WEIGH BRIDGE

One of the most important components of a conveyor scale system is the design of the weigh bridge itself. Regardless of the type of load cell used, a belt scale will not be able to weigh lightly loaded material and maintain its calibration for long if certain design features are not in place.

Secondary Lever

THAYER employs a secondary lever system, even though it cost more to do so, because it permits the following:

1. We can add mass (weight) to counterbalance the dead load (idler support frame, idlers, belts) and by using a secondary lever, we do not load down the suspension pivot.

2. The scale provides for complete mass counter-balancing of the dead load (idlers and belt) of the conveyor permitting the load sensor to react only to the net material load.

3. By positioning the load cell correctly, relative to the secondary lever we can match load cell size to the net loading. Only in this way can any capacity scale be supplied to the same high accuracy standards.

4. The resulting increased lever ratio of the secondary lever reduces idler deflection, providing additional immunity to errors associated with belt tension.

5. The secondary lever system utilizes stainless steel aircraft cables as flexural elements to transmit and FOCUS pure tension forces to the load cell. The cables, being non-extendable, but laterally yieldable connecting links, permit the lever to align itself under conditions of varying stringer distortion. This is a most significant feature. A belt scale must use the conveyor stringers as its mounting base. These stringers not only deflect under varying conveyor loads, but may also rotate (or twist). A suspension system having the least possible structural redundancy is therefore essential.

6. This unique system is not affected by dirt, shocks or vibration, and can withstand overloads in excess of 1,000 pounds without causing damage or affecting calibration.

THAYER’S RF Flexure Suspension (patented)

The axis position is permanent, being held in its horizontal position by the flexure plate and in its vertical position by the load rod which bears on the flexure plate, which in turn is bolted to the bottom side of the square and elevated suspension extension shaft.

There is insignificant rotational hysteresis. While the load rod may be likened to a dull knife edge (it is round), the flexure plate bearing surface directly in contact can rock without sliding through small rotational displacement.

The reaction to lateral forces creates an insignificant moment transfer to the weigh suspension (this is part of the patent). Since the flexure plate (which is hardened blue tempered steel) is also the upper bearing block of the pivot, tensile or compressive forces reacting to lateral forces therein have no moment arm distance to operate.

The Model LC-174 NTEP Certified Load Cell is a Strain Gauge “S” Beam Load Cell that is housed in an enclosure that has identical mounting dimensions to that of the LC-137.

Available in force ranges from 25 to 2,000 lbs with an overload protection of 300% of rated output.

THAYER Load Cell Utilization Factor

The distinct specification of continuous belt scale weighing applications and the unique environment and operational issues those applications typically encounter, places too many requirements on the load sensing system for any single technology to completely satisfy. Therefore, using THAYER’S exclusive FMSS technology in the design of its belt scale suspension system allows the choice of using either its LC‐137 LVDT Load Cell or its LC‐ 174 Strain Gauge Load cell. This puts Thayer in a unique position that allows us to offer equipment to match a wide range of applications such as light material loading, severe environmental conditions, and commercial certification.

Provides:

• Field adjustable mechanical TARE balancing of dead loads typically as high as 200 times NET loads, thereby providing the full utilization of the load cell force range.
• Reduces deflection of load receptor to a fraction of load cell deflection.
• Reduces zero shifting as a result of foundation distortion.
• Provides preferred access location of load cell for inspection or removal.
• Simplifies the application of test weights for calibration/performance verification.

Precision Belt Speed Measurement

Accurate belt speed measurement requires the use of a precision wheel and pulser. A spring is used to maintain proper contact pressure of the wheel with the tension side of the belt in all operating conditions. The THAYER belt travel pulser assembly includes a precision cast/machined wheel with a “pre-calibrated” circumferential tolerance of ± 0.05% and a high resolution digital transmitter. The transmitter produces pulses equivalent to 1/100 to 1/200 of a foot of belt travel. The speed pick-up wheel has a narrow face width so it is less susceptible to material build-up, which can result in speed measuring errors. Since belt stretch is not constant throughout the length of the conveyor, and therefore, can affect speed measurement, the speed pickup produces a more accurate speed signal than that which is produced by tail pulley mounted speed encoders.

THAYER Belt Scale Applications Program

THAYER is the only belt scale manufacturer that analyzes the customer’s conveyor and application data to predict “real-world” performance. The computer program essentially tailors each component of the scale and conveyor to maximize the performance of the complete system based on the specific requirements of the application.

We consider the parameter variations that are normally experienced in conveyor installations, the lack of dimensional precision of the conveyor components and installation imperfections occurring as the result of both the initial set up and the subsequent conveyor maintenance activities, the most logical approach to designing and installing high accuracy belt weighing equipment is to design for minimum error influences in every phase of the project. This involves conveyor analysis work to seek out preferred locations for load and speed measurements within a conveyor, suspension system configurations that are least affected by conveyor influences, particularly alignment factors (load deflection vs installed alignment conditions), and many other factors.

The typical computer analysis involves inputting eleven (11) key parameters which describe the application in sufficient detail to estimate accuracy for the installation as initially defined.

