Load Cell Based Dynamic Characterization and Adaptive PWM Dosing for Precision Electrical Conductivity Regulation in a Nutrient Mixing Tank Rizki Pratama Putra
Load Cell Based Dynamic Characterization and Adaptive PWM Dosing for Precision Electrical Conductivity Regulation in a Nutrient Mixing Tank
Abstract
Setting appropriate nutrient concentrations in a hydroponic system requires precise dosing and rapid homogenization to achieve the desired electrical conductivity (EC) without exceeding limits. However, dosing pumps, especially the peristaltic type, usually exhibit nonlinear flow characteristics, dead zones at low input voltages, and delays in mixing dynamics, which limit the performance of conventional feedback control. This study presents load cell-based dynamic characterization and adaptive PWM dosing strategy for precision EC regulation in small scale hydroponic mixing tanks.
The system tested consisted of a 12 V peristaltic dosing pump, a load cell for flow characterization, an EC sensor for monitoring electrical conductivity, and a mixing tank with a marine propeller type agitator, baffle. Test results show that the minimum voltage of the dosing pump is 9 V RMS, with flow rates ranging from 21.4 to 78.6 mL per minute.The pump response is approximated by a first-order dynamic model with a time constant of 0.83 seconds and a steady-state flow repeatability error below 3.5 percent.
To reduce excess EC caused by mixing delays or excess dosing, a dynamic PWM pulse delivery strategy is provided with dynamic values ​-​-in a single step based on the EC sensor feedback results. Based on transient sensor EC measurements, it was found that for method 1 with constant step PWM, the homogenization time was around 12-18 seconds at an agitator speed of 1100 rpm in a 5 L mixing tank with EC overshot occurring 1 to 3 times. while for method 2, adaptive PWM is applied and with the same tank conditions the homogenization time is achieved around 9-10 seconds without EC overshot from the set value range.
These findings demonstrate that adaptive PWM dosing with the integration of load cell-based dosing pump characteristics provides a promising instrumentation framework for high-precision nutrient regulation that reduces the potential for overshot and cyclic dosing in hydroponic systems
