Measurement error of electromagnetic flowmeter

Electromagnetic flowmeter measurement error, electromagnetic flowmeter with no pressure loss, high precision, moderate price and other advantages, widely loved by petrochemical, chemical and other industries companies, as a key role in the meter meter.However, in the theoretical application, due to improper actual operation, improper selection of machinery and equipment, installation, measurement deviation is difficult to avoid, for the use of convenient composition.Therefore, broad instrument people should pay attention to a variety of components of electromagnetic flowmeter deviation.

In general, the main hazards that constitute the deviation of electromagnetic flowmeter can be divided into three categories: improper model selection, hazards of liquid under test and interference.

I. the measured liquid flow velocity electromagnetic flowmeter can measure the flow velocity range of 0.5 ~ 10m/s, and the economic flow velocity range is 1.5 ~ 3m/s.In theory, the inner diameter of the tube should be measured according to the size of the measured flow and the speed range of the electromagnetic flowmeter.

Two levels, electricity and lining materials choose electric touch and lining materials directly with the measured liquid, should according to the characteristics of the measured liquid (such as corrosion, abrasion, etc.) and the operating temperature select electrode and lining materials, such as improper selection, will form attached faster, corrosion and fouling, wear, lining deformation problem, causing the measurement deviation.

Three, stability of the excitation of electromagnetic flowmeter with dc field, ac excitation type sinusoidal waveform excitation and double-frequency rectangle wave excitation, such as dc excitation easily electrode polarization and dc interference problem, ac sine excitation easily provoked zero changes, and the double frequency rectangular wave excitation is both low frequency rectangle box wave excitation of zero point stability, and high frequency rectangular wave excitation box of fluid noise strong retarding ability, is an ideal way of excitation.When applying the theory, we should try our best to ensure the stability of switching power supply voltage and frequency, so as to ensure the constant magnetic induction intensity and reduce the measurement deviation caused by the change of magnetic induction intensity.

When measuring the flow of liquid-solid mixed phase fluid (such as water containing sediment) with an electromagnetic flowmeter, it is assumed that the electromagnetic flowmeter corrected by single-phase liquid will cause the measurement deviation. At this point, the sensor should be installed in the straight pipe section that will not provoke the liquid-solid phase separation.

Liquid hazard under test

1. Drastic changes in the conductivity of the liquid under test when the conductivity of the liquid under test is very high, the apparent value will be greatly shaken. If the problem is very serious, it will be difficult for the control system to complete normal operation;However, if the conductivity of the measured liquid is too low, it is difficult for the electrical level to complete the normal output. If the conductivity of the measured liquid is assumed to be in the range below the lower limit value in the actual operation, then the electromagnetic flowmeter cannot function normally.In view of these situations, first of all, we should base on the theoretical requirements, separate from the relevant standards and entreaty, stop the electromagnetic flowmeter type selection;Secondly, install the reverberator or the straight pipe segment to ensure the full mixing of materials and promote the smooth completion of chemical reaction;Again, stop the selection of flowmeter type again.

2. The measured liquid bubbles or non-full tube bubbles are mainly derived from the dissolved gas in the liquid, which is expanded into bubbles in the state of mineral acid, and the bubbles inhaled from the outside.The flow rate, which contains a lot of bubble volume, can compromise the accuracy of the measurements.If the bubble diameter is too large to exceed the value of the electrical diameter, the measurement will show an unstable state in the process of development, shaking cannot be avoided.In view of this

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