In order to make the electromagnetic flowmeter work stably and reliably, the measurement accuracy of the thermal mass flowmeter should not be affected by the external magnetic field, and the flowmeter should have excellent independent grounding device. If the pipeline connecting the flowmeter is coated with cable sheath or non-metallic material pipeline, the flowmeter shall be modified with grounding device (liquid) ring.

The measurement accuracy and error curve of the flowmeter obtained from the price of electromagnetic flowmeter refer to the performance index under the standard in the work of the reference. The customer should note that the standard in the work of the reference according to the national standard of electromagnetic flowmeter (JB / t9248-1999) is different from the standard in the work of the specific application.

Working temperature: 20 ± 2;

Air humidity: 60% - 70%;

Switching power supply of power supply system: rated current ± 1%;

Installation standard: the distance between the upstream and downstream pipe sections is more than 10d;

The distance between the middle and downstream nozzle sections is > 6D;

Heating time: > 15min.

3.1 Wedge Flowmeter is ± 0.3% of the measuring range (water flow ≥ 10m / s); or ± 2mm / S (water flow < 10m / s). The error curve obtained by the manufacturer shows the development trend of the linear transformation of the flowmeter in its measurement scope, which is corresponding to the obtained index value of * * * degree. Based on the characteristics of electromagnetic flowmeter in Kaifeng Instrument Factory:

Therefore, at 0.5m/s, the flowmeter allows an error of ± 0.5%, and at 0.3m/s, the flowmeter allows an error of ± 1.0%.

3.2 working condition standard

Under the working condition standard, due to the hazards of many factors, the measurement accuracy will be different from the real flow calibration accuracy obtained by the manufacturer under the reference standard. For example, according to the national standard, the measurement accuracy shall not exceed 1 / 2 of the basic error limit of the instrument panel for every 10 temperature changes,

When the temperature changes 20%, the measurement accuracy of ± 0.3% will become ± 0.6%.

In the whole process of flowmeter operation, the customer shall fully consider the impact of noise, the limit of installation standard, the change of working temperature, and the change of environmental humidity (in the long-term wet and cold natural environment, the compressive strength of the insulation layer of flowmeter is reduced.) As for the harm of other factors to the measurement accuracy of flowmeter, generally, level 0.5 flowmeter should be level 1 in detail, and customers should think that it is better for the operation and maintenance of flowmeter.

4 measurement range and system software zero point

4.1 measurement range

The total flow range of electromagnetic flowmeter is relatively wide, the matched water flow range is 0-8m / s, and that of some manufacturers is 0-15m / s. Theoretically, changing the measurement range is not easy to harm the measurement accuracy and line shape of the flowmeter, but selecting a suitable measurement range is conducive to improving the 4-50ma analog output data signal enterprise pixel. If the measurement range of 100m3 / h can meet the user's requirements, it is not necessary to select the measurement range of 200m3 / h, otherwise the pixel of the analog output data signal enterprise will be reduced by half.

4.2 system zero

Under all normal operation conditions, electromagnetic current The zero point of the system software of the meter is accompanied by the long-term operation of the system software. Due to the embrittlement of electronic devices, the reduction of the compressive strength of the insulation layer of the excitation regulator wire package, the measurement of electrode polarization and environmental pollution, and the increase of the resistance (potential difference) of the system software ground wire, etc., the zero point of the system software will change and drift. The customer shall regularly maintain the zero point of the system software of the flowmeter and carry out Adjustment and maintenance. If the system software has a zero point of ± mm / s, it will cause an additional error of ± 0.5% for the total flow matching to 10m / s. In general,

When the total flow rate is small, the additional error caused by zero point of system software is larger.

Because the zero point of the system software has always been more or less, the manufacturer will adjust it to the minimum according to the technical specifications when the flowmeter is calibrated by the original factory. The customer must adjust it on the spot when using it. Therefore, the error curve obtained by the manufacturer objectively reflects the existence of zero point in the flowmeter system software, which leads to the discrete system of the instrument panel. If we only get the measurement accuracy of the electromagnetic flowmeter, but not the error curve, in fact, we can not definitely reflect the measurement accuracy of the flowmeter in all measurement areas.