INTERNATIONAL OIML R 89 OIML R 89 RECOMMENDATION Edition 1990 (E) Electroencephalographs -...

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INTERNATIONAL OIML R 89 RECOMMENDATION Edition 1990 (E) Electroencephalographs - Metrological characteristics - Methods and equipment for verification Electroencéphalographes - Caractéristiques métrologiques - Méthodes et moyens de vérification ORGANISATION INTERNATIONALE DE MÉTROLOGIE LÉGALE INTERNATIONAL ORGANIZATION OF LEGAL METROLOGY OIML R 89 Edition 1990 (E)

Transcript of INTERNATIONAL OIML R 89 OIML R 89 RECOMMENDATION Edition 1990 (E) Electroencephalographs -...

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INTERNATIONAL OIML R 89RECOMMENDATION Edition 1990 (E)

Electroencephalographs - Metrological characteristics -Methods and equipment for verification

Electroencéphalographes - Caractéristiques métrologiques - Méthodes et moyensde vérification

ORGANISATION INTERNATIONALE

DE MÉTROLOGIE LÉGALE

INTERNATIONAL ORGANIZATION

OF LEGAL METROLOGY

OIM

L R

89

Editi

on 1

990

(E)

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Foreword

The International Organization of Legal Metrology(OIML) is a worldwide, intergovernmentalorganization whose primary aim is to harmonize theregulations and metrological controls applied by thenational metrological services, or relatedorganizations, of its Member States.

The two main categories of OIML publications are:

• International Recommendations (OIML R),which are model regulations that establish themetrological characteristics required of certainmeasuring instruments and which specifymethods and equipment for checking theirconformity; the OIML Member States shallimplement these Recommendations to thegreatest possible extent;

• International Documents (OIML D), which areinformative in nature and intended to improvethe work of the metrological services.

OIML Draft Recommendations and Documents aredeveloped by technical committees orsubcommittees which are formed by the MemberStates. Certain international and regional institutionsalso participate on a consultation basis.

Cooperative agreements are established between OIMLand certain institutions, such as ISO and IEC, with theobjective of avoiding contradictory requirements;consequently, manufacturers and users of measuringinstruments, test laboratories, etc. may applysimultaneously OIML publications and those of otherinstitutions.

International Recommendations and InternationalDocuments are published in French (F) and English (E)and are subject to periodic revision.

This publication – reference OIML R 89 (E), edition1990 – which is under the responsibility of TC 18/SC 4Bio-electrical instruments, was sanctionned by theInternational Conference of Legal Metrology in 1988.

OIML publications may be obtained from theOrganization’s headquarters:

Bureau International de Métrologie Légale11, rue Turgot - 75009 Paris - FranceTelephone: 33 (0)1 48 78 12 82 and 42 85 27 11Fax: 33 (0)1 42 82 17 27E-mail: [email protected]: www.oiml.org

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ELECTROENCEPHALOGRAPHS

METROLOGICAL CHARACTERISTICS

METHODS and EQUIPMENT for VERIFICATION

1. Scope

1.1. This Recommendation concerns analogue electroencephalographs, which are defined as diagnosticmedical instruments having at least eight channels. Such instruments are intended to accuratelymeasure and record bioelectrical potentials and their time sequences as detected by electrodesattached to the surface of the human scalp.

1.2. This Recommendation does not apply to information-processing electroencephalographs, norinstruments that digitize the signals, nor other special-purpose instruments.

1.3. This Recommendation is intended for the use of metrological services and other responsiblegovernmental agencies. It specifies the metrological characteristics to be determined, methods of andequipment for testing, and initial and subsequent verifications of electroencephalographs that areregulated by laws. Metrological characteristics include errors in measuring voltage signals and timeintervals as well as a number of other characteristics that affect measurement accuracy. Proceduresare given for determining the relative error of measurement of sixteen instrument characteristics, andformulae are provided for calculating the associated permitted limits of these characteristics. Thesetesting and control procedures provide a basis for ensuring that electroencephalographs of adequateaccuracy are available for clinical measurements. The characteristics of the instrument covered arethose that have been deemed to be important in order to achieve the necessary measurement accuracyin clinical practice; therefore, any changes in the requirements prescribed should be based on clinicalexperience and the needs of electroencephalography.

1.4. This Recommendation does not address pattern approval, terminology, technical requirements,electrical safety and the associated test methods. Some of these matters are being considered by theInternational Electrotechnical Commission (IEC) in the (draft) Publication 601-2-xx "Medicalelectrical equipment — Part 2: Particular requirements for the safety of electroencephalographs"under the auspices of SC 62D on "Electromedical equipment". A subject that is also underconsideration by SC 62D is " Particular requirements for the performance of electroencephalographs".The requirements of this Recommendation are also compatible with "Recommended specificationsfor electroencephalographs" developed by the International Federation of Societies forElectroencephalography and Clinical Neurophysiology (IFSECN). Those specifications can be foundin "Recommendations for the Practice of Clinical Neurophysiology", IFSECN, Elsevier, Amsterdam-New York-Oxford (1983).

