Calibration procedure for electronic balances

First, the content of the electronic balance measurement performance verification

In daily cycle verification and routine product quality inspection, it is generally necessary to check the following items: balance sensitivity, discriminative force verification; maximum allowable error (weighing linearity error) of each load point of the balance; balance repeatability Verification; verification of the balance or quadrilateral error of the balance; verification of the balance function of the balance.

The author believes that for the standard electronic balance used for the transmission of magnitude, the error standard should be judged according to the error criterion of “first verification”.

1. Verification of sensitivity and discriminating power of electronic balance

The sensitivity of an electronic balance generally refers to the indexing sensitivity, which should be exactly equal to the verification scale value of the corresponding load of the balance. For electronic balances with digital indications and automatic or semi-automatic calibration devices, the sensitivity of the balance can be exempted. When the electronic balance verifies the index value e≥lmg, the discriminating power can be determined as follows: on an electronic balance that is in equilibrium at no load or loading, an equivalent of 1.4 times the numerical scale graduation value is added. The load (1.4d) is gently added to (or removed from) the balance pan, and the original balance value must be changed.

2. Verification of the maximum allowable error of each load point of the electronic balance

First, warm up and then calibrate the electronic balance according to the operating procedures of the manual (this step is critical). After the calibration is completed, the zero position is displayed. Starting from zero load, gradually load up monotonically until it is added to the maximum weighing value of the balance, and then gradually unloaded gradually until zero load. During the verification process, the verification operator selects the load point according to the specific conditions of the balance (this is not explicitly given in the verification procedure), but the following load points shall be verified:

(1) No load. (2) Full load. (3) Minimum weighing Min (Class I balance: 100e; Level II balance: 50e; Grade III balance: 20e; Grade IV balance: 20e). (4) Those loads corresponding to the "inflection point" of the balance error value, such as Class I balance: 50000e, 200000e; Class II balance: 5000e, 20000e; Level III balance: 500e, 2000e, etc.

The error calculation is divided into two cases:

(1) When e≠d, the formula for calculating the indication error shall be E=I-L (E: balance indication error, I: balance indication value, L balance is called load on the disc);

(2) When e=d, the formula for calculating the indication error should be E=I-L+(1 2)d-â–³L (d: the actual scale division value of the electronic balance, AL: the indication value on the scale of the balance Rounded up loads added).

In either case, the error at each of the resulting load points is required to be less than the allowable error specified in the procedure.

3. Electronic balance repeatability test

The electronic balance repeatability test should be carried out under no-load and loading conditions. There are two kinds of loads loaded: one is full load and the other is half load. It is required to read and record the equilibrium positions of the loading and the unloading in the verification, and note that the load should be returned to zero once for each additional load. The difference between the results of multiple measurements of the same load is required to not exceed the absolute value of the maximum allowable error of the balance at that load.

4, electronic balance eccentricity verification (four-angle error verification)

For a standard balance, the test load is equal to the maximum weighing of the balance, and its four-corner error is equal to the maximum indication minus the minimum indication. For working balances, the test load is equal to one-third of the maximum load of the balance, and the four-corner error is equal to the largest of the difference between the indication of each point and the indication of the center point.

5, electronic balance check function inspection

For newly purchased electronic balances, check the balance function. Generally, two load points are selected, namely: (1 3) Max, (2 3) Max. The difference between the two results obtained under the same load shall not exceed the absolute value of the maximum allowable error at that load.

Second, the electronic balance needs to pay attention to the verification

1. How to choose the standard weight

The selected standard weight may be a grade weight or an equal weight, but its error (for the grade weight is the quality tolerance, for the equal weight the verification accuracy) shall not be greater than the checked balance under the load. 1 3 of the maximum allowable error. Second, the range of the standard weight can cover the maximum weighing range of the electronic balance.

2. Exemption from the electronic balance

(1) When an electronic balance of d ≤ 1 mg, the discriminating power of the balance can be exempted;

(2) When the electronic balance of e≠d is exempt from the discriminating power of the balance;

(3) For balances with digital indications and automatic or semi-automatic calibration devices, the sensitivity of the balance can be exempted.

3. Issuance of verification certificate should be standardized

After the verification of the electronic balance is completed, a verification certificate or a notification result of the verification result shall be issued based on the actual verification result. The author believes that issuing a certificate is a very serious matter that should be legally responsible. First, the format should be standardized. The content must cover all the information of the “4.1” element in GJB2725-96. The calibration should be accurate. ,objective.

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