Research On Indoor Verification Methods For Digital Levels

Digital level has a history of nearly 30 years since it entered the market.Because of its high measurement accuracy and intelligence,it has been widely used in various engineering constructions.As a high accuracy measuring instrument,the accuracy of the measurement will have a direct impact on the quality.Therefore,the digital level is listed as a legal measuring instrument of the country,and it is necessary to verify every performance indicators of the digital level through scientific and effective verification methods.At present,the commonly used digital level verification methods include outdoor verification method,indoor and outdoor combined verification method,and imperfect indoor verification method.Although the outdoor verification method can verify all the items of the digital level,it has the disadvantages of large verification site,timeconsuming and laborious verification process,low verification efficiency,and the verification results are easily restricted by the climatic conditions and time.The combination of indoor and outdoor verification method is to verify items of the optical and mechanical parts of the instrument indoors according to the verification method of optical levels,while for other verification items of digital levels,only the matching bar code ruler can be verified outdoors,so it also has the disadvantages of outdoor verification method.In order to overcome the shortages of outdoor verification methods of digital levels,indoor verification method came into being.In the existing incomplete indoor verification methods,the segments of barcode rod images of various commonly used digital levels are micro-engraved on the diaphragm after photographing,and two identical parallel light tubes with the barcode image diaphragm are placed in diametrical alignment,so as to realize the indoor verification.This method can overcome some defects and shortcomings of the outdoor verification methods,but it also brings new problems and difficulties:(1)The unequal height of the optical tubes on both sides makes the horizontal line of sight provided by the two tubes not at the same height,which cannot meet the verification requirements of a horizontal alignment for the verification equipment.(2)the barcode rod diaphragm is fixed at a specific sight distance position and cannot be moved,which cannot fulfill the verification of the focus running error of the telescope;(3)one indoor verification equipment cannot complete all the necessary verification items of the digital level.Therefore,the ways to realize the indoor verification of digital levels are to solve the defects of inperfect indoor verification method.Thus,the paper proposes an indoor verification method for digital levels based on a special single light tube.This method combines the JSJ comprehensive verification equipment and the special light tube,then together with a precision turntable,four-dimensional micro tilting table and lifting platform to form a digital level full indoor verification equipment.The “special light tube” with a focal length of 1000 mm,which can provide a horizontal guideline with a standard deviation less than 0.5 ",and can achieve a continuously adjustable target in the range of between 2m to infinite distance.Then it can meet the requirement of different sight distance in order to verify the remaining electronic i-angle and the focus running error of the telescope.In addition,by using the principle of optical imaging,the size of barcode rod is reduced in proportion,and a barcode image of a certain length is obtained through the corresponding decoding technology.Then the barcode rod is engraved on the diaphragm of the "special light tube" by using the precision lithography technology to realize the indoor design of the barcode rod.In this way,a verification device can complete the indoor verification of the digital.By analyzing the source of the uncertainty of the equipment,calculating the uncertainty of each component and the combined standard uncertainty,the expanded uncertainty is 0.86 "(k = 2.02,P = 0.95),which is less than the required uncertainty 2".The results show that the proposed full indoor verification method can meet the metrological requirements for verifying the digital levels,which can lay a theoretical foundation for indoor verification of various digital levels.