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2. Characteristics to be verified

The characteristics shown in Table 1 should be measured during verification of electroencephalographs.

Table 1

Metrological characteristics to be verified.

Metrological characteristics PointVerified during

Initial Subsequentverification

Relative voltage-measurement error 5.3.1 + +

Relative sensitivity-setting error 5.3.2 + −

Relative time-interval measurement error 5.3.3 + +

Relative error of the recording speed 5.3.4 + −

Recording hysterisis 5.3.5 + −

Relative errors of internal calibrator and timemarker

5.3.6 + +

Overshoot 5.3.7 + −

Time constant 5.3.8 + −

Amplitude-frequency response curve 5.3.9 + +

Input impedance 5.3.10 + −

Common-mode rejection ratio 5.3.11 + +

Baseline width 5.3.12 + −

Baseline drift 5.3.13 + +

Intrinsic noise level referred to the input 5.3.14 + +

Interchannel crosstalk coefficient 5.3.15 + −

Relative error of the interelectrode-resistancemeasurement

5.3.16 + −

Verification of current in the patient circuit is also required at initial verification (see point 5.4).

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3. Measuring instruments used for verification

The measuring instruments listed in Table 2 are recommended for the verification ofelectroencephalographs.

Table 2Measuring instruments used for verification

Measuring instrument Symbol Main characteristics

Sine-wave signal generator (*) G1 Frequency range 0.01 Hz 100 HzMax.frequency error ± 1 %Voltage range 10 mV 10 V RMSMax. voltage error ± 1 %Double-ended output

Square-wave signal generator (*) G2 Frequency range 0.01 Hz 1 000 HzMax. frequency error ± 1 %Voltage range 1 mV 10 VMax. voltage error ± 0.5 %Double-ended output

Voltage divider (**) D1 Division factor 10 000 (R1 = 100 kΩ;R2 = 10 Ω; max.error ± 1 %)Max.error of division ± 2 %

Simulated skin-electrodeimpedance (***)

Z1 R3 = 4.7 kΩ ± 1 %

DC voltage source U1 Voltage 1.5 V ± 5 %Length-measuring device Measurement length 1 mm 100 mm

Max.error ± 0.1 mm on measuring length from 0 mm to 10 mm,and ± 1 % on measuring length from 10 mm to 100 mm.

Magnifying glass Magnification × 5Resistors R4-R12 R4 = 200 Ω ; R5 = 50 Ω ; R6 = 100 kΩ ;

R7 = 620 kΩ , R8 = 5 kΩ , R9 = 1 kΩ ;R10 = 5 kΩ; R11 = 20 kΩ ; R12 = 50 kΩMax. error ± 1 %

Capacitors C1, C2 C1 = 0.5 µF; C2 = 4.7 nFMax.error ± 5 %

Impedance Z2 R7 in parallel with C2

(*) If the voltage or frequency of generator G1 or G2 do not meet the specifications of Table 2, a voltmeter and afrequency meter with the accuracy specified for the generator output voltage and frequency should be provided.(**) See Figure 1.(***) Impedance Z1 (called in the text "patient skin-electrode impedance" is intended to simulate the electricalcharacteristics of the electrode-skin interface.

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4. Verification conditions and preparation for verification

4.1. The recommended conditions for verification are as follows:— ambient temperature: 15 °C to 25 °C,— atmospheric pressure: 96 kPa to 104 kPa,— relative humidity of air: 50 % to 80 % (no condensation),— mains voltage fluctuations: ± 2 % of nominal voltage,— mains frequency: (60 Hz or 50 Hz) ± 2 %.

The ranges of atmospheric conditions may be extended for regions with extreme temperatures(or other climatic conditions) or high altitude.

4.2. Deviations of the power-supply voltage should not exceed the values indicated in themanufacturer's manual.

4.3. Before the electroencephalographs are verified, they and the measuring instruments required forverification should be assembled according to the requirements of the national metrology service orother officially authorized organizations. Measuring instruments used during verification should bechecked by authorized personnel.

5. Verification

5.1. External examination

External examination includes a check that the manufacturer's manual, which should provide thenecessary information on the electroencephalograph, is available and includes the following:— values of commonly accepted characteristics, their tolerance limits and procedures for their

determination,— diagrams and construction details necessary for carrying out verification procedures,— operating and maintenance instructions,— instructions for special medical applications.

External examination includes checks for:— absence of corrosion and mechanical damage, and— freedom from any trace of deterioration of the lead cables.

5.2. Testing

The electroencephalograph shall be tested after the warm-up period specified by themanufacturer.

The testing shall include checks for the presence and deflection of the recording trace, the penpressure, either the ink feed or the adjustment of the heating system for thermal pens, the movementof the record at different speeds and the presence of calibration signals and sensitivity controls (stepand smooth).

5.3. Determination of metrological characteristics

To determine the metrological characteristics each measurement shall be repeated at least threetimes and each of the measured values shall lie within specified limits. Unless otherwise stated, theelectrode selector shall be set so as to apply an input test signal to each channel simultaneously. Therecorded output shall be measured in a way that excludes the trace line width.

