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Planimeter Selection Guide |
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Selecting a
TOOL FOR MEASURING AREAS of both
regular and irregular shape from maps, plans, blueprints,
photographs, etc. can be confusing, since there are so many devices
to choose from.
1.
Polar Planimeters equipped with a
pole arm, which anchors the instrument to the table. Their measuring
wheel rides directly on the measuring surface, which must be
evaluated. The instruments in this category include all Mechanical
Polar Planimeters and Models 42P, 2. Wheel Planimeters. The basic concept is similar to that of a polar planimeter but with extended length range. Models 42C, 44C and 45C are typical wheel planimeters. 3. Rolling Disk Planimeters. Their measuring wheel runs on a special disk at accelerated speed. It never touches the measuring surface itself, making it independent from its condition. A Rolling Disk Planimeter also provides extended length range similar to a "Wheel Planimeter". (Models 1252, 1262) 4. Area/Line Meters (Mod. Series 1281 and KP 800)
1281
Models are basically digitizers, but configured mainly for area and
length measurements. They also offer many additional features not
provided by standard planimeters. 1281 models can be upgraded (by the
user) into fully featured digitizers and are equipped with an
interface for work with a Host Computer. 5. Lasico Graphic Digitizers (Mod. Series 1282) Incorporate all the features of the 1281 models plus digitizing capabilities along with extended computer interface qualities. Available with different arm lengths for various active measuring ranges. Which Instrument should you select ? Major considerations are: 1. Frequency of use: Instruments with mechanical measuring mechanism are rather slow and cumbersome to read but may be perfect for the occasional user. Results are unscaled and need additional processing. Electronic models permit much faster operation. All, except Mod. 44P and 44C, are self scaling and final results are shown on display. This saves time and eliminates readout and computation errors. Their higher price tag is easily justifiable if the frequency of use is relatively high. 2. Measuring Accuracy: The required level of precision eliminates some instruments from consideration. This is especially true, whenever very small areas have to be evaluated. (smaller than 1 sq.in / 6.5 sq.cm. in size on paper) . A Polar or Wheel Planimeter (mechanical or electronic) is quite marginal for evaluating such areas since the measuring resolution is rather limited. If you need to measure small areas frequently and with good precision, look for an instrument with a high level of resolution. (Models 1252/1262/1281/1282/ KP800) 3. Measuring Range: While even the smallest instrument can be used to measure large areas by subdivision, it can be accomplished only at the expense of speed and accuracy. Subdividing areas generates longer tracing distances, resulting in more tracing errors and slower operation. It is strongly recommended to select an instrument that can comfortably cover the range of areas most frequently evaluated. Model Series 1252/1262/1281and1282 outperform all other devices in this respect. 4. Measuring Surface Condition : If the measuring surface does not consist of paper or vellum, or if it is mutilated, instruments whose measuring wheel is in contact with the measuring surface are not suitable. This includes all planimeters except Models 1252 ,1262 ,1281,1282 and KP800 5. Operating Ease and Convenience: Electronic Models with their digital display facilities are much easier to use. This is especially true for operators needing corrective glasses. They may have great difficulties reading the results off a mechanical measuring mechanism. In addition, electronic models (except 44P and 44C) feature automatic scaling and provide finished results directly in any measuring unit desired. Furthermore, features like area accumulation, instant zero setting, etc. are common and help to speed up the measuring process. 6. Work with a Host Computer If work in conjunction with a PC or Mac is anticipated, i.e if results are to be transmitted to a host computer, the potential user is limited to series 42P/C and 1252/1262 models, which can be retroactively equipped with a computer interface by the user. Model Series 1281 and 1282 are readily equipped with a built in interface facility.
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