Regarding servo level gauge failures
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The float of the servo level gauge will not go up or down; it’s not possible to lower the float to show the desired level, even though the container is actually empty. Open it and take out the float to check; both the float and the steel cable are in good condition. What could be the issue, and how can it be diagnosed? What is the principle of a servo level gauge?
Servo motor-based level gauges are primarily used for highly accurate measurement of liquid levels in storage tanks. They are widely employed in modern industry, as they are multi-functional instruments that can measure not only the liquid level but also parameters such as the interface level, density, and the bottom of the tank. It operates on the principle of buoyant force balance, with a small float driven by a micro servo motor, enabling accurate measurement of parameters such as liquid level. It is mainly used for high-precision measurement of light oils, and is applicable to calm, lightweight, non-corrosive liquids.
This post was last edited by c3h5e8n1 on 2017-6-29 11:24. Shenghong? Which one? For the servo, the reason it can’t go down is definitely that the force applied isn’t right; you’re lifting it all the way up, right? If it is an Enrafu servo, using the CA command to lift it to the top may cause it to get stuck at the corner of the drum chamber. As for the method, if you can’t put it down, then try harder to do so. If I1 (level measurement command) fails, use I2 (bottom of tank measurement command). In the future, try not to use CA to lift the float; instead, use the LT command, which is used to raise the float to the setting position of MH (high motor position). The servo’s level display indicates the current position of the float. Now the float is on top of the tank, so of course the liquid level shows the highest value.
A servo-level gauge is based on the principle of buoyant balance; it uses a micro servo motor to drive a small float, enabling accurate measurement of parameters such as liquid level. As shown in Figure 1, the float is suspended inside the instrument housing by a measuring wire, which is wound around a precisely machined outer drum ； The external magnet is fixed inside the outer drum and coupled with the internal magnet fixed inside the inner drum. When the level gauge is in operation, the gravity of the float acting on the thin wire generates a torque on the magnet of the outer drum, thereby causing a change in magnetic flux. Changes in the flux between the drum components cause changes in the output voltage signal of the electromagnetic sensor (Hall element) on the inner magnet. Its voltage value is compared with the reference voltage stored in the CPU. When the position of the float is balanced, its difference is zero. When the liquid level of the medium being measured changes, it alters the buoyancy of the float. As a result, the magnetic coupling torque is altered, causing the output voltage of the hall element with temperature compensation to change. The difference between this voltage value and the reference voltage in the CPU drives the servo motor to rotate, adjusting the upward and downward movement of the float to re-establish the equilibrium point. The entire system forms a closed-loop feedback circuit (as shown in Figure 1), with an accuracy of up to ±0.7 mm. Moreover, it has a built-in loading compensation function that can compensate for changes in the tension of the wire caused by the attachment of the substance being measured to the wire or float.