Procedure

Calibration Procedure

Instrument :INSULATION TESTERNo: CI/01/I2

Revision :3

Written By : Eby Joy

QA/QC EngineerSign :

Date :

Distributed to : TD,LM,MR

All users. Original : QA File

Checked By : Miyad Hydrose

Technical SupervisorSign :

Date : Issued Date :

11/12/2014

Effective from :

15/12/2014

Approved By : Izzuddin T Mohammed

Technical DirectorSign :

Date :

Calibration Procedure

Instrument :INSULATION TESTERNo: CI/01/I2

Revision :3

Written By : Eby Joy

QA/QC EngineerSign :

Date :

Distributed to : TD,LM,MR

All users. Original : QA File

Checked By : Miyad Hydrose

Technical SupervisorSign :

Date : Issued Date :

11/12/2014

Effective from :

15/12/2014

Approved By : Izzuddin T Mohammed

Technical DirectorSign :

Date :

1. Purpose Inorder to provide the written calibration procedure for insulation testers. Insulation testers are used to verify that electrical installations are safe, to test windings on motors and to test insulation resistance on various appliances. It is essential that the tester provides the correct test voltage as the voltage may influence the measurement results.

2. ScopeThe calibration requirements specified in this document apply to all portable didital insulation testers. Insulation Test Voltage, Insulation Test Resistance, Insulation Test current would come under the scope of calibration in an inulation tester. Uncertainty budgeting of insulation tester calibration will be explained in this procedure.3. LocationThe calibration will be carried out in the Lab or customer premises depending on the customer requirement. For better accuracy, lab calibration is preferred.4. Environmental conditions to be maintained Temperature: 22C 2C Humidity: 50%RH 10%RH5. Master Equipment Used

5.1 Transmille 3200A Electrical Test Calibrator(for Insulation Resistance Voltage, I. Resistance, I. current.)

5.2 IET labs Decade Resistance box for continuity resistance measurement or any calibrated resistance standard.5.3 Standard Multimeter

5.4 Multiproduct calibrator which can source voltage (if the insulation tester has a voltage measurement funtion)

5.5 Guard Function checker for checking the Guard terminal functioning.

5.6 Calibration Capability5.7 Insulation Resistance- 10k to 100 G (Upto 5000 V insulation tester can be verified, if using the adpator)

5.8 Insulation Volatge- 50V, 100V, 250V, 500V, 1000V, 2500V, 5000V

5.9 Insulation Current-0.5mA and 1 mA

5.10 Continuity Resistance6. Reference international standards/guidelines/Manuals6.1 Guidance on the calibration of Insulation Testers, TG-02-01, South African Accreditation body6.2 Transmille 3200 Electrical Test calibrator manual.

7. Calibration Procedure 7.1 Precautions before and during calibrationa. Set the function switch to the appropriate position before measuring.b. Warm-up time for the reference instrument is 30 minutes and for the UUT, refer the operation manual of the instrument. Calibration can only carried out after the warm-up time.

c. Do not try to calibrate the insulation resistance if it is damamged or if metal parts are exposed. Also check the meter for cracks or missing plastic.d. Ensure that the test leads are placed and firmly connected in the proper input terminals. Connect the common test lead before the live test lead and remove the live test lead before the common test lead.e. Examine the test leads for damaged insulation or exposed metal. Check test lead continuity. Replace damaged leads.

f. Ensure that the insulation tester is switched off when opening the battery compartment.

g. Always remove the test leads before replacing the battery in the tester. h. The instrument must not be low battery while carrying out the calibration.

i. Remove the teast leads and the range selector switch to the OFF position after use.

7.2 Insulation Resistance Measurementa. A resistor of known value and voltage coefficient should be connected to the insulation tester for calibration(Refer figure 1). Connect the insulation tester(unit under test) to the Black & Red 4mm terminals of Transmille 3200A(which acts as the standard resistor).b. Set insulation voltage range on the tester. Calibrate the instrument on at least two points along the scale of each range.c. Enter the required resistance from 10k to 10,000M on the keyboard followed by Enter in transmille 3200 to set the output. An alternative way to select the required resistance is to use the digital Control to increment / decrement the digit indicated by the cursor. The Left and Right arrow keys allow the selected digit to be changed.d. Measure the insulation Resistance set by Transmille 3200 by pressing the test button in the insulation tester for 1 minute at the selected voltage range. At the end of the 1 min record the resistance indicated by the unit under test. Repeat the measurement for 5 times at each point.e. Care should be taken not to exceed the voltage and current limits marked on the specification of the calibrator when applying voltage from the insulation tester. While applying voltages above 5kV, an voltage adaptor needs to be used along with the electrical test calibrator inorder to test insulation tester above 1kV voltage capacity.

