Centre for Length, Time and Acoustics
Laboratories:
Contact:
Ing. Jozef Ondruš
Director of the Centre
phone: +421 2 60294 359
fax: +421 2 65429 592
e-mail: ondrus@smu.gov.sk
Mgr. Anna Fodreková
Deputy Director of the Centre
phone: +421 2 60294 222
fax: +421 2 65429 592
e-mail: fodrekova@smu.gov.sk
Mária Weinrebová
Secretariat
phone: +421 2 60294 542
fax: +421 2 65429 592
e-mail: weinrebova@smu.gov.sk
LENGTH LABORATORY
Methods of measurement:
The vacuum wavelength of working HeNe lasers is determined using a beat frequency method. The beat frequency is equal to the frequency between the frequency of the national Standard of Length and the frequency of the laser to be calibrated.
With regard to the reference standard a division of measuring methods into two groups is possible:
- the reference standard is the wavelength of the stabilized working HeNe laser. This method is being used on 1 m intereferometer, LID, Line Interference Comparator, combination Of ULM3m ZEISS with laser interferometer. The exception are two INKO ZEISS comparators, which use interference method (kr lamp as the light source), but the traceability is indirect via 100 mm gauge block calibrated at 1 m interferometer;
- the reference standards are marerial measures (gauge blocks or line standards), calibrated using the interference method.This method is being used at ULM3m ZEISS (long gauge blocks and possible line standards) are vertical length measuring machine TESA (gauge blocks).
Instrument in use:
The National Standard of Length is represented by two iodine stabilized HeNe lasers, developed at the SMU and devices for the transfer og length unit. The frequency of these lasers was internationally compared in 1988 and 1994 to the BIPM laser frequency, as well to the lasers of nine foreign metrological institutes, with an expanded uncertaiunty of 5 x 10-11. All transfer devices, serving for the calibration of material measures, are directly traced to the National Standard of Length.
1 m Interferometer is the laser interferometer of Michelson's type. It is used for the calibration of gauge blocks from 100 mm up to 1000 mm of length.
The set of INKO ZEISS interference comparators serves for the calibration of gauge blocks up to 100 mm of length by means of chosen wavelengths of the Krypton lamp. The traceability to the National Standard of Length is realised through the calibration of 100 mm gauge blocks calibrated interferentially.
The vertical length measuring machine TESA, Abbe's length measuring device with the laser interometer LMS-100 (LID), the MPVCD-Leitz Microscope serves for the calibration of special length standards used in electronics and ranging from 1 µm to 300 µm, the Line Interferometric Comparator has been developed and made in the SMU containing the laser interferometer LOS with the HeNe laser 633 nm as the light source, the Length measuring device ULM3m ZEISS combined with TESA MODUL serves for the calibration of line scales from 100 mm up to 1000 mm using the comparison method.
All standard devices are installed in air-conditioned laboratories at (20 ± 0.1)°C. Laboratories are equiped with a floor vibration isolation.
PLANE ANGLE AND FORM & SURFACE ROUGHNESS LABORATORY
PLANE ANGLE AND FORM
Quantity - plane angle and deviation from straightness.
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Unit - °, ´, µm.
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Tasks - the main task is the realisation and maintenance of the plane angle standard.
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International comparisons
EUROMET 371, CCL-K3.
Instrument in use:
The National Standard of Plane angle consists of the following devices and artifacts: Laser goniometer GS1L (Arsenal, Kiev, Ukraine), the standard device EZB-3 (ČSMÚ, Bratislava), adapted small angle generator TA 48 (Hilger & Watts, England) and set of standard polygons.
Calibration of optical polygons is performed with the laser goniometer GS1L (using a ring laser for realisation of the angular scale).
All kinds of autocollimators and levels are calibrated on the adapted small angle generator TA 48.
The angle ancoders are calibrated at the standard device EZB-3 by comparison with the standard polygons.
All the devices with angle scale (tables, heads, goniometers, etc.) are calibrated by standard polygons and autocollimator.
The angle blocks and pentagonal prisms are calibrated by the optical method on laser goniometer GS1L.
