The Why and How of Choosing Level Sensors to Fit Your Process Needs

Level indicators have been around for decades. From simple switches and rotaries, to advanced non-contact sensors, there’s no shortage of technology to choose from. But what role do level sensors actually play in today’s manufacturing operations, and how do you choose the best fit for your needs?

Sensors Save Time – and People

Whether your operation is large or small, at one central location or spread across geographically dispersed sites, utilising utilising level control sensors can maximise efficiency by automating cumbersome – and often dangerous – manual tasks. Simple, yet effective, point level sensors can serve as high, mid-, or low-level indicators. Fail-safe models help control processes and warn of overfills, outages, or equipment failure.

Continuous level sensors such as the versatile 80 GHz non-contact radar are not only accurate, even in extremely dusty or noisy environments, they can integrate with LAN or cloud-based inventory management programs to make it easy to access, manage, and report on inventory any time, from anywhere.

Streamlining data in this way cuts down on time spent on cumbersome spreadsheets, optimises inventory turnover, and—with permission-based user roles—makes it simple for everyone from the plant floor to accounting to access and work from the same information without wasting time on communication confusion.

Sensors Prevent Problems

Overfilling vessels ruins materials, wastes time, makes a mess, and causes unnecessary down time. Utilising level controls streamlines material monitoring and process control. Automated alerts prevent overflows, empty conditions, clogged chutes, and jammed conveyors.

For a long life and maximum ROI, choose a sensor that is designed for your operation’s environment. High temperature models or non-stick coatings ensure the long life of equipment with minimal maintenance.

In applications where material piles unevenly, 3D level sensors can be used to circumvent issues caused by bridging or silo wall buildup. By using advanced acoustics-based technology and multiple-point measurements, this type of sensor can display a three-dimensional representation of inventory level as well as calculate volume. This both eliminates concerns about accurate inventory and helps pinpoint vessel stress areas where uneven loading may impact the life of a silo.

Making the Choice

Today’s manufacturing operations are increasingly automated with more sophisticated and complex systems. Plus, with increased consolidation, multinational corporations, and a global economy, the needs of the industry have changed.

The market for level indicators has responded with new solutions to address those demands, creating flexible options and integrative software to allow manufacturers to customise their solutions to achieve their best fit for inventory level monitoring.

The most crucial part to choosing a level control sensor or system to meet your needs is understanding the options available.

Point Level Indicators

As the name implies, point level indicators alert when the level in a silo reaches a certain point. For timely replenishment or process control, a point level indicator uses a relay to send an alert to a control room, horn, light, or an alarm panel when material reaches or falls away from the device. They can be used for high, mid, or low-level alerts in a wide variety of dry bulk solids including granules, pellets, and many powders.

It is very common for point level indicators, such as rotaries, capacitance probes, vibrating rods, diaphragm switches or tilt switches, to be wired to a horn or light to indicate a full or empty status. This happens most frequently when the level indicator is used to start or stop a process to prevent running out of an ingredient or wastefully overfilling a silo.

Common point level indicators include:

Rotary:

The familiar workhorse of the manufacturing world, rotaries have a continually rotating paddle. When the paddle meets resistance due to the presence of material, it stops rotating and sends an alert. Conversely—as a low-level indicator—rotaries can be set to alert when the material drops below the level of the paddle and it resumes rotation.

Rotaries can be customised with a variety of paddle types, extensions, and mounting options and are available in fail-safe models, making them ideal for continuous processes as well as an inexpensive backup option for other monitoring systems.

Capacitance Probe:

Capacitance sensors operate by detecting the presence or absence of material in contact with the customisable probe by sensing minute changes (as low as 0.5 picofarad) in capacitance caused by the difference in the dielectric constant of the material versus the air.

Capacitance probes can easily be configured for a wide range of applications. When selecting a capacitance probe, understanding the radio frequency range of the device and its potential impact on other equipment in the plant is an important consideration.

Vibrating Rod:

The vibrating level sensor is a piezoelectric-driven, vibration-type level switch that can be used for level detection in bins, silos, and hoppers filled with powders and other dry bulk solid materials. The rods of these rugged sensors are often constructed of durable stainless steel and are almost wear and maintenance-free.

A vibrating level sensor can be mounted on the side of the vessel when used as a high-, mid-, or low-level alert. Alternatively, they can be used for high-level, top-mounted applications when built with a rigid or flexible extension.

Diaphragm Switch:

A diaphragm switch, also called a pressure switch, is a very basic, affordable level sensor commonly used as a high-level alert on a silo wall. It can be mounted internally or externally. Internal mounting doesn’t require a hole to be cut in the vessel wall.