Figure 1

7.3 Insulation Voltage Measurement (Figure 2)-Method 1a. The output voltage is measured on each range to ensure that the tester delivers at least the minimum specified voltage. b. This measurement should be conducted at the load recommended by the manufacturer, normal case we take the load as 1G. The output voltage measured as well as the value of the load shall be stated on the calibration certificate.c. The voltage applied by the insulation tester can be measured by Transmille 3200 Electrical Test calibrator.

d. To measure the insulation voltage, Connect the insulation tester to the 4mm sockets at the top of the calibrator using the set of silicon test leads, or the leads supplied with the instrument.

e. From the Insulation Resistance menu displayed on the 3200A, select the VOLTAGE function using the soft key.f. Press the test button in the insulation tester to inject voltage to the calibrator. Record the measured value in the transmille 3200 and the applied value from the tester. Record the error.

7.4 Insulation Voltage Measurement - Method 2a. To measure voltages above 1000 V the following method shall be used.b. The insulation Tester is to be connected to 1 G load(CB 101). Across the load a mulimeter will be connected through a high voltage probe as the voltage rating for multimeters cannot exceed 1000V.

c. Start applying the voltage across the load and measure the voltage across the load using the mulimeter.d. Check the error between the insulation tester voltage and the voltage measured by the reference multimeter.

7.5 Insulation current Measurement (Figure 3)e. Select the required voltage range to be measured using either the digital Control or the up / down arrow keys in Transmille 3200 Electrical Test Calibrator. Ranges include 50V, 100V, 250V, 500V and 1000V.The impedance of each range is automatically set to give the correct load 1mA / 0.5mA (see test current below) at the applied nominal voltage range. Figure 2 Screenshot of transmille 3200 display

Figure 3g. Select the required measurement current using the Soft Keys. The default setting for current load is 0.5mA nominal which is thecorrect load/test current for the 17th Edition equipment -e.g. must be able to supply 0.5mA at the specified test voltage.Older insulation testers (16th Edition) produced 1mA current at the specified test voltage. The 3200A should be set to 1mA current for these instruments. Very old testers may only produce a very small current and the voltage will collapse under any load these should be tested using additional equipment.7.6 Insulation Tester with Continuity functiona. Calibrate the low value ohms/continuity ranges by applying at least two low ohm resistance values.b. Note that insulation testers are 2-terminal and are often calibrated with the leads supplied. This shall be reported on the calibration certificate.7.7 Voltage Measurement Accuracya. Calibrate the voltage measuring ranges at a minimum of two points along the range

using transmille 3041 following accredited procedure (AC/QSP/029). 7.8 Guard Terminal function Checkinga. Where a guard terminal is incorporated on an insulation tester, the functionality of this terminal shall be verified. This can be done in the following way by connecting two suitable series resistors in parallel with the resistance being measured. (See figure 1 below).

Figure:

Step 1 - Measure without the guard terminal connected (173 M expected)

Step 2- Measure with the guard terminal connected (1 G expected)8. Accuracy Criteriaa. If the UUT reading exceeds and adjustment of the same is not possible to make it within the manufacturer recommended tolerance limit,then the instrument need to be rejected without calculating the uncertainty limits.

b. If the UUT reading exceeds the manufacturer recommended tolerance limit and adjustment is possible to make it within tolernace limit as specfied by the manufacturer, then the same need to be approved, certified.The uncertainty Estimation needs to be done and given in the certificate.

c. If the UUT is within the manufacturer tolerance limit without any adjustment, then the instrument is approved,certified. The uncertainty Estimation needs to be done and given in the certificate.9. Intermediate Check for the Reference Instrumenta. Intermediate check of the reference instrument shall be done every 6 months. The reference instrument is used for calibrating an Insulation Tester @1G load under different voltages (50V, 100V, 250V, 500V, 1000V). The results would be recorded in a work sheet.b. The same nsulation Tester is calibrated again with the Megger Calibration box-CB101 @1G load under same voltages (50V, 100V, 250V, 500V, 1000V).

