About Mechanical and Electrical Planimeters to Measure Area

ANSWERS TO FREQUENTLY ASKED QUESTIONS ABOUT PLANIMETERS

What is a Planimeter?
Basically speaking, planimeters are area measuring tools. Planimeters are precision instruments used to trace around a closed loop of an object to find its area. Planimeters are used by engineers, surveyors, contractors, designers, medical professionals, and more. The "closed loop" that we mentioned can be the outline of a storm pond, a tumor in a human organ, the outline of a odd-shaped swimming pool, or the area of leather in a shoe. Yes, we had someone measuring each piece of leather in a shoe once it had been worn and disassembled. The person wanted to find out how much each piece of leather had stretched after being worn to figure a percentage of the stretch that had occurred. They were simply measuring the outline of each piece of leather before and after the shoe had been worn. Each week that passes, we hear of new ways planimeters are being used.

With a planimeter, you set the scale of your drawing or measurement, then push, pull, or roll the planimeters head around along the perimeter or outline of your object and it'll tell you the area of the loop.

What is the difference between Roller & Polar Planimeters?

Roller planimeters are attached to wheels that allow unlimited horizontal travel and vertical travel within the limits of the arm movement. Polar planimeters are attached to a weighed base by an arm that allows movement with a circular area. Roller units offer more versatility since they are not "pinned" down to your work area. Roller planimeters can roll all over the place without the restriction of an attached base and arm like the polar planimeters are.

Should I buy a Mechanical or Electronic (Digital) Planimeter?
Mechanical planimeters are the most popular types since they are economical and offer good overall accuracy and range for most applications involving medium sized areas. The measuring wheel rides directly on the measuring surface. It is integrated into a measuring mechanism with a dial, drum and vernier readout system with the typical maximum counting capacity of 4 digits (9999).

However, Electronic Planimeters offer greater precision, ease of selecting units of measure, have memory to retain multiple measurements, and some have the ability to sum multiple areas measured. Electronic Planimeters are also popular due to their speed in measuring, and ease of use.

What is the Scale Factor?
The scale factor is the x-scale multiplied by the y scale. (This must be computed when using the Planix 5 and the Planix 6 because they do not have a built-in scale computation.) The reading from the planimeter is then multiplied by this to obtain the area in the drawing.

What if the area I want to measure is larger than the reach of the planimeter arm?
All of the Planix instruments have a "hold and accumulate" feature. Subdivide the area to be measured into the smaller areas that are within the range of the unit. Measure each area pressing the hold key once to stop measurement and once again to initiate measurement once the planimeter is moved to the next area.

What direction should I move the tracer arm?
The tracer arm should be moved in a clockwise direction and returned to the original starting point. Moving the arm counterclockwise will give you a negative reading. This can be used to subtract smaller areas contained in larger ones. See instruction manual for details.

How accurate are the Planix planimeters?
Planix planimeters have a stated accuracy of 0.2% of the area measured. For accurate work, Planix recommends that the work be done slowly and carefully and the averaging function be used so that the final measurement will be the result of several measurements.

Price

If you're concerned with cost of the product you're planning to buy, consider the useful life expectancy. You should consider the price being spread out over these years and not be as concerned with price as much as the value and time saved.
 

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