Electromagnetic flowmeter as a widely used in industrial production in the flow measurement instrument, its accuracy and stability for the control and monitoring of the production process is critical. However, in practice, sometimes encounter electromagnetic flowmeter zero point inaccuracy problem, which will not only affect the accuracy of measurement, but also may cause adverse effects on production. In this paper, we will discuss the reasons why the zero point of electromagnetic flowmeter is not allowed, and focus on which two conditions can be met in order to carry out effective zero calibration operation.
First, the electromagnetic flowmeter zero point is not allowed to analyse the causes
Electromagnetic flowmeter zero point is not allowed for a variety of reasons, involving the installation environment, conditions of use, maintenance and other aspects of the instrument. The following are some of the main reasons:
1. pipeline is not filled with liquid or liquid containing air bubbles: when the pipeline is not filled with liquid or liquid containing air bubbles, objectively thought that the flow sensor within the inactivity, but in fact there is a trace of activity, which will lead to zero instability.
2. valve sealing incomplete: valve use for a long time or because of the liquid dirt caused by the sealing incomplete, may also lead to the emergence of zero instability phenomenon. Incomplete sealing of the valve will make the fluid at rest when there is still a small amount of flow, thus affecting the accuracy of the zero point.
3. changes in liquid conductivity: changes or uneven conductivity of the liquid, at rest will make the zero point change, flow will make the output wobble. Therefore, the location of the flowmeter should be far away from the point of injection of the liquid or pipeline chemical reaction section downstream, in order to avoid the impact of conductivity changes on the zero point.
4. Internal wall scaling and electrical fouling: Scaling and electrical fouling of the inner wall of the measuring tube can destroy the equilibrium state of the initial zero setting, resulting in zero point change. The degree of scaling and electrofouling on the inner wall surface cannot be exactly the same and symmetrical, which makes it impossible to maintain a stable zero point.
5. power equipment state changes: flow sensor near the state of the power equipment changes (such as leakage current increases) will form the ground potential changes, thus causing intelligent electromagnetic flowmeter zero change. This external interference is one of the important factors affecting the stability of the zero point.
6. imperfect grounding: intelligent electromagnetic flowmeter sensor grounding is not perfect will also be affected by stray currents and other external interference. Good grounding protection is to ensure that the flowmeter is the basis for normal operation, if the grounding resistance is too large or shared with other motors and electrical appliances grounding, may lead to failure of the flowmeter.
Second, to meet the two conditions, in order to effectively calibrate the zero point
Electromagnetic flowmeter zero point is not allowed for the problem, effective zero calibration operation needs to meet the following two conditions:
Condition 1: Ensure that the measuring tube is full of conductive fluid and the fluid is in a static state
Before zero adjustment, must ensure that the electromagnetic flow sensor measuring tube is full of conductive fluid, and the fluid is in a stationary state. This is because the zero adjustment is based on the measured value of the fluid at rest, if the fluid is still flowing during the adjustment process, then the adjustment results will be inaccurate.
To ensure that the measuring pipe is full of conductive fluid, close the upstream and downstream valves of the flowmeter and wait for a period of time to allow the fluid to come to a sufficient standstill. At the same time, it is also necessary to check whether there are air bubbles or debris in the pipe, if so, it is necessary to clean up to ensure the purity and stability of the fluid.
Condition 2: Correctly set the zero adjustment parameters and save the settings
In order to meet the first condition on the basis of the next need to set the zero adjustment parameters. Different models of electromagnetic flowmeter has different operation interface and parameter setting methods, but usually provide zero adjustment options.
After entering the parameter setting interface, find the zero point adjustment option, and choose automatic adjustment or manual adjustment. Under the automatic adjustment method, the flowmeter will automatically carry out zero calibration; under the manual adjustment method, the zero value needs to be adjusted gradually according to the actual situation.
In the manual adjustment process, you need to pay attention to observe whether the display value of the flowmeter gradually converges to zero. If the display value is not zero, you can use a screwdriver and other tools to adjust the zero adjustment mechanism inside the flowmeter, gradually reduce the display value until zero. In the adjustment process, should avoid over-adjustment leading to the generation of reverse error.
After the completion of the adjustment, you need to save the parameter settings and exit the parameter setting interface. At this time you can open the upstream and downstream valves, observe the flowmeter display value is normal. If the display value and the actual flow rate in line with the zero-point adjustment is successful.
Third, the verification and testing after the zero point adjustment
In order to ensure the accuracy of the zero point adjustment, it is also necessary to verify and test. Specific methods are as follows:
1. Calibration using a calibrator: Use a calibrator to calibrate the flowmeter and compare whether the flow value displayed by the calibrator is consistent with the flow value displayed by the flowmeter. If there is an error, the flowmeter needs to be further adjusted or repaired.
2. Observation under actual working conditions: Observe whether the display value of the flowmeter is stable and accurate under actual working conditions. Can be compared by comparing the flow data of multiple time points or with the data of other measuring equipment to verify the measurement accuracy of the flowmeter.
Fourth, the zero point adjustment of attention
In the zero point adjustment, you also need to pay attention to the following points:
1. Avoid over-adjustment: In the process of manual adjustment, attention should be paid to observe the trend of the flowmeter display value, to avoid over-adjustment leading to the generation of reverse error.
2. Timely repair or replacement: If the manual adjustment method can not make the flowmeter display value to zero, may be due to internal damage to the flowmeter or aging and other reasons, this time the need for repair or replacement.
3. Keep the instrument clean: regular instrument cleaning and maintenance work to ensure that the measurement of the pipeline without debris and sediment to ensure smooth fluid flow.
4. Avoid external interference: Ensure that the installation environment of the flowmeter is free from strong magnetic interference, vibration and temperature changes and other unfavourable factors, in order to reduce the impact of external interference on the stability of zero point.
5. Correct grounding: Ensure that the flowmeter grounding perfect and grounding resistance in line with the requirements, in order to avoid stray currents and other external interference on the impact of the flowmeter.
V. Conclusion
Electromagnetic flowmeter zero point is not allowed to affect its measurement accuracy and stability of one of the important factors. In order to effectively solve this problem, you need to meet the measuring tube full of conductive fluid and fluid at rest and correctly set the zero adjustment parameters and save the settings of these two conditions. At the same time, it is also necessary to verify and test to ensure the accuracy of the zero adjustment, and pay attention to avoid over-adjustment, timely repair or replacement of damaged flowmeter, keep the instrument clean, avoid external interference and correct grounding and other matters. Only in this way, to ensure that the electromagnetic flowmeter in practical applications to play a maximum role for the control and monitoring of production processes to provide accurate and reliable measurement data.
Hangzhou Economic Development Area，Hangzhou 310018，China
