Blog

What are the factors that cause deviations in the test results

2021-2-25

 
As a first-line quality inspection company, the inspection results they get are an important standard for people to measure the quality of products. With the development of social economy, the social influence of the scientificity, fairness, and accuracy of inspection results is increasing. Some inspection institutions The results of the inspection have been recognized by international economic organizations and have played an important role in my country's foreign economic and trade. Therefore, it is particularly important to strengthen the risk prevention of inspection agencies themselves.
 
 
 
 
A.   Superpower range test
 
According to the provisions of the "Metrics Law", data laboratories that provide certification to the society must be certified by the laboratory (measurement certification) and (or) CNAS accreditation, and the qualification accreditation and (or) CNAS accreditation limit the scope of laboratory capabilities, The laboratory can only issue an inspection report with the corresponding mark within the range of products (parameters) limited by the range of capabilities. If the standard used for inspection is not within the range of capabilities, we call it an out-of-range inspection.
 
The "Administrative Measures for Product Quality Supervision and Random Inspection" issued by the General Administration of Quality Supervision, Inspection and Quarantine, the "Measures for the Classification and Supervision of the Work Quality of Product Quality Inspection Institutions" and other regulations also clearly stipulate that laboratories shall not perform inspections beyond the scope of their capabilities. In the case of individual inspection agencies’ over-range inspections, there are three main types of over-range inspections:
 
1.    Intentional superpower range test
In order to meet customer requirements and strive for economic benefits for the laboratory, the laboratory or individual personnel in the laboratory conduct inspections on products that are not within the scope of ability and issue a marked inspection report; or laboratory personnel believe that individual standards in the adopted standards are in Within the scope of ability, the product was inspected by mistake and a marked inspection report was issued. In recent years, the General Administration of Quality Supervision, Inspection and Quarantine, CNCA, and provincial and municipal quality supervision bureaus have imposed severe penalties on the detection of super-capacity ranges, and even stopped the testing activities of individual laboratories.
 
Therefore, the laboratory should publicize the consequences of the super-capacity range test to every employee, and cannot deliberately conduct the super-capacity range test for economic benefit or for the sake of the enterprise; at the same time, the laboratory should carefully sort out the laboratory's range of capabilities. There are indeed equipment and inspection capabilities that are not within the scope of the standards, and expansion should be made as soon as possible to improve the ability to serve the enterprise.
 
2.    Failure to confirm capacity in time after standard changes
In recent years, whether it is product standards or method standards, the standards have been changed very frequently. In accordance with the provisions of the laboratory qualification accreditation review criteria, the documents used by the laboratory must be current and effective. Therefore, the laboratory cannot use the invalidated standard to carry out the testing work. If a laboratory adopts the new standard to carry out its work, it must go to the laboratory qualification accreditation and/or CNAS accredited certification body to make standard changes in time.
 
At present, some laboratories are afraid of trouble and often wait until re-assessment or supervisory assessment before making standard changes. If the inspection work is carried out according to the new standard between the implementation of the new standard and the passing of the laboratory re-assessment or supervisory assessment, it is an out-of-scope inspection.
 
There is also a hidden super power range situation. When the scope of the inspection capability passed by the laboratory, the actual implied meaning includes: the standards cited in the product standards also pass the laboratory review. When there are changes in the referenced standards, especially the actual changes in inspection methods and environmental facilities, the actual inspection capabilities for product inspection may change.
 
This change may cause the laboratory to be unable to carry out inspection work normally according to the current effective standards. We call this kind of change "hidden" out-of-scope testing. Due to the need to reconfirm the ability after the standard is changed, individual laboratories are afraid of trouble, and often wait until the supervisory review or re-assessment before confirming, which leads to the beyond-capability inspection.
 
Therefore, laboratories should pay attention to and avoid the occurrence of this situation, and shall not use the new standard to carry out inspections before the ability is confirmed. The laboratory should pay more attention to the changes of the cited standards in the product standards, so as to avoid the use of invalid standards to carry out inspections that may cause misjudgment of inspection results and possible inspection risks.
 
3.    Indiscriminate use of CNAS, CMA, CAL logos
 
Many laboratories have passed the CNAS accreditation and laboratory qualification accreditation, but these two accreditations are not accredited at the same time. When applying for expansion or standard change, one is often passed, and the other is still some time away Only recognized. Some laboratories, especially some small and medium-sized laboratories, are mainly capable of obtaining CMA and CAL.
 
CNAS has a very small range of capabilities. The cover of the inspection report generally has several test marks directly printed on the cover, which makes the experiment Misuse of the logo in the room. Therefore, the laboratory should print the inspection cover separately according to the passed capacity range, and use it according to the regulations.
 
