighter gas is relatively high so that the sensitivity of the gas sensor will be reduced or zero drift resulting in increased error of the gas alarm.
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How to install industrial explosion-proof gas alarm?

Unread post by vedard »

Once the fixed-point installation of combustible gas alarm is installed, the position is not easy to change. According to the work experience accumulated over the years, the specific application should consider the following points.
(1) Make clear what possible leakage points of the device to be monitored, analyze their leakage pressure, direction and other factors, and draw the probe location distribution diagram, according to the severity of the leak is divided into Ⅰ, Ⅱ, Ⅲ three grades. (2) Determine the leakage direction of combustible gas when a large amount of leakage occurs according to specific factors such as the direction of air flow and wind direction at the location.
(3) According to the density of the leaking gas (greater than or less than air), combined with the air flow trend, the three-dimensional flow trend diagram of the leakage is synthesized, and the initial set point scheme is made at the downstream position of its flow.
(4) Study whether the leakage state of the leakage point is micro-leakage or jet. If it is micro leakage, the position of the point should be close to the leakage point. If it is a jet leak, move slightly away from the leak. Synthesize these situation, work out the final site plan. In this way, the quantity and variety required for purchase can be estimated.
(5) For places with large flammable gas leakage, a detection point should be set up every 10-20m in accordance with relevant regulations. For the small and discontinuous operation pump house with no one on duty, it is necessary to pay attention to the possibility of flammable gas leakage. Generally, a detector should be installed in the lower tuyere.
(6) For places with hydrogen leakage, the detector should be installed on the plane above the leak point.
(7) For the medium with gas density greater than air, the detector should be installed on the lower plane below the leakage point, and pay attention to the characteristics of the surrounding environment. For places prone to combustible gas accumulation, special attention should be paid to the setting of safety monitoring points.
(8) For open combustible gas diffusion and escape environment, if the lack of good ventilation conditions, it is easy to make the content of combustible gas in the air of a certain part close to or reach the lower explosive limit concentration, these are not ignored safety monitoring points. According to the analysis results of field accidents, more than half of them were caused by incorrect installation and calibration.
Therefore, it is necessary to introduce the precautions for correct installation and verification to reduce faults.
(1) There can be no strong electromagnetic field (such as high-power motor and transformer) around the alarm that has an impact on the work of the instrument. The surrounding space is not less than 0.3m.
(2) The alarm is a safety instrument, sound, light display function, should be installed in the staff easy to see and easy to hear the place, in order to eliminate hidden dangers in time.
(3) the installation height of the alarm should generally be 160-170cm, in order to facilitate the maintenance personnel for daily maintenance.
(4) The alarm probe is mainly the detection element of the contact combustion gas sensor. It is composed of aluminum oxide and adhesive ball on the platinum wire coil. The outer surface is attached with platinum, palladium and other rare metals. Therefore, care must be taken during installation to avoid breaking the probe.
(5) 2. When detecting harmful gases heavier than air, the installation height of the detector should be 0.3-0.6m higher than the floor (or floor). Too low easy to cause water, splash damage; Too high and beyond the height at which gas tends to accumulate. (Under standard condition, gas density greater than 0.97kg/m3 is considered heavier than air.)
(6) When detecting harmful gases lighter than air, the installation height of the detector should be 0.5-2m higher than the release source. The horizontal distance of the release source should be reduced to less than 5m.
(7) When detecting hydrogen, it should be installed around and within 1m above the release source.
1. Combustible gas detector: effective cover horizontal plane diameter, indoor should be 7.5m, outdoor should be 15m.
2. Toxic gas detector: The distance between the detector and the release source should not be greater than 2m indoors and 1m outdoors.
(8) The installation of open probe can be selected according to the density of the measured gas installation height, special attention to the point that the probe should be installed on the downwind side.
(9) The connecting cable of the alarm loop should be added with a protective sleeve, and it is best to add a metal hose at the wiring of the probe, and pay attention to be consistent with the explosion-proof grade of the factory.
(10) After installation and debugging, be sure to install breathable waterproof cover, so as not to rain into the damage probe.
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The reading on the gas detector is negative. Why?

Unread post by vedard »

All electrochemical or catalytic bead gas sensors are prone to enter the positive and negative reading drift regime due to environmental factors such as temperature and humidity variations. But these are not the common reasons for negative sensor readings.
1. Zero readings in the polluted atmosphere
More negative sensor readings occur when the instrument is "zeroed out" in a polluted atmosphere where a small amount of the sensor's target gas is present. When the instrument is later placed in a clean air environment, the sensor will display a negative reading, corresponding to the pollutant concentration at that time when the device is zeroing out. For example, if the carbon monoxide concentration is 5 PPM when the sensor returns to zero, the reading will be -5 PPM when the sensor returns to clean air.

2. Negative cross interference
Negative readings can also occur when the sensor is placed in a gas that generates negative cross interference. If the sulfur dioxide sensor, which normally has -100% cross interference with nitrogen dioxide, is placed in 2 PPM of nitrogen dioxide, the sulfur dioxide reading on the instrument will be -2 PPM.
So, does this indicate that you should avoid using sensors that have negative cross interference with each other in the same instrument? Absolutely not! If both nitrogen dioxide and sulfur dioxide are present in the atmosphere, the way to tell you the true concentration of each gas is to use both sensors in a multi-gas detector.

In the example we used above, if the atmosphere contains 2 PPM of sulfur dioxide and 2 PPM of nitrogen dioxide, the reading of sulfur dioxide will be zero due to negative cross interference. The way to know that there is 2 PPM sulfur dioxide is to confirm the presence of nitrogen dioxide and understand its effect on the sulfur dioxide sensor. Removing a sensor from an instrument does not eliminate the hazard - instead, you are exposed to the hazard without knowing it.
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