-
E-mail
mkt.siwe@minebea-intec.com
-
Phone
18017281877
-
Address
Room 411, 4th Floor, Building 12, No. 9 Anqing Street, Shunyi District, Beijing, China
Yintaike Industrial Weighing Equipment (Beijing) Co., Ltd
Your weighing scale may not be accurate! (Above)
Date: 2024-11-05Read: 8
With the popularization of automated production lines in the 1970s, automatic weighing scales have become an indispensable part of large-scale production. In order to ensure the safety during the official productionReliable operationIn order to meet national regulatory requirements, the accuracy of the weighing scale must be tested.
There are many materials related to weighing scale testing that can be found online, but most of them are copied from each other, or the language is obscure and the calculations are complex, making their descriptions difficult to understand and increasing misunderstandings.
In this article, we will attempt to use the simplest language to guide users of weighing scalesTest the accuracy of the automatic weighing scaleThe previous article introduced two major misconceptions that should be avoided, as well as how to conduct repetitive testing of weighing scales.
Are all scales tested using the same method?
Two major misconceptions!
No matter what weighing equipment it is, its accuracy is affected by two major factors:repetitivenessandaccuracyThese two parameters are also the only comparable parameters for dynamic weighing (automatic weighing) and static weighing (static scale).
By conducting two small tests, you can use the automatic weighing scale with peace of mind. However, before introducing these two tests, let's first talk about two common misconceptions.
The first and most common misconception isUsing the method of detecting static scales to test weighing scalesIn a normal weighing scale application environment, the conveyor belt is continuously moving, which can cause certain weighing errors and cannot be directly compared with the results in a stationary state. This is also required for the sensor of the automatic weighing scaleSpecially designedThe reason for meeting the accuracy requirements.
The weight obtained by an object under static conditions is only a reference point for service engineers to establish dynamic weighing standards. For example, when an automatic weighing scale is stationary, it weighs 500g of an object; when it is dynamic, it weighs the same object and becomes 502g. At this point, the weighing scale needs to be calibrated by subtracting 2g. Generally speaking, the weighing scale can be adjusted by placing a static reference object, comparing it, and automatically adjusting this value.
Examples of dynamic and static weighing
Actual weight on the horizontal axis, weight reading on the vertical axis
Another major misconception isRead the value of a known weight substitute through a weighing belt to confirm the accuracy of the scaleEven if the weight of this item is equal to the weight of the product, it may cause significant differences in readings due to its dynamic characteristics (such as length, shape) during belt transmission.
repeatability test
Error in multiple weighing readings of the same product
The first test is to confirm Zoi (Zone of Uncertainty). Zoi is 6 times the standard deviation of multiple readings of the same product, and is also a globally recognized method for calculating uncertainty factors in dynamic weight checks.
This test will determine the repeatability of the automatic weighing scale, which is also the test we recommend you to conduct first. Because if the repeatability of the weighing scale is not satisfactory, the subsequent test values cannot be trusted.
The test is as follows: Pass the same product on the weighing scale 10 to 20 times and ensure that the direction of the product is the same as the actual production direction.
1. Record each value and calculate the standard deviation. Some weighing scales already have relevant functions, such as Intico's Velus Go automatic weighing scale, which canAutomatically record and calculate correction factorsIf not available, the STDEV function built into Excel can also be used for calculation.
2. Multiply the standard deviation by 6 to obtain Zoi
3. Calculate your T-value from the table below. For example, if the product is 200g, the T-value can be obtained as 4.5% or 9g
4. Calculate one fourth of 9g to obtain a reproducible limit of 2.25g
If the Zoi of the weighing scale is greater than 2.25g, then this weighing scale cannot be used according to the prescribed standards
T-Value Calculation Table | Taken from OIML R87 Recommendation 2016 Edition
All product types and weights applied to automatic weighing scales should undergo this test and record the values. It is recommended to repeat this test and establish a trend analysis, which can not only predict the degree of change of the weighing scale over time, but also determine the frequency of executing this test in the future.
How to pass a simple testUnderstand the accuracy of automatic weighing scales?In the next section, we will continue to introduce the second necessary test of the weighing scale. Subscribe to the official account for more information~