GB/T 19878-2026General specification for grain moisture meters using capacitance and resistance methods (English PDF)

5.3 Reading device

5.3.1 Moisture meter reading device with pointer.

a) The scale markings should be clear, and the width of the pointer tip should be consistent with the width of the scale line;

b) The pointer should rotate clockwise, and the rotation should be uniform and smooth, without any obvious jumping.

5.3.2 Moisture meter reading device with display screen.

a) Numbers, text, images, symbols, and signs displayed against different backgrounds, such as bright light or dim light, should be conspicuous, neat, and clear;

b) The connectors of the display device should be secure and reliable, and should not fall off due to vibration.

5.4 Moisture content measurement range The manufacturer should specify the full range of moisture content measurement for major grain varieties and the main moisture content measurement methods in the product instruction manual. The scope should meet the requirements of Table 1.

5.5 Measurement Performance

5.5.1 Moisture content measurement time The time from sample placement to completion of a single measurement and data acquisition (excluding pre-selection, quantification of samples, and instrument warm-up time).

a) Capacitive moisture meter. should not exceed 30 seconds;

b) Resistance moisture meter. should not exceed 1 minute.

5.5.2 Accuracy of Moisture Content Measurement The maximum permissible error for major grain varieties, namely. the difference between the moisture content measured by a moisture meter and the direct drying method specified in GB 5009.3-2016. The difference between the results of moisture content determination by the method should not exceed the accuracy specified in Table 2.

5.5.3 Repeatability of Moisture Content Measurement The standard deviation of repeatability for the measurement of major grain varieties should not exceed the standard deviation of repeatability specified in Table 2.

5.6 Electrical Performance

5.6.1 Undervoltage alarm When a moisture meter is powered by batteries, there should be a warning when the voltage is low, such as displaying a low voltage indicator (text or symbol) or an audible or visual alarm.

5.6.2 Electromagnetic Compatibility The electromagnetic compatibility of a moisture meter should meet the following requirements.

a) The DC power supply variation immunity (mains power supply) meets the requirements of

12.1 in GB/T 42554-2023.

b) The AC power supply change (grid power supply) complies with the requirements of

12.2 in GB/T 42554-2023.

c) Power supply interference complies with the requirements of section

12.3 of GB/T 42554-2023.

d) Electromagnetic interference tests shall comply with the requirements of Chapter 13 of GB/T 42554-2023.

e) The built-in battery low voltage meets the requirements of

14.1 in GB/T 42554-2023.

5.7 Security

5.7.1 Insulation Resistance The insulation resistance between the power supply circuit and the outer casing of the moisture meter should not be less than 20MOmega.

5.7.2 Dielectric strength The power circuit and casing of the moisture meter should be able to withstand a 50Hz, 1500V sinusoidal AC current without any abnormal noise, breakdown, or flickering. And the arcing phenomenon.

5.8 Environmental adaptability

5.8.1 Climate and Environmental Adaptability Under operating conditions, the moisture meter should function normally under both high and low temperatures; under non-operating conditions, the moisture meter should be able to withstand constant temperature fluctuations. Store in hot and humid conditions or at low temperatures.

5.8.2 Adaptability to the transportation environment When not in operation, the moisture meter should function normally after impact and free fall, with no loosening, displacement, or damage to components, and the casing should be intact. It should not deform. Drop testing allows the product to be used with its original packaging box.

5.9 Stability Under normal operating conditions, the moisture analyzer should be able to work continuously and stably for one week without any measurement or calibration performance failures.

5.10 Durability The moisture meter should be tested multiple times under normal operating conditions without any power supply or mechanical failures.

5.11 Moisture meter calibration function If the moisture meter's error exceeds the standard, the moisture meter should have at least one of the following calibration methods.

a) Calibration is performed by adjusting the potentiometer (changing the instrument's zero point or gain) to correct the instrument's coefficients;

b) Calibration is performed by determining the deviation value based on the error value, either through manual input or automatic calculation by the instrument;

c) Based on the error value, either manually input or automatically calculated by the instrument, determine the instrument's coefficients or curves for moisture content measurement. Full-range calibration.

5.12 Moisture Analyzer Self-Test Function The moisture meter should have a function to check its own operational status and be able to promptly and accurately issue operational errors or malfunction warnings. Self-test items. The requirements are specified by the product standards.

6.4 Measurement Performance Test

6.4.1 Moisture Content Measurement Time Test Using a stopwatch, start timing immediately when the sample is placed in the container and continue until the data is obtained after one measurement. Measure the time taken during this period.

