TRS-I soil water potential and temperature monitor instructions

The TRS-I soil water potential and temperature monitor uses a soil moisture sensor and a temperature sensor to measure a multi-point soil water potential and temperature. It not only ensures the accuracy of the measurement, but also reduces the cost of multi-point observation. Suitable for moisture and temperature determination of farmland and potted soil.

First, the principle of the method

(1) Determination of soil water potential:

Figure 1 Schematic diagram of the working state of the water potential and temperature monitor

As shown in Figure 1, a plurality of water potential probes are buried in the field. As long as the top of the cylinder is injected with a needle plugging the rubber plug on the top of the water potential probe, the water potential value in the water potential probe will be read out on the display. A pressure sensor is mounted in the cylinder, one end of which is connected to the injection needle. The other end is connected to the display via a cable. On the one hand, the circuit in the display supplies power to the sensor, and the output signal of the sensor is amplified and digitized by A/D conversion and displayed on the display. A single display can perform hundreds of water potential probes, which significantly saves costs.

The liquid crystal display value is 0 to 100 KPa. The accuracy is ±1KPa. The display unit is displayed in kilopascals (KPa).

(2) Temperature measurement:

A platinum resistance temperature sensor is used, and the sensor is mounted on the top of the probe. The resistance of the extremely fine white gold wire in the sensor changes linearly with temperature. This change is sensed by the impedance detector inside the display and is displayed on the display by analog to digital conversion.

Second, the method of use

(1) Determination of soil water potential:

1. Before use, the water potential probe (ceramic head) should be immersed in water for more than 3 hours.

2. Fill the plastic tube of the water potential probe with cold water and plug the rubber stopper. Drill holes with a soil drill to a predetermined depth at the selected embedding point. Pour about 5 ml of mud into the bottom of the hole and insert the water potential probe into the hole. The soil around the plastic rod is compacted. The depth of the water potential probe is calculated from the distance from the middle of the ceramic tube to the soil surface.

3. Preparation of the display:

Push the top selector switch toward the water sensor socket.

Plug the sensor cable plug into the display socket and turn on the power switch. At this time, the display shows “0”. If it is not “0”, the zero potentiometer should be turned to “0” (see the third adjustment of the display for the zero adjustment method).

4. The water potential probe is buried in the moist soil for 1 hour. After drying the soil for several hours, the soil water potential can be measured. When measuring, just turn on the power of the display and puncture the needle on the measuring tube into the rubber plug of each water potential probe one by one, then the water potential data of each measuring point can be read from the display. The reading should be taken in the morning when the temperature changes little.

5. Turn off the power after the test is completed.

6. Calculation:

Soil water potential (KPa) = water potential reading - probe water column height (cm) / 10.2

In the formula: 10.2 is the conversion factor of centimeters of water column height converted to kilopascals (KPa).

The probe water column height is from the lower edge of the rubber stopper to the center height of the ceramic head.

(2) Temperature measurement

Push the monitor top selector switch toward the temperature sensor socket. Turn on the monitor's power switch.

Insert the top of the temperature sensor into the position where water temperature is required, and read it after 2 minutes. If the soil is hard, use an iron rod to help punch the hole to the position you need to measure. Push the sensor in.

Third, the calibration of the instrument:

    (1) Calibration of soil water potential sensor:

Zero adjustment of the instrument

1. The display has been calibrated before leaving the factory. Therefore, the screw with full adjustment cannot be turned. After plugging the cable plug of the sensor cylinder into the display socket, turn on the power switch and the display should show 0. If it is not 0, the zero point should be calibrated by the zero adjustment knob. The two knobs below the display panel are the zero adjustment knobs. If the display shows a negative value, first turn the left potentiometer clockwise to the head (bottom), then turn the right potentiometer counterclockwise to make the display number zero. If the display is positive, first turn the right potentiometer clockwise to the head (bottom), then turn the left potentiometer counterclockwise to make the number on the display zero.

To adjust the two zero potentiometers, the principle is that one of the potentiometers must be screwed clockwise to the head.

2. Calibration of the instrument:

The instrument has been calibrated at the factory. Just use the above zero adjustment when using.

Only when the sensor is replaced or the full-scale potentiometer is turned (normally, the mouth of the full-scale potentiometer can be sealed with adhesive tape to avoid any twisting). Instrument calibration is required.