B.   Equipment and environmental facilities cannot meet standard requirements
 
Equipment and environmental facilities are necessary tools for laboratory testing. Whether the equipment and environmental facilities meet the standards will directly affect the accuracy of the data and have a significant impact on the test results and judgments. The main reasons why equipment and environmental facilities cannot meet the requirements are:
 
1.    The traceability of the value is not as required
 
The traceability of the value of the instrument and equipment is one of the main means to ensure the accuracy of its measurement. According to the requirements of the laboratory qualification accreditation review criteria, the instrument and equipment should be verified or calibrated before use, and if necessary, between the second verification or calibration. Check during the period to ensure the accuracy of the data. However, some laboratories failed to send the instrument to the metrology department for verification or calibration as required, causing the instrument to be inaccurate, and some verification/calibration laboratories issued certificates without verification/calibration.
 
There are often instruments and equipment in the laboratory that do not have verification procedures or calibration methods. The metrology department often saves time and only verifies or calibrate the measuring instruments used by the instruments, and the overall equipment is not comprehensively judged, so that the equipment displays The accuracy of the data is unknown. If proficiency testing or laboratory comparison methods are not used to verify the instrument at this time, it will bring great risks.   
 
2.    Equipment accuracy is reduced
 
Some inspection agencies, especially small and medium-sized inspection agencies, due to insufficient funds, make the equipment long-term service and cannot be updated in time. Due to the long service life of the equipment, or the harsh environment, the accuracy of the equipment decreases and the reliability of the inspection data decreases. Therefore, the laboratory should update the equipment in time.
 
When the equipment cannot be updated for a while, it should increase the frequency of calibration, perform periodic verification, and verify the reliability of the equipment by means of inter-laboratory comparison or inter-equipment comparison to ensure that the test data is accurate and reliable.    
 
3.    Environmental facilities do not meet standard requirements
 
Many tests have high requirements on environmental facilities and have a great impact on the inspection results. However, some inspection agencies do not pay much attention to environmental facilities and cannot meet the inspection requirements well.
 
For example, in the water curing of cement inspection, the water temperature is specified as (20±1)℃, which exceeds the temperature range specified by the standard, especially when the temperature is exceeded, which will have a great impact on the inspection results. However, we found in the review that in some cement laboratories, water curing is carried out in a pool. The water temperature is lower to heat the water, and the water temperature is higher to add cold water. Such a temperature control method cannot guarantee the accuracy of water temperature control. The inspection after curing The data is also inaccurate.
 
Therefore, for tests that require high environmental facilities, the laboratory should ensure that the environmental facilities tested meet the standard requirements.
 
C.   Lack of effective control over the quality of the testing process
 
Incorrect inspection conclusions or inaccurate data due to the non-standard inspection process also occur from time to time, mainly in:
 
1.    Inspection and calculation carelessness:
 
Inspection is a process that requires concentration. A little negligence can easily lead to errors. With the popularity of mobile phones, it is very common for inspectors to answer the phone during the inspection or data calculation process after the inspection. This and other careless cases of inspection errors also occur from time to time. Although the inspection errors caused by carelessness in the inspection and calculation process are not common, once this happens, it will directly lead to errors in the inspection results.
 
2.     Not sensitive to suspicious data
 
Generally speaking, each substance has its own characteristics, and its test data should be within a certain range. For example, the thermal conductivity of benzene board cannot be 0, and the building exterior windows using different aluminum alloy building profiles and ordinary single-layer glass are not May meet the requirements of thermal insulation windows and so on. When the inspector or the inspector of the inspection report finds suspicious data that does not conform to the general rules, the suspicious data shall be reviewed and whether there is a problem with the equipment or the inspector has made an operating error.
 
The ability to correctly judge whether the data is suspicious is based on a large accumulation of theories and testing practices of the tested product. This is also a mature inspector. The basic quality of inspection report review and approval personnel should be without long-term training. It is impossible to sensitively detect suspicious inspection data.
 
3.    The processing of the critical value is biased
 
In the inspection process, due to the existence of measurement uncertainty, it may lead to deviations in the judgment of the critical value of the inspection items. For example: coating thickness. For ordinary decorative aluminum-plastic panels, because the coating thickness is relatively small, the precise calibration of the "0" point during measurement is particularly important for products in the critical state specified by the standard. If you use an ordinary standard substrate to adjust 0, there may be a deviation of (1~2)um, which may cause the product to slide from "qualified" to "unqualified" edge.
 
For ordinary decorative aluminum-plastic panels, the product can be removed from the coating and adjusted to 0 on the exposed substrate to ensure the accuracy and objectivity of the results. Therefore, for inspection results with critical values, multiple comparison tests should be organized by different inspectors or equipment to ensure that the inspection results are scientific and fair.
 
4.    Deviations in standard understanding
 
Inspection is a very rigorous work. Incorrect understanding and use of standards by individual inspectors also directly affects the accuracy of inspection results. For example: the detection of fluorocarbon coated ordinary decorative panels, GB/T22412-2008 stipulates that for fluorocarbon coated ordinary decorative aluminum-plastic panels, the coating performance testing should be conducted in accordance with GB/T17748-2008. In the test, it is easy to preconceive the concept of "ordinary decoration" and ignore the fact that "it is a fluorocarbon coating", which leads to incorrect inspection standards and ultimately invalidation of the inspection results.
 
