Figure 12-6.—Rotating laser level.such as temperature and atmospheric pressure thatthe built-in atmospheric correction system needs, andby proper manipulation of the instrument controls,the operator can obtain horizontal angles, verticalangles, slope distances, horizontal distances, relativeelevation, and coordinates of an unknown point. Thedata obtained is displayed through a liquid crystaldisplay and can be transmitted and stored in aseparate data collector. Complete operatinginstructions are provided with the tacheometer.LASER EQUIPMENTLaser light is of a single color, the light wavesare in step with each other, and the light beamspreads only slightly as the distance from the lightgeneratorto the target increases. Thesecharacteristics make the laser useful for surveyingequipment used in various types of constructionlayout. Although a wide variety of special-purposelaser instruments are manufactured, most of thesehave been designed for construction layout and areclassified into two general groups as follows:1. Single-beam laser alignment instruments.These instruments project a single beam of light thatis visible on targets under all lighting conditions.Included in this group are laser equipped theodolitesand transits, and lasers used for alignment of pipes,drains, and tunneling equipment.2. Rotating laser levels. These are instrumentsin which the laser beam is rotated by rapidlyspinning optics to provide a reference plane in spaceover open areas.SINGLE-BEAM LASERALIGNMENT INSTRUMENTSA typical single-beam laser alignmentinstrument can be mounted on a transit-likeframework with horizontal and vertical motions, aspirit level that is parallel to the axis of the laser, andboth vertical and horizontal circles. A telescope isattached to the laser housing to allow the operator tosight the location of the transmitted laser spot. Aseparate fanning lens, when attached, allows thelaser beam to be converted to a horizontal or verticalline instead of a spot.ROTATING LASER LEVELA self-leveling, rotating laser is shown in figure12-6. In this instrument, the laser unit is mountedvertically on a platform containing two orthogonallymounted sensors that act like spirit levels and deviatefrom center when the platform is not level. Theamount of deviation is detected electronically, and the12-6
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