Test Your Knowledge

What do you know about
temperature compensation --
an important component
of gaging technology?

by Paul Sagar

If you're making precision components, but you're not compensating for the effects of temperature in your dimensional measurements, you're still living in the Dark Ages. Tolerances are getting tighter every day, so temperature becomes a bigger and bigger factor. Do you understand the discipline of temperature compensation? Test yourself -- take the following quiz:

1. What is the difference between an “accurate” and a “precise” gaging system?

a. A precise gage has greater resolution than an accurate gage.

b. A precise gage has better R&R than an accurate gage.

c. There is no difference.

d. An accurate gage gives results that are closest to true dimension, while a precise gage is repeatable, even if inaccurate.

2. What is the standard international reference temperature at which all measurements are specified, as stipulated by ISO and ANSI?

a. 60°F/16°C

b. 70°F/21°C

c. 68°F/20°C

d. 72°F/22°C

3. What is a tolerance ratio?

a. A ratio that compares total tolerance to nominal dimension.

b. A mechanism used by designers to specify tolerances.

c. A system used in setting up cutting tools.

d. A ratio that expresses the relationship of your patience to the expectations of your boss.

4. What is the purpose of a tolerance   ratio?

a. To calculate the effect of temperature on gage R&R.

b. To express the relationship of the temperature of a part to the temperature of its gage.

c. To assess the risk of thermal errors occurring in a shop floor gage.

d. To compare coefficients of thermal expansion between work piece and master.

5. How is a tolerance ratio calculated?

a. Total tolerance divided by nominal dimension, expressed as a percentage.

b. COE (coefficient of expansion) of master, divided by COE of work piece.

c. Nominal dimension divided by total tolerance, expressed as a percentage.

d. Total tolerance of work piece divided by total tolerance of its mating part.

6. Which elements of a measurement system (gage) can contribute to temperature-induced error?

a. Work piece

b. Gage fixture

c. Setting master

d. All of the above

7. How large a dimensional variation will be observed in a three-inch (76 mm) steel component as a result of it changing temperature by 20°F/11°C, from 65°F/18°C to 85°F/29°C? Calculators allowed. (Clue: Coefficient of expansion for steel is about 6.5 parts per million per degree F.)

a. 0.0002 in/0.005 mm

b. 0.0003 in/0.0075 mm

c. 0.0004 in/0.010 mm

d. 0.0006 in/0.015 mm

8. What do the letters “TEI” stand for?

a. Theorized expansion indicator -- an estimate of thermal expansion coefficient.

b. Thermal error index -- an ANSI-defined estimate of overall thermal error in a measurement system.

c. Temperature equalization inversion -- the amount of thermal error offset experienced when setting master and gage vary in temperature by the same amount.

d. Thermal energy input -- the amount of thermal energy generated in a part as a result of a production process.

9. What is a full electronic temperature compensation system?

a. A method by which temperature is controlled at nominal temperature.

b.  sensor and electronic interface that senses the temperature of parts while they are being measured.

c. A system of temperature sensors and an electronic controller that senses temperatures of master, work piece and gage fixture during measuring operations and generates a net correction for thermal  errors.

d. An offline computer into which an operator punches temperatures and dimensions in order to calculate thermal errors.

10. About how much of the thermal error in a measurement should a full electronic temperature compensation system consistently eliminate?

a. 80 percent or better

b. 92 percent or better

c. 65 percent or better

d. 50 percent or better

11. What do the letters COE stand for?

a. Correction of error

b. Cost of energy

c. Coefficient of expansion

d. Cold or emissive

12. Which of the following terms refers to the rate at which a body changes its size as a result of a change in temperature?

a. Differential response

b. Temperature variation error

c. Coefficient of expansion

d. Thermal error index

13. Which of the following describes the speed with which a body responds to a change in temperature?

a. Temperature variation error

b. Measurement cycle time

c. Time constant of a body

d. Differential expansion

14. What is the principal benefit of a full temperature compensation system?

a. Measurements are always given at reference temperature, regardless of actual temperatures.

b. The system constantly displays the temperatures of work piece and gage during measuring operations.

c. A cheaper coolant can be used in metal-cutting processes.

d. Machine operators can take the afternoon off.

15. What kind of gages can be equipped with an electronic temperature compensation system?

a. Mechanical indicators

b. Handheld micrometers

c. Any electronic handheld, benchtop or automatic gage

d. Column gages

16. What is meant by the “characterization” of a gage or measurement system?

a. Calibration to NIST dimensional measurement standards.

b. Empirical testing to determine thermal correction coefficients.

c. Providing the gage with its own identity and sense of self-esteem.

d. Determining the best location for mounting temperature sensors in a gage.

17. How long does the average temperature compensation system take to pay for itself?

a. Five days

b. Two months

c. Six months

d. One year

Scoring: If you scored more than 15 correct, you must have done some excellent research, or maybe you have a temperature compensation system already installed. Ten to 15 correct is impressive -- you already have a good start on the subject. Less than 10 correct -- maybe you need to find out more about this technology of the present and future.

Answers: 1. d; 2. c; 3. a; 4. c; 5. a; 6. d; 7. c; 8. b; 9. c; 10. b; 11. c; 12. c; 13. c; 14. a; 15. c; 16. b; 17. b

About the author

Paul Sagar is president of Albion Devices Inc., a Southern California-based company specializing in temperature compensation of precision in-process and post-process measurement and positioning systems.

Telephone (619) 792-9585, fax (619) 792-9644, e-mail pbsagar@juno.com.