Vacuum table tensiometer soil moisture sensor water potential sensor

Description

Vacuum table tensiometer soil moisture sensor water potential sensor
model:
TEN（45CM）
TEN（30CM）
TEN（15CM）
TEN（20CM）
TEN（40CM）
Vacuum gauge tensiometer
A mechanical negative pressure meter with an accuracy of 2.5Kpa is used to determine the water suction and index irrigation of the field or potted soil.
The soil hygrometer (see photo) consists of a clay tube and a vacuum gauge. The clay tube is an inductive part of the instrument and has many small pores. After being infiltrated with water, the clay tube forms a water film in the pores. When the water-filled and sealed soil hygrometer is inserted into the unsaturated soil, the water film will be connected with the soil water, which will cause negative pressure in the water inside the instrument. In this way, the negative pressure indicated by the vacuum gauge is the soil water suction.
Soil water suction is an indicator of the strength of soil water potential, and is closely related to the flow of soil water and the effectiveness of plants. It has a different meaning from soil moisture content. It reflects the strength of the soil water potential and does not reflect the amount of soil. Dryness and wetness, generally speaking, the greater the soil suction, the smaller the water content; the smaller the soil suction, the more water content, so the data of the soil hygrometer index can also roughly reflect the soil water content status.
The instrument has the advantages of simple structure, high sensitivity, easy to use and so on. It can be positioned to continuously determine the operation of soil moisture and reflect the vertical and horizontal changes of soil moisture in time. Provide the necessary scientific basis for irrigation, drainage and crop growth.
The soil hygrometer is composed of a gas collecting tube, a vacuum meter and a clay tube. The upper end of the gas collecting tube is a water injection port and is tightly plugged with a rubber plug. There is an interface on the side to connect with the vacuum gauge, and the lower end is connected to the clay head through a plastic tube.
The instrument is divided into three types according to length, A, B, and C, with a total length of 350 mm, a total length of 550 mm, and a total length of 750 mm. If the unit requires a specific length, you can contact our company for customization. If you need a specific length can also be customized. The buyer did not indicate that we will ship in the regular size (30CM)!
Instruction Manual of Negative Pressure Soil Hygrometer (Tenometer)
1. Principles and characteristics
Soil hygrometer is an instrument for measuring soil moisture. As we all know, the soil moisture is affected by the capillary gravity of the soil pores and the molecular gravity of the soil particles, so that the water in the soil pores is under negative pressure (suction). The greater the soil suction, the less water in the soil pores, and the soil water content. The lower it is; on the contrary, the smaller the soil suction, the more water in the soil pores, the higher the soil water content. Therefore, the data indicated by the soil hygrometer can roughly reflect the water content of the soil. The negative pressure test soil hygrometer (also called tensiometer) is an instrument for measuring this soil suction (or soil matrix potential).
Negative pressure soil hygrometer is composed of clay head, cavity, gas collection chamber, metering indicator and other components. The clay head is the inductive part of the instrument and has many tiny pores. After being infiltrated with water, the clay head forms a water film in the pores. When the pores in the clay head are fully filled with water, the water in the pores has tension. This tension can ensure that the water passes through the clay head under a certain pressure, but prevents air from passing. When a water-filled and sealed soil hygrometer is inserted into unsaturated soil, the water film is connected to the soil water, creating a hydraulic connection. When the water potential of the soil system is not equal, the water flows from the high water potential through the clay head to the low water potential until the water potential of the two systems is balanced. When the gravity potential, temperature potential and solute potential are neglected, the water potential of the system is the sum of the pressure potential and the matrix potential, the pressure potential of the soil (referenced by atmospheric pressure) is zero, there is no matrix in the instrument, the matrix potential is zero, the soil The matrix potential of water can be measured by the pressure (difference) indicated by the instrument. The matrix potential of unsaturated soil water resists the pressure potential in the instrument, and the soil absorbs water through the clay head to the instrument until it is balanced. Because the instrument is sealed, vacuum or suction (pressure against atmospheric reference pressure) is generated in the instrument. In this way, the negative pressure meter or sensor in the instrument measures the line, which is the suction of the soil. The soil water suction and soil water matrix potential are equal in value, but the signs are opposite. In unsaturated soil, the base potential is negative and the suction is positive. The tensiometer is mostly used on unsaturated soil, and its matrix potential Negative value, mine tension gauge is also called negative pressure gauge.