c. Both the calibration results shall not have a variation of more than 1% from each other at any of the points.

d. If a varaition is found more than the acceptable limit, a corrective action form will be raised by the concerned technician and investigation to be done to find out the root cause of the problem. A corrective action will have to be taken to rectify the error. Until the case is resolved the calibration would be stopped using the instrument in question.10. Uncertainty Budgeting For Insulation Tester Calibration

10.1 Type A Uncertainty (uA)

a. Type A uncertainty is determined by the statistical analysis of a series of measurements. Ten measuremnts are taken to find this random uncertainty.

10.2 Type B uncertainty (uB1, uB2, uB3, uB4)a. All the other uncertainties that cannot be determined statistically, during the measurement process. They fall in to the category of Type B uncertainties

Calibrator Uncertainty , uB1 Measurement error due to limitations of the UUTs resolution uB2 Uncertainty due to thermal emf of test leads, uB3 (Only taken in Voltage measurement ) I year specifications of the reference instrument, uB4 Uncertainty due to Drift, uB510.3 Combined Uncertainty (uc)a. It is a summation of Type A and Type B uncertainties ( U1+UB1+UB2+UB3+UB4.) using law of error propagation.10.4 Expanded uncertainty (U)

a. Expanded measurement uncertainty (or expanded uncertainty) is defined as the product of a combined standard measurement uncertainty and a factor larger than one to provide a certain level of confidence. It is combined uncertainty multiplied by 2 (coverage factor k) to provide a level of confidence of 95%.

11. Model Equation

Yi = Ym +Ymc UB1+UB2+UB3+UB4

Ym= Value from the master instrument

Yi = Indicated value in the UUTYmc= Correction from the master instrument

UB1= Calibration of the reference meter

UB2= Resolution of The UUT

UB3= Thermal EMF in the Leads (Only applicable if a Voltage measurement fearure is available in the unit)UB4= Drift in the master instrument.

12. Formula used for estimating uncertainty 12.1 Type A Uncertainty (uA) Stanard deviation (S) Where n Total Number of Measurements

S = n 2 Xi value of individual measurements

Xa Average of total number of measurement

Xi - Xa

i = 1

n 1

Estimated standard uncertainty uA = S ------------------- Eq(1) n

where S estimated standard deviation.

Probability Distribution is Normal 12.2 Type B uncertainties

a. Uncertainty from Master Equipment Certificate (uB1) uB1 = Expanded Uncertainty

2 ------------------- Eq(2)

Probability Distribution is Normal b. Uncertainty due to UUTs resolution (uB2)

Resolution ------------------- Equ(3) uB2 = 2 X 3 Probability Distribution is Rectangularc. Uncertainty due to thermal emf of test leads (uB3) uB3 = Average of +ive and ive voltage of test leads ------------------- Equ(4) 2

This uncertainty contribution will be considered only in voltage measurement function in the Insulation tester. Probability Distribution is Rectangulard. Uncertainty Due to Drift (uB4) Drift in direct reading instruments is defined for a specific time interval of interest. The standard uncertainty for drift is uB4= |Y0-Yt|/3 ---------------------- Equ(5)

Y0- Measurement at Time 0

Yt- Mesaurement at Time t Probability Distribution is Rectangular12.3 Formula used for Estimation of standard combined uncertainty

Standard combined uncertainty, uc = uA + uB12+ uB12+ uB12+ uB12+ uB12 ----------Equ(6)12.4 Formula used for calculating expanded uncertainty

U= uc x 2 (k is the coverage factor which is =2) ----------Equ(7)13. Procedure

13.1 Type A Uncertainty (Random Errors)

a. Estimation of Type A uncertainty limit

1. Ensure the indicated reading of UUT is within the tolerance limit given by the manufacturer

2. Take minimum 5 readings on each parameter and range.

3. Calculate the average value for the series of measurement for all ranges and parameter

4. By using the above mentioned formula,calculate the standard deviation ( S ).

5. Apply estimated standard deviation to Eq(1) above to calculate the Type A uncertainty limit ( U1 ).

13.2 Type B Uncertainties (Systematic Errors)

a. Estimation of Imported Uncertainty (uB1)

1. Calibrators uncertainty is mentioned in the calibration certificate of the Master instrument as expanded uncertainty hence divide the value by 2 to get the combined uncertainty.

