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how to check your speedometer
Speed measuring device:
Rollers, speed sensors and lifters in speed measuring devices composition. There are four rollers in two groups, and they are installed on the frame through rolling bearings. In order to prevent the slippage of the automobile differential gear during the test, the two front rollers of the test bench are connected together by a coupling. The speed sensor generally uses a photosensitive tube or a Hall sensor, which is installed at one end of the drum, and sends the voltage signal (or pulse signal after processing) corresponding to the drum speed to the speed indicating device. In order to make it convenient for the car to enter and exit the test stand, a lifter is provided between the front and rear rollers. The lifter is mostly driven by pneumatic or hydraulic pressure. The lifter is linked with the drum brake device, when the lifter is raised, the drum is braked and cannot rotate.
Speed indicating device:
The speed indicating device is based on the electric signal (voltage signal or pulse signal) sent by the speed sensor and the parameters such as the outer circumference of the drum. After processing, the driving display device indicates the vehicle speed in km/h.
speed warning device:
The speed alarm device is set up to determine whether the error of the speedometer is within the acceptable range. Generally, there are three types:
a) Use the test bench alarm device to indicate and detect the speed of the vehicle.
When the actual driving speed reaches a specified value (such as 40km/h), the alarm device light will be on or the buzzer will sound to remind the driver that the vehicle has reached the detection speed. Pay attention to observe whether the speedometer indication value in the cab is within the qualified range (The qualified range is 38km/h~48km/h);
b) Use the green area painted on the indicating instrument to indicate the qualified range of the error between the indicated value of the speedometer and the actual vehicle speed. During the test, when the indicated value of the vehicle speed reaches a certain detection speed (such as 40km/h), observe the indicated value of the speedometer on the test bench at the same time. Whether it is within the qualified green zone (such as 37.3km/h~42.1km/h):
c) An alarm device equipped with the above two devices at the same time.
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