| 电容式电磁流量计你了解吗？ |
| 信息来源： 流量变送器 | 2019-04-09 点击量： 5052 |
电容式电磁流量计你了解吗？西安华恒仪表制造有限公司为您介绍：电容型电磁流量计在解决固一液两相浆液型流体测量能够发挥出测量稳定的特点，能够真正有效地解决直流极化干扰带来的输出摆动的现象。电容变送型流量计能够高精确度测量低电导率流体的流量。但在使用时必须注意到前面所叙述的低电导率“流动噪声”问题。此时，流量计测量的流速范围应上限流速在可用范围内。
Capacitive electromagnetic flowmeter can play a stable role in solid-liquid two-phase slurry fluid measurement,and can effectively solve the output swing caused by DC polarization interference.Capacitance transducer flowmeter can measure the flow of low conductivity fluid with high accuracy.However,the problem of low conductivity"flow noise"described above must be noticed in use.At this time,the flow velocity range measured by the flowmeter should be within the available range.
藕合电容容量的变动将造成大的噪声，影响测量精确度与稳定性。电容介质的衬里材料，应具有绝缘强度高、介质损耗系数小、温度系数小、刚性好等性能。新型衬里材料PFA（聚四氟乙烯）和高纯氧化铝工业陶瓷能够满足这些要求。
The change of coupling capacitance capacity will cause large noise,which will affect the accuracy and stability of measurement.The lining material of capacitive medium should have high insulation strength,low dielectric loss coefficient,low temperature coefficient and good rigidity.The new lining material PFA and high purity alumina industrial ceramics can meet these requirements.
电容式电磁流量计把电极埋人衬里内，使被测流体与电极不接触。这样，能从根本上解决电极腐蚀、污染、液体泄漏问题。这样的传感器，其流量信号是通过电极与衬里形成的电容藕合传输到转换器。这就是电容式电磁流量计。
The capacitive electromagnetic flowmeter buries the electrodes in the lining so that the measured fluid does not contact the electrodes.In this way,the problems of electrode corrosion,pollution and liquid leakage can be fundamentally solved.The flow signal of such a sensor is transmitted to the converter through a capacitive coupling between the electrode and the lining.This is the capacitive electromagnetic flowmeter.
为了增大电容的容量，减少容抗上的信号损失，通常采用大面积电极或多电极结构形式。藕合电容的容量仅在几十个至上千个皮法范围。为保证信号能够大部分传输给放大器，转换器的输人电阻必须提高到10 8以上。
In order to increase capacitance and reduce signal loss on capacitance reactance,large area electrodes or multi-electrodes are usually used.The capacitance of coupling capacitors is only in the range of tens to thousands of skins.To ensure that most of the signal can be transmitted to the amplifier,the input resistance of the converter must be increased to more than 108.
由此，电容式电磁流量计具有能够测量低电导率液体的优点。例如，测量经脱去离子的净化水处理的纯水，其电导率可能在10-5 s/m以下。用一般电磁流量计的测量，可达5％以上测量误差。
Therefore,capacitive electromagnetic flowmeter has the advantage of measuring low conductivity liquid.For example,the conductivity of purified water treated by deionization may be less than 10-5 s/m.The measurement error of general electromagnetic flowmeter can reach more than 5%.
励磁线圈与电极间存在着分布电容和绝缘电阻。励磁电压通过励磁线圈与电极间分布电容和绝缘电阻与信号内阻抗分压，能在电极上形成大的共模干扰电压。电容型电磁流量计的信号内阻很高，分压的共模干扰可能更大。
Distributed capacitance and insulation resistance exist between excitation coil and electrode.The excitation voltage can form a large common mode interference voltage on the electrode by distributing capacitance between the excitation coil and the electrode,insulating resistance and internal impedance voltage of the signal.The signal internal resistance of capacitive electromagnetic flowmeter is very high,and the common mode interference of partial voltage may be greater.
因此，提高仪表的共模抑制比，成为电容式电磁流量计的另一技术难点。电容式电磁流量计的共模抑制比要求在CMR R≥120dB。把前置放大器放在传感器内，那样的自举阻抗转换和静电屏蔽措施，能有效地抑制大的共模干扰。
Therefore,improving the CMRR of the instrument becomes another technical difficulty of the capacitive electromagnetic flowmeter.Common mode rejection ratio of capacitive electromagnetic flowmeter requires CMR(>120dB).If the preamplifier is placed in the sensor,the bootstrap impedance conversion and electrostatic shielding can effectively suppress the large common mode interference.
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