All squares are calibrated on the standard device NME 90° using a comparison with the standard square.
Quantity - Parameters of surface roughness.
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Unit - µm.
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Tasks - The main task is the realisation and maintainance of surface roughness and the unit transfer to the working standards.
Methods of measurement - secondary standards are calibrated with the skidless profile recording instruments, according to the internal calibration procedures.
Instrument in use:
The contact profile recording instruments of the laboratory type - TALYSURF 6, installed in the laboratory with the floor vibration isolation at temperature of 20°C ± 0.5°C.
ACUSTICS MEASUREMENT LABORATORY
Quantity - sound pressure.
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Unit - Pa.
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Tasks of the laboratory
The main task of the laboratory is the realisation and development of the Sound Pressure National standard which based on reciprocity method for calibration of standard microphones.
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International comparisons
The intercomparison of laboratory standard microphones have shown mutual deviation of less than 0.04 dB between SMU and NPL England, PTB Germany, VNIIFTRI Russia and DTU Denmark. The laboratory participates in EUROMET, COOMET and DUNAMET acoustic projects.
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Available metrological services
Verification of measuring microphones with nominal diameter 24 mm, 12 mm, 6 mm (IEC 61094-1, IEC 61094-4). Calibration of sound calibrators (IEC 60942). Verification of sound level meters, classes 0, 1, 2, 3 (IEC 60651). Calibration of acoustic couples and artificial aers (IEC 60318-3, IEC 60318-1). Verification of audiometers, classes 1, 2, 3, 4, 5 (IEC 60645-1). Within an additional acoustic instruments: verification of electronic filters (classes 1, 2, 3 - IEC 61260), calibration of generators, analysers, noise analysers, noise dose meters, level recorders, testing of hearing aids, personal aound exposure meters (IEC 61252).
Methods of measurement:
- a pressure sensitivity of a laboratory standard microphone (typr LS IEC 61094-1), reported in terms of an open-circuit voltage per unit of sound pressure applied uniformity to the diaphragm, is obtained through a reciprocity method with two microphones and an auxiliary sound source (an active coupler). Microphone electrical terminals are attached to a groung-shield configuration in according with the IEC 61094-1 standard. Pressure calibration of type LS microphones is performed within a range from 63 Hz to 2.5 kHz with an uncetrainty of approximately 0.04 dB;
- lumped paremeters, representating acoustic impendance are obtained by an indirect method based on the measurement of the electrical admittance of the microphone acoustically terminated with a closed quarter-wavelength tube. Another method used for frequency and loss factor by exciting the diaphragm with an electrostatic actuator while terminating the diaphragm with the quater-wavelength tube;
- a front cavity volume and the equivalent volume is evaluated using an acoustical method for comparison of a microphone under test with a number of cavities with known volumes;
- calibration of working standard microphones is performed using a computer controlled comparison method which uses an active coupler with a laboratory standard microphone. This microphone, in turn, is calibrated by the reciprocity technique. The frequency response of a microphone is determinated by the electrostatic actuator method;
- methods of verification and calibration of instruments meet technical standards the IEC 61094-2, PNU 181-2, PNU 1811-2 and PNU 1803-2 respectively.
Ranges and uncertainties of calibrated and verified instruments. Click for details!
Instruments in use:
The instrument equipment consists of a National Standard of Sound pressure based on a computer controlled reciprocity method for determination of open circuit pressure sensitivity of condenser microphones. The device development at the SMU uses an active measuring coupler of nominal l volume 4cm3 and a special microphone preamplifier, anabling microphone function as receiver and transmitter without a mechanical change during the measurement. The open circuit sensitivity of standard microphones can be evaluated in a range of 63 Hz - 2500 Hz with an uncertainty less than 0.04 dB.
A set of equipment of Brüel & Kjaer completed with calibrated attenuators and digital voltmeters is used for verification of sound level meters, audiometers, filters and other electro-austic instruments testing.
An instrument development at the SMU will be used for a determonation of acoustic impendance of microphones.
