Reducing Level Detection Operating and Maintenance Costs with Dwyer’s Series DBOB Continuous Level Measurement System

As you know, Dwyer Instruments has a variety of level detection technologies – each with their own set of advantages and disadvantages.  One of our recent developments to our level detection product line offers our most robust level sensing method that may be used in 
practically every powder and bulk application imaginable.  Our Series DBOB Continuous Level Measuring System electromechanically combines the old fashioned, tried, and true method of determining powder and bulk solid levels using a weight and tape measure with 21st century technology, 4-20mA continuous level output signal, and an HMI (Human Machine Interface). 

The DBOB Series is a low maintenance, electromechanical device designed for the continuous measurment of level or volumes in silos, tanks, or hoppers.  Commonly refferred to as a yo-yo or plumb-bob system, our Series DBOB has several advantages over competing technologies and products.  The main advantage is that the DBOB reduces maintenance and improves reliability over other alternative level measurement systems.  It works by using a motor to gently lower a weight until it reaches the surface level of the material.  Once the weight reaches the material, an internal spring that is mechanically-linked to its spindle senses a reduced tension in the tape.  The sensing of reduced tension in the tape actuates a lever, which reverses the direction of the motor to raise the weight back up.  The tape spins a single pulley which is coupled to a microprocessor to process a 4-20mA signal that is accurate to within 1% of reading. 

It is important to understand the limitations and advantages inherent in any technology used.  The few problematic applications that do not work well for the DBOB Continuous Level Measuring System include: coating materials such as liquid tar in asphalt, glue, or molasses that dries and accumulates on the weight.  As material coats the weight, it becomes heavy and could prevent the motor from returning the weight from the material and generate an error message.  However, the DBOB level measurement may be used in unique applications that would otherwise be difficult or impossible.  The DBOB Continuous Level Measurement System may also be successfully utilized to determine the position of liquid-solid interfaces.  For example, it has been successfully used to determine how much un-dissolved salt is in a brine tank to maintain salinity and to determine how much sludge is at the bottom of a wastewater treatment activated sludge clarifier in order to effectively process waste.

Due to the mechanical nature of the DBOB Level Measurement System, it is impervious to many problems associated with capacitive, conductivity, ultrasonic, and radar level sensors.   Depending on the type of material, seasonal changes in relative humidity may change the dielectric constant and conductivity of powder and bulk products that have a capacity to absorb moisture.  Since capacitive or conductivity level sensors rely on constant dielectric and conductivity properties, capacitive and conductivity level sensors may need to be re-calibrated too often for some applications.  As powder and bulk material is piled into a silo, dust is often generated.  Ultrasonic and radar signals may reflect off of dust just the same as a pile of powder and bulk material.  Consequently, these technologies may not be suitable for dusty applications.  Since changes in material dielectric constant, conductivity, and dust do not affect the DBOB’s level measurement – that translates to reduced maintenance costs for you when using the DBOB.

Due to the electronic nature of the DBOB Continuous Level Measurement System, we utilize an easy-to-use HMI that makes setup and troubleshooting as intuitive as can be.  Error messages let the operator determine if the sensor weight is buried or jammed, a sensor tape is broken, and if service is needed when 90% of its expected lifetime has been used.  In order to reduce or eliminate the possibility of entanglement, a “maximum move distance” parameter may be adjusted so a weight does not get caught in an auger, piece of machinery, or anything else of concern.  Silo dimensions may be programmed so the DBOB sends a 4-20mA or 20-4mA signal proportional to volume or level height.  An external relay may be wired to the DBOB so measurements may be taken on-demand or across equal time intervals ranging from once every 6 minutes to once every 4 days.  In order to prevent the weight from being buried under product during one of its measurement cycles, measurement interruption terminals are provided that may be wired to an external switch that will return the weight to its upper stop position while material is being dumped into a tank, silo, or hopper.  Two relay outputs default to indicate a failure mode and that the weight is in its upper stop position and may be configured to provide a counting pulse output and reset pulse input for use with a PLC or counter.  Since the DBOB has the smarts to automate and help troubleshoot, that translates to reduced operating costs for you when utilizing the unit.

The Series DBOB level measurement technology clearly offers several advantages over competing technologies in most applications. What about competing products of the same technology?  Most notably, Dwyer Instruments standardizes on a tangle-free tape-based system that is wound on a single spindle rather than a cable-based system that is wound on a spool, which becomes entangled.  As the tape is wound back up on its spindle, two flat spring-loaded metal surfaces scrape off excess product in order to prolong the life of the DBOB.  Additionally, motor run-time is stored in non-volatile memory that is sufficient to let an operator know maintenance is required a decade or more in the future so no battery-backup is required.  Finally, upon power-loss, the DBOB automatically returns the weight to the upper stop position and resumes normal operation without the need of any operator intervention.

The Series DBOB Continuous Level Measuring System may be provided with various application-specific accessories as well.  PVC or SS weights with/without pins which help keep the weight from tumbling, tangling, and keeps material off of the tape may be ordered a-la-carte.  When working with ultra-low density materials, a “spider-weight” is available that has a higher surface area-weight ratio.  Mounting is a snap with its standard 1-1/2” NPT connection or an optional aiming flange which may be mounted on an incline for applications without a flat mounting surface.  Finally, an optional protective cover helps shield the already-weatherproof enclosure from the elements, dust, or corrosive bird waste.  This helps keep the DBOB in good condition for decades to come. 

The Series DBOB Continuous Level Measuring System quite often reduces overall costs of competing technologies that have a lower up-front cost, at the expense of considerable maintenance and operating costs.  With mechanical technology that operators trust, electronic capabilities that facilities need, and brand name recognition our customers have come to expect, Dwyer Instruments, Inc. Series DBOB will keep you trouble-free for decades to come.