2. Use the above mentioned formula Eq(2) to get UB1b. Estimation of Uncertainty due to Limited Resolution of the UUT (uB2)

1. Resolution of the UUT is taken into consideration. The limit to the ability of an instrument to indicate small changes in the quantity being measured, referred to as resolution or digital rounding error, is treated as a systematic component of uncertainty. Half scale of the resolution is taken and the probability distribution is rectangular, therefore the divisor is 3 . 2. Use the equation, (Equ3) to get uB2.c. Estimation of Uncertainty due to Thermal EMF (uB3)

1. Refer to the technician guide to get the value of uB3. 2. If an electrical conductor passes through a temperature gradient then a potential difference will be generated across that gradient. This is known as the Seebeck effect and these

unwanted, parasitic voltages can cause errors in some measurement systems in particular, where small dc voltages are being measured.3. Take the leads which are used for the calibration. Short circuit one end of the cables and other ends are connected to the voltage terminals. Take readings with the leads connected to the positive and negative of the voltage terminal and readings taken with the leads switched at the voltage terminal.4. The probability distribution is rectangular, therefore the divisor is 3 . 5. Use the equation, Equ(4) to get uB3.d. Estimation of Uncertainty due to Drift (uB4)

1. Refer to technician guide to get the values of uB4.

2. Electronic instruments are expected to have drift. Drift can be identified from the certificates of two consecutive calibration done to the instrument.

3. The probability distribution is rectangular, therefore the divisor is 3 . 4. Use the equation Equ(5) to get uB4e. Estimation of Combined Uncertainty (UC)

1. Take the individual uncertainty values of Type A, uB1, uB2, uB3 and uB42. Add all uncertainties above, using the Law of Error propagation.3. The probability distibution is normal because it is a summation of many standard probability distributions. The divisor is 1

4. Use Equ(6) to get the combined Uncertaintyf. Estimation of Expanded Uncertainty

1. Although the combined standard uncertainty is used to express the uncertainty of many measurements, some commercial, industrial and regulatory applications may require a measure of uncertainty that defines an interval about which the measurement value will lie with a certain level of statistical certainty. This type of measure is termed expanded uncertainty, and is determined by multiplying the combined standard uncertainty by a coverage factor, k. The coverage factor is usually in the range of 2 to 3. That is the expanded uncertainty of the measurement which is multiplied by a coverage factor k=2,providing the level of confidence of approximately 95%.

e. Uncertainty Budgeting for Insulation Tester Calibration.SymbolSource of UncertaintyProbability DistributionDivisorSensitivity Coefficient(Ci)

uARepeatabilityNormal11

uB1Calibration of the Master InstrumentNormal21

uB2Resolution of the UUTRectangular31

uB3Thermal Emf(Error due to leadsRectangular31

uB4DriftRectangular31

ucCombined UncertaintyNormal1-

UExpanded UncertaintyNormal(k=2)1-

14. Documentation

a. Record all calibration points (includes applied value and measured value) in the work sheet (AC/WF/003) before and after ( if required ) adjustment. b. If the instrument is out of tolerance and not possible to adjust , it is forwarded to the technical supervisor with a fault report. c. Readings are enterd in to the central suystem along with all the details of the instrument ( if calibration completed )d. Certificate of calibration is suued to the customer.

15. Data to be recorded.

a. Applied readings and indicated readings to be recorded in work sheet.

b. Applied readings and indicated readings after adjustment ( if need be ) to be recorded in the same worksheet ( May use more than one page as required but need to bind together and the assigned certificate number to be mentioned in each page)c. Calculation of tolerance limit and calculation of uncertainty values are to be performed.

Prepare calibration certificate / service report as per the procedure16. Affixing the identification marka. The due date of calibration will be mentioned as per the clients requirment or will be mentioned as one year.b. The calibration sticker must be affixed in the instrument in such a way that it doesnt block any of operation of the instrument.

17. Reason for Revision Revision 1 : 1.Changes in the format. 2.Inclusion of documentation chapter.Revision 2 : 1.Inclusion of RangeRevision 3 : The whole procedure was revised to meet the requirements of ISO/IEC 17025 standard.

Inclusion of Uncertainty procedure.

Date : 11/Dec/2014****END OF PROCEDURE****

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