1、 Selection of sensors
This paper mainly talks about the relationship between the accuracy of the sensor and the precision of the weighing instrument. It is said that "the sensor is the heart of the weighing instrument", which shows that the accuracy and performance of the weighing instrument can not exceed the accuracy and performance of the sensor used. International recommendation R76 for non automatic weighing instruments was developed earlier than oimlr60 for load cells. Because both of them use subsection ladder to express the error, the maximum allowable error (MPE) of the device is determined according to the calibration scale and the calibration division value of the error, and then the accuracy level of the weighing instrument and the sensor is determined. Therefore, the following conditions should be met between them.
(1) According to the error distribution of R76, the component coefficient of sensor is defined as pi = 0.7. The maximum allowable error of the sensor is 0.7 times of the corresponding accuracy and the maximum allowable error of the weighing instrument (MPE).
(2) The maximum weighing capacity of the load cell must be greater than the maximum weighing capacity max of the weighing instrument.
(3) In the whole application range, it must meet the following requirements: n ≤ nmax, V ≥ Vmin, nmax is the maximum calibration division number of the weighing sensor. Vmin is the minimum calibration value of the sensor, which is determined by the temperature effect of the minimum load.
(4) 2DR ≤ e, where Dr is the minimum static load recovery value of the sensor, e is the scale value of the weighing instrument, and is the maximum allowable error of the first verification.
(5) Relative to Dr, i.e. z = Emax (/ 2 × DR), the ratio is used to describe the multi scale scale, which determines the division value that the sensor can use and does not exceed the maximum tolerance. Relative to y = Emax / Vmin, this ratio describes the maximum resolution independent of the sensor capacity, that is, the maximum number of divisions allowed when the sensor is used.
(6) "The grading principle of load cells, which divides sensors into definite accuracy levels, is to facilitate the application of sensors in various quality measurement systems. It must be recognized in the application of this Regulation (jjg669-2003) that the performance of a sensor can be improved by compensation in the measurement system using the sensor. Therefore, this procedure does not require the sensor to have the same accuracy level as the weighing system in which it is used, nor does it require the use of an approved separate sensor for the weighing instrument displaying the quality. " If we can't understand the connotation of the above technical conditions correctly, we can't design the weighing instrument correctly according to the technical parameters of the sensor, which will cause confusion and confusion to the two constraints of n ≤ nmax and V ≥ Vmin.
For example, can a sensor with nmax = 3000 be used to make a weighing instrument with a division number higher than or equal to 3000? How to design multi index and multi range weighing instrument according to Z and Y values? For a long time, these problems are difficult to be solved in the weighing instrument field. Since some people have formed a fixed mode of thinking about these problems, we need to have sufficient reasons to change them. A detailed description requires a large space, and I am going to write another article to elaborate.