The core of maintaining and calibrating digital soil water temperature and salinity sensors is to prevent malfunctions through regular cleaning and status checks, and to correct errors through standard comparison to ensure long-term accurate measurement. The following are specific maintenance and calibration methods, clearly divided by module.
1、 Daily and regular maintenance (to prevent performance degradation)
Maintenance should revolve around "pollution prevention, damage prevention, and aging prevention" and be divided into two categories: daily inspections and regular in-depth maintenance.
1. Daily use and maintenance (after each sampling/weekly)
Clean the sensor probe: Immediately rinse the surface of the probe with clean water after sampling to prevent salt or organic matter from adhering and clumping. If there is stubborn dirt, gently brush with a soft bristled brush (hard brush is prohibited to prevent scratching the probe coating), wipe dry and store.
Appearance and connection inspection: Check for cracks and wear on the probe housing (especially in temperature/salt sensing areas), damaged data cables, and loose connectors. If the shell is found to be cracked, it should be stopped immediately to prevent soil moisture from seeping into the interior and damaging the circuit.
Storage environment control: When not in use, place the sensor in a dry, ventilated, and non corrosive gas environment, avoiding direct sunlight or high temperature and humidity. The probe should be kept away from metal objects to prevent interference with salt measurement.
2. Regular in-depth maintenance (adjusted every 3-6 months depending on usage frequency)
Circuit and sealing testing: Use a multimeter to check whether the output signal of the sensor is stable (refer to the standard signal range in the manual, such as 4-20mA or 0-5V). If the signal fluctuates too much, it may be due to moisture in the internal circuit, and the manufacturer needs to be contacted for maintenance.
Probe coating protection: Some salt sensor probes have special sensing coatings, and the coating should be regularly checked for detachment. If the coating is slightly worn, a special protective agent can be applied according to the manufacturer's requirements; When the wear is severe, the probe needs to be replaced.
Data cable maintenance: Check if the shielding layer of the data cable is intact to avoid electromagnetic interference caused by shielding failure (such as abnormal salt measurement values when there are high-power devices nearby). If the data cable ages, replace it with a shielded cable of the same specification in a timely manner.
2、 Calibration method (correcting measurement errors, once every 6-12 months)
Calibration needs to be carried out separately for the three parameters of "temperature, moisture, and salt", and corresponding standard materials and equipment need to be prepared, strictly following the process of "standard environment → comparison correction → verification".
1. Temperature parameter calibration (easiest to operate, can be completed by oneself)
Prepare standard equipment: high-precision mercury thermometer (accuracy ± 0.1 ℃) or standard temperature calibrator, and a temperature controlled container (such as a constant temperature water bath).
Calibration steps:
Place the sensor probe and standard thermometer together in a constant temperature water bath, and set three typical temperature points (such as 5 ℃, 25 ℃, and 40 ℃, covering the commonly used measurement range of the sensor).
After the water temperature stabilizes (at a constant temperature for more than 30 minutes), record the temperature display value of the sensor and the reading of the standard thermometer, and calculate the error between the two.
If the error exceeds the accuracy range of the sensor (such as ± 0.5 ℃), adjust it through the sensor's calibration software (some sensors support computer connection calibration) or hardware buttons (such as calibration keys) to make the displayed value consistent with the standard value.
2. Calibration of soil moisture parameters (requires simulation of soil environment, semi professional operation is recommended)
Prepare standard materials: standard soil samples with different moisture contents (which can be prepared by the "drying method", such as sandy loam soil with moisture contents of 5%, 15%, and 25%, consistent with the actual soil type sampled), or standard soil moisture calibration modules.
Calibration steps:
Load the standard soil sample into a dedicated calibration container, gently compact it (simulating the compactness of natural soil), and insert the sensor probe to the specified depth (refer to the instruction manual, usually 2/3 of the probe length).
Wait for 5-10 minutes until the sensor reading stabilizes, record the displayed moisture value, compare it with the actual moisture content of the standard sample, and calculate the error.
If the error exceeds the standard (such as ± 2% volumetric water content), input the standard value through calibration software to automatically correct the measurement curve of the sensor; Sensors without software functionality need to record error values and manually correct them during subsequent data processing.
3. Calibration of conductivity (salinity) parameters (requires standard solution, recommended to be supported by the manufacturer)
Prepare standard substances: KCl standard solutions of different concentrations (such as 100 μ S/cm, 1000 μ S/cm, 10000 μ S/cm, covering the salt measurement range of the sensor), and plastic beakers (to avoid interference from metal ions).
Calibration steps:
Place the sensor probe into a beaker containing standard KCl solution, ensuring that the probe is completely submerged (the liquid level does not exceed the sensing area) and avoiding touching the beaker wall.
Let it stand for 3-5 minutes, wait for the reading to stabilize, record the conductivity value displayed by the sensor, compare it with the concentration of the standard solution, and calculate the error.
If the error exceeds the allowable range (such as ± 5%), it is necessary to contact the sensor manufacturer and use a dedicated calibration tool (such as the calibration instrument provided by the manufacturer) to recalibrate. Some sensors can be calibrated through a mobile app or computer software.