WI - Intermediate Check Balance [PDF]

Citation preview

WI -01: INTERMEDIATE CHECK FOR ELECTRONIC WEIGHING MACHINE



WORK INSTRUCTION INTERMEDIATE CHECK FOR ELECTRONIC WEIGHING MACHINE



1.0



SCOPE This document specifies the Working Instruction for the Intermediate Check of Weighing Machine(Balance) of electronics types .



2.0



3.0



4.0



5.0



REFERENCE 2.1



NATA Technical Note 13 — May 2010



2.2



Balance Instruction Manual.



EQUIPMENT / APPARATUS 3.1



Standard Weight Class E1 & M1 or Reference Block ; close to full capacity (not less than 80%) of the balance range being checked



3.2



Hand Glove



3.3



Twizzer



DEFINATION 4.1



LINEARITY : A measure of the degree to which a response maintains a linear relationship with given input stress.



4.2



REPEATABILITY : This is the ability to reproduce the same level of accuracy under the same conditions of test, using the same measurement procedure, the same measuring and test equipment and the same environmental conditions.



4.3



ACCURACY : How close the result of the experiment comes to the “ True Value”.



4.4



PRECISION : How exactly the results is determine without reference to any true value.



PREPARATION PROCEDURE 5.1



Ensure that the standard weights/reference block and the balance are placed in the same environmental conditions for at least 30 minutes to achieve equilibrium ie same body temperature and humidity.



5.2



The weighing balance should be inspected for any damage such as dents, cracks before intermediate check. Should there be any dirt on the surface of the weighing balance, it should be cleaned by using suitable solvent ,wipe cloth and brushes or blower.



5.3



Ensure balance is located on the rigid body/platform that can resist vibration disturbances and at most stable conditions, free from direct air draft and extreme environmental conditions.



5.4



Power ON the balance and perform self-calibration/auto-calibration(certain balances) .



Issue 1,27 April 2018



Page 1 of 2



WI -01: INTERMEDIATE CHECK FOR ELECTRONIC WEIGHING MACHINE



6.0



ONE POINT CHECK PROCEDURE (Monthly Check) 6.1



Use OPC Worksheet in Appendix 1 to record the data.



6.2



Tare the balance and record the zero reading (z1);



6.3



Place the calibrated or assigned value mass(es) (mass M) on the balance and record the indicated mass (m1);



6.4



Remove the mass(es) from the balance. Do not tare the balance;



6.5



Place the calibrated or assigned value mass(es) on the balance and record the indicated mass (m2);



6.6



Remove the mass(es) from the balance and record the balance reading (z2).



6.7



Calculate the correction,C for each separate weighing: C1 = M – (m1 – z1) C2 = M – (m2 – z2) Correction,C = (C1 + C2)/2 Criteria, C < 3S (S of repeatability of last calibration). If Correction,C has changed by more than 3 times the standard deviation of the repeatability as provided on the last calibration report, then the balance may require servicing, adjustment and recalibration. The end user of the balance must decide if the balance is still fit for purpose and recalculate the limit of performance if required.



7.0



REPEATABILITY CHECK PROCEDURE (Six Monthly Check) 7.1



Use Repeatability Worksheet in Appendix 2 to record the data.



7.2



Tare the balance and record the zero reading (z1);



7.3



Place the selected mass(es) which is close to the maximum capacity of the range being checked on the balance and record the indicated reading (m1);



7.4



Remove the mass(es) from the balance and record the balance reading (z2);



7.5



Without taring the balance, place the same selected mass(es) on the balance and record the indicated reading (m2);



7.6



Remove the mass(es) from the balance and record the balance reading (z3);



7.7



Repeat (d) and (e) so that 10 complete set of readings are obtained.



7.8



Calculate the difference (ri) between each reading and its corresponding zero reading: ri = mi – zi



7.9



Calculate the standard deviation (s) of the difference r1, r2,..…rn from the formula If the standard deviation (suser check) is less than twice (sCalibration report), the standard deviation determined at the last full calibration, the balance is fit for continued use (refer to Assessment of user checks below).



Issue 1,27 April 2018



Page 2 of 2