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Balluff explains how to prevent standard capacitive sensors false triggering in applications involving liquids that create films, foams or material build-up.

Level detection applications of heavily foaming and filming liquids are a difficult task for standard capacitive sensors today, as thicker container walls require time consuming set-up procedures and material build-up of adhesive media on the inside of container walls cause sensors to repeatedly false trigger.

However, Baluff is introducing a self-adjusting capacitive sensor technology that overcomes all of these problems.

Capacitive sensors are commonly used for presence detection of a range of non-metallic objects and liquids.

In level-sensing applications, capacitive sensors can be mounted in two different ways, depending on the target material and the tank wall composition.

In direct sensing mode, the sensor is in direct contact with the target material in order to indicate if the material level rises above or falls below the sensor location.

In indirect sensing, the sensor is typically mounted flush against a non-metallic wall to detect the target material through the container wall.

The advantage here is that the container wall doesn’t have to be penetrated, which reduces the risk of leakage and allows lower installation costs.

The active sensing area of a capacitive sensor is comparable to open electrodes of a capacitor.

Both electrodes are in a feedback loop of a high-frequency oscillator arranged in a way that they are in harmonic balance.

The oscillator doesn’t react unless a target material is introduced into the electro-static field formed between the two electrodes.

The target material causes a change proportional to its dielectric constant in the couple capacitance, which causes the oscillator amplitude to rise.

A signal evaluation circuit activates the output at the user-adjusted threshold level.

In order to get reliable and dependable sensing results, the user is required to use a trim potentiometer to adjust the signal sensitivity to meet the application requirements.

Generally speaking, a capacitive sensor would be adjusted to the point where it always ignores the non-metallic container wall but activates safely from the sum of container wall and target material capacitance – and here lies the major difficulty.

Standard capacitive sensors often false trigger when confronted by applications involving liquids that create films or material build-up on container walls or the sensor itself.

Setup procedures are usually difficult, time consuming and error-prone – or simply impossible.

Frequent readjustments offer only short-term results and the overall operational reliability of conventional capacitive sensors is unsatisfactory.

Smartlevel sensors eliminate virtually all problems associated with standard capacitive level sensor technology.

They accurately sense correct levels of aqueous or high conductive liquids through glass or plastic walls up to 12mm thick.

Technology allows these sensors to automatically distinguish between non-metallic tank walls, possible interferences from foaming of material build-ups and the true level in the tank.

The sensors also readjust themselves when confronted with changing container compositions during checking procedures or changes in liquids during different production runs.

An added benefit is that, in direct sensing applications, reverse mounting eliminates any sensor mounting thread inside the vessel, aiding production hygiene.

These sensors are simple to install and require no teach-in.

They find true liquid level automatically for ‘mount and forget it’ convenience.

In virtually all applications, the sensors never require maintenance cleaning procedures.

This means for the first time a capacitive sensor, even when in direct contact with the media, can operate accurately for an indefinite amount of time regardless of debris build up or in the presence of heavy foam, eliminating downtime, production loss, false triggering, maintenance and process interruptions.

The sensors are suitable for all water-based liquids and other highly conductive liquid compositions such as acids, detergents and organic wastes.

Common applications include filling situations, storage and mixing stations, and general process monitoring in chemical or medical environments.

Smartlevel sensors work with a high-frequency oscillator whose amplitude is correlated to two independently acting sensing electrodes.

The sensors measure independently (contrary to standard capacitive sensors) the capacitance of the container wall without ground reference and the capacitance of the conductivity of the liquid with ground reference.

This second capacitance, being significantly higher than the first one, affects the oscillation inversely to the first one and pulls the amplitude down to 0V, triggering the sensor’s output.

This technology is the reason why Smartlevel sensors provide a high level of reliability and safety, do not require any individual adjustments to the specific container wall and do not falsely recognise material build-up, foaming, or filming in the application.

Smartlevel sensors provide cost-effective and reliable point-level monitoring for a range of industries and applications.

Balluff offers this technology in a range of sensor configurations to accommodate various applications and environments.

Balluff has over 50 years of sensor experience and is a leading global sensor specialist with its own line of connectivity products for every area of factory automation and industrial control.

Everyday, all over the world, Balluff sensors are increasing production throughput and product quality for thousands of satisfied users striving to improve their manufacturing processes and lower their costs. No matter what the application, Balluff has the practical experience, expertise, and product range to make that improvement. Products include:

  • inductive, photoelectric, magnetic field, ultrasonic, capacitive, vision sensors 
  • linear transducers, linear encoders systems 
  • distance  measurement and level sensors
  • industrial RFID 
  • power supplies
  • connectivity and bus systems.

Our manufacturing, sales, and service offices are located around the world. That means the excellent service we provide in England, Germany, or Brazil is the same as we offer in the United States, Japan, or India.

Fast delivery, global pricing, attention to detail and the ability to lower our customers’ costs, no matter where our customers are located. Although our programs are global, our customer relationships are local.

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