The full scale is marked with a mercury pressure gauge as a standard pressure gauge (as shown in Figure 2). If the height difference between the two mercury columns at this time is 70 cm, the water potential is:

S=(70×13.6) ÷ 10.2=93.3KPa

The screen is displayed as 93.3 KPa by adjusting the full potentiometer.

Pull the needle out of the rubber stopper and adjust the number on the screen to zero by adjusting the zero potentiometer (as described above).

Then puncture the needle into the rubber stopper and adjust the full scale number again. Then, pull out the needle again to adjust the zero position. After repeated adjustments, the calibration of the instrument is completed.

Figure 2 calibration diagram of water potential sensor

(2) Calibration of temperature sensor:

This temperature sensor is a platinum resistance sensor. Its resistance at 0 ° C is 1000 ohms. The resistance at 50 ° C is 1194 ohms. The calibration of the temperature sensor is performed approximately once every six months.

Carry out the steps:

1. Open the back cover of the monitor.

2. Lead two wires from the temperature sensor access socket. Connect the resistor box terminal.

3. Adjust the resistance of the resistor box to 1000+A ohms. A is the temperature sensor cable resistance. If the cable has a single wire resistance of 0.14 ohms. The cable is 2 meters long. Then A = 0.14 ohms / meter * 2 meters * 2 = 0.56 ohms (the sensor is a double line, so the actual line length is 4 meters).

4. Please see the schematic. To the north of the open display, you can see two blue adjustable potentiometers at the top right of 2K and 10K. They are adjustable potentiometers at 0 ° C and 50 ° C respectively.

While looking at the back display digits, adjust the 2K potentiometer with a small screwdriver to make the display show 0.

5. Adjust the resistance of the resistor box to 1194+A ohms. Adjust the 10K potentiometer so that the display is 50.

6. Repeatedly adjust the resistance to 1000+A and 1194+A ohms. Make the display 0 and 50, respectively, until they change. The calibration is completed.

If there is no resistor box, it can also be wound with a standard resistance. The temperature is marked according to the actual value of the resistance for calibration. Because the resistance of the sensor is closely related to temperature, it is very linear.

Temperature sensor calibration diagram

Fourth, the instrument's power supply

The instrument should maintain a certain voltage. When the voltage is lower than the working voltage, the word Lo BAT is displayed on the screen. At this time, it should be charged, otherwise the reading accuracy will be affected.

The instrument power supply is equipped with a NI-Cd8.4V nickel-cadmium rechargeable battery and is equipped with a special charger. The soil water potential monitor does not work when charging. Plug in the charging plug first, then plug the charger into a 220V AC power outlet. It should be charged for 6-10 hours after the red light of the charger turns green, or the battery voltage should be measured when charging with a voltmeter, which should reach 9.8V.

In order to save electricity, the instrument automatically turns off the power supply function (about 15 minutes). After the power is turned off automatically, when it is used again, the power switch should be turned off before the power switch is turned on.

Five, instrument parameters:

The water potential measurement accuracy is ±2Kpa. The reading response time is no more than 2 seconds.

Temperature measurement accuracy ± 0.5 ° C. The reading response time is no more than 2 seconds.

Working power: 9VDC.

Six, matters needing attention

1. Water frequency of water potential probe:

The water potential probe buried in the field will gradually increase the bubbles in the instrument. The rate of increase is related to soil dryness. To maintain the sensitivity of the instrument, periodically open the rubber stopper to fill the tube with water. The time interval between each addition of water can be judged according to the measured soil water potential value:

When the measured soil water potential is in the range of 0 to 20 KPa, water is added once every 12 days.

When the measured soil water potential is in the range of 20 to 50 KPa, water is added once every 7 days.

When the measured soil water potential is in the range of >50 KPa, water is added for about 5 days.

Each time water is added, the reading is taken on the same day.

2, rubber plug replacement:

The rubber plug of the water potential probe should be tight. The Piset is made of neoprene, which is not easy to age and has good elasticity. The cork after acupuncture will not leak. If the air leak occurs during long-term use, the rubber plug can be replaced. Each water potential probe is equipped with 3 pissors.

3, the replacement of the injection needle:

If the needle breaks, replace it with a new one.