What is an electronic weighing instrument "peeling device"？

What is an electronic weighing instrument "peeling device"？

"Tare peeling device" is a device that sets the indication value to zero when there is a load on the carrier. According to the function, it can be divided into: non-automatic peeling device, semi-automatic peeling device and automatic peeling device.

The accuracy index of the peeling device is a stricter assessment requirement. In the current implementation of JJG555-96 "General Verification Regulations for Non-Automatic Scales", since there is no stipulation on the size of the "tare value", it only talks about "at least two different tare weights should be weighed and tested", and the operating range is "The peeling device shall not be used at or below the zero point and above the maximum peeling amount". So if the selected tare value can be 90% of the maximum weighing, that is, it is also possible to range from zero to 90% of the maximum weighing; the tare value can also be 10% of the maximum weighing. This brings about two problems: first, after each tare, the zero setting accuracy must be maintained at ±0.25e; second, after each tare, the allowable error system must be established according to the new zero point, as shown in the figure below Shown. "0" is the original coordinate origin, "0'" is the coordinate origin of the first tare weighing, and "0"is the coordinate origin of the second tare weighing.

In the 2006 edition of R76-1 "Non-Automatic Weighing Apparatus", it is stipulated that the tare removing device is required in electronic weighing instruments: the weighing instrument shall be subjected to the tare weighing test under the following conditions:

Weighing instrument / weighing apparatuswith tare weight deducted: use a tare value between 1/3 and 2/3 of the maximum tare weight;

Weighing instrument with tare weight: use the two tare weight values of 1/3 and 3/3 of the maximum tare weight (Since most of the non-automatic weighing instruments / weighing apparatus we are facing now are "tare weighing instruments/ weighing apparatus", we will not discuss " “Add tare weighing instrument /weighing apparatus”).

1: The tare value is determined

What is the tare value that should be selected in the "tare" test? In theory, the "tare value" can be arbitrarily selected within the entire weighing range. If this is the case, although it should not affect the weighing accuracy of a weighing instrument that is qualified in design, manufacture, and installation, it will inevitably affect the scope of use of the instrument.

The international recommendation in R76-1 "Non-Automatic Weighing Apparatus" stipulates that when the tare test should be carried out under different tare values, at least 5 load values should be selected. Including the minimum weighing, the load value at or near the maximum allowable error change, and the possible maximum net weight load value.

In R76-1, "7.1.2 Mandatory Marks When Necessary" points out: The maximum tare addition effect is expressed as: T=+..., the maximum tare deduction effect, if different from Max, it is expressed as: T=-....In the "4.6.4 Operating Range" of R76-1, it is pointed out that the de-tare device shall not be used at and below the zero point and above the maximum indicated value.

From the above passage, I personally think that the "tare value" cannot be arbitrarily selected within the entire weighing range for three reasons:

First, the reason why a weighing instrument /weighing apparatus needs the tare function is because the weighing instrument has this requirement during the weighing process, and this function can be used to easily obtain the net weight of the weighed item. But if the selected "tare value" is relatively large, it will affect the normal weighing range of this instrument (here it refers to the "tare weight" weighing instrument/weighing apparatus).

Second, the error value we are currently using is required for segmentation. According to international recommendations, when the tare weight is different in the tare test, the remaining weighing is still assessed according to the maximum allowable error of the weighing instrument under the same load value. In fact, this greatly increases the difficulty of designing and manufacturing the weighing instrument.

Third, the manufacturing enterprise should determine the weighing load of each batch of weighing instrument products based on the raw materials used in the production of the products and the structural characteristics of the products. In addition, together with the purchaser's use requirements, a "tare removal effect value" is proposed and marked on the product nameplate as a mandatory mark.

Therefore, this "tare value" is the weighing value of a weighing instrument after deducting the load value changed by the maximum allowable error, which is about 1/3Max.

2:Test method

As a large weighing scale, it is troublesome to perform a tare weighing performance test. It is specifically stipulated in the R76-1 "Non-automatic weighing instrument" international recommendation: During the first and subsequent verifications, other appropriate procedures can be selected for tare Weighing test; such as: using mathematical formulas or graphing methods to translate the origin of the coordinate system representing the maximum allowable error limit curve to any point on the inherent error curve (ie, weighing test curve) to simulate tare balance operations, Then check whether other points on the inherent error curve and hysteresis curve are still within the maximum allowable error limit curve after translation.

In the weighing indicator test, the influence of tare weight on weighing performance depends entirely on the linearity of the error curve. The determination of linearity is carried out during the normal weighing performance test. If the error curve shows obvious nonlinearity, translate the maximum allowable error envelope along the nonlinear error curve, and check whether the weighing indicator meets the weighing requirements when the tare value corresponds to the steepest part of the error curve.

3:Accuracy

The maximum allowable error of any tare value of the tare weighing device is the same as the maximum allowable error of the weighing instrument under the same load value. Under the current technical conditions, the performance of the load cell and weighing instrument can be guaranteed not to affect the accuracy of the weighing instrument. However, the manufacturing quality of load-bearing devices in my country has become a key factor affecting the accuracy of weighing devices.