On the compatibility of weighing instrument and weighing instrument

When checking the compatibility, it is necessary to check the performance data of the weighing instrument and the selected module to determine whether the selected module can achieve the expected measurement performance of the weighing instrument The typical modules of weighing instrument include weighing sensor, weighing instrument (weighing indicator), analog or digital data processing device, weighing module, terminal and main display Due to the rapid development of science and technology and the improvement of application level, the digitalization, integration, networking and intelligence of weighing instrument products will become the development direction and focus of weighing instrument industry in the world Due to oimlr76 - 12006 (E) It is allowed to give the type approval certificate for the module Therefore, for the weighing instrument based on the module scheme, if the module type approval certificate and relevant information are submitted, the structure can obtain the type approval certificate (license) for the whole machine if the compatibility between the submitted module and the whole weighing instrument meets the requirements according to the weighing instrument requirements and some tests can be completed only under the condition of the whole weighing instrument ) This provides a broader development space for the production and design of weighing instrument manufacturers As a measurement technology institution in China, when conducting type evaluation test on weighing instrument assembled by module method, compatibility check can be carried out according to the new international recommendations The function of weighing instrument is to display the weight of objects on weighing platform in the form of digital display after amplifying the voltage or current signal obtained by weighing sensor General weighing instruments are composed of a / D conversion circuit (including analog amplification, filtering, a / D chip), CPU processor, digital display, keyboard, printing and communication interfaces Weighing instrument is the key of electronic weighing instrument, which directly affects the quality of electronic weighing instrument Therefore, before the compatibility check, it is necessary to ensure that the weighing instrument, as one of the key components of the weighing instrument, has the corresponding type batch certificate and a complete set of test data If the data is not complete and the corresponding items of compatibility check cannot be completed, it is necessary to supplement the data or carry out the type batch test according to the mode of the whole machine It is necessary for manufacturers and measurement technical organizations to understand the key points of compatibility inspection *The relevant parameters of weighing instrument require that when the manufacturer assembles a complete weighing instrument by using the weighing sensor and weighing instrument which have obtained the type batch certificate respectively, the weighing instrument shall have the measurement parameters and technical parameters Correction coefficient: the correction coefficient Q > 1 is the consideration of the possible influence of the eccentric load (the uneven distribution of load), the static load of the carrier, the initial zero setting range and the added tare weight It is calculated by the following formula: q = (MAX + DL + iszr + NUD + T +) / max second, the relevant parameter requirements of the weighing instrument In order to ensure that the weighing instrument can correctly display the weighing results and meet the measurement performance and technical requirements specified by the weighing instrument, the following technical parameters are required: 1 Accuracy level accuracy level, including temperature range and humidity stability evaluation, must meet the requirements of weighing instrument (WI) 2 Zui large allowable error coefficient if the value of Zui large allowable error coefficient of weighing instrument is not specified in the type approval certificate, then PIND = 0.5 If the coefficient is specified separately, it can be 0.3 ≤ PIND ≤ 0.8 3 Temperature limit if the temperature range of weighing instrument is not specified in the type approval certificate, then the lower limit of temperature range Tmin = - 10 ℃, and the upper limit of temperature range Tmax = + 40 ℃ If the manufacturer has special requirements, the temperature range can be limited 4 For each weighing instrument, the nind of Zui large calibration scale shall not be less than the calibration scale n: nind ≥ n for multiple weighing ranges or multiple scales, this requirement is applicable to any individual weighing range or local weighing range: nind ≥ Ni In the case of multiple weighing ranges or multiple graduation values, these functions must be included in the weighing instruments that have been type approved 5 The electrical parameters related to the weighing instrument, especially the Zui small input voltage Δ UMIN of each calibration division value of the weighing instrument, are indicated in the above parameters It refers to the weighing instrument's ability to truly reflect the Zui small input voltage signal, it represents the accuracy of the instrument, and also determines the Zui small applicable voltage value of the verification graduation value of the electronic weighing instrument When the measuring range of the instrument is constant, the quotient of Zui large input voltage signal and Zui small voltage signal corresponding to the calibration index value can be represented by the symbol nmax, which represents the relative accuracy of the instrument Corresponding to the non automatic weighing apparatus E and N, we find that there is a certain degree between different weighing sections of the same accuracy level through comparison For example, for a class III weighing instrument with n = 3000, the tolerance corresponding to 0-500e, 500e-2000e, 2000e-3000e is ± 0.5E, ± 1.0e, ± 1.5E respectively, while the tolerance corresponding to the same accuracy level of the instrument in the three weighing sections of low, medium and high is ± 0.25e, ± 0.5E, ± 0.75e respectively It is obvious that the tolerance of the weighing instrument in the middle weighing section is 1:1 in relation to its calibration division value, while the tolerance of the instrument in the low weighing section is 1:4 in relation to its calibration division value Then, we can determine the Zui small calibration index value of the instrument as the same as the tolerance of its low weighing section With reference to the above relationship, when we know the Δ UMIN and nmax of the instrument, we can obtain the Zui small voltage signal of the scale e, the applicable range of N, and provide reference for supporting load cell, bridge voltage and other performance parameters through simple calculation 6 The compatibility check of connecting cable requires the ratio of the length of single core cable of a certain material (copper, aluminum, etc.) to the unit cross section (M / mm2) For other cases, the ratio must be calculated according to the cable length (m), cross-sectional area (mm2), conductive material parameters and the large resistance (Ω) of each core Zui We know that there are two connection modes between the load cell and the weighing instrument - four wire system and six wire system In R76, only the six wire connection mode is required This is because the cable resistance changes with the change of temperature, which leads to the change of the excitation voltage of the sensor In order to ensure the true value of the bridge voltage, the six wire connection mode is often used in today's weighing instrument application field From the above content of weighing instrument and weighing instrument compatibility check, the workload is still relatively large Only when all items meet or are established, can the selected weighing instrument meet the weighing performance specified by weighing instrument In the application for type approval, it is not only necessary for the measurement technical organization to carefully review it, but also for the manufacturer to provide relevant technical parameters as much as possible, so as to save a lot of manpower and material resources for the subsequent type evaluation test Only when we realize the importance of checking the compatibility of the main modules of the scale, can we better meet the needs of all walks of life for the use of the scale.