In order to realize automatic measurement for liquid level of oil tank

a new type of vision automatic measurer is developed based on S3C2440 ARM9 platform.A type of adaptive image processing algorithms are developed by C language and embedded development tool

arm development suite（ADS）.According to measuring range

a 30 m long ruler is specially made.Pretreatment algorithms of ruler image are presented on the basis of adaptive threshold binarization

mathematic morphology noise-removing and characters segmentation.After features of ruler characters and scales are summarized

the algorithm of integer recognition and decimal reading is analyzed.Experimental results indicate that it takes no more than 0.4 s averagely in each auto-reading and the recognition accuracy rate is 98 %

and the precision is 0.1 mm.The algorithm has the advantages of high precision

high speed

well stability

high automation

and can effectively solve the problem of low measurement precision of manual measurement methods

thus completely satisfied requirement of real-time measurement for oil tank liquid level.