Chlorophyll meter design principle

Chlorophyll meter is a special instrument for determining chlorophyll content. TYS series chlorophyll meter determines the relative amount of chlorophyll in the leaf by measuring the light transmittance coefficient of the leaf in two wavelength ranges. The instrument is compact in appearance and can be directly placed in the pocket and brought to the field. Therefore, it is also called a portable chlorophyll meter. Chlorophyll is widely found in green plant tissues such as fruits and vegetables, and combines with proteins in plant cells to form chloroplasts. Chloroplasts are the main sites for crop photosynthesis, and photosynthesis is the process by which plants absorb sunlight to produce organic matter. Therefore, the content of chlorophyll, Directly affecting the accumulation of organic matter in crops will also affect the final crop yield. Chlorophyll can be divided into several types; it is divided into chlorophyll a, chlorophyll b, chlorophyll c, and chlorophyll d. The content of different chlorophylls in crops is different, but the chlorophyll a and chlorophyll b contents are generally higher. Determination of chlorophyll content, from ancient times to the present, there have been many methods, such as spectrophotometry, chlorophyll meter method, photoacoustic spectroscopy and so on.
The chlorophyll meter method is the quickest and simplest method for determining chlorophyll content. You only need to add the blade to the light sensing part of the instrument and press the sensor head. The SPAD value of the current blade will be immediately displayed on the display of the instrument. SPAD value is an expression form of chlorophyll content because there is a certain correlation between SPAD value and chlorophyll content, and we can obtain the chlorophyll content of the leaf through SPAD value. The first to apply the SPAD value to chlorophyll determination is the Konica Minolta company in Japan. The SPAD502 developed and produced by them is to determine the leaf chlorophyll content by measuring the SPAD value of the plant. The SPAD502 is now widely spread in the market, and A lot of effects have been achieved. The original design principle of the chlorophyll meter is as follows: The two LED light sources on the measuring head emit two kinds of light, one is red light (peak wavelength 650nm), and the other is infrared light (940nm), two kinds of light shining on the blade, penetrating The blade, shining on the receiver, the light signal is converted into an analog signal, the analog signal is amplified by the amplifier, and converted by the analog/digital converter into a digital signal. The digital signal is used by the microprocessor to calculate the SPAD value and display it on the display. , Automatically stored in memory. The specific process for the lighting system -> receiver -> amplifier -> analog / digital converter -> microprocessor -> display. The structure of the instrument is: The two LED light sources are mounted on the measuring head. When the measuring head is closed, the two light sources emit light sequentially. The emitted light passes through the emission window and then passes through the sample, and then enters the receiving window. The silicon photodiode receiver is converted to an analog signal. Then the analog signal is amplified by the amplifier, converted into a digital signal by an analog-to-digital converter, and then displayed on the LCD screen by the microprocessor. At this time, we can use the different keys on the LCD screen of the instrument to select the data we need. Among them, the SPAD value range of the TYS series chlorophyll meter is 0.0-99.9 SPAD, while the SPAD502 of Japan has greatly expanded its measurement range and can reach -9.9-199.9 SPAD units. Of course, behind the more powerful functions, it is certain that the price of the SPAD 502 is much higher than that of the ordinary chlorophyll meter.

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