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# General test circuit of electromagnetic flowmeter

by：Sure     2021-08-04
5.2.4 Liquid pressure When practicable, the flowmeter should check the influence of the pressure change of the fluid on the output signal within the entire working pressure range. The maximum influence is expressed as a percentage of the output range. Table 4 Test No. Description of the distance from the outlet of the pipe elbow to the electrode plane. Remarks. Piping configuration diagram 1 The minimum elbow in the electrode axis plane 2 and the electrode axis plane 5.2.4 Liquid pressure When practicable, the flow meter should test the fluid The influence of pressure change on the output signal in the whole working pressure range, the largest influence is expressed by the percentage of the output range. Table 4 Test serial number description The distance from the outlet of the pipe elbow to the electrode plane Remarks The pipeline configuration diagram 1 The minimum elbow in the electrode axis plane 2 An elbow at right angles to the electrode axis plane The minimum 3 Same number 1 Test 5 DN4 Same number 2 Test 5 DN 5 Minimum of two adjacent elbows in the same plane 6 Minimum of two adjacent elbows in an orthogonal plane 7 Same serial number 5 Test 5 DN 8 same serial number 6 Test 5 DN 9 same serial number 5 Test minimum 2 elbows of 5 test serial number The electrode plane of the flowmeter is at right angles 10 Same number 6 The minimum test number 6 Two elbows are at right angles to the flowmeter electrode plane 11 Same number 7 Test 5 The two elbows of the DN test number 7 are at right angles to the plane of the flow meter electrode 12 Same No. 8 Test 5 The two elbows in DN Test No. 8 are at right angles to the electrode plane of the flowmeter) Flowmeter 5.3 External influence 5.3.1 Distortion of power supply 5.3.1.1 Change of main power supply Adjust the following values u200bu200bof power supply, and the load impedance is according to 5.1 The lower limit of the range and the change of the range should be measured. a) Voltage: 1) Nominal value; 2) Reference value plus 10% of it, if it is lower than this regulation, according to the manufacturer's limit; 3) Reference value minus 15% of it, if it is lower than this regulation, according to manufacturing Factory limited. b) Frequency: 1) Nominal value: 2) The reference value plus 2% of it, and the reference value minus 10% of it. If it is narrower than this range, it is defined by the manufacturer. In the case of low voltage/low frequency, a check should be performed to verify that when the input is close to the upper limit of the range, the output is not sent to the limit value below the upper limit of its range. The influence should be expressed as a percentage of the output range. 5.3.1.2 Short-term interruption of power supply The purpose of this test is to determine the performance of the flowmeter when it is switched from the specified normal power supply to the standby power supply. The flow rate remains unchanged at 50% of the range during the test. The DC power supply shall be interrupted for 5ms, 20ms, 100ms, 200ms and 500ms; the AC power supply shall be interrupted for 1 cycle, 10 cycles and 25 cycles at the crossover point. The following values u200bu200bshould be recorded: a) The maximum instantaneous positive and negative changes in the output: b) The time required to restore the steady-state output value to 99% after the power is turned on; c) Any permanent changes in the output. In order to obtain a better estimate of uncertainty, the test must be repeated ten times, and the time interval between the two tests is at least equal to ten times the interruption time. 5.3.1.3 Distortion of the power supply should superimpose the 5% distortion third harmonic with variable phase on the power supply voltage. The maximum change of the flow signal should be measured and expressed as a percentage of the range. 5.3.2 Electrical interference During all the tests specified in this clause, the flow rate should remain unchanged at 50% of the range. 5.3.2.1 The transient overvoltage of the power supply shall superimpose the peak voltage on the power supply. The peak voltage energy should be 0.1J, and the peak amplitude should be 100%, 200%, and 500% of the effective value of the power supply voltage. The spike voltage can be generated by the discharge of a capacitor or by any device that can generate an equivalent waveform. The power supply line should be protected by an appropriate suppression filter, which includes at least one 500 yoke coil capable of carrying current. For each amplitude, two pulses in phase with the peak value of the main power supply voltage shall be applied, or at least 10 pulses of random phase for the main power supply shall be applied, and any transient or DC output changes of the meter output shall be recorded. 5.3.2.2 The influence of interference voltage may be necessary to adjust the secondary device so that both positive and negative changes are detected. Figure 12 shows a typical circuit. Figure 12 General test circuit 5.3.2.2.1 Common mode-the influence of AC voltage between the ground of the primary device and the secondary device (artificially introduce common mode voltage) (Figure 13) The ground between the primary device and the secondary device The potential difference will produce a common mode voltage on the measuring electrode. This potential difference is often at the same frequency as the power supply. The following test is used to measure the effect of the common mode voltage with the same frequency as the main power supply on the performance of the electromagnetic flowmeter. A 50V (effective value) AC voltage with the same frequency as the power supply should be applied between the ground terminal of the primary device and the secondary device. Two series of tests should be carried out: one is that the interference voltage is in phase with the main power supply voltage; the other is that the interference voltage is orthogonal to the main power supply voltage. During these tests, it is necessary to ensure that the primary device and its internal liquid are insulated from the earth. The error should be expressed as a percentage of the output range. 5.3.2.2.2 The influence of the AC voltage between the ground and the main power supply (high neutral line voltage) (Figure 13) should be applied between the neutral line and the grounding terminal of the primary device, the same adjustable 0～5V (effective value) as the power supply frequency Potential difference. The process is similar to the process described in 5.3.2.2.1.
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