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The limiting values of error include both the errors of the EUT (*) and of the reference instruments.

If the settings for filters or sensitivities indicated by the manufacturer differ from those specified inthis Recommendation the procedure shall be modified to take these settings into account (see footnote,Table 3).

The associated diagrams in this Recommendation are given for a 16-channel instrument as an example.The diagrams for other instruments having at least 8 channels are similar.

5.3.1. Determination of relative voltage-measurement error

Definition: The relative voltage-measurement error is the difference between the voltage recorded by anelectroencephalograph and the voltage applied to its input (whose reference value is taken as aconventional true value), divided by the input voltage.

Method of measurement: The relative voltage-measurement error shall be determined directly bymeasuring the amplitude of the square-wave signal recorded, referring it to the input using the sensitivity-setting, and comparing it with the amplitude of the input voltage as determined by the reference voltmeter(conventional true value).

Measurement circuit: The measurement set-up is shown in Figure 1. The appendix presents the table ofcorrespondence between the system of numerical definitions of electrodes and the International "10-20"System.

Measurement procedure: The switches of the low-frequency (time constant) and high-frequency filtersare set to cover the necessary EEG band width (e.g. 1 s and 70 Hz respectively). The electrode selector (s)is (are) set as shown in Figure 1. The recording speed is set at 30 mm/s. Switch S1 is set at position 2 (Z1is switched on) and switch S2 at position 3. Generator G2 is set at a frequency of 10 Hz. The sensitivity ofall channels is set as specified in Table 3. A square-wave signal from generator G2 and voltage divider D1with a peak-to-peak amplitude shown in Table 3 is applied to the electroencephalograph's input throughthe simulated skin-electrode impedance Z1. For each voltage of the input signal and correspondingsensitivity the dimension of the recorded signal is measured. The measurement is repeated in the presenceof a constant voltage that simulates the maximum value of electrode potential polarization equal to± 300 mV, switch S2 being set at positions 1 and 2, in turn.

Table 3Sensitivity-setting and input signal voltage

for determining the relative voltage measurement error (**)

Input voltage, µV(peak-to-peak) Sensitivity-setting, µV/mm

5 25 50

100 250 500

1050

100 200 500

1 000

2010

200 400

1 0002 000

15

102050

100

(*) EUT: Equipment under test.(**) If a listed sensitivity is not available on the instrument, the next lower available value may be used with the inputvoltage scaled down proportionately. See also note (*) page 9.

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Calculation: The relative voltage measurement error, in percent, shall be calculated by the followingformula:

100U

UUδin

inmu ⋅−= (1)

where:Um = h m ⋅ Sn

* is the recorded voltage peak-to-peak amplitude, in µV,hm is the peak-to-peak amplitude of the recorded output signal, in mm,Sn

* is the nominal value of the sensitivity setting, in µV/mm, (*)

Uin is the peak-to-peak amplitude of the input voltage, in µV.

Requirement: For the signals recorded with and without a constant D.C. polarization voltage of± 300 mV, the error given by formula (1) shall not exceed the value:

10 (1 + U1 / Uin ) (2)where:U1 is the lowest value of the voltage measurement range, e.g. 5 µV.The commonly accepted polarity shall be checked by applying a negative input signal to input 1 (G1)which shall cause the pens to deflect upwards.

5.3.2. Determination of relative sensitivity-setting error

Definition: The relative sensitivity-setting error is the difference between the nominal and measuredvalues of sensitivity, divided by the nominal value.

Method of measurement: The relative sensitivity-setting error shall be determined directly bymeasuring the peak-to-peak amplitude of the recorded sine-wave signal and of the stimulus, calculating thevalue of sensitivity and comparing it with the nominal value.

Measurement circuit: The measurement set-up is shown in Figure 2.

Measurement procedure: The filter switches are set as specified in point 5.3.1. The sensitivity is set at1 µV/mm and the recording speed at 30 mm/s. A sine-wave signal from generator G1 and voltage dividerD1 with a peak-to-peak amplitude of 20 µV and a frequency of 10 Hz is applied to theelectroencephalograph's input. The amplitude of the recorded signal is measured. The measurements arerepeated for sensitivity equal to 5, 10, 20, 50 and 100 µV/mm and for input signals with peak-to-peakamplitude of 100, 200, 400, 1 000 and 2 000 µV respectively. The footnote of Table 3 applies.

Calculation: The relative sensitivity-setting error, in percent, shall be calculated by the followingformula:

100S

SSδ *n

*m

*n

s ⋅−= (3)

where:Sm

* = Uin / hm is the measured sensitivity value, in µV/mm,hm is the recorded signal peak-to-peak amplitude, in mm,Um is the input voltage peak-to-peak amplitude, in uV,Sn

* is the nominal sensitivity value, in µV/mm.

