Eeny, Meeny, Miny, Mo Sensors

“Within each point level sensor technology, there are so many options. It can be overwhelming. You don’t want to use a baseball bat to hit a hockey puck,” said Scott Bonine, BinMaster Sales Manager and industry veteran. “We’re one of those rare companies where you can dial a phone and talk to a human. We’ll come up with just the right sensor with you.”

In real estate, people chant, “Location, location, location!” Bonine says this principle also applies to sensors, as material and location must be considered during the selection process.

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Bonine says users` sensor research should start with an understanding of the difference between point level and continuous inventory sensors. 

"Point-level sensors alert you when material in the bin reaches a certain point,” he said. “You’ll want to stop filling a vessel when it’s almost full. These sensors` alerts are great for that. You may also want an alert at low levels to order more stuff.”

Continuous inventory sensors include non-contact, guided wave radar, cable-based sensors, ultrasonics, or 3DLevelScanners. These continuously measure as levels change. 

“Continuous level sensors are a step up for ongoing inventory management,” says Bonine. “But it`s always a good idea to use a point level indicator as a backup. It`s peace of mind.” 

Rotary Level Indicators

Rotaries are by far the most common point-level device for high- or low-level point-level indication in bins, tanks, and silos. They are versatile sensors used for nearly any material: from powders and granules as light as 2 lb./ft.³ to coarse, lump materials with bulk densities up to 150 lb./ft.³.

“Rotaries work in about any dry solid material,” Bonine said. “There`s nothing to calibrate. You might not realize how versatile a rotary can be or how many options there are. We offer 19 different paddles for very light to heavy materials, plus vertical, horizontal, and flexible extensions, heat tubes for high temperatures, and stainless-steel connection options for sanitary or corrosive applications. Mini versions of rotaries are good for small vessels and tight spaces.”

Rotary paddle indicators are simple. The paddle rotates until materials reach its level. The material presses the paddle, causing it to stop rotating; it then sends an alert to a control room or sounds a horn, illuminates a light, or displays on an alarm panel. When tied to process control, rotaries with a fail-safe feature ensure operators are alerted in the event of power or equipment failure.

A vertical rotary extension can extend the sensor as far as 12 ft. down into a bin, tank, or silo for high-level detection. This configuration is recommended for a center-fill vessel when the operation requires a specific amount of headroom.

Capacitance Probes

“I always joke that capacitance sensors have a special `spidey sense,`" said Bonine. “They don’t move, but they can feel when material hits the probe.”

Capacitance sensors operate by detecting the presence or absence of material in contact with the probe. It senses tiny changes in capacitance—the change in electrical charge—experienced when the dielectric constant of the material differs from the air. Capacitance sensors come in a huge selection of sizes, extensions included. Some consist of stainless-steel, while others are coated in Delrin for high-temperature vessels and chemical storage tanks.

Bonine advises keeping the probe as short as possible to avoid the possibility of material bending it—but bendable probes are also available to prevent damage. Heavy-duty probes are available for places like power plants and mining. When materials are changed often in a silo, the probe may need recalibration. If this isn`t ideal for your application, he’d recommend using a rotary instead.

Capacitance probes are made for a multitude of purposes. The sensors can be modified to operate in areas with excessive vibration. They are mounted on the top of tanks, sides of vessels, and in narrow spaces.

Vibrating Rods

Some sensors use the piezoelectric effect to measure pressure, temperature, and force, then convert these changes to electric charges. BinMaster has harnessed this potential within its vibrating rod level sensors to accurately measure dry bulk solid materials in bins, silos, and hoppers. A vibrating rod is the only point-level sensor that can detect sediment at the bottom of a tank.

“When measuring super-lightweight materials, users should certainly consider vibrating rods,” Bonine said. “Stuff like styrofoam won’t cause enough resistance to affect a rotary, so we point people to the vibrating rod. The trick is to make sure the material isn’t sticky or clingy, as that might cause false signals.”

Vibrating rod sensors excel in detecting extremely light, fluffy materials such as powders and flakes as light as 1.25 lb./ft.³. They can also be used for heavy materials, such as aggregate.

These sensors vibrate when no material covers the active rod. When the rod is covered with material, the vibration is restricted and the sensor sends an alert. When the material falls away from the rod, vibration restarts and the relay will switch back. Additionally, vibrating rods include fail-safe alerts when power is interrupted. 

BinMaster has advanced its vibrating probe products to the point that most sensors do not require calibration and can easily be adjusted to the desired sensitivity level.

Vibrating rods can be custom-manufactured for high temperatures (up to 482°F) and may involve remote electronics. Models can also be extended up to 13 ft. to fit custom lengths, allowing sensors to be utilized for high-level detection in a top-mounted application. Hazardous locations can be equipped with vibrating rods or forks manufactured with FM or CSA approvals.

Diaphragm Switch

A diaphragm switch—or pressure switch—was BinMaster`s first point level sensor and is still popular today.

These switches are affordable and highly reliable when used in free-flowing dry and granular materials. Models are available for ordinary and hazardous environments where there is a risk of combustible dust.

It works by activating a sensitive microswitch when the material reaches the level of the sensor in a bin. The diaphragm switch then sends a signal that can be used to alert to a high, medium, or low level in the vessel or start or stop a process. Diaphragm switches can be mounted internally or externally and with a variety of diaphragm materials.

Tilt Switch

A tilt switch is an affordable, reliable high-level indicator that is easy to install and requires no routine maintenance.

A hanging tilt switch is installed by suspending it from a flexible cable over a control point. Its principle of operation is quite simple: as material rises to the switch, the sensor tilts. A microswitch is activated when an angle of 15° is reached. These switches are routinely used in bins or silos, over a conveyor belt or open pit, or for plugged chute detection.

Alternatively, a fixed-mount tilt switch mounts on the top of a vessel through a process connection. It utilizes an angular motion that is transferred into linear motion to activate an electrical microswitch. This can be used for direct input to a control system or to activate a light or horn alarm. Fixed-mount tilt switches can be custom-made in lengths from 1–8 ft., depending on the distance from the top of the bin that an alert should be activated.

Newer, patented models are available in a mercury-free design for applications that prohibit the presence of the substance in their operations.

Myriad Mounting Options

Flexibility is a key attribute of point level sensors. They can be installed to trigger an alarm anywhere along the vessel wall, in the cone, or within a hopper, alerting to low levels for timely refills and adjusting for variances in seasonal high-level inventory fluctuations.

Still at “Eeny, Meeny, Miny, Mo?”

The easiest way to avoid mistakes is to connect with any BinMaster representative. More than sales, our professionals hold years of experience and will point you to the correct solution appropriate to your unique material and storage vessel requirements.