Viewpoint: microwave does its level best

Accuracy in level detection and measurement is highly important in industries where water, oil and other fluids are stored, dispensed into containers of all sizes and/or used in processing and other operations.

There are many applications where precise level detection is critical to productivity and ensuring continuity of process.

Microwave radar technology

The development of guided microwave radar technology has led to a number of versatile sensing options. They can achieve high performance, unaffected by density or conductivity. In more advanced sensors the presence of foams or coating deposits can be ignored due to the use of special algorithms built into the level sensor.

The development of guided microwave radar technology has led to a number of versatile sensing options

The consistent accuracy of the technology has seen quick adoption and sensor manufacturers are being asked to come up with ways to expand its uses through the adaptation and configuration of the sensor’s probes for different applications.

Fluid difficulties

A particular problem with some process fluids is their low surface tension and high propensity for foaming. Many additives dissolved in the fluids increase foaming properties and there are also cases, such as in beverage manufacture, where foam enhances the finished product, so it is desirable even though it can create measuring difficulties for some technologies.

As a result, standard level technology, such as floats, capacitance, tuning forks and ultrasonics, can struggle when trying to deliver a precise measurement, both through the blanketing effect of foam and the difficulty of defining a precise liquid air interface point.

Foam conquered

With a fluid level probe, accurate measurement in the presence of thick foam is ensured through a patented ‘foam algorithm’, enabling microwave radar probes to see through large amounts of foam and detect the true fluid level.

Excellent success rates and cost savings have been demonstrated for applications in liquids such as milk, beer and detergents in the presence of wet, dense foams. On high-speed filling lines, the wastage caused by under or over-filling and line downtime due to false head tank level readings can be significantly reduced.

Extended probe length

In response to the needs of end-users, fluid level probes have had practical adaptations to meet specific production challenges. As many level measuring applications have long level ranges, either in large tanks or slim deep ones, an extended probe length up to 4m can provide accurate measuring options.

Installations with limited headroom above the tank can now be solved using a flexible variant. This is achieved by substituting a weighted stainless steel rope up to 4m long for the solid probe, to guide the microwave pulse.

High process temperatures

Remote amplifier models provide a solution for higher process temperatures, up to 180 ̊C, or where the separation of the probe and electronics provides easier access to the device for setup and diagnostics.

The separation of the probe and amplifier even facilitates autoclaving, a process where the whole tank is removed for deep sterilisation, with the fitted probe provided with a sealed connection.

Awkward tanks

A co-ax tube accessory has shown success with applications where the liquids measured have a very low dielectric (eg oils and cutting fluids). They are also suitable for use in tanks that are open topped, have non-metallic walls or metal protrusions inside that could disrupt the sensing of the reflected radar pulse. Here, a stainless steel, perforated sleeve over the probe facilitates measurement of the liquid level.

For use where stainless steel would be rapidly corroded or dissolved by chemical and/or galvanic reaction, such as in metal plating or with hot, concentrated acid solutions, titanium wetted parts can be introduced.

• Darren Pratt is SICK UK’s industrial instrumentation specialist.