Soil water suction is the strength index of soil water potential and the flow of soil water, which is closely related to the effectiveness of plants. Different from the meaning of soil moisture content, it reflects the degree of soil dryness and wetness in terms of the strength of the soil water potential and not in how much. Generally speaking, the greater the soil suction, the smaller the water content; the smaller the soil suction, the more water content. Therefore, the data of the soil hygrometer index can also roughly reflect the soil moisture content.
The instrument has the advantages of simple structure, high sensitivity, easy to use, etc. It can be positioned to continuously determine the operation of soil moisture and reflect the vertical and horizontal changes of soil moisture in time. Provide the necessary scientific basis for irrigation, drainage and crop growth.
2. Structure and indicators
The negative pressure gauge is composed of clay head, cavity, gas collection chamber, metering indicator and other components.
A vacuum gauge is used as a measurement indicating device called a vacuum gauge negative pressure gauge (with photos).
Vacuum gauge negative pressure gauge (the accuracy of vacuum gauge is 2.5):
Measuring range: 0-85Kpa;
Accuracy: 2.5Kpa;
Sensitivity: The sensitivity of the instrument depends on the substitution capacity of the negative pressure gauge (the change of negative pressure value caused by the change of unit water volume) and the water permeability of the clay head. The sensitivity of the instrument directly affects the equilibrium time of the measurement. Of course, the equilibrium time also depends on the degassing degree of the instrument, the humidity of the soil and the process of soil desorption.
The instrument is divided into three types according to the depth of the soil, 30cm, 50cm, 70cm. If the unit requires a specific length, please contact our company for customization.
3. How to use
Instrument installation: The instrument has been installed before leaving the factory and can be used directly.
If it is not installed at the factory, the instrument must be degassed first: the steps are as follows:
1. After boiling tap water for 20 minutes, place it for cooling.
2. Open the lid of the gas collection tube, tilt the instrument, and slowly pour the boiled air into the plastic bottle with air until it is full, the instrument stands upright for 10-20 minutes (do not add a lid), let the water take the clay tube Wet and see water dripping from the surface of the clay head.
3. Fill the instrument with airless water, use a dry cloth or paper with good water absorption performance to absorb water from the surface of the clay head (or insert a rubber device with an injection needle in the water injection area, and use a syringe to evacuate and evacuate. Note that the needle tip must pass through the rubber plug and extend into the instrument. At the same time, use the left hand to press the rubber plug to prevent it from loosening and leaking). At this time, you can see the pointer of the vacuum gauge, pointing to about 40 Kpa, and bubbles escape from the vacuum gauge and gradually gather in the gas collector. Slowly pull out the stopper and let the pointer of the vacuum gauge slowly return to the zero position. Continue to fill the instrument with airless water, and still use the above method for pumping. This is repeated 3-4 times, most of the air in the vacuum gauge can be removed.
4. Fill the instrument with airless water, add a plug, seal it, and stand the instrument upright to allow the clay tube to evaporate in the air. After about two hours, you can see that the pointer of the vacuum gauge points to 40 Kpa or higher. At this time, there will be bubbles escaping from the plastic tube and the gas collecting tube of the clay tube vacuum gauge. At the same time, gently turn the instrument upside down to concentrate the bubbles into the gas collecting tube.
5. Immerse the clay tube in airless water. At this time, it can be seen that the vacuum gauge pointer returns to zero, open the cover, refill the airless water, add the cover, and let the clay tube evaporate in the air. At this time, the pointer of the vacuum gauge can be raised to 50 Kpa or higher. At the same time, gently turn the instrument upside down to collect the escaping air.