(*) In this Recommendation, the term "sensitivity" is defined by the ratio of the input to the output amplitude, isexpressed in µV/mm and is represented by the symbol S*. This definition of sensitivity, commonly used in the field ofelectroencephalography, is opposite to the definition of sensitivity S in all the other fields (S* = 1/S).

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Requirement: The relative sensitivity-setting error as determined by formula (3) shall not exceed ± 5 %.

5.3.3. Determination of relative time-interval measurement error

Definition: The relative time-interval measurement error is the difference between the measured andconventional true values of the input signal period, divided by the latter.

Method of measurement: The relative time-interval measurement error shall be determined directly bymeasuring the period (linear length) of the recorded square-wave signal, dividing it by the nominalrecording speed and comparing it with the reciprocal of the input frequency.

Measurement circuit: The measurement set-up is shown in Figure 1.

Measurement procedure: The switches S1 and S2 are set at positions 2 and 3 respectively. The filterswitches are set as specified in point 5.3.1. The sensitivity is set at 10 µV/mm. A square-wave signal fromgenerator G2 and voltage divider D1 with a peak-to-peak amplitude of 200 µV is applied to theelectroencephalograph's input. The values of frequency of generator G2 and the recording speed values aretaken as specified in Table 4, for different intervals of measurement. In each case no fewer than 3 cycles ofthe input signal are recorded. It is sufficient to measure top and bottom channels only.

Table 4Generator G2 frequencies to be adjusted and time intervals to be measured

Time intervalsto be measured, s 5 1 0.5 0.5 0.3 0.2 0.2 0.1 0.05Generator G2frequency, Hz 0.6 3 6 6 10 15 15 30 60Recording speed,mm/s 15 30 60

Calculation: The relative time-interval measurement error, in percent, shall be calculated by thefollowing formula:

100T

TTδin

inmT ⋅−= (4)

where:Tm = Lm/Vn is the recorded time interval, in s,Lm is the length of 3 cycles, in mm,Vn is the nominal recording speed, in mm/s,Tin is the time interval corresponding to 3 cycles of the input signal, in s.

Requirement: The relative time-interval measurement error determined by formula (4) shall not exceedthe value:

5 (1 + T1/Tin) (5) where:T1 is the lower limit of the time-interval measurement range, e.g. 0.05 s.

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5.3.4. Determination of the relative error of the recording speed

Definition: The relative error of the recording speed is the difference between the measured value ofthe recording speed and the nominal value, divided by the nominal value.

Method of measurement: The relative error of the recording speed shall be determined directly bymeasuring the recorded sine-wave signal period, calculating the value of the recording speed from thegenerator frequency, and comparing it with the nominal value.

Measurement circuit: The measurement set-up is shown in Figure 2.

Measurement procedure: The filter switches are set as specified in point 5.3.1. The sensitivity is set at10 µV/mm, and the recording speed is set at the value to be determined. A sine-wave (or square wave)signal from generator G1 (or G2) and voltage divider D1 with a peak-to-peak amplitude of 180 µV isapplied to the electro-encephalograph's input. Measurements are made at speeds of 15, 30 and 60 mm/s.The generator frequency is chosen so that the length of the period of the recorded signal is at least 2 mm.At least 10 cycles are recorded at each speed.

Calculation: The relative error of the recording speed, in percent, shall be calculated by the followingformula:

100V

VVδn

nmv ⋅−= (6)

where:Vm = Lm/nTe is the measured value of the recording speed, in mm/s,Lm is the length of the section recorded for n cycles (n ≥ 10), in mm,Te is the period of the input signal, in s,Vn is the nominal value of the recording speed, in mm/s.

Requirement: The relative error of the recording speed as determined by formula (6) shall not exceed± 5 %.

5.3.5. Determination of recording hysteresis

Definition: The recording hysteresis is the distance between the base lines of a trace obtained,respectively, after a positive and a negative input signal is returned to zero (see Figure 3).

Figure 3Determination of recording hysteresis

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Method of measurement: The recording hysteresis shall be determined directly by measuring thedistance between the baselines, respectively after a positive and a negative input signal is returned to zero.

Measurement circuit: The measurement set-up is shown in Figure 4.

Measurement procedure: For determination of recording hysteresis a differentiating circuit with thetime constant equal to 50 ms (e.g. R6 = 100 kΩ, C1 = 0.5 µF), is connected between voltage divider D1and the input. The filter switches are set as specified in point 5.3.1. The sensitivity is set at 50 µV/mm andthe recording speed is set 30 mm/s. A differentiated signal of 500 µV and 1 Hz is applied to theelectroencephalograph's input, and the recording hysteresis is measured.

Requirement: The recording hysteresis hi shall not exceed 0.5 mm.

5.3.6. Determination of relative errors of internal calibrator and time marker

Definition: The relative error of the internal calibrator or of the time marker is the difference betweenthe measured and nominal values of voltage output of the internal calibrator or of the time interval of thetime marker, divided by their respective nominal values.

Method of measurement: The relative errors of the internal calibrator and of the time marker shall bedetermined by comparing the nominal values of the voltage and time interval of the internal signals of theinstrument with the voltage and time interval of a signal applied to the input, the recorded value of thesignal being made equal to the recorded internal value.

