毕业论文外文翻-水准尺和水准仪.docVIP

外文资料 Level Rods and Lenels There are many kinds of lenel rods available.Some are in one piece and others (for ease of transporting) are either telescoping or hinged.Level rods are usually made of wood and are graduated from zero at the bottom.They may be either selfreading rods that are read directly through the telescope or targetrods where the rodman sets a sliding target on the rod and takes the reading directly. Most rods serve as either self-reading or as target rods. Among the several types of level rods available are the Philadelphia rod,the Chicago rod, and the Florida rod. The Philadelphia rod, the most common one, is made in two sections. It has a rear section that slides on the front section. For readings between 0 and 7 ft, the rear section is not extended; for reading between 7 and 13 ft, it is necessary to extended the rod. When the rod is extended,it is called a high rod. The Philadelphia rod is distinctly divided into feet, tenths, and hundredths by means of alternating black and white spaces painted on the rod. The Chicago rod is 12 ft long and is graduated in the same way as the Philadelphia rod, but it consists of three sliding section. The Florida rod is 10 ft long and is graduated in white an red stripes, each stripe being 0.10 ft wide. Also available for ease of transportation are tapes or ribbons of waterproofed fabric which are marked in the same way that a regular level rod is marked and which can be attached to ordinary wood strips. Once a job is completed, the ribbon can, be removed and rolled up. The wood strip can be thrown away. The instrumentman can clearly read these various level rods through his telescope for distances up to 200 or 300 ft, but for greater distances he must use a target. A target is a small red and white piece of metal attached to the rod. The target has a vemier that enables the rodman to take a reading to the nearest 0.001 ft. If the rodman is taking the readings with a target and if the line of sight of the tel