6. Follow the above steps 2-3 times. After each time, the pointer of the vacuum gauge can be raised even higher, until the pointer reaches 60 Kpa, the clay tube is immersed in airless water, and the vacuum pointer turns back to zero. Open the lid, fill it with water, close the lid tightly, immerse the clay tube in airless water and set aside.
Zero calibration: After the instrument is sealed, there is a hydrostatic pressure value between the vacuum gauge and the measuring point (the middle of the clay head). If accurate measurements are made, this hydrostatic pressure difference should be eliminated, which requires zero calibration.
Calibration method: The instrument evaporates in the air after irrigation, so that when the negative pressure rises to about 20 Kpa, half of the clay tube is immersed in water. After static, the vacuum meter pointer slowly returns to zero until it does not move. The reading at this time is the zero calibration value of the instrument. The measured value minus the zero correction value is the soil suction at the measuring point.
On-site installation: at the place where the suction of the soil needs to be measured, use a drill with a diameter equivalent to the clay pipe to the depth to be measured (calculated by the center of the clay head), pour a little mud, and insert the instrument vertically to make the clay pipe and The soil is in close contact, and then ram the surrounding soil (do not step on it) to prevent rainwater from seeping along the loose soil around the pipe wall to the measurement point, making the measurement inaccurate.
Data acquisition: 24 hours after the instrument is installed, data acquisition can be performed. Soil water suction is affected by temperature, bulk density, etc. You should be careful not to step on the soil around the instrument, and try to collect it at a time when the temperature change is small (preferably in the early morning) to avoid errors caused by different temperatures between the measuring point and the instrument. If you are suspicious of the data, you can gently tap an empty watch to eliminate possible friction.
Moisture measurement: The soil hygrometer measures the soil suction value at a certain measuring point of the soil. During installation, the middle part of the clay head must be placed at the position of the measured point. The measuring range of the instrument is 85 Kpa. When this limit is exceeded, the instrument leaks due to the rupture of the water film on the wall of the clay pipe, making the instrument useless.
Plot the continuously collected soil suction readings on coordinate paper, and the curve drawn is an excellent reference for irrigation and drainage.
The scale of the vacuum gauge of the instrument adopts the standard of weights and measures published by the state, and its unit is kilopascal (Kpa).
Unit conversion: 1000 Kpa = 1 bar = 1000 mbar = 75.01 cm Hg = 1020 cm water column
4. Regular inspection
1. During the use of the instrument, the air volume in the air collection pipe must be checked regularly. If the air volume exceeds half of the volume of the air collection pipe, the water must be refilled. Do not pull out the instrument or shake the instrument when replenishing water. Open the lid and fill with airless water. If the clay pipe is loose from the original contact soil during the operation, it should be re-perforated nearby and reinstalled.
2. Generally speaking, if the air in the instrument is basically removed before embedding, and the humidity of the soil is within the measurement range of the instrument, it can be continuously maintained for 10-25 days without adding water again.
Five, matters needing attention
1. The clay head should avoid oil pollution, so as not to block the micropores and make the instrument malfunction.
2. The measuring range of the instrument is 85 Kpa. When it exceeds this limit, the instrument leaks due to the water film rupture of the wall of the clay pipe, making the instrument useless.
3. When opening the box, it should be opened slowly, otherwise, the pointer of the vacuum gauge will suddenly hit the 0-point stop post due to the sudden disappearance of the pressure difference, which may easily cause damage to the oil wire (clock oil wire) in the vacuum meter and cause the vacuum meter to malfunction.
4. When closing the lid, screw it in slowly to seep excess water from the clay head. Never press the rubber plug into the instrument quickly, otherwise, a high positive pressure will be generated in the instrument, which will damage the vacuum gauge and the sensor.
5. When the temperature drops to freezing point, the instruments buried outdoors should be withdrawn to avoid frost cracking.
Annex I:
Soil suction range when plants need watering (for reference)
Species
10-20 Kpa
20-30 Kpa
30-50 Kpa
>50 Kpa
flowers
Wet flowers and plants:
Tropical orchids; Flamingo flowers; Bromeliaceae flowers; Begonias; Guanyin lotus; Crystal candles; Adiantum; Fanleaf Pteridium fern.