An external mount has the advantage of mounting from the outside via a hole cut in the wall, so there is no need to get into the silo for installation. There are models for non-hazardous locations or with explosion proof certifications. Pressure switches are also used for plugged chute detection.

Tilt Switch:

Tilt switches are designed to install easily and require no routine maintenance. They serve as a high-level indicator, activating an alert when material rises and tilts the switching mechanism 15°.

A fixed-mount tilt switch mounts from the outside on the top of the silo though a process connection. It is custom-made to a specific length determined by the distance from the top of the silo an alert should be activated.

Alternatively, a hanging tilt switch is installed by suspending it from a flexible cable within the silo or over a pile of material or a conveyor. A hanging tilt switch also can be used for plugged chute detection.

A note of caution: some tilt switches are made using mercury, so be sure to select a mercury-free model if one is required for compliance with environmental regulations.

Continuous Level Sensors

Integrating continuous level sensors allows an operation to monitor how much is in one or all silos in real time or at scheduled intervals. Cable-based sensors, non-contact acoustics-based, open-air radar, or laser level sensors are commonly used in large storage silos. Open-air radar and laser are also appropriate for narrow silos. Guided wave radar is ideal for smaller silos containing solids or liquids.

Bob or cable-based sensors:

A cable-based or bob-style sensor works like an automated tape measure but eliminates the need for climbing silos to take manual readings. It reliably, accurately, and repeatedly takes measurements at pre-determined time intervals or on demand.

Data can integrate with LAN or cloud-based software for monitoring and alerting when pre-determined high- or low-level thresholds are encountered.

Open-air radar:

80 GHz non-contact (open-air) radar is an ideal solution for precise targeting to avoid obstacle interference.] Open-air radar, also referred to as non-contact radar, transmits a radio‐frequency signal to the material surface, reflecting a small portion of the signal back to the sensor’s antenna.

The sensor processes this returned signal to determine the material’s level. Sensor models are available with different antenna types and operating frequencies (typically ranging from 6 GHz to 80 GHz).

Which model will perform successfully in an application depends on the vessel height, the material being measured, the presence or absence of dust, and the sensor’s operating frequency.

An 80 GHz radar measures in a very focused 4° beam angle that is ideal for precise targeting and works well in tall, narrow vessels and in silos that need precise targeting to avoid obstacle interference.

3D scanners:

3D level scanners use dust-penetrating acoustic technology to provide very precise volume accuracy. They can measure and map the material surface to detect irregular material surfaces, cone up/down conditions, or sidewall buildup.

A 3D scanner is unique because it can map the topography of the silo and create a computerised profile of its contents. They are proven to perform in high-dust environments where some other types of non-contact technologies struggle to perform reliably.

Multiple 3D scanners can be combined to measure the entire surface of large diameter silos as well as domes. Specialised software can enable viewing of all silos across an entire location or organisation.

Laser:

A laser level measurement sensor is used for level control, plugged chute detection, and monitoring buildup. It is a non-contact device that can be used in bulk solids, pellets, or granular materials of all material dielectrics in a variety of vessels.

The advantage of laser is it measures in a tight beam, making it suitable for use in very narrow vessels or constrained spaces. Laser can be pointed at an outlet to ensure timely replenishment of material or mounted near the sidewall to detect buildup.

Laser is ideal in low or no-dust environments. Some battery-powered models are available, making them useful in situations where wiring may be difficult.

Guided wave radar:

A guided wave radar is a sensor that suspends a cable down into the silo to measure liquids, powders and bulk solids with a dielectric constant greater than 2.1 in vessels up to 78’ tall. It utilises time domain reflectometry (TDR) to measure the distance, level and volume of material.

The sensor is immune to dust, humidity, temperature, pressure, and bulk density changes as well as noise present when filling or emptying the vessel. Guided wave is often used for smaller vessels containing ingredients or additives. It is a good complement to other types of continuous level sensors in a network.

Conclusion

Utilising level control sensors will save time, reduce risks, and improve the overall efficiency of your operation. A wide variety of sensors, accessories, and sensor configurations are available. The ROI of your sensor choice will depend greatly on your operation’s size and type, the number and size of vessels you use to store materials, and the type of materials being stored.

Additional considerations include how often you need to measure your material levels, who needs access to the data and how it will be shared, and – of course – your budget. Most sensor suppliers offer an online application worksheet addressing many of these questions to help evaluate your application.

Completing the worksheet is great preparation for working with a supplier to select the right continuous level sensor for your needs. Custom systems using a variety of sensors and software are easily configured working directly with a level sensor specialist.