Major factors include:

• Conveyor design & Scale suspension design
• Location of load and speed sensors in relation to both conveyor terminal equipment and loading points
• Installed alignment conditions
• Duration and constancy of loading cycle
• Condition of rolling conveyor elements
• The uniformity and stiffness of the belt itself
• Condition and size of take-up apparatus
• The precision with which the system can be routinely calibrated & adherence to a calibration schedule
• Operating environment

Subsequent runs are performed to evaluate the effects under various conditions, using different belt scale weigh bridge configurations, weigh bridge locations, idler spacing, weights and locations of gravity take-up, etc.

Actual “bias error” (offset between THAYER totalized weight and check scale weight) and “as-found error” (random error, i.e. repeatability) can be calculated for a given conveyor application using Thayer’s belt scale performance math model.

This unique program was developed by THAYER, and is based on many years of experience in the field of high accuracy continuous weighing. The objective of the program is quite simple: To provide a means of producing a high performance Belt Scale installation.

WEIGH BRIDGE

One of the most important components of a conveyor scale system is the design of the weigh bridge itself. Regardless of the type of load cell used, a belt scale will not be able to weigh lightly loaded material and maintain its calibration for long if certain design features are not in place.

Secondary Lever

THAYER employs a secondary lever system, even though it cost more to do so, because it permits the following:

1. We can add mass (weight) to counterbalance the dead load (idler support frame, idlers, belts) and by using a secondary lever, we do not load down the suspension pivot.

2. The scale provides for complete mass counter-balancing of the dead load (idlers and belt) of the conveyor permitting the load sensor to react only to the net material load.

3. By positioning the load cell correctly, relative to the secondary lever we can match load cell size to the net loading. Only in this way can any capacity scale be supplied to the same high accuracy standards.

4. The resulting increased lever ratio of the secondary lever reduces idler deflection, providing additional immunity to errors associated with belt tension.

5. The secondary lever system utilizes stainless steel aircraft cables as flexural elements to transmit and FOCUS pure tension forces to the load cell. The cables, being non-extendable, but laterally yieldable connecting links, permit the lever to align itself under conditions of varying stringer distortion. This is a most significant feature. A belt scale must use the conveyor stringers as its mounting base. These stringers not only deflect under varying conveyor loads, but may also rotate (or twist). A suspension system having the least possible structural redundancy is therefore essential.

6. This unique system is not affected by dirt, shocks or vibration, and can withstand overloads in excess of 1,000 pounds without causing damage or affecting calibration.

THAYER Load Cell Utilization Factor

The distinct specification of continuous belt scale weighing applications and the unique environment and operational issues those applications typically encounter, places too many requirements on the load sensing system for any single technology to completely satisfy. Therefore, using THAYER’S exclusive FMSS technology in the design of its belt scale suspension system allows the choice of using either its LC-137 LVDT Load Cell or its LC-174 Strain Gauge Load cell. This puts Thayer in a unique position that allows us to offer equipment to match a wide range of applications such as light material loading, severe environmental conditions, and commercial certification.

The performance of a load cell and its instrumentation is specified on the basis of the load cell’s rated output. If the load cell is supporting a quantity of dead-weight (i.e. idlers, belting, suspension system) and has been further oversized to accommodate problems of overload protection, off-center conveying, shock, vibration and negative integration, then the amount of range left to do the job of weighing is only a fraction of the cell’s rated output. The percentage of the load cell’s rated output reserved for the actual job of weighing material is called the LOAD CELL UTILIZATION FACTOR.

Thayer’s “RF” Belt Scales with “FMSS” Force Measurement Suspension System mass counter balance technology assures better than 80% Load Cell Utilization.

Provides:

• Field adjustable mechanical TARE balancing of dead loads typically as high as 200 times NET loads, thereby providing the full utilization of the load cell force range.
• Reduces deflection of load receptor to a fraction of load cell deflection.
• Reduces zero shifting as a result of foundation distortion.
• Provides preferred access location of load cell for inspection or removal.
• Simplifies the application of test weights for calibration/performance verification.

On high capacity scales where it is impractical to apply the test weight directly to the end of the weighbridge because of the physical size of the test weight, a special arrangement of the secondary lever is used.

In this configuration, the test weight provides tare mass counter-balance in its “storage” position on the secondary lever and a test load of known value in its “calibrate” position. By taking advantage of ratios in the secondary lever, smaller, easily manageable test weight(s) can be used to produce significantly higher loading values. This method of applying the test weight does not introduce error on inclined conveyors. Since the test weight is on the scale at all times, its moments due to the sine component remains constant regardless of the test weight’s position on the lever.

The weight is always present on the secondary lever, which also serves as a means to counterbalance dead loads and control the force range presented to the load cell. In the movable poise weight design the weight resides in either one of two locating “V” notches, but is never added or subtracted from the lever itself.

In one position, the weight serves as “counterbalancing” weight for a portion of the dead load. In the other position, the weight serves as the calibration test load. This unique method, whereby the movement of the weight alone affords the means to apply a large effective test load, is the only practical and economical system known for calibrating “heavily loaded” conveyor scales.

THAYER’S RF Flexure Suspension (patented)

The axis position is permanent, being held in its horizontal position by the flexure plate and in its vertical position by the load rod which bears on the flexure plate, which in turn is bolted to the bottom side of the square and elevated suspension extension shaft.

