Some common sense of gas detection instruments
1. Term Explosion range In the mixture of combustible gas and air, the concentration range between the lower explosion limit of the combustible gas and the upper explosion limit is called the explosion range.
"Parts Per Million" (PPM) concentration measurement unit, generally used in the field of gas detection. For example, 1 ppm of hydrogen sulfide in mixed air means one unit volume of hydrogen sulfide per million units of gas.
Flammable limits are divided into Lower Explosive Level and Upper Explosive Level. The units of LEL and UEL are usually percentages and refer to the percentage of a gas contained in air (or oxidant). In an environment lower than LEL, there is too little flammable gas to burn. When the concentration of flammable gas in the environment is higher than UEL, it may not be combusted due to too much gas. The LEL value and UEL value of various combustible gases can be obtained in related materials.
The Threshold Limit Values ​​(TLV) TLV indicates that when the content of a certain gas in the air is less than this threshold, the health of workers who are sufficiently and continuously exposed to the environment is not impaired. The reference to this value must be based on the standards promulgated by the country and the latest corrections should be used. TVL consists of the following two parts:
Average Threshold (TLV-TWA) This value represents the time-weighted average concentration value in the environment. The vast majority of workers do not have health problems when working in this environment for 8 hours a day, 40 hours a week.
Instantaneous Threshold (TLV-STEL) This parameter is defined as a 15-minute weighted average. The concentration of a harmful gas in the workplace must not exceed its specified threshold at any time of the working day, even if it is The weighted average reaches the average threshold. The number of times that exceeds the average threshold and is below the instantaneous threshold during the day must not be greater than 4 times, and the duration must be less than 15 minutes.
Dangerous Concentration (IDLH) If a worker does not wear a gas mask or lacks escape experience and the concentration of gas in the work environment reaches a dangerous concentration, 30 minutes of retention can cause permanent damage to the human body or impair the health of the human body (eg reduced vision) ).
The RS485 serial bus specifies a two-terminal electrical interface format, the standard of which is the double-ended line transmission signal. If one of the lines is in a logic 1 state, the other is a logic 0. Since the voltage loop is bidirectionally differential, common mode interference in the transmission loop can be suppressed, and communication performance is greatly improved.
Zero gas does not contain clean air or nitrogen from the gas or other interfering gases.
The standard gas composition, concentration and precision are known gases.
Town gas generally includes natural gas, liquefied petroleum gas and artificial gas.
Response time Under test conditions, the time from when the detector contacts the gas being measured until the steady indication value is reached. Usually, the time to reach a stable value of 90% is read as the response time.
Recovery time The time from the detector to the gas being tested to the state of recovery monitoring under test conditions. Usually, the time to return to the stable indication value of 10% is read as the recovery time.
Explosive environments and explosion-proof electrical equipment contain an explosive mixture environment called an explosive atmosphere. Electrical equipment designed and manufactured according to the specified conditions without causing explosion of the surrounding explosive mixture to become an explosion-proof electrical equipment for explosive environments.
Explosion-proof marking countries have clear regulations on various explosion-proof types of explosion-proof electrical equipment for explosive environments. d IICT6 indicates that the explosion-proof type is explosion-proof type, II indicates electrical equipment for the factory, and C indicates the maximum test safety clearance or minimum of explosive gas mixture. The most stringent level of ignition current ratio (A, B, C), T6 indicates the most stringent level (85 ° C) allowing the highest surface temperature
After the sensor preheating sensor is powered on, the output value is unstable, and waiting for the output value to stabilize is the preheating of the sensor.
Sensor Poisoning When the sensor is energized, if it is exposed to a gas whose concentration is far beyond its range, it may cause the sensor's output value to remain high. Some poisoned sensors recover after a while and some are unrecoverable.
The bus and split bus and split are in terms of how the controller is connected to the detector. If each detector requires a wire to complete communication with the controller, the connection is said to be a split connection. If several detectors can share a single wire to complete communication with the controller, the connection is said to be a bus connection.
Binary In the bus system, the encoding of the device on the bus adopts binary, 8 is high, 1 is low, 0 is on the ON side, and 1 is on the OFF side. The coding formula is as follows: code number=1×N1+2×N2+ 4×N3+8×N4+16×N5
II. Common flammable gas-related properties Gas name Molecular weight (air = 1) TLV-TWA (PPM) TLV-STEL (PPM) TLV-IDLH (PPM) LEL (V%) HEL (V%) Hydrogen H2 0.0695 4 75 Ammonia NH3 0.58 25 35 500 15 28 Carbon monoxide C0 0.976 25 1500 12.5 74 Hydrogen sulfide H2S 1.115 4.3 45 Chlorine CL2 0.5 1 30 Propane C3H8 1.56 2 9.5 Propylene C3H6 1.49 2.4 10.3 Butane C3H6 2.01 800 1.9 8.5 Butene-1 C4H8 1.937 1.6 10 Butene-2 ​​C4H8 1.94 1.8 9.7 Butadiene C4H6 1.87 2 20000 2 12 Isobutane (CH3)3CH 2.068 1.8 8.4 Methane CH4 0.554 5 15 Ethane C2H6 1.035 3 12.5 Ethylene C2H5 0.975 2.7 36
The explosive limit of combustible gas and air mixture
The explosive limits of combustible gas and air mixtures are related to the type and chemical nature of the combustible gas; the form, energy and ignition position of the ignition source; the geometry and size of the explosive vessel; the temperature and pressure of the combustible gas and air mixture. And humidity. Purity of combustible gas; uniformity of combustible gas and air mixture;
4. Gas detector classification According to the object of detection, there are flammable gas (including methane) detection alarm, toxic gas detection alarm, oxygen detection alarm. Classified by sampling method, there are diffusion type and pumping type. According to the principle of detection, flammable gas detection includes catalytic combustion type, semiconductor type, thermal conductivity type and infrared absorption type; toxic gas detection has electrochemical type, semiconductor type, etc.; oxygen detection has electrochemical type. Classified by function, there are gas detectors, gas alarms and gas detection alarms. Classified by usage, portable and fixed. Classified according to the place of use, there are conventional and explosion-proof types.
The 10MM Dice are small but still usable for gaming. They're great to use when you need to roll many dice at once, since 8-10 will fit comfortably in the palm of your hand.
For 10MM dice we have only square style for choice. But custom color for both plastic and painting is available. The material we use for 10MM dice is mainly acrylic.
Information about the dice measurement: Dice are measured in millimeters (mm) from side to side, and while dice can range in size from 8mm all the way up to 100mm or more, there are a few dice sizes that are considered "standard": 8mm, 12mm, 16mm, 19mm, 25mm.
10MM Dice
Where to Buy Dice,Six Sided Dice,Wholesale Dice,10MM Colored DiceÂ
BESCON INDUSTRIAL CO., LIMITED , https://www.besconcn.com