Advances in level sensor technology help to improve inventory management
Level indicators have been around for decades. From simple switches and rotaries, to advanced non-contact sensors, there’s no shortage of technologies to choose from. But there’s more to levels than just the sensor.
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. Manufacturers of bin level indicators have responded with new solutions to address those demands.
The good news is if your operation is small or large, has one silo or hundreds, has a single location or a global presence, there is a solution for you. The solution starts by determining your sensor needs and applying the right sensor for the material and vessel. Then, comes another set of considerations: Once you have all this data, how do you get it from your silos and all of your plants to where you need it, and what do you do with it when it gets there?
Here are some things to ask of your operation:
- Do you want point level alerts or inventory management?
- Is the data needed locally or at multiple locations?
- Do you need the ability to run reports?
- Where do you want your data stored?
- How long do you want to keep historical data?
- Who has access to the data? Does everyone have the same access?
- Does your data need to be secure or kept confidential?
- Do you want alerts for low or high level thresholds?
- Is mobile access to the data needed?
SENSORS FOR INVENTORY MANAGEMENT
When sensors are used as part of an inventory management system, there are different options available dependent on how an operation wants to use, secure and store the data.
Local or company-wide monitoring. An important consideration is the scope of the system. Is there a need to moni-tor just a few silos at a single location? Or, is it necessary to monitor all silos across an entire organization? Both are easily achievable and monitoring systems are very scalable, allowing additional silos to be added at a later time as operations grow and budget becomes available
Another decision to be made is where the data will reside. Options include storing the data locally on a corporate LAN or WAN and providing remote access via a VPN or using a cloud-based service for anywhere, anytime access via any device with an Internet connection. Both types of systems can be set up with varying levels of access and security.
Reports and historical data. For some operations, current data is all that is needed. However, many operations are using data for much more than identifying a full or empty condition. Level monitoring data is not only used in production, but also by purchasing and finance. Just-in-time replenishment practices and reducing safety stocks can be achieved using current and historical usage data.
Inventory valuation and financial reporting can be streamlined significantly using an operation-wide inventory management system. Historical reports, charts, graphs and other useful information can be generated using automated reports sent to key individuals on a routine basis.
Cloud-based applications. As with many corporate business applications, cloud-based inventory management is becoming a more popular option for manufacturing operations. Users today need anytime, anywhere data access from a variety of devices whether they are in the office, about the facility, or in a vehicle. Plus, they need it from their smartphone, tablet or PC.
Web-based monitoring solutions can take the data from a variety of different sensor types to a gateway that gets the data to the cloud for access from an internet site or phone app. Automated SMS text alerts and emails are a popular feature of cloud-based systems.
Software. For inventory management there are PC-based software programs compatible with sensors for measuring granules, pellets, flakes or dry powder ingredients as well as tanks containing liquids that may be on premises. The software can reside on a single PC or can be installed across multiple PCs on a local area network. If the company has a VPN, the data can be accessed from any site where the user has a connection to the company’s private network. Data from all sites resides securely on a server at a corporate office for monitoring inventory, making purchases, and preparing financial reports.
Text and email alerts. One of the most simple — and becoming more popular — types of alerts are sent via an email or an SMS text message. Generally these are automated messages sent to a smartphone, mobile device or desktop that simply alert to a high or low level threshold determined by the user. They are convenient for busy personnel who aren’t typically sitting at a desk, but attending to other parts of the operation. Texting and email services often are included as an option in inventory management software or cloud-based applications.
Consoles. Consoles are a very affordable and convenient way to monitor inventory. Generally, cable-based sensors are networked together with the data from one or multiple silos going to a single console. The dimensions of each vessel are input into the brains of the console and allow it to provide information about either the percentage full, the headroom distance, or convert the reading to a number of pounds or tons for each bin. Readings are set up on a time interval schedule and also can be initiated on demand by pushing a button. By simply scrolling through a keypad, the data from each silo can be noted. Consoles can store data and have a protective memory in the event of a power loss.
The upside of consoles is they are very economical and can install in a centralized protected area in the vicinity of the silos being monitored. Often, they are set at truck height so drivers can take readings before they load out. They are especially helpful when trying to determine which silos have capacity for filling or when they are nearing empty, such as with vendor manage inventory (VMI). The downside is that you can only view the data for one bin at a time. Consoles are frequently used in tandem with either a software program installed on the local network or with a cloud-based Internet application.
HMI or PLC. In many manufacturing operations, the control room is king. There is a vast infrastructure of equipment specifically designed to manage storage and process control equipment. Operations monitor and measure many different parameters such as flow, temperature, moisture, vibration, pressure, speed, position, and weight in addition to level. All information is centralized in a single location and is generally secured on a local network. It is commonplace in many operations for data from level sensors to be sent to a control room for processing and monitoring.
SENSORS AND SENSOR TECHNOLOGY
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, radar, or laser level sensors are commonly used in large storage silos.