There is insignificant rotational hysteresis. While the load rod may be likened to a dull knife edge (it is round), the flexure plate bearing surface directly in contact can rock without sliding through small rotational displacement.

The reaction to lateral forces creates an insignificant moment transfer to the weigh suspension (this is part of the patent). Since the flexure plate (which is hardened blue tempered steel) is also the upper bearing block of the pivot, tensile or compressive forces reacting to lateral forces therein have no moment arm distance to operate.

Precision Belt Speed Measurement

Accurate belt speed measurement requires the use of a precision wheel and pulser. A spring is used to maintain proper contact pressure of the wheel with the tension side of the belt in all operating conditions. The THAYER belt travel pulser assembly includes a precision cast/machined wheel with a “pre-calibrated” circumferential tolerance of ± 0.05% and a high resolution digital transmitter. The transmitter produces pulses equivalent to 1/100 to 1/200 of a foot of belt travel. The speed pick-up wheel has a narrow face width so it is less susceptible to material build-up, which can result in speed measuring errors. Since belt stretch is not constant throughout the length of the conveyor, and therefore, can affect speed measurement, the speed pickup produces a more accurate speed signal than that which is produced by tail pulley mounted speed encoders.

1RF-3ASG “Quarry King” Conveyor Belt Scale

The suspension system is longitudinally restrained and pivoted at the in-feed (approach) end on Thayer Scale’s proprietary RF Fulcrum arrangement, while the downstream end is supported from a single NTEP certified strain gauge load cell loaded in pure tension, protected from effects of all extraneous lateral forces (belt tension, friction, torsion, etc.). A key advantage is that the load cell can be quickly and easily removed and replaced without disturbing the weigh idler itself, thereby eliminating the tedious task is re-setting and aligning the idler, and conducting another material test upon re-commissioning. The non-weighed Bridge Element that supports the load cell also includes the supporting brackets for storing the Test Weight which can be easily moved to its “calibration” position on the suspension system whenever desired.

Precision Belt Speed Measurement

Accurate belt speed measurement requires the use of a precision wheel and pulser. A spring is used to maintain proper contact pressure of the wheel with the tension side of the belt in all operating conditions. The THAYER belt travel pulser assembly includes a precision cast/machined wheel with a “pre-calibrated” circumferential tolerance of ± 0.05% and a high resolution digital transmitter. The transmitter produces pulses equivalent to 1/100 to 1/200 of a foot of belt travel. The speed pick-up wheel has a narrow face width so it is less susceptible to material build-up, which can result in speed measuring errors. Since belt stretch is not constant throughout the length of the conveyor, and therefore, can affect speed measurement, the speed pickup produces a more accurate speed signal than that which is produced by tail pulley mounted speed encoders

Conveyor Belt Scale Integrator

Thayer Scale’s Model I-340 Conveyor Belt Scale Integrator is a full featured instrument specifically designed to match with Thayer’s single idler “Quarry King” Belt Scale. It performs the same functions as an instrument costing many times more without sacrificing accuracy that is associated with THAYER weighing products. Simplicity of use has always been a very important factor in designing an instrument and the Model I-340 has inherited all the time and labor saving methods THAYER has developed over the years.

The Model I-340 enables easy set-up, calibration and maintenance. Its intuitive menu interface is very easy to use. Step-by-step on-screen instructions guide the user through set up, calibration and customization of inputs and outputs. Multiple checks and balances built into the software virtually eliminates human error.

Virtual Weigh Span

As an added bonus, the Model I-340 Integrator contains special patented software package called “Virtual Weigh Span” Technology that has been specifically designed to be used with lower cost and lower accuracy single idler belt scales.

WEIGH BRIDGE

One of the most important components of a conveyor scale system is the design of the weigh bridge itself. Regardless of the type of load cell used, a belt scale will not be able to weigh lightly loaded material and maintain its calibration for long if certain design features are not in place.

Secondary Lever

THAYER employs a secondary lever system, even though it cost more to do so, because it permits the following:

1. We can add mass (weight) to counterbalance the dead load (idler support frame, idlers, belts) and by using a secondary lever, we do not load down the suspension pivot.

2. The scale provides for complete mass counter-balancing of the dead load (idlers and belt) of the conveyor permitting the load sensor to react only to the net material load.

3. By positioning the load cell correctly, relative to the secondary lever we can match load cell size to the net loading. Only in this way can any capacity scale be supplied to the same high accuracy standards.

4. The resulting increased lever ratio of the secondary lever reduces idler deflection, providing additional immunity to errors associated with belt tension.

5. The secondary lever system utilizes stainless steel aircraft cables as flexural elements to transmit and FOCUS pure tension forces to the load cell. The cables, being non-extendable, but laterally yieldable connecting links, permit the lever to align itself under conditions of varying stringer distortion. This is a most significant feature. A belt scale must use the conveyor stringers as its mounting base. These stringers not only deflect under varying conveyor loads, but may also rotate (or twist). A suspension system having the least possible structural redundancy is therefore essential.

6. This unique system is not affected by dirt, shocks or vibration, and can withstand overloads in excess of 1,000 pounds without causing damage or affecting calibration.

