The use and zero calibration method of level instruments
1、 The reason for the zero position error of the level gauge:
Factors such as transportation, placement, vibration, temperature, wear, and adhesive aging can all cause inaccurate zero position of the level. Therefore, the accuracy of the zero position indication error of the level should be checked before use. During the calibration process in the laboratory, the accuracy of the zero position is also checked before proceeding with the next calibration work.
2、 Zero calibration method for level instruments
There are two methods for zero calibration of box and bar level instruments: one is to check the accuracy of zero error on a roughly horizontal flat plate (or machine tool guide rail); The second is to calibrate the zero position error according to JJF1084-2002 (Calibration Specification for Frame Level and Bar Level). It is now described as follows:
1. Check the accuracy of zero position error on a roughly horizontal flat plate (or machine tool guide rail).
After the bubble stabilizes, read at one end (such as the left end) and set it to zero. Turn the level again 180 degrees., If it is still placed in the original position of the flat plate, it is usually advisable to place a positioning block. After the bubble stabilizes, if it still reads (A grid) at the original end (left end), the zero position indication error of the level is 1/2A grid, which should comply with the provisions of Table 1.
2. According to JJF1084-2002, perform zero position error calibration on the level zero position calibrator.
JJF1084-2002 introduces zero position error calibration methods based on five different working surfaces
Introduce the zero position error based on the working surface.
Before measuring, place the calibrated level (which has been polished and cleaned) on the workbench of the level zero calibration device, close to the positioning block. After the bubble stabilizes, place a few o on one end of the bubble.; Then turn the level to 180o and accurately place it in its original position. Record the reading on one side of the first reading and the reading on the other end of the bubble. The difference of half of the two readings is the zero position error. According to the requirements of Table 1, determine whether it is qualified or not. If the zero position error exceeds the allowable range in Table 1, it is necessary to adjust the zero position adjustment mechanism of the level (adjusting screw or nut) to reduce the zero position error to within the allowable range. Do not arbitrarily tighten screws and nuts that are not regulated for adjustment. Before calibration and adjustment, the working surface of the level and the calibration table of the flat plate must be wiped clean.
3、 Method for Adjusting the Zero Position Error of a Level Gauge
The zero adjustment of the level is roughly classified into the following two categories based on the number and location of the zero adjustment devices:
1. One side adjustable
There are two fixing screws on both sides, one end serves as a fixing device, and the other end serves as an adjustment mechanism. A special wrench or screwdriver can be used to adjust the zero position error of the working surface on the flat plate. First, remove the cover of the adjustment mechanism, and the two adjustment fastening screws can be seen. Place the level gauge on the flat plate tightly against the positioning block. After the bubble stabilizes, read n ^ at the left end (A-end) of the bubble, and then rotate the level gauge 180 degrees., Accurately place it in its original position. Record the reading 0n on one side of the first reading on the other end (B-end) of the bubble. If>, then the B end is high. Use a wrench to adjust the screw so that the bubble moves 1/2 (aB one notch) towards the lower end. After standing still for half an hour, retest and adjust according to the same method. After the zero position error meets the requirements, it is necessary to use a fine adjustment mechanism wrench to tighten the screw. After the final zero position error meets the requirements of JJF1084-2002, it is placed on the flat plate for 4 hours and measured again to determine whether it is qualified. Sometimes, there may be situations where the deviation is still out of tolerance, usually within 2 divisions of the glass tube scale. The method used in this case is not to move the previous adjustment screw, but to use a screwdriver to slightly rotate the screw of the fine adjustment mechanism (see Figure 3). Let it stand for another 4 hours and measure again until it is qualified. A fixed level without any adjustment device can only be adjusted by grinding the measuring surface or replacing bubbles when the zero position is incorrect. Only limited to level gauges or rulers with high graduation values and low accuracy.
