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Soil 4-Level Moisture/Temperature sensor

4-channel soil moisture sensor4-channel soil moisture sensor

The sensor is designed for use in automatic irrigation systems.

12mm diameter. Ideally for garden, greenhouse and home plants. 

 

 

 

 

 

General desription. 

The sensor uses a capacitive moisture measurement principle. The sensor measures soil moisture at four different depth levels. This allows you to control the soil moisture at the required depth, depending on the stage of plant growth. In addition, the sensor contains a thermosensor designed for measuring soil temperature.

 

A feature of this sensor is the use of a thick dielectric separating the measuring electrodes and the soil. This design of the sensor improves the accuracy of measurements in various types of soil. For example, the use of a thick dielectric makes it possible to reduce the influence of the heterogeneity of the soil. This is due to the significantly less influence of the air layers on the thickness of the sensor housing. This is also true for the density of contact with the soil. After installation in the soil, the sensor is much less susceptible to changing the measured values ​​at small displacements, which distinguishes it from most of the sensors on the market.

The sensor is completely protected from dust and moisture. The entire space of the sensor body is filled with a special resin, which allows it to be used in the open ground. Sensor fully electrically isolated from soil which gives it an excellent service life. 

 

Technical data

Sensor dimensions: length 130mm, diameter 12mm
The length of the working area of the measurement: 40mm (4 levels of 10mm each)
Power supply voltage: 4.5V..5.5V
Current consumption: 5..25 mA (25 mA less than 10% of the total time)
Absolute error of temperature measurement: no more than 0.5C
Protection class:  IP68
Change of values with a voltage change from 4.5V to 5.5V      less than 0.5%
Interface type: RS232 TTL
Cable length: 1m

 

 

Interface

The sensor is connected to an external device by means of a three-core cable in metal braid. The braided cable is connected to the minus supply inside the sensor body. The purpose of the conclusions is as follows:

  • Black [Blue] - Minus Power (GND)
  • Red [Yellow] - plus power
  • Green - RS232 output TTL (TX)

The sensor transmits the data as a text string containing the values ​​of the four humidity channels, the temperature value and the checksum. The transmission interval is approximately 2 seconds. The sensor data output can be connected directly to the RX UART microcontroller. UART settings for receiving the 9600 / N / 8/1 sensor data. It is also possible to connect the sensor to a conventional computer via an RS232-USB adapter. Example of data transmitted by the sensor

 

The format is: #<tab>A:nnnn<tab>B:nnnn<tab>C:nnnn<tab>D:nnnn<tab>T:tttt<tab>@:cccc<CR><LF>

# is character signaling start of data line
<tab> abulation character
A: B: C: D:    channel signature
nnnn channel data (0..1000)
T:  temperature signature
tttt temperature value in 0.1C (238 means 23.8C)
@:cccc check sum, may be ignored
<CR><LF>  standard end of line 

 

Several sensors can be combined into a network and connected to one input of the RX UART controller. In this case, all data outputs and plus terminals of the sensor power supply are combined with each other. The minus pins are connected to various MCU pins. The sensor selection is done by setting a low level (logical 0) on the corresponding MCU pin.

 

Installation and calibration

The accuracy and stability of the humidity measurement of the sensor depends on the correct installation and calibration. The need for calibration is due to different types of soil and, accordingly, the ability of the soil to retain water.

The sensor is placed in the soil at an angle of 30 to 45 degrees from the vertical. The inclination of the sensor reduces the effect of possible voids and cracks in the soil, which are usually located vertically. In addition, the flow of running water does not "wash in" the voids around the sensor housing. The sensor is buried so that about 5
mm of the white part of the body.

Calibration is to determine 100% of the moisture value. Those. determination of the maximum possible saturation with water of this type of soil. To do this, the soil with the sensor installed is spilled with water until the humidity readings on all channels stop growing. After this, it is necessary to wait for the order of one or two hours (to allow excess moisture to flow into the deeper layers of the soil). The moisture values obtained in this way can be taken as 100% of the moisture content of a given type of soil.

The sensor is pre-calibrated when fully immersed in water. The indications of each channel are 1000 units. This range of measurements is sufficient to determine the soil moisture with an accuracy of not worse than 1%.

 

* Ask about availability before purchase