5.   New inspectors lack effective supervision
 
In recent years, many inspection institutions have carried out a new round of expansion, resulting in a serious shortage of experienced inspectors. New recruits in individual laboratories can start inspection after only a few months of training. Such inspectors are not very good at inspections. Skilled, lack of sensitivity to abnormal data, and lack of effective supervision of such personnel, making them more likely to make mistakes than mature employees. Therefore, the use of new inspectors who are inexperienced and lack of supervision is potentially risky.
 
Therefore, in accordance with the requirements of the laboratory qualification accreditation review criteria, there should be adequate supervision of the personnel in training. When the laboratory uses newly hired personnel or transferred personnel, in addition to the assessment of the induction, the laboratory supervisor should strengthen supervision during the inspection to prevent inspection errors.
 
D.   Inspect the original records for irregularities and lack of traceability
 
The original inspection record is not standardized. Although it will not change the inspection result, the original record is the proof of the laboratory's inspection process. Once the laboratory has a dispute with the inspection client or related third parties, the original inspection record cannot serve as evidence. , Putting the laboratory in a dangerous situation. Each laboratory will formulate its own record management regulations in accordance with the laboratory qualification accreditation review criteria, but individual laboratories cannot implement them well, as shown in:
 
1.    Incomplete records of preparation, disposal and preparation of test samples The most basic requirement for the original inspection record is to record the observed conditions and data.
The observed conditions here include the whole process observed from the preparation, disposal and preparation of the sample to the end of the inspection. The laboratory often records the observations during the inspection process in detail, but the preparation, disposal and preparation process of the sample, such as the isothermal process of the sample in the constant temperature and humidity room, the water curing process of the cement, and other processes are incomplete or even not recorded.
 
In accordance with the requirements of “laboratory records should be timely, accurate, and complete”, the preparation, disposal, and preparation of test samples are also the process of testing. They should also be recorded in a timely, accurate and complete manner. At the same time, the education of inspectors should be strengthened. Have the consciousness to record the original record completely and accurately.
 
2.    Citation data lacks traceability
 
It is often necessary to quote some constants or coefficients in the calculation process after inspection. All quoted data should be sourced. The constants are mainly given in the standard, and the coefficients are obtained after the standard curve is drawn before the test. The standard curve is not made once and then used forever, but the standard curve should be made regularly. Therefore, in When using the standard curve, the standard curve used in this test should be attached to the original record or the standard curve number should be indicated.
 
However, some laboratories do not attach the standard curve to the original record or indicate the source in the original record when recording the original record, so that the data cited is not traceable. Therefore, when recording the original record of inspection, the inspector should attach the referenced standard curve to the original record, or indicate the number of the referenced standard curve in the original record, so that the referenced data in the original record can be traced.
 
3.    Copy the inspection record from the notebook
 
The original inspection record is the original observation record and should be recorded in real time during the observation. Some inspectors keep the original records clean and tidy for the reason of keeping the original records. In the notebook, and then copied to the formatted original record. Therefore, it is necessary for the laboratory to require the inspector to record the records in a controlled formatted original record form in a timely manner, instead of recording it in a notebook and then transferring it to the formatted original record.
 
E. Errors in the preparation of inspection reports
 
The inspection report is the final product handed over to the customer by the inspection agency. Therefore, the quality of the inspection report should also be one of the key concerns of the laboratory. Errors in inspection reports usually have the following two manifestations:
 
1.    Report preparation errors
 
In the process of preparing the inspection report, the inspection report preparers often make input errors due to negligence, such as: technical requirements, actual measurement data, individual judgments and other text or number input errors, causing misjudgment; commissioned inspection date, sample production date, inspection Dates such as dates are entered incorrectly, causing time logic problems.
 
At present, most laboratories use the business management network system to compile inspection reports. For time logic problems, you can set time-related reminders on the system to remind you of unlogical time, which can effectively prevent time logic errors; For other input errors, it is necessary to strengthen the sense of responsibility of report compilers and review and approval personnel.
 
2.    Signature of unauthorized person
 
According to the requirements of laboratory qualification accreditation, the issuance of the inspection report should be signed by an authorized signatory. The authorized signatory should be very familiar with the testing technology, result evaluation, equipment maintenance and calibration, record and report verification procedures, etc.
 
Therefore, the authorized signatory’s ability to sign and test address range are limited. During the operation of the laboratory, some unauthorized signatories issued inspection reports, or authorized signatories did not understand their authorized signature capabilities or test address range, and issued inspection reports beyond the authorized scope, resulting in errors in the inspection report.
 
Such approval of inspection reports beyond the scope of competence violates the regulations on the use of laboratory signs and will make the inspection report lose its legal effect. It can be said that the risks of the inspection process are ubiquitous, and the risks are not limited to the above mentioned in this article. However, we cannot not carry out inspection activities because of risks, but should analyze and study the risk points of the inspection process. Find effective countermeasures, and ultimately reduce their own risks.

ASK US A QUESTION
 

We'll respond within 24 hours