6.4.2 Accuracy and repeatability test of moisture content measurement

6.4.2.1 Sample Preparation Choose any three grain varieties specified in the product standard for this moisture meter. Those with testing functions for corn, rice, and wheat varieties should be included first. Prepare three samples for each of the three varieties mentioned above, with each sample weighing approximately 1 kg. One of the samples should have a moisture content of 8% ± 1.5%; the moisture content of the other two samples should be 10%~30% for corn and 10%~20% for other samples. The difference in moisture content between the two samples is... It should be above 5%. If it is a major grain variety, the portion with lower moisture content should be within the main moisture measurement range for that variety, and the other portion should be... The moisture content is outside the main moisture measurement range for this variety. The sample was prepared according to the method for preparing cereal samples in Appendix B of JJG891-2019. The product should be stored in a refrigerator at 5°C.

6.4.2.2 Inspection Procedure 6.4.2.2.1 Before testing, ensure the grain sample and moisture analyzer are at the same temperature. Samples removed from the refrigerator before testing should be... Place the sample and moisture analyzer at the ambient temperature for at least 16 hours to allow them to reach thermal equilibrium, and record the results. The temperature at which thermal equilibrium is reached. If the sample being tested has deteriorated, it should be discarded; if this occurs in a batch, the process should be restarted. 6.4.2.2.2 For the prepared test sample, perform the determination according to the following steps.

a) In accordance with the direct drying method specified in GB 5009.3-2016, take two samples of the same sample and determine the moisture content using the direct drying method. For the content, the arithmetic mean of the measured values of two samples is taken as the result of the direct drying method.

b) Each sample shall be measured four times consecutively using a moisture analyzer under the "repeatability conditions" specified in JJF1059.1, and four measurements shall be taken. The arithmetic mean of the values is taken as the result of the moisture meter measurement. The measurement time should meet the requirements of 5.5.1.A capacitance-based moisture meter is used for measurement. When processing whole grain samples, a large number of experimental samples are usually required. Each batch of experimental samples should be returned to the original sample container. After thorough mixing, take another sample for the next measurement. When measuring the moisture content of crushed grain using a resistance method moisture analyzer, it is usually necessary to... For very small samples (not exceeding 50g), grinding and testing should be strictly performed according to the product instructions, and the samples should be discarded after testing.

6.4.2.3 Representation of Test Results 6.4.2.3.1 Error The error is calculated according to formula (1), and the result is rounded to one decimal place. 6.4.2.3.2 Repeatability According to the "Measurement Repeatability" specification in JJF1059.1, the number of repeated measurements in 6.4.2.2.2 is taken as 4, and the repeatability Sr is given quantitatively, that is, according to

6.5 Electrical Performance Testing

6.5.1 Battery power undervoltage alarm test When the moisture analyzer is powered by battery, observe whether the moisture analyzer has a low voltage when the voltage drops to a critical point and it cannot function properly. hint.

6.5.2 Electromagnetic compatibility test The test method for DC power supply variation immunity (mains power supply) shall be carried out in accordance with section

12.1 of GB/T 42554-2023. The test method for AC power supply variation (grid power supply) shall be carried out in accordance with section

12.2 of GB/T 42554-2023. The power supply interference test method shall be carried out in accordance with section

12.3 of GB/T 42554-2023. The test methods for electromagnetic interference testing shall be carried out in accordance with Chapter 13 of GB/T 42554-2023. The test method for low voltage of built-in battery shall be carried out in accordance with section

14.1 of GB/T 42554-2023.

6.6.1 Insulation resistance test Using a 500V megohmmeter with an accuracy of

1.0 class, measure the distance between the power plug or power input terminal of the moisture meter under test and the casing or exposed parts on the casing. Insulation resistance between metal components. The power switch of the moisture analyzer under test is in the ON position, but its power plug is not connected to the power grid. Apply After the 500V test voltage stabilizes for 5 seconds, read the insulation resistance value. It should meet the requirements of 5.7.1.After the test, the moisture analyzer under test should be able to work normally.

6.6.2 Dielectric strength test A 50Hz sinusoidal test voltage with an effective value of 1.5kV was applied between the power circuit and the casing of the moisture meter using a withstand voltage tester. The current was tested at the 5mA setting for 1 minute.

6.7 Environmental adaptability test

6.7.1 Climate and Environmental Adaptability Test After conducting the test according to the test conditions specified in Table 3, remove the moisture meter by raising or lowering it to room temperature and leave it at room temperature for more than 24 hours.