Hand-held chlorophyll meter procedures and precautions
The handheld chlorophyll meter is an instrument that can be taken directly in the hands of a chlorophyll meter and taken to the field for chlorophyll content determination. Because the instrument is compact and can be held at any time, it is called a handheld chlorophyll meter. The measurement principle of the handheld chlorophyll meter is to measure the transmittance coefficient in two wavelength ranges to determine the relative amount of chlorophyll in the leaf. The handheld chlorophyll meter has a measurement range of 0.0-99.9 SPAD. A lot of chlorophyll content is now shown by the SPAD value, because there is a certain correlation between SPAD value and chlorophyll content, because the chlorophyll content of the leaf can be known by measuring the SPAD value. In addition, in the study of plant species, we often use live leaf area meters and other instruments to determine the leaf area of ​​plants, which is an important step for crop yield estimation.
The specific work flow of the handheld chlorophyll meter (SPAD502) is as follows: Two LED light sources emit two kinds of light, one is red light (peak wavelength 650nm), and the other is infrared light (940nm). Two kinds of light penetrate the blades and hit the receiver. The optical 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. It is also automatically stored in the memory. . Its internal process can be represented as lighting system -> receiver -> amplifier -> analog/digital converter -> microprocessor -> display.
The SPAD value of plants has a certain proportional relationship with the chlorophyll content. The higher the SPAD value, the better the growth status. When we use the chlorophyll meter, the method is relatively simple. You only need to hold the handheld chlorophyll meter and then clamp the measuring head of the instrument to the ends of the blade. Press the measuring head to obtain the SPAD value of the plant. The specific operations are: (1) In the calibration process, the measurement head does not clamp the sample, the two LEDs emit light in order, and the received light is converted into an electrical signal, and the ratio of the light intensity is used for calculation. (2) After the sample is clamped by the measuring head, the two LEDs emit light again. The light transmitted through the blade hits the receiver and is converted into an electrical signal. The intensity ratio of the transmitted light is calculated. (3) The values ​​of steps 1 and 2 are used to calculate the SPAD measurement, that is, the current relative chlorophyll content of the clamped sample leaf. When using the chlorophyll meter, the following points need attention: 1. The reading verification card can only be used in inspection mode. 2. Only the random reading card (same serial number as the machine) can provide the exact value. 3. The reading verification card can not be used outdoors, and can not be used in direct sunlight, high temperature and high humidity environment. 4. When the measured value is different from the value on the reading verification card, it cannot be corrected by inputting the compensation value. 5. Do not touch the glass surface of the calibration card. If it is dirty, use a wet, soft cloth. 6. Protect the reading verification card in the accessory bag and do not place it in a hot, humid environment.
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