IPP&T Magazine Online

Difficulties and Innovations in Level Control

November 15, 2021   Don Horne




CAPACITIVE SENSORS: A QUICK OVERVIEW

CAPACITIVE SENSORS AND MATERIAL DIELECTRIC

Rechner sensors specializes in capacitive sensors for level control applications. Capacitive sensors detect liquids, powders, or solid materials by measuring a change in capacitance. The amount of change in capacitance is dependent on the dielectric constant of the material being sensed. The larger the dielectric constant, the easier the material is to detect.

This means that materials with a high dielectric constant can be detected at greater distances than materials with low dielectric constants. Also, materials with high dielectric constants can be detected through the wall of containers made of material with a lower dielectric constant. For example, water (with a dielectric constant of 80) can be detected through a sight glass or the wall of a glass container (with a dielectric constant of 4 to 10).

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Standard Rechner capacitive sensors can detect materials with a dielectric constant of 1.2 or greater. Special capacitive sensors can even detect materials with a dielectric constant down to 1.1. The dielectric scale ranges from 1 to 80. Air has a dielectric constant of 1 while Water has a dielectric constant of 80.

MEDIA OPTIMIZED SENSORS

Rechner High-Performance capacitive sensors include a design principle that we named ‘media optimized’ sensing. This term refers to the ability of our HP models to detect a wider range of dielectric materials at an adjustment setting. Rechner understands that materials used in factories are not always uniform at the customer’s production facility. Materials between batches (and even within the same batch) can vary in size, density, and temperature. With media optimized sensor models it is also possible to be able to detect a wider range of different products at the same adjustment (e.g., different types of plastics).

SENSOR DESIGN

Level Sensors and proximity sensors are often grouped into two categories: flush (shielded) and non-flush (non-shielded). Both types can be used to detect products at a distance or in direct contact with the sensor.

Flush mount sensors can by mounted flush with the side of a container and are shielded on their sides. These sensors do not detect at their sides. They only detect straight ahead. The benefit of flush mount sensors is the highly directed sensing field. This allows sensors to be embedded in metal frames. As the name implies, they can be mounted flush with the surface of a metal wall.

Non-flush sensors detect at their sides as well as in front. The benefit of a non-flush sensor is a larger sensing field and farther sensing distances. These sensors must have clearance from metal parts inside the wider sensing field.

ADJUSTING A SENSOR

The standard method for adjusting a capacitive sensor is by adjusting a potentiometer on the sensor. Rechner models use a 20-turn potentiometer instead of a ¾-turn potentiometer for 25 times more accurate adjustment. New innovations in electronics now allow for automatic teaching methods.

ADJUSTING WITH EASYTEACH

Rechner’s EasyTeach technology can program a sensor automatically. Just place the sensor in the product you wish to detect and press a button until the sensor’s indication light flashes. This process can also be done remotely by wire.

LEVEL SENSING

CHOOSING A LEVEL SENSOR

Sensor design plays a critical role in industrial automation applications. Sensors are often designed to be the most reliable for only the applications they are intended to be used.

When choosing a sensor for the highest reliability then a test for the worst-case scenario should be performed. The worst-case scenario can of course be mitigated. The worst-case scenario can be lessened by implemented proactive measures that prevent some scenarios from happening.

To download the latest Industrial Automation handbook, click here.

Having a clear idea of failure scenarios is the first step. We should also understand how close to each failure mode our implementation is. For example. How much material can build up on a sensor before a false signal is generated.

THE COST OF FALSE SIGNALS

Increasing reliability for sensors primarily means reducing false signals. This includes false signals OFF (the sensor not detecting the product when it should be), false signals ON (the sensor detecting product when it should not be), and premature sensor failure.

A false signal OFF will cause an overfill situation. Overfills are dangerous to people and they contaminate the production facility. This may incur costly cleanup of the overfill area.

False signals ON will cause an underfill situation. Underfills can cause elevated temperatures or fires in applications where heating elements are used.

A sensor failure may cause an overfill or an underfill situation depending on how the sensor failed.

False signals can cause injury to employees. Overfilled material can be slippery, hot, or cause chemical burns.

Overfills also have a monetary cost for clean-up. Machines need to be shut down and reports filed. This downtime can easily cost tens of thousands of dollars per hour. Overfills can also have an environmental impact. If your company has an environmental policy, overfill protection may be a process that should be reexamined for a greener outcome.

MATERIAL BUILD-UP

EMPTY TANK VS CLEAN TANK

When considering a level sensor, taking the difference between an empty tank and a clean tank into account is critical. A clean tank is empty, but an empty tank is not always clean. Even smooth stainless-steel tanks only dealing with liquids must undergo regular sanitization processes. Some materials will leave behind more residue than others. Dust and viscous liquids will collect on even the smoothest of surfaces. This should be taken into consideration when choosing a sensor.

RESIDUE

Residue will usually be left behind inside of the tank in any process that requires a tank to be emptied and refilled. Residue left behind can accumulate over time on the surfaces of the tank and on the level switch. This residue can be liquid, bulk solid, or powder.

In general, capacitive sensors with larger sensing fields can ignore more buildup of material without creating a false ON signal.

HYGIENIC DESIGN

WHAT IS HYGIENIC DESIGN?

Hygienic design is a set of principles and standards that reduce the risk of food safety issues. The most important factor in hygienic design is that the equipment and premises be easily cleanable.