Technologies such as guided wave radar can also be used in smaller silos containing solids or liquids. Ultrasonic sensors, pressure sensors, and float-type sensors can be used successfully in chemicals, fuels, water, or wastewater.
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 measurements to improve safety and efficiency with timely inventory data. They reliably, accurately, and repeatedly take measurements at pre-determined time intervals or on demand. Data is sent and cloud-based applications can also send text and email alerts when pre-determined high- or low-level thresholds are encountered.
3D scanners. A 3DLevelScanner provides continuous, non-contact level measurement using dust-penetrating tech-nology to provide very precise volume accuracy. It measures and maps 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 computerized profile of its contents. Advanced acoustics-based technology is proven to perform in high-dust environments where some other types of non-contact technologies struggle to perform reliably. A scanner can be used in silos as well as domes, warehouses, open bins, and piles.
A 3D scanner is ideal for silos with multiple filling and emptying points where the topography of the material is highly irregular. A 3D scanner can deliver 1% to 3% volume accuracy when mounted in the proper location and used in a silo that is less than 45 ft. in diameter. For silos greater than 45 ft. in diameter, a multiple scanner system can record measurement data from multiple devices and then combine the data to report volume to a personal computer and provide a single graphical representation of the tank contents. Scanners come equipped with software that displays the level and volume data in an easy-to-read format. The mea-surements are sent to a main display screen and includes data such as average, minimum, and maximum distances; level; temperature inside the vessel; and volume percentage. For operations with multiple silos, there is MultiVision software that allows for all silos to be monitored simultaneously from a single screen.
Non-contact radar. Non-contact radar can be used successfully in most liquids, but getting reliable performance in solids is much more challenging. There are radar level sensors designed specifically for application in solids or powders. Look for models with a high dynamic range and a narrow beam focus to ensure the best performance in tall silos, reflective materials, or materials with a low dielectric constant. Adjustable or swiveling mounts make it easier to aim the antenna to get the most accurate level readings. However, keep in mind that radar will only measure the distance to the material at one point, which may render volume estimates inaccurate in materials that pile unevenly in a silo.
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. It may also be appropriate for measuring opaque liquids in applications where the beam must be precisely targeted to avoid walls or structure. 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.
Guided wave radar. A guided wave radar is a sensor that suspends a cable down into the silo to measure liquids, pow-ders and bulk solids with a dielectric constant greater than 2.1 in vessels up to 78’ tall. It utilizes 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 complement to other types of continuous level sensors in a network.
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 is wired 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.
A simple option for point level alerts is an alarm panel. This is a display module that can handle multiple point level devices for high or low level alerts. When a full or empty condition occurs, the display module begins to beep and a light starts to flash. It tells you which silo has the alert and whether it is a high or low level alert, depending on how the display module is configured by wiring. Alarm panels can be used with rotary, diaphragm, capacitance probe, vibrating rod and tilt switch point level indicators.
Rotary. The rotary level indicator is the familiar workhorse of the manufacturing world. Fail-safe rotaries that alert to the device status are becoming the model of choice in many solids applications because continuous operation of the rotary is critical to the process. A fail-safe rotary will alert to a failure of the motor or loss of power and send an immediate warning or a visual indication that something has gone awry.
With a variety of paddles, extensions, and mounts, they can be applied in a variety of ways. Rotaries can be mounted on the sidewall of the silo or alternatively, can be mounted on the roof for high level detection. A vertical extension on a rotary can allow it to be extended up to 12 ft. down into the silo for high level detection. An adjustable rotary mount can be used to vary the height seasonally when less inventory might be desired. For side-mounting in cement-walled silos, there are vertical extensions designed for installation through thick bin walls. Collapsible, insertable paddles enable installation without entering the silo.
Capacitance probe. Capacitance sensors are designed for an array of applications and can be customized with different types of probes, lengths or extensions. There are thousands of configurations for hazardous locations, sanitary applications, flexible hanging probes, flush mounting, remote electronics, auto calibration, heavy duty, compact and bendable probes. These sensors may be used for high-, mid-, and low-level de-tection in bins, silos, tanks, hoppers, chutes, and other types of vessels in which solids or powders are stored, processed, flowing or discharged.
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. These rugged sensors often are 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 or pressure switch is a very basic, affordable level alert commonly used as a high-level alert on the silo wall. There are models for either internal or external mounting. Internal mounting doesn’t require a hole to be cut in the bin wall, while 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 to install it. There are models for non-hazardous locations or with explosion proof certifications. Pressure switches are also used for plugged chute detection.
Tilt switch. A tilt switch is a high-level indicator designed to install easily and require no routine maintenance. The switch is activated 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.
JENNY NIELSON CHRISTENSEN, MBA, is vice president of marketing for BinMaster, a manufacturer of continuous level sensors, point level indicators, liquid level sensors, flow and dust detectors, temperature and moisture monitoring systems, and a diverse range of data monitoring solutions. You can email her at firstname.lastname@example.org