Measurement circuit: The measurement set-up is shown in Figure 1.

Measurement procedure: Switches S1 and S2 are set at positions 1 and 3 respectively and the internalcalibrator is selected. The filter switches are set as specified in point 5.3.1 with the recording speed of15 mm/s. Signals are recorded from the internal calibrator and the time marker. Then the electrodes areselected. A square-wave signal from generator G2 and voltage divider D1 with a frequency of 1 Hz and anamplitude equal in value to the internal calibrator voltage, is applied to the input of the device to beverified. Generator G2 voltage and frequency is adjusted so that the dimensions of the recorded signalsinduced respectively by the internal and external stimuli coincide. The tests are performed at the values ofthe internal-calibrator voltages and the sensitivities given in Table 5.

Table 5

The values of sensitivity to be selected

and internal-calibrator voltages to be measured

Internalcalibrator voltage

µV1 000 500 200 100 50 20 10 5 2

SensitivityµV/m 100 50 50 10 5 5 1 1 1

Calculation: The relative internal-calibrator error, in percent, shall be calculated by the followingformula:

100U

UUδcn

cncmc ⋅

−= (7)

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where:Ucm is the measured peak-to-peak amplitude of the internal-calibrator voltage, in µV,Ucn is the nominal value of peak-to-peak amplitude of the internal-calibrator voltage, in µV.

The relative time-marker error, in percent, shall be calculated by the following formula:

100T

TTδn

nmtm ⋅−= (8)

where:Tm is the recorded value of the time-marker interval, in s,Tn is the nominal value of the time-marker interval, in s.

Requirement: Neither the relative internal-calibrator error nor the relative time-marker error asdetermined respectively by formulae (7) and (8) shall exceed ± 2 %. If there is no time marker on the EUT,the EUT shall be considered to have met the relative time-marker error.

5.3.7. Determination of overshoot

Definition: The overshoot is the difference between the maximum peak-to-peak amplitude of arecorded square-wave signal and its minimum value, divided by twice the minimum value (see Figure 5).

Figure 5 Determination of overshoot.

Method of measurement: The overshoot shall be determined directly by measuring the peak-to-peakamplitude of the recorded square-wave signal.

Measurement circuit: The measurement set-up is shown in Figure 1.

Measurement procedure: Switches S1 and S2 are set at positions 1 and 3 respectively. The filter switchesare set as specified in point 5.3.1. The sensitivity is set at 10 µV/mm and the recording speed is 30 mm/s. Asquare-wave signal from generator G2 and voltage divider D1 with a peak-to-peak amplitude of 180 µV anda frequency of 10 Hz is applied to the electroencephalograph's input. At least 3 cycles are recorded, and themaximum and minimum peak-to-peak amplitude of each cycle is measured.

Calculation: The overshoot, in percent, shall be calculated by the following formula:

1002h

hhδmin

minmaxo ⋅−= (9)

where:hmax and hmin are the measured values of the linear dimensions of the maximum and minimum peak-to-peak

amplitudes respectively of each period recorded, in mm.Requirement: The overshoot as determined by formula (9) shall not exceed 10 %.

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5.3.8. Determination of time constant

Definition: The electroencephalograph time constant is defined as the time interval required for arecorded square-wave signal amplitude to decay to 1/e (37 %) of an initial value (see Figure 6).

Figure 6Determination of time constant.

Method of measurement: The time constant shall be determined directly by measuring the lineardimensions of the decay of the recorded square-wave signal following the overshoot.Measurement circuit: The measurement set-up is shown in Figure 1.

Measurement procedure: Switches S1 and S3 are set at positions 1 and 3 respectively. The high-frequency filter switch is set as specified in point 5.3.1 and the time-constant and low-frequency switchesare set at a value to be determined. The sensitivity is set at 20 µV/mm and the recording speed is set at30 mm/s. A square-wave signal from generator G2 and voltage divider D1 with a peak-to-peak amplitudeof 180 µ.V and a frequency of 0.1 Hz is applied to the electroencephalograph's input. The length of thesegment recorded between the moment of maximum overshoot and the moment when the amplitude of therecorded signal decreases to 37 % of the initial value is measured. The measurements are repeated for allpositions of the time-constant switch.

Calculation: The time constant, in s, for each of the recorded signals shall be calculated by thefollowing formula:

Tc = Lm/Vn (10)

where:Lm is the length of the segment in which the signal amplitude decreases to 37 % of the initial value, in mm,Vn is the nominal value of the recording speed, in mm/s.

Requirement: The time constant as determined by formula (10) shall be within ± 10 % of the valuesspecified by the manufacturer.

5.3.9. Determination of amplitude-frequency response curve

Definition: The amplitude-frequency response curve is the variation with frequency of the recordedsignal amplitude, the input signal amplitude being constant.

Method of measurement: The amplitude-frequency response curve shall be determined by comparingthe peak-to-peak amplitude of the sine-wave signal recorded at different frequencies with the peak-to-peakamplitude of the signal recorded at 10 Hz.

