signal distortion will appear in the process of signal disposal, the problem of signal is amplified, and the instrument measurement error will be larger with the increase of running time, in order to solve these problems, this paper puts forward the fundamental wave electromagnetic flowmeter signal disposal method of average and intermittent excitation method, test results show the effectiveness of this method.
Electromagnetic flowmeter is applied scope of * * * to a wide range of conductive medium (
Volume flow measuring instruments.
At present many domestic manufacturers in the production of the corresponding products, such as production LDZ integration of the intelligent electromagnetic flowmeter in tianjin university of technology, Shanghai guanghua love meetall instrument co. , LTD production of SCAIc electromagnetic flowmeter, west the source of instrument and meter plant production LDZ a 4 a electromagnetic flow type converter and LDE series electromagnetic flowmeter, etc.
These flow meter
s in chemical industry, mining and metallurgy, steel, coal, water conservancy, hydraulic, water supply and drainage was widely applied in industrial process and sewage such ll]
, but technology testing shows that the product is in use when there are a lot of problems, such as some measuring range is not higher than 1:20, measurement of * * * low flow is only 0.
4 f s, and below this value measurement precision is difficult to meet the requirement of measurement, and some only USES the general circuit module and signal disposal technology, measurement accuracy is only, velocity range of l: only 40, 0.
3 a 12 m/s.
Foreign products in the domestic market mainly Fisher0Rosemount0Endress + Hauser, Yakogawa foreign big companies such as products, this product while on the measurement range and accuracy of measurement indicators better than domestic products, but its products for the es operating mode, difficult to grasp, and complex, expensive, so it is difficult to meet domestic market demand.
Aiming at the status quo, we to Japan, Germany, the United States and the domestic product technical data for deep research and analysis found that a lot of electromagnetic flowmeter signal processing method for peak sampling, capacitance isolation (
Bipolar time-sharing filtering and digital filter with the combination of double filtering technology, this technology can not well solve the problem such as induction signal distortion and the signal is amplified, and we also found that one year after the scene in some domestic product after the operation, the error of measurement instrument e. l many times, more than severe unqualified phenomenon;
So 'we conducted a study on the above question, and puts forward solutions, are discussed below.
Two fundamental wave signal disposal 2 average method.
1 the basic working principle of electromagnetic flowmeter basic block diagram is shown in figure 1.
By Faraday electromagnetic induction principle, when the conductive fluid flow through the measuring tube for velocity protection for cutting the magnetic induction intensity B lines of motion (
As shown in figure l sensor part)
, in a pair of detecting electrodes between the voltage produced by the induced electromotive force E U and the relationship between the magnetic induction intensity B, liquid flow rate Q is: when constant excitation current, magnetic induction intensity B is constant, a linear relationship with U and Q, t measuring the voltage value and after conversion circuit, can draw volume flow l3]
2 signal disposal fundamental wave average method above a pair of detection electrodes between the induction electromotive force is millivolt order of magnitude of the weak signal, and a variety of frequency and noise, expressed as as mentioned above, the capacitance isolation method is adopted to suppress zero drift, as shown in figure l differential amplifier inhibit common-mode signals before, after capacitance FGC by ac amplifier amplification, in figure 4 sampling to keep with the time, the dc output, enlarge the magnification of the machine for k.
This circuit structure is simple, can have effective inhibitory effect of high frequency, but our experimental results show that the resistance ability of the circuit is particularly bad.
To this end, this paper presents a fundamental transformation of the average signal disposal method, its structure diagram as shown in figure 2.
3 mentioned in the preamble of the intermittent excitation, some domestic product after about a year of field operation and instrument of measuring t error will greatly exceed the specified value, the field technicians and common analysis, the reason is that flip teach magnetoelectric road way of excitation and excitation power consumption was not well integrated consideration, caused due to temperature instability.
At present, the commonly used rectangular wave excitation, as shown in figure 3, but in the constant current source will produce larger pressure drop, increase the cost.
For this, we adopt the intermittent excitation party remove to reduce power consumption (
See figure 4)
The above research results have been applied in our research and development of intelligent integrated electromagnetic flowmeter, obtain ideal effect.
Verification results as shown in table l: in this paper, the fundamental wave average conversion method, namely the narrow-band filtering method is used to extract the signal's fundamental component, and its average, in the process also better filter in addition to the signal and noise in the points, though, improved the traffic signal and noise ratio, improve the capacity of electromagnetic flow falsely 20 t.
And put forward the intermittent excitation method, YangShi the excitation power consumption effectively, suppress the temperature rise.
Make the product under test t range, on the important index of measuring accuracy and repeatability are achieved improved significantly.
But in terms of zero characteristics, dynamic response is not perfect, it can be associated with dual frequency excitation applied to improve its performance, this method still have shi Yu Jinjia step research.
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