Abstract
Real-time detection of liquid level in complex environments has always been a knotty issue. In this paper, an intrinsically safe liquid-level sensor system for flammable and explosive environments is designed and implemented. The poly vinyl chloride (PVC) coaxial cable is chosen as the sensing element and the measuring mechanism is analyzed. Then, the capacitance-to-voltage conversion circuit is designed and the expected output signal is achieved by adopting parameter optimization. Furthermore, the experimental platform of the liquid-level sensor system is constructed, which involves the entire process of measuring, converting, filtering, processing, visualizing and communicating. Additionally, the system is designed with characteristics of intrinsic safety by limiting the energy of the circuit to avoid or restrain the thermal effects and sparks. Finally, the approach of the piecewise linearization is adopted in order to improve the measuring accuracy by matching the appropriate calibration points. The test results demonstrate that over the measurement range of 1.0 m, the maximum nonlinearity error is 0.8% full-scale span (FSS), the maximum repeatability error is 0.5% FSS, and the maximum hysteresis error is reduced from 0.7% FSS to 0.5% FSS by applying software compensation algorithms.
Highlights
Liquid level sensing in flammable and explosive environments has always been a technical challenge.Generally, liquid level can be detected with reported various methods such as the float, ultrasonic [1], magnetostrictive [2], differential pressure [3], optical [4,5], and capacitive methods [6,7], etc
The magnetostrictive liquid-level measurement technique is based on the detection of the propagation time of the elastic wave produced by the magnetostrictive effect in ferromagnetic materials
The magnetostrictive liquid-level sensor suffers from the significant disadvantage of requiring the active float, which is easy to get stuck in special environments such as the turbid liquid
Summary
Liquid level sensing in flammable and explosive environments has always been a technical challenge. Capacitive sensors are increasingly common over other existing ones in the field of electrical liquid-level sensors due to remarkable advantages such as low cost, high linearity, low energy dissipation, and easy adjustability to the geometry of the application [10]. Currently used capacitive liquid level sensors are limited in application to potentially flammable or explosive environments due to the complex structure and non-intrinsic safety. Once the intrinsic safety issue is resolved, capacitive sensing design reduces the costs and may provide a handy solution for liquid-level measurement in flammable and explosive environments. Unable to measure the turbid liquid level and other liquid with sticky substance Based on such considerations, a novel, intrinsically safe liquid-level sensor system is designed and implemented to realize liquid level detection in flammable and explosive environments by using the poly vinyl chloride (PVC) coaxial cable.
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