Multi-Channel, Microwave-Based, Compact Printed Sensor for Simultaneous and Independent Level Measurement of Eight Liquids

Industrial automation relies on sensing the process parameters like liquid levels. Simultaneous sensing of multiple fluids is especially useful for many automation processes involving multiple ingredients. Some of the desirable features in any level sensor are its non-intrusiveness, high accuracy, and consistent performance. These features can be achieved with typical microwave radar-based level sensors. However, this paper presents a microwave resonance method instead of typical microwave reflectance (radar) to reliably sense the liquid level at fraction of the cost using a unique printed sensor. In addition to that, sensor design presented in this paper enables sensing liquid level of eight liquids simultaneously and independently utilizing its multiple channels. An array of eight modified microwave T-resonators has been compactly packed inside a metallic cylinder of just 4" diameter where the resonators share the same ground plane. Sensors' performance, to measure the unknown level of eight different fluids (with dielectric constant (∈_r) ranging from 2.8 to 80), has been measured in real time using a custom-built software. Simple one point calibration procedure has also been proposed in this paper which has resulted into measurement accuracy of ~0.6% which is better than 1%, realizable with high-end and expensive radar based level sensors.