liquid level Archives - AUTOMATION INSIGHTS

Recap of our top 5 posts of 2015

As we wrap up the old and begin to open up the new, let’s take a moment to reflect on what this past year has brought us. Apart from the triumphs and the hard lost battles, we want to bring you some of our top posts from 2015. These posts are as follows:

#5: 5 Tips on Making End-of-Arm Tooling Smarter

Everyone wants their robot to work faster, smarter, and more efficiently. In this post we review five easy tips to help you improve the efficiency of your end-of-arm tooling.

Example of discrete sensors used to detect tank level

#4: Liquid Level Sensing: Detect or Monitor

Who doesn’t like complicated concepts broken down into easy to understand terminology? In this post we break down the differences between point level detection and continuous position sensing as well as provide you with technologies to put into practice.

#3: How Can I Convince My Boss to Send Me to Training?

As Aristotle once said “All men (and women) by nature desire knowledge.” Here we are giving you the tools needed to break down the barriers your boss (or you) might have against investing in training.

#2: Back to the Basics: How Do I Wire a 2-Wire Sensor?

So you just got a brand spanking new 2-wire sensor for the holidays but you realize you don’t know exactly what wire goes where. In this post we make wiring that bad boy easy and even break down what polarized and non-polarized mean.

So we have covered four of the top posts from 2015, are you ready for the number one post from the past year? So are we! And we will have it for you right after a quick message from our sponsors! (just kidding!)

#1: Inductive Coupling – Simple Concept for Complex Automation

Through the use of magnetic induction, we are able to reduce the downtime of a machine due to the failure of a slip ring. Inductive couplers pass power and data over an air gap creating a maintenance free, non-contact environment to operate a variety of machinery.

We want to thank you for the wonderful year that is behind us and be sure to be on the look-out for even more exciting news to come this year!

Requirements for Sanitary Fill Level Sensors

In a previous entry here on the SensorTech blog, we discussed the concept of liquid level sensing, and the difference between discrete liquid level detection and continuous liquid level monitoring. In this entry, we are going to talk about the requirements for liquid level sensors that are used to measure or monitor liquid products that will ultimately be consumed by humans.

In these applications, it is necessary and critical that sanitary standards be met and maintained. Sensor designed for sanitary applications are usually designed from the ground up to meet these requirements.

Basically, there are two key criteria that come into play when considering the suitability of a sensor to be used in a sanitary environment:

Cleanability – Sanitary filling systems typically need to be regularly cleaned and/or sterilized to prevent the growth of potentially harmful bacteria. It is desirable in most cases that the cleaning/sterilization process be done as quickly and as easily as possible, without having to remove components (including sensors) from the system. For this reason, many sanitary fill sensors are designed to withstand “cleaning-in-place” (CIP). Factors such as water-tightness, and ability to withstand elevated cleaning solution temperatures come into play for CIP suitability.

Mechanical Sensor Design – Sensors for sanitary fill applications are usually designed such that there are no mechanical features that would allow liquid or debris to collect. Crevices, grooves, seams, etc. can all act as collection points for liquid, and can ultimately lead to contamination. For this reason, sanitary sensors are designed without such features. The physical make-up of the sensor surface is also important. Exterior surfaces need to be very smooth and non-reactive (e.g. high-grade stainless steel). Such materials also contribute to cleanability.

Consistent standards for sanitary equipment, products, and processes are defined and maintained by 3-A SSI, a not-for-profit entity that provides consistent, controlled, and documented standards and certifications for manufacturers and users of sanitary equipment, particularly in the food, beverage, and pharmaceutical industries. Equipment that meets these sanitary standards will usually display the 3-A symbol. For more information on this solution visit the Balluff website.

Liquid Level Sensing: Detect or Monitor?

Pages upon pages of information could be devoted to exploring the various products and technologies used for liquid level sensing and monitoring. But we’re not going to do that in this article. Instead, as a starting point, we’re going to provide a brief overview of the concepts of discrete (or point) level detection and continuous position sensing.

Discrete (or Point) Level Detection

In many applications, the level in a tank or vessel doesn’t need to be absolutely known. Instead, we just need to be able to determine if the level inside the tank is here or there. Is it nearly full, or is it nearly empty? When it’s nearly full, STOP the pump that pumps more liquid into the tank. When it’s nearly empty, START the pump that pumps liquid into the tank.

This is discrete, or point, level detection. Products and technologies used for point level detection are varied and diverse, but typical technologies include, capacitive, optical, and magnetic sensors. These sensors could live inside the tank outside the tank. Each of these technologies has its own strengths and weaknesses, depending on the specific application requirements. Again, that’s a topic for another day.

In practice, there may be more than just two (empty and full) detection points. Additional point detection sensors could be used, for example, to detect ¼ full, ½ full, ¾ full, etc. But at some point, adding more detection points stops making sense. This is where continuous level sensing comes into play.

Continuous Level Sensing

Example of in-tank continuous level sensor

If more precise information about level in the tank is needed, sensors that provide precise, continuous feedback – from empty to full, and everywhere in between – can be used. This is continuous level sensing.

In some cases, not only does the level need to be known continuously, but it needs to be known with extremely high precision, as is the case with many dispensing applications. In these applications, the changing level in the tank corresponds to the amount of liquid pumped out of the tank, which needs to be precisely measured.

Again, various technologies and form factors are employed for continuous level sensing applications. Commonly-used continuous position sensing technologies include ultrasonic, sonic, and magnetostrictive. The correct technology is the one that satisfies the application requirements, including form factor, whether it can be inside the tank, and what level of precision is needed.

At the end of the day, every application is different, but there is most likely a sensor that’s up for the task.

Are all capacitive sensors for liquid level detection created equal?

When standard capacitive sensors are used for liquid level detection in an indirect level detection application, the sensor must be adjusted to the point where it ignores the container wall but reliably detects the capacitance change caused by the changing liquid level. Typically, a standard capacitive sensor can be adjusted to disregard a wall thickness of approximately 4mm. In addition, the dielectric strength of the liquid must be higher than the container wall for reliable level detection.

Capacitive sensors detect any changes in their electrostatic sensing field. This includes not only the liquid itself, but also application-induced influences such as condensation, foaming, temporary or permanent material build-up. High viscosity fluids can cause extensive delays in the accurate point-level detection or cause complete failure due to the inability of a standard capacitive sensor to compensate for material adhering to the container walls.

A perfect capacitive sensor for non-invasive level detection applications would not require any user adjustment after the initial setup process. It would detect the true liquid level of any type of water-based liquid through any non-metallic type of tank wall while automatically compensating for material build-up, condensation, and foam. While ignoring these interferences, the sensors would still detect the relative change in capacitance caused by the liquid but use additional factors to evaluate the validity of the measurement taken before changing state.

These sensors would be fundamentally insensitive to any non-conductive material like plastic or glass up to 10mm thick, which would allow them to be utilized in non-invasive level applications. The enhanced capacitive sensors only limitation is it would require electrically conductive fluid materials with a dipole characteristic such as water to operate properly. This is a great concept but does a sensor like this exist today? The short answer is yes, and it is called Smart Level!

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