Measurement circuit: The measurement set-up is shown in Figure 2.

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Measurement of the pass band: The filter switches are set as specified in point 5.3.1 and the recordingspeed is set at 15 mm/s for frequencies less than 10 Hz and 30 mm/s for all other frequencies. A sine-wavesignal from generator G1 and voltage divider D1 with peak-to-peak amplitude of 180 µV (held constant)is applied to the input, successively at frequencies 0.16, 0.5, 1.5, 5, 10, 15, 30, 60, 75 Hz. In each case atleast 5 cycles are recorded and the peak-to-peak amplitudes of the recorded signals are measured.

Requirement: The peak-to-peak amplitude of the signal recorded at frequencies between 1 and 60 Hzrelative to the peak-to-peak amplitude of a signal recorded at 10 Hz shall be between 90 % and 110 %.

Measurement of the cut-off frequencies of the filters: The procedures are the same as those specifiedabove except that the filter switches are set at values to be determined. The generator G1 frequency is set,in turn, at 0.9 Fc and 1.1 Fc, where Fc is the cutt-off frequency value to be determined. The linear dimensionof the peak-to-peak amplitude of the recorded signal is measured. The measurements are made for allvalues of cut-off frequencies of the high-pass and low-pass filters. The entire amplitude-frequencycharacteristic for all filters should be provided in the manufacturer's manual.

Requirement: The linear dimension of the recorded signals shall meet the following conditions:A0.9Fc ≤ 0.7 × A10 ≤ A1.1Fc for low frequenciesA0.9Fc ≥ 0.7 × A10 ≥ A1.1Fc for high frequencies

where:

A0.9Fc is the linear dimension of the signal peak-to-peak amplitude recorded at a frequency of 0.9 × Fc, inmm,

A10 is the linear dimension of the signal peak-to-peak amplitude recorded at a frequency of 10 Hz, inmm,

Al.lFc is the linear dimension of the signal peak-to-peak amplitude recorded at a frequency of 1.1 × Fc, inmm.

5.3.10. Determination of input impedance

Definition: The input impedance is an impedance measured between any two inputs of the device.

Method of measurement: The input impedance shall be determined by comparing the linear dimensionsof peak-to-peak amplitudes of the sine-wave signals recorded with and without supplementary impedanceconnected in series.

Measurement circuit: The measurement set-up is shown in Figure 7.

Measurement procedure: The filter switches are set as specified in point 5.3.1. The sensitivity is set at10 µV/mm and the recording speed is set at 30 mm/s. Switches S1 and S2 are set at 1 and 3 respectively. Asine-wave signal from generator G1 and voltage divider D1 with a peak-to-peak amplitude of 180 µV anda frequency of 10 Hz is applied to the input with the recorded length of 25 mm. The recorded signal peak-to-peak amplitude is measured. Then the measurement is repeated with S1 at position 2. The measurementsare repeated in presence of a DC voltage of ± 300 mV, with S2 being set at 1 and 2, in turn.

Calculation: The input impedance, in MΩ, shall be calculated by the following formula:

21

22in HH

HZZ−

= (11)

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where:H1 is the linear dimension of the signal recorded with S1 at position 1, in mm,H2 is the linear dimension of the signal recorded with S1 at position 2, in mm,Z2 is the value of the impedance Z2 connected in series, in MΩ.

Requirement: The input impedance as determined by formula (11) shall not be less than 1 MΩ when thesame pair of input terminals is selected by up to 8 channels.

5.3.11. Determination of common-mode rejection ratio

Definition: The common-mode rejection ratio is the ratio of the peak-to-peak amplitude of an in-phase signalapplied at the input of the EUT to the peak-to-peak amplitude of an out-of-phase signal that results in the samepeak-to-peak amplitude of the recorded signal.

Method of measurement: The common-mode rejection ratio shall be determined indirectly by measuring thelinear dimension of the peak-to-peak amplitude of the signal recorded by the EUT, when a sine-wave signalwith the frequency 50 Hz or 60 Hz of a given amplitude is applied in common mode (between input and groundor earth).

Measurement circuit: The measurement set-up is shown in Figure 8.

Measurement procedure: The filter switches are set as specified in point 5.3.1 and switch S is set at 1. Thesensitivity is set at 5 µV/mm and the recording speed is set at 15 mm/s. The peak-to-peak amplitude of thevoltage of generator G1 is set at 400 mV with a frequency of 50 Hz or 60 Hz. The peak-to-peak amplitude ofthe recorded signal is measured. Then switch S is set to position 2 (unbalanced) and the measurements arerepeated with a sensitivity of 100 µV/mm.

Calculation: The balanced and unbalanced common-mode rejection ratio shall be calculated by the followingformula:

3*

n

10Sh

UK ⋅⋅

= (12)

where:h is the linear dimension of the recorded signal peak-to-peak amplitude, in mm,Sn

* is the nominal value of the sensitivity setting, in µV/mm,U is the peak-to-peak amplitude of the input voltage, in mV (in this case equal to 400 mV).

