The electric instrument of tank truck can be divided into two types of electric heating type and electromagnetic type according to different working principles.
Electric heating instrument system: This type of tanker instrument is most commonly used. The basic structure of the water temperature gauge, oil pressure gauge and fuel gauge of this system are the same, but the dial is different. The performance of this type of meter is: ① The pointer of the meter moves slowly and smoothly. Even if the electrical signal from the sensor changes suddenly, the pointer will not swing sharply. ② A voltage regulator is installed in the instrument circuit, and the accuracy of the displayed value is basically not affected by the voltage of the charging system. The fuel gauge's sensor can be a variable resistance type or a pulse current type. If it is the latter (pulse current type), the meter does not need to be equipped with a voltage regulator because it is not affected by power supply voltage fluctuations. ③Although the ambient temperature will affect the heating coil of the instrument, because the bimetal of the instrument is U-shaped, the movable arm and the fixed arm will deform in the opposite direction and have a mutual compensation effect, so the indicated value will not be affected by the ambient temperature. Impact.
Electromagnetic instrument system. The performance of this type of tanker meter is: ① The indicator value of the meter pointer depends on the balance of the electromagnetic force of two or three electromagnetic coils in the table. Because the coil is easy to damage, it is also sensitive to the fluctuation of the sensor signal, so the stability of the indicated value is poor. ② In order to suppress the pointer swing caused by the vehicle driving, a silicone damping liquid is often installed in the instrument. When the ignition switch is turned off, the pointer should stay in the original position for a short time before gradually swinging to the high or low end of the instrument panel; if the pointer is already in a balanced position, it may also be in its original position. Do not use this during use. The situation is considered a malfunction. ③ The change of the voltage of the charging system will not affect the indication value of the meter pointer. There is no need to set a voltage regulator in the meter circuit.
The sensor performance of electric heating and electromagnetic tank truck instruments is quite different. The variable resistance sensor of the electric fuel gauge has the smallest resistance value when the fuel tank is full, the largest resistance value when the fuel tank is empty, and the opposite is the case with the electromagnetic type. Another example is the sensor of the electric oil pressure gauge, whose resistance value decreases when the oil pressure rises, and the resistance value increases when the oil pressure decreases, while the electromagnetic type also has the opposite. Another example is that the thermistor of an electric water temperature sensor has a high negative temperature coefficient. The thermistor value is 220 ohms at 50 degrees Celsius, and the resistance value drops to 20 ohms when the temperature rises to 115 degrees Celsius. The sensor has a higher resistance value when the water temperature is 100 degrees Celsius, but the resistance value decreases significantly when the temperature continues to rise.
In addition, the ammeters used on tank trucks are generally electromagnetic, and a few use dynamic magnetism (such as Dongfeng tank trucks). The difference lies only in the rotor of the meter. The rotor of the electromagnetic ammeter is made of soft steel. The rotor is deflected by the combined magnetic field of the charge and discharge current magnetic field and the permanent magnet magnetic field. The rotor of a moving magnetic ammeter is made of a permanent magnet. The rotor is deflected under the action of the charge and discharge current magnetic field alone. The measurement range of this ammeter is larger than that of an electromagnetic ammeter. But no matter what kind of ammeter, if it works continuously for a long time, it must limit the current to extend its service life.