Food Evaluation, Food Resource [http://food.oregonstate.edu/], Oregon State University, Corvallis, OR

PHYSICAL AND CHEMICAL METHODS OF EVALUATION FOODS

Compensating Polar Planimeter

A planimeter is used for measurement of various types of areas. If one can draw the shape, one can measure that area with this instrument. The planimeter is an instrument used in food science to measure the area of a portion of food products. Use of this instrument is conenient because once the outline is drawn , the meaurements and calculations can be made anytime, sometimes by a different operator. Some of the types of areas that might be pertinent are:

area of cross-sectional tracing of cakes or muffins

area under the curve of some instrumentation like mixograph or Brabender amylography

area of the "spread" of a cooking

area of cross-sectional tracing of a loaf of bread

area before and after cooking meat for shrinkage

area of thick portion of egg [i.e. egg quality]

Measurement of Area with a Compensating Polar Planimeter

Trace the sample on paper with a sharp pointed pencil or pen. The method of tracing should be consistent for the entire treatments and replications. Control the angle of the pen and the point at which one traces the product.

Procedure:

1. Put a piece of paper that is not folded, torn, or uneven in any way on a flat surface and attach it with tape or thumb tacks. If you get a large enough pieces of paper, several samples can be traced on one paper.

2. Put item to be measured on the paper and draw around it with a soft pencil, being careful not to press product out of shape. Remove item.

3. Assemble instrument by placing carriage with tracer arm parallel to frong edge of table and the tracer arm parallel to front edge of table and the tracer point to the right center of the traced area to be measured.

4. Adjust the tracer stop to that the tracer point just clears the paper. Be sure that the pole is set so that as the point moves around the figure, the angel between the pole arm and the tracer arm will not be smaller than 15 degrees or larger than 165 degrees.

5. Make a starting point on the pencil tracing. Place the tracer point exactly on the starting point and take a reading.

6. Reading the planimeter is similar to reading a vernier scale.

First digit is read using the dial. If the point is between two digits, record the smaller digit, unless it is 9 and 0, then record 9. If the point is between 0 and 1 on the second reading, after having gone full scale, record the reading as 10.

Second and third digits are read from the measuring whell by observing the line which is opposite or has just been passed by the zero on the vernier scale. The second digit is the number or major division on the measuring wheel, and the thrid is found from the single divisions on the measuring wheel.

C. The last digit is the graduation on the vernier which coincides with one on the measuring wheel.

D. A sample reading may be seen in the example as 272.3 square centimeters.

7. Holding the grip, follow the tracing carefully, moving in a clockwise direction. If the tracer leaves the line, do not go backwards, but try to compensate by deviating to about the same extent in the opposite direction the tracer is moving. Be sure that the pole does not move while the rectangular portion of the carriage moves freely.

8. When the tracing has been fully circumscribed take a second reading.

9. Area is calculated by subtracting the first reading from the second. Multiply the difference by 0.1 to get area in square centimeter. Repeat at least once and report the average.

10. Repeat area determination for agreement of values.

11. The following helpful hints will assist in instrument usage and accuracy.

Leave the planimeter in its case when not in use

Do not drop the planimeter.

Do not touch the metal rim of the measuring wheel or the axle.

The axle bearings should be lubricated occasionally with a small drop of watch oil on a toothpick. The excess oil should be wiped off.

Results:

With a carefully drawn curve and proper use of the instrument high accuracy in the results can be obtained. These results may be used for the comparison of food products made using various ingredients, methods of preparation and methods of processing.

REFERENCES to Top

Funk, K., M.E. Zabik and D.A. Elgidaily. 1962. Objective measurements for baked products. Journal Home Economis 61(2):119.

Platt, W. and P.D. Kratz. 1993. Measuring and recording some characteristics of test sponge cakes. Cereal Chemistry 10: 73.

Keuffel and Esser Company
Hoboken, New Jersey 07039

~$55.0

´ ´ Updated: Wednesday, October 31, 2007. ´
´ OSU Disclaimer. ´ ´

1.	Put a piece of paper that is not folded, torn, or uneven in any way on a flat surface and attach it with tape or thumb tacks. If you get a large enough pieces of paper, several samples can be traced on one paper.
2.	Put item to be measured on the paper and draw around it with a soft pencil, being careful not to press product out of shape. Remove item.
3.	Assemble instrument by placing carriage with tracer arm parallel to frong edge of table and the tracer arm parallel to front edge of table and the tracer point to the right center of the traced area to be measured.
4.	Adjust the tracer stop to that the tracer point just clears the paper. Be sure that the pole is set so that as the point moves around the figure, the angel between the pole arm and the tracer arm will not be smaller than 15 degrees or larger than 165 degrees.
5.	Make a starting point on the pencil tracing. Place the tracer point exactly on the starting point and take a reading.
6.	Reading the planimeter is similar to reading a vernier scale. First digit is read using the dial. If the point is between two digits, record the smaller digit, unless it is 9 and 0, then record 9. If the point is between 0 and 1 on the second reading, after having gone full scale, record the reading as 10. Second and third digits are read from the measuring whell by observing the line which is opposite or has just been passed by the zero on the vernier scale. The second digit is the number or major division on the measuring wheel, and the thrid is found from the single divisions on the measuring wheel. C. The last digit is the graduation on the vernier which coincides with one on the measuring wheel. D. A sample reading may be seen in the example as 272.3 square centimeters.
7.	Holding the grip, follow the tracing carefully, moving in a clockwise direction. If the tracer leaves the line, do not go backwards, but try to compensate by deviating to about the same extent in the opposite direction the tracer is moving. Be sure that the pole does not move while the rectangular portion of the carriage moves freely.
8.	When the tracing has been fully circumscribed take a second reading.
9.	Area is calculated by subtracting the first reading from the second. Multiply the difference by 0.1 to get area in square centimeter. Repeat at least once and report the average.
10.	Repeat area determination for agreement of values.
11.	The following helpful hints will assist in instrument usage and accuracy. Leave the planimeter in its case when not in use Do not drop the planimeter. Do not touch the metal rim of the measuring wheel or the axle. The axle bearings should be lubricated occasionally with a small drop of watch oil on a toothpick. The excess oil should be wiped off.