等级传感器：联系或不联系？

（www.ktekcorp.com），Praireieville，La.的水位仪器供应商。

通过空中不与储存船只的内容或过程联系，Notes Lauro Cantu Jr.，雷达专家，埃默森流程管理的Rosemount部门（www.emersonprocess.com/rosemount），德克萨斯州奥斯汀，德克萨斯州，提供过程传感器。当在过程中使用这些非接触式传感器时，Cantu表示一个优点是用户能够隔离传感器并具有它仍然的功能。“您可以通过阀门或Teflon窗口隔离单元 - 窗口充当屏蔽 - 这使得更高的安全性和更少的停机时间。”其他优点不太维护，以及与更多粘性流体一起使用。

通过天线或角，通风传感器将雷达波播放到液体或固体表面上 - 然后用那些天线或角接收反射信号，Hotard解释说明。这些传感器通常在大型储罐中找到更多使用，其中库存控制和监护需要高精度。“已经应用的很多地方是其他技术不起作用的地方，”他指出。

效率更高

Two types of through-air radar sensors—frequency modulated continuous wave, or FMCW, and pulse—exist, notes Bogdan Cherek, president of ABM Sensor Technology Inc. (www.abmsensor.com), an industrial sensor supplier in Peterborough, Ontario, Canada. He believes the pulse system delivers higher efficiency. Existing pulse-radar systems—which have fixed power, transmit fixed pulse lengths and have fixed gain in their receivers—may encounter problems with different tank dimensions, Cherek believes. “Sometimes their (the unit’s) power is too high; sometimes, too low.” His company’s pulse-radar technology self-adjusts power and, overall, requires less power, transmitting in the low-microwatt range.

引导波雷达电平传感器类似地运行到通过空气，Hotard解释 - 除了引导波的天线滴入并渗透产品表面。他说，微波能量通过探头送到罐头，进入液体的探针。“当液体变化的介电常数时，它产生了反射，”州Cantu。介电常数，也称为介电常数，测量材料在其本身内承受电场的能力。

Typically, guided-wave radar level sensors find use in water and petroleum liquids, Cantu remarks, especially in oil-water separators and chemical industry vessels in which two liquids have a distinguishable interface. “One advantage of guided-wave is that it’s not influenced by tank obstacles or geometry,” he adds.

This technology has become more popular in the past two years, Hotard says. Noting that guided-wave has no moving parts, he asserts, “Regardless of a temperature, pressure or specific gravity change (of a vessel’s contents), it can give a true measurement.” Product buildup on the antenna is possible, though it will still operate, he notes, but users apply this technology to replace float technologies.

Guided-wave radar level sensors, which are also called time-domain reflectometers, use one or two wires, Cherek notes. But now, two-wire 4-20 milliamp (mA)-loop powered non-contact radar sensors are available, says Cantu. “[However], I’m starting to see that instead of using 4-20 mA, the units are being powered digitally by field buses such as the Foundation Fieldbus or Profibus,” he comments.

Historically, guided-wave has cost less than through-air, Cantu observes. That’s changed in the past few years, though, because installation and configuration of through-air has been simplified, he says. “Through-the-air is the future,” Cherek adds.