Process industry operations face questions of level instrumentation technology daily. Whether specifying liquid level controls for a greenfield facility or upgrading existing instrumentation for improved efficiencies in an existing plant, instrumentation and control managers must stay abreast of numerous technology options.
Since this blog is dedicated to advancing the understanding of level and flow control solutions across all process industries, we regularly profile instrumentation technologies. Over the course of the next few weeks, we’ll discuss pulse burst radar, also known as non-contact or through air radar, outlining how the technology works, application considerations, and comparison to other level control technology, specifically ultrasonic level sensors.
Radar is presently the fastest growing measurement technology for industrial level control. But radar’s beginnings were less than auspicious. Early level instruments were costly, bulky, over-specialized and complicated. The development of simpler, less costly and easier-to-use devices would be made possible by solid state components and by a growing cache of applications knowledge.
Radar level sensing devices detect the position of process liquids by measuring the interval between the emission and return of high frequency radio waves. Guided wave radar, used by Magnetrol® Eclipse® transmitters, is a contact technology that launches its signal along a waveguide that runs directly into the process media. Pulse burst radar, utilized by Pulsar® and Model R82 level transmitters, is a non-contact technology that launches its signal into open air along a trajectory directed toward the process media.
Of the two operational technologies commonly used for radar, MAGNETROL products employ a pulse burst approach rather than frequency modulated continuous wave (FMCW). Pulse burst radar operates in the time domain and does not require complex and expensive processing as needed to enable FMCW. Because echoes are discrete and separated in time, pulse burst radar is able to sort through extraneous echoes and select the one generated by true level. Pulse burst radar also has excellent averaging characteristics, important in those applications where a return signal is attenuated by process conditions (which we’ll discuss in the next blog post of this series).
Unlike true pulse devices that transmit a single, sharp (fast rise-time) waveform of wide-band energy, MAGNETROL products emit short bursts of 5.8/6.3 GHz (PULSAR) or 26 GHz (Model R82) energy and measure the transit time of the signal reflected from the liquid surface. Distance is calculated utilizing the equation:
Distance = C × Transit time (C = speed of light)
The level value is then developed by factoring in tank height and sensor offset information. The exact reference point for distance and level calculations is the sensor reference point—bottom of an NPT thread, top of a BSP thread, or face of a flange.
|Pulse burst radar technology uses equivalent time sampling circuitry and emits short bursts of 26GHz microwave energy, which then are reflected from the liquid level surface.|
Equivalent time sampling (ETS) measures the high speed, low power electromagnetic energy (EM). ETS is critical in the application of radar to vessel level measurement. The high-speed EM energy is difficult to measure over short distances and at the resolution required in the process industry. ETS captures the EM signals in real time (nanoseconds) and reconstructs them in equivalent time (milliseconds), which is much easier to measure with today’s technology.
ETS is accomplished by scanning the waveguide to collect thousands of samples. The round trip event on a 65-foot (20-meter) tank takes only 133 nanoseconds in real time. After it is reconstructed in equivalent time it measures 200 milliseconds.
In our July 9th post, we’ll take a look at various application considerations that affect specification of pulse burst level sensing technology. For more information on the subject of pulse burst radar, you can also download the MAGNETROL Pulse Burst Radar Technology Guide or subscribe now to get the rest of the posts in our pulse burst radar series delivered directly to your inbox.