Sample calibration example of electromagnetic flowmeter test point distribution
4.4.1 The reference ambient atmospheric conditions for reference environmental conditions calibration should meet the following specifications: Temperature: 20℃ Relative humidity: 65% Atmospheric pressure: 101.3kPa Reference atmospheric environmental conditions are: values u200bu200bmeasured under any other environmental conditions Must be corrected by calculation. It has been recognized that in many cases it is impossible to obtain the humidity correction factor. In this case, the reference ambient atmospheric conditions calibrated by the standard reference 4.4.1 Reference environmental conditions should meet the following specifications: Temperature: 20°C relative humidity: 65% Atmospheric pressure: 101.3kPa reference atmospheric environmental conditions: the value measured under any other environmental conditions must be corrected by calculation. It has been recognized that in many cases it is impossible to obtain the humidity correction factor. In such cases, the standard reference atmospheric conditions only consider temperature and pressure. This atmospheric condition is the same as the normal reference working condition generally agreed by the manufacturer. 4.4.2 Allowable range of environmental conditions during test and measurement The allowable range of environmental conditions during test and measurement is listed in Table 1. The maximum temperature change rate allowed during any test is 5°C/h. Table 1 Conditions Allowable Range Conditions Allowable Range Temperature Relative Humidity 4℃～35℃ 35%～75% Atmospheric Pressure Electromagnetic Field 86kPa～106kPa If relevant, the value shall be specified 4.4.3 Standard environmental conditions for arbitration measurement should be a parameter that is very sensitive to environmental conditions When the correction coefficients adjusted to their standard atmospheric values u200bu200bare unknown, and the measurement results obtained within the allowable range of environmental conditions specified in Table 1 are not satisfactory, repeated measurements must be performed under strictly controlled environmental conditions. For this reason, this standard specifies the environmental conditions for arbitration measurement as shown in Table 2. Table 2 The nominal value of the conditions, the allowable error temperature, the relative humidity, and the atmospheric pressure 20℃65％, 86kPa~106kPa±2℃±5%. For tropical and subtropical regions or other special requirements, the environmental conditions for arbitration measurement shall be in accordance with other relevant regulations. 4.5 Normal calibration conditions during the test 4.5.1 Reference value The reference value should be specified by the manufacturer. 4.5.2 Tolerances The tolerances of the power supply listed in Table 3 are applicable, unless the user and the manufacturer specify otherwise more precise tolerances. Table 3 Variable Tolerance Variable Tolerance Rated Voltage Rated Frequency ±1% ±1% Harmonic Distortion Ripple <5% (Alternating Current) <0.1% (Direct Current) 4.5.3 Reference Conditions for Connecting Cables Connecting the primary device and the secondary The cable of the device should not be longer than necessary and must meet the requirements of the manufacturer. 4.6 Signal output 4.6.1 The analog load impedance should be the arithmetic average of the allowable maximum and minimum values, or the reference value specified by the manufacturer. 4.6.2 The frequency load impedance should be the minimum allowable value. 4.7 Zero position check In order to check the zero position of the flowmeter, the liquid should be stationary and full in the primary device. 4.8 Other conditions should not have pressure fluctuations or pulsations that affect the measurement results. 4.9 Calibration of flow meters-requirements and methods The flow meters under test and related test equipment should be stable (that is, preheat at least 15 minutes under stable environmental conditions before any test starts). During the warm-up period, its output should be adjusted approximately in the middle of the output range. Observe and record the environmental conditions that may affect the test results. Unless otherwise specified, the error of the lower limit value and upper limit value of the range of the flowmeter should be adjusted to the minimum before the test. In order to evaluate the performance of the flow meter system within the specified flow range, several test points should be used for the flow setting, which are about 10%, 25%, 50%, 75%, and 100% of the range (see Figure 8). It is recommended to measure at least three times at each test point. Figure 8 shows an example of sampling calibration for the distribution of test points. The average value of the output readings should be calculated based on the readings of each flow. The difference between the values u200bu200bcorresponding to the reference standard system is the error referred to in this standard. This error can be expressed as a percentage of the output range or as a percentage of the measured flow rate. The uncertainty of flow measurement should be evaluated according to relevant national standards or ISO/TR5168 and ISO/TR7066. If the equipment is equipped with a range converter, the above-mentioned test procedures should test the respective flow ranges, but the consistency of the readings in the corresponding intervals of each range should be cross-checked by the conversion range. 5 Evaluation of the influence of the influence amount 5.1 Overview Two types of influence shall be considered, one is to affect the liquid in the primary device of the flowmeter, and the other is caused by the outside. Internal influences include changes in liquid temperature, flow rate distribution, and changes in liquid conductivity. External influences include changes in temperature, humidity, and atmospheric pressure, as well as changes in power supply current, voltage, or frequency. Unless otherwise specified, these influence quantities shall be assessed individually. The method is to determine the deviation between the output of the flowmeter and the result obtained under the reference condition. During the test, other unchecked conditions should remain unchanged under the reference value. Unless otherwise specified, the primary device and the secondary device connected to the public power supply should be evaluated under the equivalent liquid flow rate of 1m/s. If the flow rate range set by the secondary device can be adjusted, it should be set at 2m/s. The output (analog) load impedance should be the maximum value recommended by the manufacturer. 5.2 Internal influence 5.2.1 Liquid temperature The influence of liquid temperature changes should be measured at different liquid temperatures, while the ambient temperature of the flowmeter remains unchanged. The temperature range should be significantly different from the temperature under the reference test conditions in order to clearly show the effect of temperature, and there should be sufficient time in each case to reach a steady state condition. During the test, the lower limit of the range and the steady-state change of the range caused by the change in liquid temperature should be measured. The influence should be expressed as a percentage of the output range. The specific details of the test must be agreed by the manufacturer
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