Liquid level linear measurement method based on impedance measurement

Abstract

The invention discloses a liquid level linear measurement method based on an impedance measurement. The method comprises the following steps: the liquid impedance is measured by using a measuring electrode and simultaneously ia group of reference electrodes are introduced; according to the inverse relation between the liquid impedance and the depth that the parallel or coaxial measuring electrode dips into the liquid to obtain the quotient between the two impedance figures measured by the reference electrode and the measuring electrode respectively; as a result, on the one hand, the final liquid impedance figure measured by the measuring electrode is linked with the liquid depth instead of the liquid composition; on the other hand, the inverse relation between the liquid impedance and the depth that the measuring electrode dips into the liquid is converted into a linear relation between the depth that the measuring electrode dips into the liquid and the final output signal, and the final output signal is linked with the liquid linearity instead of the liquid composition and property.

Description

technical field [0001] The invention relates to a liquid level linear measurement method based on impedance measurement. It belongs to the technical field of sensor measurement. Background technique [0002] At present, liquid level measurement has been widely used in daily life and industrial production, such as the water level in water tanks and water towers, the liquid level in the pipeline network and industrial production liquid reaction tanks such as chemical industry, and the liquid level of the fuel tank of motor vehicles. bit measurement. However, the current liquid level measurement has the following types: (1) Ultrasonic distance measurement: Fix the ultrasonic transmitting and receiving device above the water body, use ultrasonic waves to measure the distance change of the liquid surface, and obtain the water level. This method is costly and requires installation environment. More spacious; (2) Pressure sensing: According to the principle of pressure changes ca...

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Problems solved by technology

However, the current liquid level measurement has the following types: (1) Ultrasonic distance measurement: Fix the ultrasonic transmitting and receiving device above the water body, use ultrasonic waves to measure the distance change of the liquid surface, and obtain the water level. This method is costly and requires installation environment. More spacious; (2) Pressure sensing: According to the principle of pressure changes caused by liquid depth changes, a pressure sensor is placed on the bottom of the water, and the water level is calculated according to the pressure changes. This method has high requirements for water quality, such as sediment or scale deposits It is easy to be misaligned or even damaged. In addition, because it is generally installed at the bottom of the water tank, it has certain requirements for sealing; (3) Float / float type: The float type is widely used in motor vehicle fuel tanks. The principle is similar to that of sliding resistors. Floating up and down changes the resistance; the float type uses the float up and down as a mechanical switch, and each float can calibrate a water level. This method is a mechanical measurement method, and the contact carbon film of the float type will wear out with time , and is not suitable for conductive liquids such as water. Float-type mechanical switches have certain requirements for the manufacturing process, and the structure is complex, and the number of measurement points is limited; (4) Capacitive sensing: use water (liquid) as a switch between two electrodes If the liquid level rises and falls, the capacitance will change, and the water level can be detected by detecting the capacitance change through resistance-capacitance oscillation and other methods. This method also has high requirements on water quality and is greatly affected by the blockage of sediment and scale.

(5) DC electrode type: An electrode is installed at a certain distance on the insulating upright support structure (such as rubber, epoxy, plastic rod, etc.). When the water overflows the electrode, it is equivalent to grounding the electrode, so that it can be short-circuited Measure a part of the resistance string of the circuit, change the total resistance of the resistance string, and then detect the change of the resistance value of the resistance string through other methods such as resistance-capacitance oscillation to know the change of the water level. This method has a simple structure and low cost. It is currently used in solar water heater tank sensors. It can be widely used, but once a small amount of scale is formed on the surface of the electrode, which increases the contact resistance, it will fail

Higher failure rate due to faster scaling of hot water tanks

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