Extrusion 7-2017

kompakt

Extrusion 7/2017

➠

ZUMBACH Electronic AG

www.zumbach.com

Calibration in measurement technology means characteriz-

ing the measurement behaviour of a measuring unit by compa-

ring the indications provided by the unit with a known “mea-

surement standard” (a physical object) used in the calibration

procedure.

During the calibration, the measuring instrument is not subject

to changes, as opposed to adjustment where a measuring unit

is tuned or modified in order to minimize the measurement er-

rors or to guarantee that the measurement errors do not ex-

ceed predetermined bounds. Verification in legal metrology,

however, pertains to the examination and marking and/or is-

suing of a verification certificate for a measuring system. The

examining authority thus verifies whether the measuring unit

satisfies the corresponding legal prerequisites.

Unlike for legal verification, where the validity of a marking or

certificate is defined by law, the validity of a calibration interval

follows practical requirements such as manufacturer indicati-

ons, requirements of the applied quality standards, or company

internal and customer specific regulations.

Traceability and calibration hierarchy

: In order for measure-

ment results to be compared, they must be traced back to a na-

tional or international measurement standard to this purpose,

the display of the measuring must be compared with the mea-

surement standards in one or more stages. On each of these

stages a calibration is carried out with a measurement stan-

dard, which has been previously calibrated with a higher-level

measurement standard. According to the ranking of the mea-

surement standard – from a working or company reference

measurement standard to a national or international measure-

ment standard – there is a calibration hierarchy to be respected

by the organization performing the calibration. This stretches

from the in-house laboratory through accredited laboratories

up to the national metrological institute.

Correct Calibrations

: Different standards, regulations and di-

rective must be respected when carrying out calibrations. A

measurement unit must satisfy basic requirements before it can

be calibrated. One must also know and consider the physical

conditions under which a calibration is carried out.

(Self)compensation of Measuring Units Increases Accuracy of Measurements

Regulations are essentially applicable when a company decides

to respect a standard or directive or when it delivers products

that are subject to legal requirements (like in the medical or

transportation markets)

Standards for Quality Control – Statutory Regulations

Standards and directives, such as the ISO 9000 series, are be-

coming increasingly important for quality assurance in all indu-

strial nations. This standard explicitly requires, among other

things, to calibrate all test equipment that directly or indirectly

influences the quality of the product. This includes, for exam-

ple, test equipment that is used as reference measurement

standard during the production process.

Zumbach Electronic adheres to different directives and stan-

dards. The regulations of the FDA (American Food and Drug

Administration), for example, are important worldwide with

respect to international trading relations. The CFR (Code of Fe-

deral Regulation) requires “the calibration of instruments, ap-

paratus, gauges, and recording devices at suitable intervals in

accordance with an established written program containing

specific directions, schedules, limits for accuracy and precision,

and provisions for remedial action in the event accuracy and/or

precision limits are not met”. European legislation has similar

requirements.

Example of a Zumbach measuring unit – Calibration and

self-compensation functions of ODAC

Measuring Heads

Zumbach’s measuring units are calibrated using reference and

also working measurement standards which are certified by the

federal office for metrology

(www.metas.ch)

or by accredited

laboratories. Each unit is supplied with a detailed calibration

protocol.

A regular check for measuring errors along with the correspon-

ding protocol can be carried out according to the customer re-

quirements. The regularity of these calibrations depends on the

customer specific requirements (internal regulations). The com-

pany recommend a verification of the measurement error every

12 to 24 months.

All the measuring heads of the ODAC

series have a self-com-

pensation function (Patent DE3111356), which makes a regular

calibration superfluous, except when components had to be re-

placed.

All the relevant parameters for accuracy are continuously moni-

tored by the measuring electronics and automatically compen-

sated. This is particularly important for counteracting possible

ageing effects of the scanner motor or possible long-term drifts

of the measuring electronics.

Documentation:

A calibration protocol presents the results of

the calibration and documents the traceability to a national

measurement standard for the considered physical units in ac-

cordance with the International System of Units (SI).

Picture: Typical ODAC

laser diameter measuring gauge

with a certified measurement standard used to calibrate the

device