In JJG 178-2007 the colorimeter is divided into four grades of I, II, III, and IV according to the level of measurement performance. However, in the daily verification process, it is found that a large number of instruments have incomplete grade marks on the nameplates, which makes it difficult to judge the grade before the verification. Whether the instrument should be graded after the verification needs to refer to the manual, and whether the instrument can determine whether it can be downgraded is questionable. This article will analyze and discuss one by one and make suggestions for revision.
Difficulty in judging the level before the test
Taking color colorimeters as an example, a large number of instruments do not have the instrument level marked on the nameplate. Even if the user manual of the Chamin instrument is found, most of the manuals do not have instrument level information, but only the technical indicators of the instrument. However, usually, the technical index items on the manual are not complete in the verification procedures, and only the level of the instrument can be roughly judged. If cannot provide the instruction manual for customers, the instrument level cannot be judged before the verification. This situation is caused by imperfect verification regulations. According to JJG 178-2007, it is required that the instrument should be marked with the name, model, serial number, manufacturer’s name, date of manufacture, working power supply voltage, and frequency, but there is no requirement to mark the instrument level. Also, refer to the general technical requirements of JJF 1641-2017 “Outline of UV-Vis calorimeter type Evaluation”, and there is also no requirement to mark the instrument level. It can be seen that there is no grade that the instrument can pass in the type evaluation. It is also qualified if there is no level during the verification, which leads to the fact that the instruments produced by a large number of manufacturers do not have the level marked. The difficulty in judging the level before the test is because the level of the instrument cannot be accurately judged before the test, and it can only be graded according to the test results after the test.
Judging the colorimeter level
According to the regulations of G’178-207, the qualified instruments will be issued with a verification certificate, and the lowest grade in the verification results will indicate the qualification level of the instrument; qualified. Then, it is generally judged in the usual way: if the indicators on the manual of an instrument conform to level I, but the verification result only conforms to level IV, then the instrument will be judged to be in conformity with level IV.
For the colorimeter, there is no standard grade on the instrument nameplate, but there are technical parameters in the manual, that is to say, the instrument is actually forged, but due to the omission of the meter type evaluation outline and verification procedures, the instrument level is not clear. If the instrument has a clear grade, such as a grade II color colorimeter verification result is grade IV, then the instrument should be judged as unqualified. Now, not only is the level of the instrument unclear, but the regulations also do not clearly state whether it can be downgraded or not, which brings a lot of trouble to the determination of the instrument.
Classification of colorimeters
Taking the caliber 8mm portable colorimeter as an example, before the 1990s, the production technology was relatively low, the relatively backward prism-type spectroscopic system was generally used, and the wavelength accuracy was low. Accuracy: (350-600) mt3 m(60C70) not nm, transmittance accuracy: 25%, transmittance repeatability: 0.5%. Such indicators can only meet the V-level standards in the regulations. The regulations were issued in 2007. Although most of the colorimeters had been switched to light-temperature spectroscopy systems at that time, the wavelength accuracy was significantly improved, but the regulations were still divided into 1. There are four levels of I, III, and V, which may be for the reason that the existing colorimeters can be used continuously and reduce the cost of replacing the equipment. Therefore, the low-accuracy levels III and NV are reserved.
Now, 15 years after the 2007 regulations were released, the production of older, lower-grade colorimeters has long since ceased. After checking the instrument manually, it can be found that the colorimeters produced, sold, and used now basically meet the Class II standard or above. Moreover, the accuracy of grades III and V is too different from that of grades I and II. Taking the maximum allowable error of the wavelength in the day section as an example, the standard of the working grade is 10 m, while the standards of grades III and V are 4.0 m and ± 6.0 nm, it is conceivable that the detection with a Class IV instrument will introduce a large uncertainty.
There are too many levels of colorimeters, and instruments of different levels have almost no limit to the scope of use in the detection standard, resulting in the simultaneous use of instruments with different accuracies, which affects the accuracy of the test results. That is to say, the detection of chemical reagents can use 4 levels of colorimeter, so the detection results are inevitably uneven. If the backward level III and IV instruments can be eliminated, it will help to improve the detection accuracy. To sum up, the classification of grades should be clarified, the criteria for determination should be clarified, and low-grade instruments should be eliminated.
