Say whether the following statements are true or false.

1. At present time only the following independent units of measurement are acknowledged all over the world: temperature interval, linear distance, electrical current, frequency and mass.

2. Voltage and resistance units are independent.

3. It is common knowledge that each of independent units of measure will be defined in terms of the other four independent units.

4. Length (meter) and time (second) are not connected items.

5. The relationship between the luminance and current is worldwide known and obvious.

6. Some units of measure have much more resolution than others.

7. Luminance (candela) can only be reproduced to 15% of reading despite having sensors that are capable of 50 parts per million (0.0005%) precision.

8. Temperature (kelvin) is defined by accepted fixed points which are defined by the state changes of nearly pure materials, generally as they move from solid to liquid.

9. Uncertainty is uniform over the entire range of temperature measurement.

10. Engineering, manufacturing and ordinary living now routinely challenge the limits of measurement.

11. There are a lot of measurement devices used by people who do not understand properly the basic principles involved.

12. Despite of advances in metrology there are still unanswered questions and a lot of work to be done.

Make the plan and retell the text according to it.

Complete the crossword.

1 , 6 . Cities which defined the meter as quarter of the terrestrial meridian.

2. Morphology the earliest systems of weights and measures were based on.

3. Measuring device providing playback and (or) storage unit.

4. Standards for the meter and the kilogram established as the basis of the metric system on June 22, 1799.

5. Country where was introduced the decimal metric system on 7 April 1795 by the law "On weights and measures"?

7. Person who did in 1893 Saturated Standard Cell design, which allowed the volt to be reproduced to 1 part in ten to the fourth power directly.

8. One of the first natural measures.

Unit 2

TRACEABILITY AND CALIBRATION

Practice reading the following words.

Traceability, procedure, mutual, issue, influence, caliper, reference, gauge, approximate, conventional, value, assume, comparator, metre, spacer, insurance, minimize, significant, humidity, carrier.

2. What is the role of calibration in measurement?

Do you think calibration ensures traceability of measurement?

Discuss in groups.

Read and translate text A

Text A

Traceability

A traceability chain is an unbroken chain of comparisons, all having stated uncertainties. This ensures that a measurement result or the value of a standard is related to references at the higher levels, ending at the primary standard. In chemistry and biology traceability is often established by using CRMs and reference Procedures. An end user may obtain traceability to the highest international level either directly from a National Metrology Institute or from a secondary calibration laboratory. As a result of various mutual recognition arrangements, traceability may be obtained from laboratories outside the user’s own country.

Calibration

A basic tool in ensuring the traceability of a measurement is the calibration of a measuring instrument or reference material. Calibration determines the performance characteristics of an instrument or reference material. It is achieved by means of a direct comparison against measurement standards or certified reference materials. A calibration certificate is issued and, in most cases, a sticker is attached to the calibrated instrument.

Three main reasons for having an instrument calibrated:

1. To ensure readings from the instrument are consistent with other measurements.

2. To determine the accuracy of the instrument readings.

3. To establish the reliability of the instrument i.e. that it can be trusted.

By calibrating an instrument it is possible to obtain the following:

· The result of a calibration permits either the assignment of values of measurands to the indications or the determination of corrections with respect to indications.

· A calibration may also determine other metrological properties such as the effect of influence quantities.

· The result of a calibration may be recorded in a document, sometimes called a calibration certificate or a calibration report.

The VIM defines calibration as the set of operations that establishes, under specified conditions. The relationship between the value of a quantity indicated by a measuring instrument and the corresponding value realized by a measurement standard.

In general, a measurement standard, or simply a standard, is a material measure, measuring instrument, reference material or measuring system intended to define, realize, conserve or reproduce a unit or one or more values of a quantity to serve as a reference.

Calipers are normally calibrated using standards of the material measure type. These are devices intended to reproduce or supply, in a permanent manner during their use, one or more known values of a given quantity.

Date: 2016-04-22; view: 967