Increased standards for hygienic applications have increased in recent years. Rechner Sensors now tracks from start to finish the materials used in each sensor from raw to the final sensor serial number. During production special gloves are used to handle all sensor that are to be used in hygienic applications. The surface finish of sensors for hygienic applications are tested to ensure they meet cleanability standards. The most common materials used for hygienic designs are PTFE and PEEK.

Rechner has sensor models that meet IP69K standards. The IP69K standard requires that the sensor be sprayed with water at a pressure between 1160 and 1450 PSI and at different angles without damaging the sensor.

INTEGRATION OF HYGIENIC DESIGN SENSORS

When dealing with hygienic design, it is just as important to consider the integration of the sensor into the process as it is to consider the design of the sensor. Incorrect mounting hardware can leave gaps, create crevices, or expose threads that become a place for bacteria to collect, avoid cleaning/sanitization, and grow.

CLEANING SHADOW

Large sensors can cause unintended issues regarding material build-up. Water coming from a point source will create a cleaning shadow that prevents proper cleaning on the far side of an object blocking the water. The larger the object blocking the source, the larger the cleaning shadow will be.

EHEDG VS 3-A

Rechner has EHEDG certifications for sensors. This certification requires that design principles be followed as well as a certification test be passed. The 3-A website has a harmonization matrix for EHEDG products that comply with 3-A standards.

SENSORS IN CONTACT WITH THE PRODUCT

In industrial automation, there is sometimes an aversion to sensors being in contact with the bulk material. A sensor being in contact with the material does not diminish the hygienic design of the sensor. A false signal causing an overflow or cause a tank to run empty is often a more serious hazard.

The most reliable sensor may be the model that is in direct contact with the product. With proper hygienic design and implementation: sensors that are in contact with the material should not be dismissed.

INDUSTRY 4.0

INCREASING PRODUCTIVITY THROUGH INCREASED CONNECTIVITY

OVERVIEW

Industrial automation has come a long way. From mechanization (1.0) to electrification (2.0) to automation (3.0) and globalization (3.5), we have arrived at 4.0: the digital manufacturing revolution. At the heart of Industry 4.0 is the idea that we can increase efficiency, reduce downtime, and improve quality by increasing information gathering and using computers to make our processes more efficient.

FUTURE TECHNOLOGIES: BLUETOOTH, IO-LINK

For us to gather more data, we need smarter sensors. New technologies like IO-link and BlueTooth have entered the mainstream. These technologies can now be found in Rechner model sensors. These technologies enable the possibility for two-way communication to the sensors. With this we can retrieve internal sensor data (like temperature) which allows us to monitor the health of the sensor. With IO-link, we can send commands to adjust or reprogram sensors remotely and automatically.

THE RISING DEMAND FOR ANALOG SENSORS

While not exactly a new technology, analog sensors have come a long way. From simple RC-circuits to new programmable IC-packages, analog sensors are easier to use than ever before. Output data from new analog sensors are more linear and less susceptible to electrical interference resulting in more accurate readings.

Integrating analog sensors has never been easier with the abundance of computers and PLC presence in modern factories. The demand for analog sensors has risen as such. Analog level sensors have some very interesting use cases.

Rechner offers analog level systems that are self-programming. No adjustment is necessary when a new material is used in a tank with a TrueLevel sensor.

PREDICTIVE LEVEL

Analog level systems that tell you how much product is left in a tank can now be used with predictive software to plan further ahead. These analog systems allow the ability to track detailed usage over time. Usage over time can be used to predict when a vessel will be empty and when more product will need to be ordered. Usage over time also allows more short-term predictions, like when a batch will be finished. Maintenance and changeover teams can be scheduled more efficiently.

POINT LEVEL USE CASE 4.0

An analog sensor detecting the point level in a tank may not appear to be useful at first glance, however it allows for more complicated processes since more data is being transferred. A single point level sensor with an analog output can distinguish between different types of materials. This type of sensor allows different processes to be carried out depending on which material is detected. A few examples will be given here.

In an oil sump application outdoors, three conditions are possible: The sump will be empty, the sump will be full of rainwater, or the sump will be full of oil leaking from a transformer. A single analog sensor can detect the difference between air, water, and oil. In the condition that air is detected the pump will turn off. In the condition that water is detected, the rainwater will be pumped out back out into the environment. In the condition that oil is detected an alarm is sent to the company so that proper environmental cleanup can be performed.

An analog sensor may also detect an empty tank, the foam buildup on the top of a product, and the actual liquid level of the product. You could also detect the cleaning product during automated wash cycles.

An analog sensor may also be used to detect a very wide range of products. In a condiment factory, many kinds of condiments or flavors of a single condiment may be processed it the same tank. An analog sensor could reliably detect the full tank and empty tank condition of many different products just by reading a recipe of analog values from the sensor into a PLC.

Call us at 1-800-544-4106 or visit www.rechner.com for more information.

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Highlights 2021

OVER 50 YEARS IN NORTH AMERICA

Rechner Sensors has proudly served the North American market for over 50 years. We have helped provide specialized sensors for many demanding industrial automation applications. Rechner Sensors has played a major role worldwide in the development and design of capacitive sensors through dedication, product innovation, and top quality. Innovation that is primarily led by application driven custom solutions.


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