Requirement: The common-mode rejection ratio as determined by the formula (12) shall not be less than104 for the balanced condition and 200 for the unbalanced condition for each channel.

5.3.12. Determination of baseline width

Definition: The base line width is the width of the line drawn on the paper, the input of the EUT beinggrounded.

Method of measurement: The baseline width shall be determined directly by measuring it perpendicularto the trace (Figure 9).

Figure 9Determination of baseline width.

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Measurement procedure: All input terminals are connected to ground (earth) and the filters are set toprovide the narrowest band width. The sensitivity is set at 100 µV/mm and the recording speed is15 mm/s. The width of the recorded line is measured.

Requirement: The baseline width shall not exceed 0.5 mm.

5.3.13. Determination of baseline drift

Definition: The baseline drift is the deviation of the baseline during a given time interval, the input ofthe EUT being grounded (earthed) (see Figure 10).

Figure 10

Determination of the baseline drift.

Method of measurement: The baseline drift shall be determined directly by measuring the baselinedeviation during the time interval of 10 min.

Measurement procedure: The sensitivity and recording speed are set as in point 5.3.12 and the filterswitches are set as in point 5.3.1. The deviation of the baseline in 10 min is measured.

Requirement: The baseline drift in 10 min shall not exceed 1.0 mm.

5.3.14. Determination of intrinsic noise level referred to the input

Definition: The intrinsic noise level referred to the input is the maximum peak-to-peak amplitude ofthe signal recorded when the electroencephalograph's input is connected to the skin-electrode impedanceZ1; it is evaluated for a given time interval and referred to the electroencephalograph's input (seeFigure 11).

Method of measurement: The intrinsic noise level referred to the input shall be determined directly bymeasuring the maximum peak-to-peak amplitude of the recorded signal for a time interval of 60 s andreferred to the input through the sensitivity-setting.

Measurement circuit: The measurement set-up is shown in Figure 12.

Measurement procedure: The inputs are connected to simulated skin-electrode impedances Z1. Thefilter switches are set as specified in point 5.3.1. The sensitivity is set at 1 µV/mm and the recording speedis set at 15 mm/s. The recording lasts for 60 s. The linear dimensions of the maximum peak-to-peakamplitude of the recorded signal are measured for the entire record and also for 3 (15 mm long) segmentsi.e. for a time interval of 1 s. In addition the deviation of the medium value of the baseline (noisecomponent less than 0.5 Hz) on the segment of 90 mm (i.e. for 6 s) is measured.

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Note: In order to avoid external noise pickup, it is recommended that the resistors and switches of themeasurement set-up (shown in Figure 12) should be placed in a shielded metal box with its caseconnected to ground (earth) (pin No. 24 of the terminal box). The resistors (or box containing theresistors and switches) should be connected to the terminal box by unshielded, untwisted leads thatare as short as possible but no longer than 1.5 m.

Calculation: The noise level referred to the input, in µV, shall be calculated by the followingformula:

U N = h n ⋅ S n* (13)

where:hn is the linear dimension of the maximum peak-to-peak amplitude of the noise measured on a

recording, in mm,Sn

* is the nominal value of the sensitivity-setting, in µV/mm.

Requirement: The intrinsic noise level referred to the input shall satisfy the following conditions:no more than 1 deflection greater than 4 µV in 60 s,no more than 1 deflection greater than 2 µV in 1 s, andthe remaining deflections shall not exceed 1.5 µV in 60 s.

Figure 11Determination of the intrinsic noise level referred to the input.

5.3.15. Determination of interchannel crosstalk coefficient

Definition: The interchannel crosstalk coefficient is the ratio of the peak-to-peak amplitude of thevoltage induced on the channel under test to the peak-to-peak amplitude of the voltage applied at allthe other channels.

Method of measurement: The interchannel crosstalk coefficient shall be determined by comparingthe peak-to-peak amplitude of signals recorded on the channel under test to the peak-to-peakamplitude of signals recorded on all other channels.

Measurement circuit: The measurement set-up is shown in Figure 13.

Measurement procedure: The filter switches are set as specified in point 5.3.1. The channel under test isconnected through simulated skin-electrode impedance Z1 to ground and the sensitivity of this channel is set at1µV/mm. The sensitivity of other channels is set at 200 µV/mm. A sine-wave signal from generator G1 and

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voltage divider D1 with a peak-to-peak amplitude of 1 mV and frequencies manually swept from 10 Hz to40 Hz are applied to these channels. Linear dimensions of the signal peak-to-peak amplitude recorded atthe channel under test are measured. The measurements are repeated successively for each channel.

Calculation: The interchannel crosstalk coefficient, in percent, shall be calculated by the followingformula:

100U

ShWin

*ii

i ⋅⋅= (14)

where:i = 1,2,..n is the number of the channel under test,n is the number of channels,hi is the peak-to-peak amplitude of the signal recorded on the channel influenced by the noise, in mm,Uin is the peak-to-peak amplitude of the voltage applied to the inputs of the remaining channels, in µV,Si

* is the nominal value of the sensitivity of the channel under test, in µV/mm.

