Plant stem flow meter is an important tool for monitoring plant transpiration. By measuring the sap flow rate of plant stems, the dynamics of plant water transport can be quantified. The debugging process involves multiple steps such as equipment installation, parameter calibration, data acquisition and optimization, and requires strict adherence to operating standards to ensure data accuracy. The following are the detailed steps and technical points for debugging plant stem flow meters:
1、 Preparation before debugging
1. Equipment inspection
-Confirm that the main unit, probe (sensor), connecting wires, power supply and other components of the stem flow meter are complete and undamaged.
-Check if the probe model matches the stem size of the target plant (e.g. the thermal diffusion probe needs to be adapted to stem diameter).
-Test the power supply voltage and signal line connectivity to avoid data abnormalities caused by circuit problems.
2. Environment and Plant Preparation
-Choose healthy and representative plants to avoid pests, diseases, or mechanical damage to individuals.
-Clean the surface impurities of the stem (such as soil and leaves) and wipe them clean with a damp cloth to reduce probe contact errors.
-Mark the installation height (usually 20-50 cm above the base of the main stem) to ensure that the probe is parallel to the direction of water flow.
2、 Probe installation and fixation
1. Installation method
-Thermal diffusive stem flow meter: Install heating needles and temperature probes symmetrically at the upper and lower ends of the stem, with spacing adjusted according to the stem diameter (usually 5-15mm).
-Thermal pulse type stem flow meter: embed the heater and temperature sensor into the stem, wrap them with waterproof tape or special fixing tape to avoid compressing the stem and affecting the liquid flow.
-Ultrasonic stem flow meter: The stem needs to be cut and an ultrasonic sensor inserted, and caution should be taken during operation to avoid plant damage.
2. Sealing and Protection
-Seal the contact surface between the probe and the stem with waterproof materials such as silicone gaskets and heat shrink tubing to prevent rainwater or condensation from seeping in.
-When fixing the probe, the tightness should be moderate to avoid liquid flow blockage or stem deformation caused by compression.
3、 Parameter setting and calibration
1. Initial parameter configuration
-Sampling frequency: Set according to research needs (usually 1-30 minutes/time). Short term experiments can use high-frequency sampling, while long-term monitoring should reduce the frequency to save electricity.
-Heating parameters: The thermal diffusion probe needs to set the heating pulse duration (such as 1-5 seconds) and power to avoid overheating and damage to plant tissues.
-Zero point calibration: After installation, let it stand for 30 minutes until the data is stable, and then reset the flow rate to zero (some equipment requires manual calibration).
2. Calibration method
-Zero point calibration: Disconnect the heating function, record the temperature difference in natural state, and adjust it to the reference value (such as 0 mV).
-Full range calibration: Verify probe response and correct measurement bias by simulating liquid flow using known flow rates (such as gravity titration).
-Temperature compensation: Input environmental temperature data to eliminate the impact of temperature fluctuations on the sensitivity of thermal diffusion probes.
4、 Data collection and debugging optimization
1. Real time data monitoring
-After starting the device, observe the initial flow rate curve, which should normally exhibit a circadian rhythm (high during the day and low at night).
-If the data remains zero or fluctuates violently, check the probe connection, power supply, and installation direction (such as aligning the axial direction of the thermal diffusion probe with the flow direction).
2. Interference elimination
-Environmental interference: Avoid strong winds, direct sunlight, or rainy days during debugging to prevent sudden changes in temperature and humidity from affecting sensor performance.
-Mechanical interference: Ensure that there are no vibration sources (such as shaking tree branches) around the probe to avoid signal noise.
-Biological interference: Drive away animals or insects that gnaw on stems, and install protective covers if necessary.
3. Comparative verification
-Use staining tracing method (such as methylene blue solution) to verify the liquid flow path and ensure that the probe installation position is reasonable.
-Multi probe synchronous monitoring: Install multiple probes at different heights on the same plant or adjacent plants to compare data consistency.
5、 Common Problems and Solutions
1. Abnormal high/low data
-Reason: The probe is installed too tightly, the heating power is insufficient, and the calibration is not completed.
-Solution: Adjust the tightness of the probe again, check the heating module and recalibrate it.
2. Signal drift or high noise
-Reason: Poor line contact, environmental electromagnetic interference, insufficient battery power.
-Solution: Replace the data cable or power supply and keep it away from electromagnetic sources such as motors and transformers.
3. Lack of circadian rhythm
-Reason: Probe damage, abnormal closure of plant stomata (such as drought stress).
-Solution: Replace the probe or combine meteorological data (such as VPD, lighting) for comprehensive analysis.
6、 Long term monitoring precautions
1. Equipment maintenance
-Regularly clean the surface dirt of the probe, check the sealing and fixing status.
-Replace aging batteries or solar panels to ensure stable power supply.
2. Data storage and backup
-Annotate the date, weather, and plant growth stage (such as fertilization and pruning) when exporting data.
-Cloud storage or local backup to prevent data loss.
3. Assessment of plant growth impact
-Long term monitoring requires evaluating the interference of probes on plant growth (such as probe loosening caused by stem thickening), and adjusting the installation position in a timely manner.