THAYER’S RF Flexure Suspension (patented)

The axis position is permanent, being held in its horizontal position by the flexure plate and in its vertical position by the load rod which bears on the flexure plate, which in turn is bolted to the bottom side of the square and elevated suspension extension shaft.

There is insignificant rotational hysteresis. While the load rod may be likened to a dull knife edge (it is round), the flexure plate bearing surface directly in contact can rock without sliding through small rotational displacement.

The reaction to lateral forces creates an insignificant moment transfer to the weigh suspension (this is part of the patent). Since the flexure plate (which is hardened blue tempered steel) is also the upper bearing block of the pivot, tensile or compressive forces reacting to lateral forces therein have no moment arm distance to operate.

THAYER Load Cell Utilization Factor

The distinct specification of continuous belt scale weighing applications and the unique environment and operational issues those applications typically encounter, places too many requirements on the load sensing system for any single technology to completely satisfy. Therefore, using THAYER’S exclusive FMSS technology in the design of its belt scale suspension system allows the choice of using either its LC‐137 LVDT Load Cell or its LC‐ 174 Strain Gauge Load cell. This puts Thayer in a unique position that allows us to offer equipment to match a wide range of applications such as light material loading, severe environmental conditions, and commercial certification.

Calibration

A belt scale should be thought of as a precision instrument and its performance should be quickly and easily checked. Thayer Scale can provide an accurate reliable calibration using a calibrating weight instead of test chains for all scale capacities. Thayer Scale developed and patented the first automatic calibration system in 1971.

The 3RFS-6 and 3RFS-8 use a test weight in the form of a round bar which resides in one of two positions (“V” notches) on an intermediate lever between the approach suspension and the load cell itself. This bar provides tare counterbalance in its “zero” position, and simulated calibration loading in its “span” position. This method of “test weight” application is referred to as the “moveable-poise” method, in contrast to the additive weight method.

Precision Belt Speed Measurement

Accurate belt speed measurement requires the use of a precision wheel and pulser. A spring is used to maintain proper contact pressure of the wheel with the tension side of the belt in all operating conditions. The THAYER belt travel pulser assembly includes a precision cast/machined wheel with a “pre-calibrated” circumferential tolerance of ± 0.05% and a high resolution digital transmitter. The transmitter produces pulses equivalent to 1/100 to 1/200 of a foot of belt travel. The speed pick-up wheel has a narrow face width so it is less susceptible to material build-up, which can result in speed measuring errors. Since belt stretch is not constant throughout the length of the conveyor, and therefore, can affect speed measurement, the speed pickup produces a more accurate speed signal than that which is produced by tail pulley mounted speed encoders.

Specialized Scale design assures reliable, accurate weighing.

The most important element of the FP Belt Scale is its scale system, which utilizes Thayer Scale’s “FMSS” technology (see below). The FP has a unique combination of features that make it ideal for low density belt weighing:

• High efficiency “dead Load” counterbalancing, up to 500 lbs.
• Load sensor sized to utilize its full range for “live load” only
• Calibration maintained under heavy overloading, 1,000+lb.
• Ultra-low deflection ( Non-tilting platform design for conveyor alignment stability.
• Provisions for built in automatic test weight.
• Easy to re-range in the field.

“FMSS” Scale Technology

A Force Measurement Suspension System (FMSS) is the arrangement of active mechanical elements interposed between the load receptor (belt) and load cell. Properly designed, the FMSS functions as a force vector filter that permits the sum of the chosen uni-directions force components to pass through the system to the load cell while blocking all other nuisance, erroneous or destructive force vectors.

“FMSS” FLEXURE PLATE SYSTEM

Flexure plate system eliminates all wearing parts, such as bearings, pivots and knife edges and is not susceptible to vibration. Flexure suspension system transfers all loading forces to a single load transducer, which accurately measures load regardless of load position. Most platform scales are not designed to be immune to side loading and/or tortional loading caused by the plant environment and by the movement of the feed screw, agitator, etc. These factors can cause poor accuracy and poor calibration stability. Thayer’s flexure system cancels all horizontal force vectors and also allows heavy tare loads (weight of feeder and hopper) to be completely mass counterbalanced , permitting load cell sizing based on net rather than gross weight.

Thayer Scale’s new Model i340 Conveyor Belt Scale Integrator is a full featured instrument specifically designed to match with Thayer’s single idler “Quarry King” Belt Scale. It performs the same functions as an instrument costing many times more without sacrificing accuracy that is associated with THAYER weighing products. Simplicity of use has always been a very important factor in designing an instrument and the Model i340 has inherited all the time and labor saving methods THAYER has developed over the years.

The Model i340 enables easy set-up, calibration and maintenance. Its intuitive menu interface is very easy to use.  Step-by-step on-screen instructions guide the user through set up, calibration and customization of inputs and outputs.  Multiple checks and balances built into the software virtually eliminates human error.

As an added bonus, the Model i340 Integrator contains special patented software package called “Virtual Weigh Span” Technology that has been specifically designed to be used with lower cost and lower accuracy single idler belt scales.

