Tape measure
A tape measure, tape measure also called in surveying usually measuring tape or tape rule, in Austria and Switzerland regionally also the tape measure, the determination of short distances with millimeter accuracy and longer lengths from 10 m to 100 m with cm-accuracy serves. It is placed on the floor or stretched between the measuring points. In surveying thus intermediate points and control or overflow Dimensions are determined.
Steel tapes are made of thin steel strip with varnish, plastics or glass fiber coating and be rolled up for transport. The standard lengths of such tapes are 3 m, 5 m, 20 m, 30 m and 50 m. In the measuring tape beginnings there are two different variants in which the zero point is located on the retaining ring or about 10 cm from the retaining ring.
There are also tapes of coated canvas, but they are less accurate. They are mostly used in the tailoring part where the material to be processed is itself flexible and where the other part mostly convex forms such as body circumferences or arm lengths are to be determined. In the French tailoring, they were introduced around 1825 to 1830. Measuring tapes made of fiberglass- reinforced plastic are mainly used for applications in which is to be expected with significant impurities and moisture, are used. Another application area is the proximity of electrical cables without insulation. Metal measuring tapes pose here the risk of short circuits or power flow to the body of the user. Steel tapes may also have a magnetic effect here is also on plastic strips to fall back. Its accuracy makes it suitable lower than that of Stahlmaßbändern.
Since about 1990 tapes are partially replaced by laser distance measurement.
Tapes with a hand crank or similar to curl as they are used in crafts or even the school sports is known as tape measure. These can be housed in a plastic, metal or leather capsule or an open frame. Tapes with lengths up to 10 m, which are housed in compact capsules and are rolled usually with a spring mechanism is referred to as a pocket tape measures. Often at the beginning of this pocket tape measures, a small metal bracket attached, which facilitates the reading of external dimensions - it is to simply hung on the workpiece. Sometimes this metal bracket is displaceable about its material thickness, in order to facilitate the proper reading of both internal and external dimensions.
Accuracy
For linear encoders accuracy classes are specified according to the EC Directive 2004/22/EC. The accuracy class ( also referred to as EC accuracy class ) can be found together with the EC approval number in the initial region of the scale.
The MPE (positive or negative in mm ) may be expressed by the formula a b * L. Where L is the rounded up to the next whole meter of the length to be measured, a and b are taken from the table. Is the limiting division by a surface, the MPE for any distance is increased starting at this point by the value c given in Table 1.
( 1) Applies for combinations of measuring tape and sinker. (2 ) For a nominal length of the measuring tape in excess of 30 m, the error limit may be increased for each 30 m of tape length by 0.75 mm.
Use in surveying
The measuring tape has lost with the advent of electro-optical distance meter, especially in electronic total stations in importance, but it is still essential part of any surveying equipment. For example, you can control a tachymeter by measuring the horizontal distance between two points picked independently. Also can be examined, by improving the distance from the associated securing points (for example, bit characters ) are measured and compared to the AP card receiving points (AP). It worked almost exclusively with steel measuring tapes; with electrical hazards, etc. with Polyamid-/Glasfaser-Messbändern. Line measuring tapes are not suitable for surveying purposes. The length of steel measuring tapes is by DIN 6403 usually 20 m, 30 m, 50 m or 100 m.
Corrections
Corrections in the length measurement with free-hanging steel measuring tapes and wires still need some corrections are applied to the height measured additively:
To Kalibrierkorrektion is to say that each surveyor his surveying equipment itself must calibrate because the surveying is not subject to mandatory verification. The deviation from the nominal length is determined, which is then, if necessary, take account computationally. The enumerated corrections are not appropriate for short distances, which are to be determined with centimeter accuracy.
Great importance play this but for precision measurements with wires, which are usually made of Invar, whose thermal expansion coefficient is close to zero. These wires are exposed by weights or springs a constant voltage. Normally you work with free-hanging wires. To keep the slack small, the cross section of the wires is small. Measuring wires have no division, but dimensions are generally provided at both ends with a short metal strips of the same material, which has a zero point and often an additional division on either side of the zero point.