Application Considerations When Specifying Pulse Burst Radar (Non-Contact Radar) for Liquid Level Sensing

Assessing your level instrumentation needs correctly is essential for process efficiency and performance. To do this, it’s important to have an understanding of the many liquid level sensing technology options available – as well as the pros and cons of each technology, relative to the application.

In this post, we’ll discuss application considerations and configuration characteristics of pulse burst radar (also called non-contact radar). Pulse burst radar represents a subset of the radar technology category, the fastest growing measurement technology for industrial level control. A previous post summarized pulse burst radar technology’s principles of operation. To continue to receive information about pulse burst radar, as well as other level and flow control topics, consider subscribing to our blog.

The Three Ds
Radar applications are influenced by three basic conditions: (1) the dielectric of the process medium; (2) the distance, or measuring range of the application; and (3) a variety of disturbances that attenuate or distort the radar signal.

The distance, or measurement range, is a function of the instrument’s frequency and selected antenna, the dielectric constant of the media and the presence of signal interference. Disturbances caused by turbulence, foam, false targets (interior tank obstructions causing false echoes), multiple reflections (reflections from off the tank roof) or a high rate of level change, can weaken, scatter or multiply radar signals. Very high and very low liquid levels can also be problematic.

Pulse Burst Radar
Pulse Burst Radar technology and advanced signal processing help manage common disturbances: 1. False echoes caused by obstructions, or multi-path reflections caused by waves hitting a sidewall; 2. Turbulence generated by agitators or aggressive chemical reactions; and 3. A layer of light to medium density foam.

Signal Processing
Radar’s signal processing function is critically important because radar exhibits interference effects similar to those that affect light. It is the quality of a device’s signal processing that separates today’s leading-edge radar transmitters from the others.

Most disturbances mentioned above can be readily managed by pulse burst radar signal processing capabilities, where true level can be extracted from false targets and other background noise. Using extremely energy-efficient circuits, no duty cycling is necessary to accomplish effective measurement.

For this reason, Magnetrol® pulse burst radar products (Pulsar® and Model R82 level transmitter devices) can also track high rates of change that have been impossible with other loop-powered radar transmitters. Although these products feature powerful false target recognition and rejection routines, minimizing false target reflections is significantly affected by proper installation and orientation.

Antennas
The transmitter’s antenna transmits and receives the radar signal. Pulse burst radar transmitters can utilize a variety of dielectric rod and horn types or an encapsulated horn antenna. Maximum measuring range of the instruments is chiefly dependent upon the instrument’s capabilities, dielectric constants, and the degree of turbulence.

Installation
Using MAGNETROL pulse burst radar products as an example, a typical installation procedure provides the key steps for mounting, wiring and configuring transmitters. Transmitters typically come configured from the factory, but some models (such as the PULSAR and Model R82 devices) can be reconfigured in the shop at any time. Bench configuration provides a convenient and efficient way to set up the transmitter before going to the tank site to complete the installation. The transmitter is generally password protected to secure configuration values.

A HART® remote unit, such as a HART communicator, can be used to provide a communication link. When connected to a control loop, measurement readings shown on the transmitter will be shown on the communicator. The communicator can also be used to configure and troubleshoot the transmitter.

Benefits
Pulse burst radar instrumentation is engineered to measure a large number of liquid media in a broad range of process conditions, from calm product surfaces and water-based media to turbulent surfaces and aggressive hydrocarbon media. As a non-contact device, these products are not susceptible to the complications that arise whenever a probe contacts the process media, such as coating by viscous media or corrosive attack due to aggressive chemicals. The greater the measuring range, the more pulse burst radar proves itself to be an economical solution, given the cost of extended probe lengths.

Radar in general is virtually unaffected by the presence of vapors, or air movement within a vessel’s free space. Changes in specific gravity, conductivity and dielectric constants also have no effect on measurement accuracy. As a 100% electronic instrument, the absence of moving parts translates into low maintenance costs. As a two-wire, loop-powered device, power requirements and installation are greatly simplified.

Follow Our Pulse Burst Radar Discussion
In our July 16th post, we’ll demonstrate how pulse burst radar may be a cost-effective – and more robust – technology alternative to ultrasonic level control. For more information on the subject of pulse burst radar, you can also download the MAGNETROL Pulse Burst Radar Technology Guide.




 

 

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