Imperfections in conveyor belting and its supporting elements can adversely affect weighing accuracy of belt scales. Virtual Weigh Span can be programmed to adjust for variations in the belt conveyor weighing system. Advantages include, higher degrees of accuracy and calibration to account for changes in the belt or belting system over time using non-mechanical adjustments. In addition, weight measurement error producing effects, some that may not be particularly known, may be reduced.

By selecting the Virtual Weigh Span feature it creates many of the performance benefits of having a multi-idler belt scale. With more idlers and corresponding longer weigh span, a belt scale becomes less sensitive to extraneous loading variations due to such things as splice-impact shocks, gust of wind, non-uniformity of belting weight, varying belt loading effects that are due to impressed belting curvatures (lack of flatness) that tend to decay or change inconsistently under operation, idler “wobble” effects due to T.I.R. (total indicator runout), and numerous other extraneous disturbances that can cause instantaneous measurement errors. Since a longer weigh span provides a greater degree of load averaging the scale’s response to loading changes is more gradual and its output signals used for downstream control actions (i.e. additive feeder control) exhibit slower rates of change that are more compatible with the response limits of the controlled downstream equipment.

Input Power Requirements

• Voltage Range: 120 to 240 VAC
• Frequency Range: 50 to 60 Hertz
• Phase Requirement: Single Phase
• Power Consumption: < 25 W
• Supply Protection: Fused

Environmental Requirements

• Area Classification: Non-Hazardous
• Operating Temperature: 14 to 149° F (-10° to +65° C)
• Operating Humidity: 10 to 90% Non-Condensing
• Storage Temperature: -4 to 185° F (-20° to +85° C)
• Storage Humidity: 5 to 95% Non-Condensing
• Altitude Operational: Up to 2000 Meters
• Altitude Storage: Up to 3000 Meters (70 kPa)
• Cooling Method: Natural Convection
• Pollution Degree: 2

Standard Dimensional Requirements

• Enclosure Type NEMA 4X-12 (IP66)
• 8.5″H x 10.5″W x 4.125″D (216 x 267 x 105 mm)
• Foot mounting kit adds 1.25” (31.75 mm) to height or width.

Load Sensor

• Strain Gauges: (Typical 3mV/V)
• Excitation: 5 VDC Alt Square Wave @ 20-675 Hertz, 62.5mA, 85-1.2K Ohms
• Return:4 to 10.1 mVDC for 25 to 75 % Rated Capacity ( mVDC *
• Excitation VDC * Loaded Percentage)
• Resolution: 24 Bit A/D Convertor

Speed Sensor

• Power Supply: +12 VDC, Max Current 250 mA
• Frequency Limits:33 to 7500 Hz for 0 – 100 % Speed

Quadrature Pulser

• Sensor Output: Dual Channel Line Drivers
• Resolutions Typical: Pulses per Revolution = 20, 200, 800 and 2000

Ring Gear Pick-up

• Sensor Output: NPN Open Collector
• Resolution Typical: Teeth per Revolution = 60

Inductive Proximity Pick-up

• Sensor Output: NPN Open Collector

Temperature Sensor

• Power Supply: +5 VDC, Max Current 1.5 mA
• Sensor Output: Digital pulse stream

Instrumentation Upgrade

If you are presently using THAYER Weigh Feeders and/or Conveyor Belt Scales equipped with earlier generations of THAYER instrumentation (I-128, ORT-132, ORT-132A, I-133, IFC-133, PI-164, PIC-168 or EZ-3200), or gravimetric feeders and conveyor belt scales supplied by other manufacturers, then you may benefit by upgrading to this latest technology.

Instrument upgrade kits can be installed and commissioned oftentimes using existing wire and conduit runs to reduce installation costs and with minimal impact to your operations and production goals.  No matter what your schedule we can work with you and your maintenance staff to minimize process downtime.

Since the S52 Series and Series 5200 families of instrumentation feature many of the same calibration routines, alarm messages, menu structures, and diagnostic tools as some of the previous generations of THAYER instrumentation, learning curves for new instrumentation are substantially reduced.

THAYER SCALE supplies comprehensive, detailed upgrade packages inclusive of all necessary hardware, drawings, manuals, programming data sheets and wiring/cabling requirements.

Contact us today for a free analysis of your existing gravimetric feeder and belt scale instrumentation.  Simply tell us how you want your process control equipment to work for you and we’ll show you how to get there!

Features and Benefits:

• Gain-In-Weight systems
• Loss-In-Weight Systems
• Continuous Weighing
• Major and Minor ingredient systems
• High accuracy load cell and scale controllers
• Recipe management and reporting.

GAIN-IN-WEIGHT SYSTEMS

THAYER Accumulative Ingredient Batch Scales are designed to accurately weigh solids and liquid materials ranging from highly fluid powders to corrosive chemical and ores.

Typical industries served: steel, aluminum, foundry, plastics, fertilizer, chemicals, food, cement, and many more.

Standard designs available in capacities ranging from 500 lb to 10,000 lbs. and bucket sizes from 10 to 100 ft3.

The batch scales can be fed by a front end loader, installed directly under storage silos or fed by screw conveyors, screw feeders, pumps or belt conveyors.