Lagerstroemia; Hydrangea; Magnolia; Hypericum; Rhododendron; Trollius; White Jade Ivy; Selaginella japonica.
Peony; Osmanthus; rose; rose; cherry blossom; hibiscus; Begonia axillaris; fig; honeysuckle; camellia; jasmine; ivy (Japan);
Drought-tolerant flowers:
Cactus; Crassulaceae flower; Agaveaceae; Chlorophytum flower; Yellow-edge short-leaved bamboo plantain; Sweet plum.
vegetables
Fruit tree
Cucumber (greenhouse);
Good night eggplant (greenhouse)
Leafy vegetables such as small greens; strawberries.
Celery; green peppers; cucumbers; melons; open field tomatoes; citrus fruits; pears and apples during fruit expansion.
Peas; potatoes; lemons; grapes; bananas.
Cabbage; lettuce; onion; carrot; cauliflower; garden tree; avocado; apple; pear.
Other crops
tea.
Tobacco; sugar cane; turf grass.
Corn; Wheat; Barley; Millet; Forage; Sorghum
Product certification
product name
Soil hygrometer (tension meter)
Product number
Negative pressure vacuum type
Inspectors
Check word
date
2007 Month Day
Annex II:
Determination of soil moisture characteristic curve
Soil moisture characteristic curve (also called characteristic curve, water holding curve) is the relationship curve of soil water suction and soil water content. Due to different soil properties and conditions, different soils have their own water characteristic curves. The characteristic curves of the soil moisture drying and wetting process do not coincide (hysteresis). For a certain soil, it is the characteristic curve of two different processes of dehydration and water absorption. The measurement of the characteristic curve can be carried out in the field, or it can be sampled indoors.
Field measurement method: When a tensiometer is buried in the field, at different depths of soil water suction, the soil moisture content is sampled and measured at the same depth near the tensiometer, the wet or dry process is recorded, the data is gradually accumulated, and then the curve is drawn.
Indoor measurement method: (Take mercury column soil thermometer as an example) Prepare a special bracket, install a tensiometer on the bracket, the tensiometer must have a volume scale, the mercury tube must be measured in advance, and the clay tube should be adjusted to the Need height, and after degassing treatment. Immerse the clay tube in the water, the water level reaches the center of the clay tube, read the height of the left side of the mercury column (h1), remove the water container, wipe off the water stains outside the clay tube, and quickly weigh the whole device (g2). Use a bulk weight ring knife (g1) to collect the soil sample from the field, place it on the support, bury the clay tube in the soil sample, and then measure the dehydration process. The measurement must be carried out under constant temperature conditions, soak the soil in water until saturated. Remove the water container, wipe off the water stain on the outer wall of the ring knife and the bracket, record the height of the mercury column (h1·h2), and weigh the whole set together with the ring knife and the soil sample (g3). Let the soil sample evaporate naturally, record the height of the mercury column during the evaporation process, and weigh it at the same time. When bubbles accumulate in the gas collection chamber, the bubble volume should also be recorded, but degassing is not necessary, and the drying process is measured until 640 mm Hg. Then measure the water absorption process, add a small amount of water to the soil surface, seal the soil surface with plastic paper, and let the water gradually distribute evenly in the soil. The next day, the plastic paper was lifted for measurement. After the measurement, water was added to cover the plastic paper. After the moisture balance, the measurement was carried out next day. Repeat this way until the soil sample is saturated. Take out the clay tube, all the soil on the clay tube and the ring knife should be scraped out, the soil sample is dried (105℃) and weighed (g). Result calculation:
The soil water suction is calculated as described above.
The formula for calculating soil moisture is as follows:
g3-( g2+ g1+g-g4)
W% = X100%
g
Where W is the soil water content (%);
g is the weight of dry soil (g); g1 is the weight of ring cutter (g); g2 is the weight of whole set of tension meter (g); g3 is the weight of the whole set of tension meter, ring knife and wet soil
Packing: 1PC
Warranty period: 120
On Jun-28-20 at 18:42:08 PDT, seller added the following information: