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The temperature error of magnetoelectric system instrument and its compensation technology

by:Sure     2021-08-23
Reasons for this temperature error 1. The elasticity of the hairspring changes. When the ambient temperature changes, the elasticity of the hairspring will change. When the temperature rises, the elasticity of the balance spring and the shrapnel that produce the reaction torque will weaken. When the temperature rises by 10°C, the elasticity will weaken by 0.3%-0.4%, and the meter reading is fast, showing a positive additional error. 2. The magnetism of the permanent magnet changes. The reason for this temperature error when the temperature changes. 1. The elasticity of the hairspring changes. When the ambient temperature changes, the elasticity of the hairspring will change. When the temperature rises, the elasticity of the balance spring and the shrapnel that produce the reaction torque will weaken. When the temperature rises by 10°C, the elasticity will weaken by 0.3%-0.4%, and the meter reading is fast, showing a positive additional error. 2. The magnetic change of the permanent magnet When the temperature changes, the magnetic change of the permanent magnet with a fixed magnetic field is produced. The magnetic temperature coefficient is a negative value, that is to say, the magnetism of the permanent magnet will be weakened by 0.2%-0.3 every time the temperature rises by 10℃. %, there is a negative additional error in the meter reading. 3. There is a temperature coefficient of resistance. The resistance of the movable coil, the resistance of the elastic parts and the resistance of the circuit part wound by copper or aluminum wire will change with the change of temperature, so it will bring certain additional errors. 4. Comprehensive error analysis When the temperature changes, the change of the elastic parts of the instrument and the additional error caused by the weakening of the permanent magnet have opposite signs, which can offset part of each other but cannot completely cancel each other. For every 10℃ increase in temperature, the decrease is about 0.1%- 0.2%. For a movable coil made of copper or aluminum wire, the resistance value changes by 4% every time the temperature increases by 10°C. For low-range voltmeters and ammeters with shunt resistors, larger temperature errors will be caused. Corresponding compensation measures must be taken in the measurement circuit. Temperature error compensation measures 1. When the temperature of the magnetic circuit compensation method increases, the magnetic field becomes weaker. Special materials can be used in the instrument system to make a magnetic shunt, such as copper-nickel alloy or iron-nickel alloy. When the temperature rises, The effect of the magnetic shunt is weakened. When the temperature decreases, the effect of the magnetic shunt is strengthened, thereby compensating for the change of the permanent magnet magnetism caused by temperature changes, and improving the linearity and accuracy of the instrument. 2. Bimetallic adjustment method When the temperature changes, the tension of the balance spring changes, causing the reaction torque to change, which plays a role of temperature compensation. 3. Negative temperature coefficient device compensation method Some components have a negative temperature coefficient and higher sensitivity, such as thermistors, whose resistance temperature coefficient is much larger than that of copper and aluminum. Negative temperature coefficient devices are used to compensate for temperature errors. , The circuit is simple, and compared with the bridge compensation method, the internal resistance of the ammeter can be reduced. It should be pointed out that due to the non-linear characteristics of the thermistor, appropriate metal resistors in parallel can be used to compensate for non-linear errors.
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