“FMSS” CABLE SUSPENSION SYSTEM

THAYER Cable Suspension Batch Scale has no equal when it comes to its ability to tolerate the unintentional operator abuse that accompanies frequent equipment clean out, setup changeovers, equipment re-positioning, and mechanical repair if necessary. This patented system utilizes a series of stainless steel cables in conjunction with Torque Transfer Tubes to accurately focus a force to a tension-type (single) load cell, which is completely independent of load position. The system is adaptable to most load cells whether they are of the strain gauge or LVDT type.

Because the system utilizes only static components, there are no active elements to maintain, even under severe operating conditions. The cable suspension system is inherently self-aligning to the direction of gravity, and therefore, is not affected by building or foundation strains. It can be hung from the ceiling or mounted on wheels without concern.

• No scale can take more abuse.
• Sustained sensitivity without maintenance.
• Inherently self aligning to gravity.
• Nullifies heavy tare loads.
• Adapts to all mounting arrangement.
• Tolerates heavy overloading.
• Withstands extraneous lateral shocks.
• Easily accepts Automatic Test Weight Lifter for calibration.
• Low Maintenance.
• Versatile and Flexible.

Secondary Lever

THAYER employs a secondary lever system, even though it cost more to do so, because it permits the following:

1. We can add mass (weight) to counterbalance the dead load (idler support frame, idlers, belts) and by using a secondary lever, we do not load down the suspension pivot.

2. The scale provides for complete mass counter-balancing of the dead load (idlers and belt) of the conveyor permitting the load sensor to react only to the net material load.

3. By positioning the load cell correctly, relative to the secondary lever we can match load cell size to the net loading. Only in this way can any capacity scale be supplied to the same high accuracy standards.

4. The resulting increased lever ratio of the secondary lever reduces idler deflection, providing additional immunity to errors associated with belt tension.

5. The secondary lever system utilizes stainless steel aircraft cables as flexural elements to transmit and FOCUS pure tension forces to the load cell. The cables, being non-extendable, but laterally yieldable connecting links, permit the lever to align itself under conditions of varying stringer distortion. This is a most significant feature. A belt scale must use the conveyor stringers as its mounting base. These stringers not only deflect under varying conveyor loads, but may also rotate (or twist). A suspension system having the least possible structural redundancy is therefore essential.

6. This unique system is not affected by dirt, shocks or vibration, and can withstand overloads in excess of 1,000 pounds without causing damage or affecting calibration.

WEIGH BRIDGE

One of the most important components of a conveyor scale system is the design of the weigh bridge itself. Regardless of the type of load cell used, a belt scale will not be able to weigh lightly loaded material and maintain its calibration for long if certain design features are not in place.

THAYER Load Cell Utilization Factor

The distinct specification of continuous belt scale weighing applications and the unique environment and operational issues those applications typically encounter, places too many requirements on the load sensing system for any single technology to completely satisfy. Therefore, using THAYER’S exclusive FMSS technology in the design of its belt scale suspension system allows the choice of using either its LC‐137 LVDT Load Cell or its LC‐ 174 Strain Gauge Load cell. This puts THAYER in a unique position that allows us to offer equipment to match a wide range of applications such as light material loading, severe environmental conditions, and commercial certification.

THAYER’S RF Flexure Suspension (patented)

The axis position is permanent, being held in its horizontal position by the flexure plate and in its vertical position by the load rod which bears on the flexure plate, which in turn is bolted to the bottom side of the square and elevated suspension extension shaft.

There is insignificant rotational hysteresis. While the load rod may be likened to a dull knife edge (it is round), the flexure plate bearing surface directly in contact can rock without sliding through small rotational displacement.

The reaction to lateral forces creates an insignificant moment transfer to the weigh suspension (this is part of the patent). Since the flexure plate (which is hardened blue tempered steel) is also the upper bearing block of the pivot, tensile or compressive forces reacting to lateral forces therein have no moment arm distance to operate.

Precision Belt Speed Measurement

Accurate belt speed measurement requires the use of a precision wheel and pulser. A spring is used to maintain proper contact pressure of the wheel with the tension side of the belt in all operating conditions. The THAYER belt travel pulser assembly includes a precision cast/machined wheel with a “pre-calibrated” circumferential tolerance of ± 0.05% and a high resolution digital transmitter. The transmitter produces pulses equivalent to 1/100 to 1/200 of a foot of belt travel. The speed pick-up wheel has a narrow face width so it is less susceptible to material build-up, which can result in speed measuring errors. Since belt stretch is not constant throughout the length of the conveyor, and therefore, can affect speed measurement, the speed pickup produces a more accurate speed signal than that which is produced by tail pulley mounted speed encoders.

THAYER Load Cell Utilization Factor

The distinct specification of continuous belt scale weighing applications and the unique environment and operational issues those applications typically encounter, places too many requirements on the load sensing system for any single technology to completely satisfy. Therefore, using THAYER’S exclusive FMSS technology in the design of its belt scale suspension system allows the choice of using either its LC‐137 LVDT Load Cell or its LC‐ 174 Strain Gauge Load cell. This puts THAYER in a unique position that allows us to offer equipment to match a wide range of applications such as light material loading, severe environmental conditions, and commercial certification.