Requirement: The interchannel crosstalk coefficient at frequencies from 10 Hz to 40 Hz shall notexceed 2 %.

5.3.16. Determination of relative error of the interelectrode-resistance measurement

Definition: The relative error of the interelectrode-resistance measurement is the difference between theindicated resistance value and the conventional true value, divided by the latter.

Method of measurement: The relative error of the interelectrode-resistance measurement shall bedetermined by comparing the data of the incorporated resistance measuring device with those of theresistor connected to the input of the EUT.

Measurement procedure: The device under test is set in the mode of measurement of the interelectroderesistance. Resistances of 1, 5, 20 and 50 kΩ (R9-R12 in Table 2) are applied to the input of the device.

Calculation: The relative error of the interelectrode resistance measurement, in percent, shall becalculated by the following formula:

100R

RRδ

o

omR ⋅

−= (15)

where:Ro is the resistance connected to the input of the device to be verified, in kΩ,Rm is the indicated resistance value, in kΩ.

Requirement: The relative error of the interelectrode-resistance measurement as determined by formula(15) shall not exceed ± 10 %.

5.4. Determination of current in the patient circuit

Definition: The current in the patient circuit is defined as the current passing through a patient whileconnected to an electroencephalograph.

Method of measurement: The current in the patient circuit shall be determined indirectly by measuringthe voltage recorded by the electroencephalograph with a resistance connected to the input of the EUT andcalculating the value of the current.

Measurement circuit: The measurement set-up is shown in Figure 14.

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Measurement procedure: The sensitivity is set at 100 µV/mm and the recording speed is set at15 mm/s. The filter switches are set as specified in point 5.3.1. The base line is recorded, then thelinear dimension of the step signal recorded peak-to-peak is measured with S open.

Calculation: The current in the patient circuit, in µA, shall be calculated by the followingformula:

3*n 10S

rhI −⋅= (16)

where:h is the linear dimension of the step voltage recorded, in mm,Sn

* is the sensitivity, in µV/mm,r is the value of the resistance R8 connected to the input, in kΩ.

Requirement: The current in the patient circuit as determined by formula (16) shall not exceed0.1 µA.

6. Verification report and certificate

6.1. The verification report shall contain the following information:(a) the designation and serial number of the instrument verified,(b) the country of origin and manufacturer,(c) the equipment used for verification,(d) the date of verification,(e) the references to the applicable regulations and the procedures used,(f) the measurement results for the various characteristics,(g) the organizations and persons responsible for verification.

6.2. Electroencephalographs verified in accordance with this Recommendation may be granted acertificate of verification in accordance with the established laws and regulations of a given country.The certification shall specify the expiry date of the validity of the verification.

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APPENDIX

Table of correspondence between the system of numerical definitions of electrodes and the international “10-20” System

1 2 3 4 5 6 7 8 9 10 11 12 13 14Fp1 Fp2 F3 F4 C3 C4 P3 P4 O1 O2 F7 F8 T3 T4

15 16 17 18 19 20 21 22 23 24T5 T6 A1 A2 FZ Cz Pz N

Figure 15Electrode lead terminal box.

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Contents

Foreword ..................................................................................................................................................... 2

1. Scope................................................................................................................................................. 3

2. Characteristics to be verified ............................................................................................................. 4

3. Measuring instruments used for verification .................................................................................... 5

4. Verification conditions and preparation for verification.................................................................... 6

5. Verification ........................................................................................................................................ 6

5.1. External examination ........................................................................................................................ 6

5.2. Testing .............................................................................................................................................. 6

5.3. Determination of metrological characteristics .................................................................................. 65.3.1. Determination of relative voltage-measurement error ..................................................................... 75.3.2. Determination of relative sensitivity-setting error ............................................................................ 95.3.3. Determination of relative time-interval measurement error ........................................................... 115.3.4. Determination of the relative error of the recording speed ........................................................... 125.3.5. Determination of recording hysteresis ............................................................................................ 125.3.6. Determination of relative errors of internal calivrator and time marker ......................................... 135.3.7. Determination of overshoot ............................................................................................................ 155.3.8. Determination of time constant....................................................................................................... 165.3.9. Determination of amplitude-frequency response curve .................................................................. 165.3.10. Determination of input impedance.................................................................................................. 195.3.11. Determination of common-mode rejection ratio............................................................................. 205.3.12. Determination of baseline width.................................................................................................... 205.3.13. Determination of baseline drift ....................................................................................................... 215.3.14. Determination of intrinsic noise level referred to the input ............................................................ 215.3.15. Determination of interchannel crosstalk coefficient ....................................................................... 225.3.16 Determination of relative error of the interelectrode-resistance measurement ............................... 25

5.4. Determination of current in the patient circuit................................................................................ 25

6. Verification report and certificate ................................................................................................... 27

Appendix: Table of correspondence between the system of numerical definitions of electrodesand the international “10-20” System....................................................................................... 28