WEIGH BRIDGE

One of the most important components of a conveyor scale system is the design of the weigh bridge itself. Regardless of the type of load cell used, a belt scale will not be able to weigh lightly loaded material and maintain its calibration for long if certain design features are not in place.

Secondary Lever

THAYER employs a secondary lever system, even though it cost more to do so, because it permits the following:

1. We can add mass (weight) to counterbalance the dead load (idler support frame, idlers, belts) and by using a secondary lever, we do not load down the suspension pivot.

2. The scale provides for complete mass counter-balancing of the dead load (idlers and belt) of the conveyor permitting the load sensor to react only to the net material load.

3. By positioning the load cell correctly, relative to the secondary lever we can match load cell size to the net loading. Only in this way can any capacity scale be supplied to the same high accuracy standards.

4. The resulting increased lever ratio of the secondary lever reduces idler deflection, providing additional immunity to errors associated with belt tension.

5. The secondary lever system utilizes stainless steel aircraft cables as flexural elements to transmit and FOCUS pure tension forces to the load cell. The cables, being non-extendable, but laterally yieldable connecting links, permit the lever to align itself under conditions of varying stringer distortion. This is a most significant feature. A belt scale must use the conveyor stringers as its mounting base. These stringers not only deflect under varying conveyor loads, but may also rotate (or twist). A suspension system having the least possible structural redundancy is therefore essential.

6. This unique system is not affected by dirt, shocks or vibration, and can withstand overloads in excess of 1,000 pounds without causing damage or affecting calibration.

THAYER’S RF Flexure Suspension (patented)

The axis position is permanent, being held in its horizontal position by the flexure plate and in its vertical position by the load rod which bears on the flexure plate, which in turn is bolted to the bottom side of the square and elevated suspension extension shaft.

There is insignificant rotational hysteresis. While the load rod may be likened to a dull knife edge (it is round), the flexure plate bearing surface directly in contact can rock without sliding through small rotational displacement.

The reaction to lateral forces creates an insignificant moment transfer to the weigh suspension (this is part of the patent). Since the flexure plate (which is hardened blue tempered steel) is also the upper bearing block of the pivot, tensile or compressive forces reacting to lateral forces therein have no moment arm distance to operate.

CALIBRATION

A belt scale should be thought of as a precision instrument and its performance should be quickly and easily checked. Thayer Scale can provide an accurate reliable calibration using a calibrating weight instead of test chains for all scale capacities. Thayer Scale developed and patented the first automatic calibration system in 1971.

The 8RF-8AR uses a test weight in the form of a round bar which resides in one of two positions (“V” notches) on an intermediate lever between the approach suspension and the load cell itself. This bar provides tare counterbalance in its “zero” position, and simulated calibration loading in its “span” position. This method of “test weight” application is referred to as the “moveable-poise” method, in contrast to the additive weight method.

Precision Belt Speed Measurement

Accurate belt speed measurement requires the use of a precision wheel and pulser. A spring is used to maintain proper contact pressure of the wheel with the tension side of the belt in all operating conditions. The THAYER belt travel pulser assembly includes a precision cast/machined wheel with a “pre-calibrated” circumferential tolerance of ± 0.05% and a high resolution digital transmitter. The transmitter produces pulses equivalent to 1/100 to 1/200 of a foot of belt travel. The speed pick-up wheel has a narrow face width so it is less susceptible to material build-up, which can result in speed measuring errors. Since belt stretch is not constant throughout the length of the conveyor, and therefore, can affect speed measurement, the speed pickup produces a more accurate speed signal than that which is produced by tail pulley mounted speed encoders.

THAYER Load Cell Utilization Factor

The distinct specification of continuous belt scale weighing applications and the unique environment and operational issues those applications typically encounter, places too many requirements on the load sensing system for any single technology to completely satisfy. Therefore, using THAYER’S exclusive FMSS technology in the design of its belt scale suspension system allows the choice of using either its LC‐137 LVDT Load Cell or its LC‐ 174 Strain Gauge Load cell. This puts Thayer in a unique position that allows us to offer equipment to match a wide range of applications such as light material loading, severe environmental conditions, and commercial certification.

WEIGH BRIDGE

One of the most important components of a conveyor scale system is the design of the weigh bridge itself. Regardless of the type of load cell used, a belt scale will not be able to weigh lightly loaded material and maintain its calibration for long if certain design features are not in place.

Secondary Lever

THAYER employs a secondary lever system, even though it cost more to do so, because it permits the following:

1. We can add mass (weight) to counterbalance the dead load (idler support frame, idlers, belts) and by using a secondary lever, we do not load down the suspension pivot.

2. The scale provides for complete mass counter-balancing of the dead load (idlers and belt) of the conveyor permitting the load sensor to react only to the net material load.

3. By positioning the load cell correctly, relative to the secondary lever we can match load cell size to the net loading. Only in this way can any capacity scale be supplied to the same high accuracy standards.

4. The resulting increased lever ratio of the secondary lever reduces idler deflection, providing additional immunity to errors associated with belt tension.

5. The secondary lever system utilizes stainless steel aircraft cables as flexural elements to transmit and FOCUS pure tension forces to the load cell. The cables, being non-extendable, but laterally yieldable connecting links, permit the lever to align itself under conditions of varying stringer distortion. This is a most significant feature. A belt scale must use the conveyor stringers as its mounting base. These stringers not only deflect under varying conveyor loads, but may also rotate (or twist). A suspension system having the least possible structural redundancy is therefore essential.

6. This unique system is not affected by dirt, shocks or vibration, and can withstand overloads in excess of 1,000 pounds without causing damage or affecting calibration.

THAYER’S RF Flexure Suspension (patented)

The axis position is permanent, being held in its horizontal position by the flexure plate and in its vertical position by the load rod which bears on the flexure plate, which in turn is bolted to the bottom side of the square and elevated suspension extension shaft.

There is insignificant rotational hysteresis. While the load rod may be likened to a dull knife edge (it is round), the flexure plate bearing surface directly in contact can rock without sliding through small rotational displacement.

The reaction to lateral forces creates an insignificant moment transfer to the weigh suspension (this is part of the patent). Since the flexure plate (which is hardened blue tempered steel) is also the upper bearing block of the pivot, tensile or compressive forces reacting to lateral forces therein have no moment arm distance to operate.

The Model LC-174 NTEP Certified Load Cell is a Strain Gauge “S” Beam Load Cell that is housed in an enclosure that has identical mounting dimensions to that of the LC-137.

Available in force ranges from 25 to 2,000 lbs with an overload protection of 300% of rated output.

LOAD CELL UTILIZATION FACTOR

The performance of a load cell and its instrumentation is specified on the basis of the load cell’s rated output. If the load cell is supporting a quantity of dead-weight (i.e. idlers, belting, suspension system) and has been further oversized to accommodate problems of overload protection, off-center conveying, shock, vibration and negative integration, then the amount of range left to do the job of weighing is only a fraction of the cell’s rated output. The percentage of the load cell’s rated output reserved for the actual job of weighing material is called the LOAD CELL UTILIZATION FACTOR.

Thayer’s “NAR” Belt Scales with “FMSS” Force Measurement Suspension System mass counter balance technology assures better than 80% Load Cell Utilization.

Provides :

• Field adjustable mechanical TARE balancing of dead loads typically as high as 200 times NET loads, thereby providing the full utilization of the load cell force range
• Reduces deflection of load receptor to a fraction of load cell deflection
• Reduces zero shifting as a result of foundation distortion
• Provides preferred access location of load cell for inspection or removal
• Simplifies the application of test weights for calibration/performance verification

An optional Thayer Scale patented ACCU-FLEX dual load-cell suspension system (scale) is sensitive for handling light loading applications in harsh environments. It is rugged, yet highly flexible.

The Model MTF includes an optimized inlet chute to achieve uniform material flow from storage bins. The correct inlet design produces maximum efficiency and low energy consumption.

ADVANTAGES

• Open or enclosed construction
• Modular design
• Easy to clean
• Easy to maintain
• Cost-effective
• Low to medium capacity

FEATURES

MATERIAL CONTAINMENT

FULL LENGTH ADJUSTABLE SKIRT BOARDS

Installation of skirt boards along the entire length of the conveyor totally confines the material flow channel which helps control dust. Skirt boards are tapered and flared from the inlet to the discharge to prevent pinching of material between the skirt and the belt.

HIGH SIDE WALL BELT

Corrugated sidewall belts are made of high-tensile rubber, which provides excellent flexibility, elongation and abrasion resistance. Can be combined with full length side skirts for highly free flowing materials.

INLET CHUTE

Inlet chutes are a major factor in achieving uniform material flow from storage bins. Careful consideration is taken in the design of the inlet section based on a given material density, particle size and handling characteristics. The correct inlet design produces maximum efficiency and low energy consumption.

PATENTED ACCU-FLEX SCALE

Thayer Scale’s patented ACCU-FLEX suspension system (scale) is sensitive for handling light loading applications. Flexure based design extremely robust, is not prone to damage, is out of the way for cleaning, and is not subject to tare build-up causing incorrect calibration.

AUTOMATED TEST WEIGHT LIFTER

An optional Automated Test Weight Lifter (ATWL) mechanism provides a means for applying a known test weight to allow completely automatic calibration. The calibration sequence can be initiated via the weigh belt instrument keypad or via a contact closure. A self-checking software algorithm in the weigh belt instrumentation prevents erroneous calibration. Test weight calibration eliminates the need for test chains.

BELT TRAVEL PULSER

Rugged speed sensor is coupled directly to the feeder tail pulley not the drive pulley and measures belt speed or belt travel.

WELDED FRAME, QUICK REMOVAL ACCESS PANELS

The Thayer Scale Model MTF weigh belt uses a rigid, box frame construction to resist deflection and deformation under heavy loads. Frame distortion adversely affects scale measurement performance.

Removable covers provide easy access, designed to meet EPA and OSHA standards. Side panels, if included, are removed with quick-release fasteners (no tools required).

DRIVE SYSTEM

Head and tail pulley are selected in accordance with CEMA standards, with lagging as required. Direct or chain drives are available.

SLACK BELT DESIGN

Low belt tension increases belt life, produces more stable measurement and eliminates the need for belt tracking devices.

BELT SCAPER

PRECISION CEMA RATED HEAVY-DUTY IDLERS