An Uncommonly Effective Technology for Difficult Weighing Applications

Hydrostatic™ Technology

Hydrostatic™ technology, an Emery Winslow exclusive, combines state-of-the-art electronic instrumentation with virtually indestructible Hydrostatic load cell weight sensing for a system with no electronics in the area of greatest potential abuse - the scale platform. Hydrostatic™ design allows the sealed Hydrostatic weight signals to be transmitted to a clean, controlled area where the signals are totalized and converted into a single electronic signal, which in turn drives the scale's digital weight indicator.

Hydrostatic™ Weighing System Sketches #1 and #2 are simplified schematics of a typical multi-load weigh system. Sketch #1 is an electronic load cell schematic and Sketch #2 is a Hydrostatic™ load cell schematic.

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If your operations depend on load cells, choose the only weighing system that guarantees they never need to be replaced.

As you can see, the system schematics appear to be similar. The significant difference is the placement of the summing network. In a typical Hydrostatic™ weigh system, the summing network (Summing Totalizer) is located in a protected environment, such as a control room or scale house. The electronic load cell summing network (referred to as the summing board) is located along with the electronic load cells in the same environment endured by the load receiving element.

In an electronic weigh system, the electronic load cells, cabling and summing boards ARE environmentally sensitive. In a Hydrostatic™ weigh system, the load cells and tubing ARE NOT environmentally sensitive.

The first environmentally sensitive component in the Hydrostatic™ weigh system is the electronic transducer, a Summing Totalizer component. By placing the Summing Totalizer away from the scale load receiving element and remote from a hostile environment, it is secure against damage and defective performance.

The basic premise of the Hydrostatic™ weigh system is: Hydrostatic™ load cell systems isolate all environmentally sensitive components in a safe and friendly location.

The ability to neutralize the effects of the environment upon weigh system environmentally sensitive components is a major advantage of Hydrostatic™ technology.

Hydrostatic™ Components

In a truck scale application, there are usually four (4) to ten (10) Hydrostatic load cells located underneath the load receiving element (weigh bridge), depending upon weigh bridge length and capacity. Each Hydrostatic load cell is connected to the Summing Totalizer with high pressure copper or stainless steel tubing. The Hydrostatic load cell output, measured in pounds per square inch (PSI) is transmitted to a Summing Totalizer. The function of the Summing Totalizer is to sum the pressure inputs from each load cell and convert the sum to a Millivolt (mV) signal, directly proportional to the sum of the Hydrostatic load cell outputs. The mV output is captured, digitized and displayed on a digital weight indicator. Sketch #3 illustrates a typical Hydrostatic™ multi-cell weigh system.

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Hydrostatic™ Load Cell

The Hydrostatic load cell is basically a simple mechanical mechanism which functions according to known Laws of Physics. It consists of a piston, a base, a cylinder and a diaphragm. A thin film of fluid is sandwiched between the base and the diaphragm. The piston presses against the diaphragm. The result is only a small amount of fluid is required (less than one (1) pint of fluid used in a 70 foot truck scale). Each Hydrostatic load cell type is designed with an exact "acting area" - a known value in units of square inches. For example, when a known weight is applied to a Hydrostatic load cell with a known "acting area", the output in PSI is predictable. A 50,000lb weight applied to an "acting area" of 50 square inches will have an output of 1,000 PSI.

The formula is:

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The secret, of course, is to design the Hydrostatic load cell with a linear relationship between weight applied and pressure output. For example, if 50,000lbs yields 1,000 PSI, then 25,000lbs must yield 500 PSI and 100,000 must yield 2,000 PSI. Sketch 4 illustrates the principle components in a Hydrostatic load cell:

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Sketch #5 illustrates the Emery Winslow Model 136 – 75,000 lb. load cell used in truck scale applications. This Hydrostatic cell type is also used in high capacity tank weighing, floor scales and custom applications:

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The load cell piston moves only vertically. This is accomplished with a stayplate shown on the piston top and a bridge ring on the piston bottom. The vertical position of the piston relative to the base plate is measured through gauging holes shown on Sketch #5. There are three (3) gauging holes located 120 degrees apart. A simple feeler gauge is used to measure proper piston motion. The gap in the Model 136 truck scale load cell measures between 0.027” and 0.033” for normal operation.

The Hydrostatic load cell has complete immunity from water, lightning, rodents, barometric pressure changes and RFI/EMI interference. Also, because the Hydrostatic load cell is non-electric, it can be used with 100% safety in explosive environments. Further, Hydrostatic load cells can be manufactured from mild steel or exotic metals, such as titanium and thus utilized in the severest of corrosive environments.

Because the Hydrostatic load cells have virtually no moving parts, life expectancy is long - surviving 30, 40 and more years.

During normal Hydrostatic load cell operation, the Hydrostatic fluid remains static within the predetermined compressibility of the fluid. The nature of this action is to filter out vibration and shock loading, thus making the Hydrostatic load cell suited to tough, rough, shock loading applications.

Finally, a Hydrostatic load weigh system can be sized to meet the exact requirements of the application. The unique Summing Totalizer has the capability of maximizing the millivolt signal strength based upon total system loading; not based on individual load cell capacity.

Load Cell Signal Lines

As explained and illustrated in Sketches #1, #2 and #3, each Hydrostatic load cell is connected to a Summing Totalizer by either high pressure copper or stainless steel. Connection points are a very high quality pressure fitting, capable of tolerating up to 15,000 PSI a safety factor of approximately 10. These fittings are either brass or grade 316 stainless. These same quality fittings are routinely used on high pressure Hydrostatic systems throughout process industries.

Summing Totalizer

The Summing Totalizer is a primary component in a multi-load cell Hydrostatic™ weigh system. Hydrostatic load cells have been used in industry for decades, but until the development of the Summing Totalizer, multi- Hydrostatic load cell weigh systems were not suited to the rigorous accuracy demands of NTEP and the National Institute of Standards and Technology (NIST). In its simplest form, the Summing Totalizer converts the output pressure of each Hydrostatic load cell to a force, sums the forces and converts the sum of the forces to a millivolt output signal. The Summing Totalizer is composed of a series of Hydrostatic receiver cells, each accepting the PSI from its assigned Hydrostatic load cell. The PSI input is converted to a vertical force measured in pounds and summed in the Summing Totalizer. Sketch #6 is a schematic illustration of a four (4) cell Totalizer:

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The Force Frame applies the load to a single high precision electronic strain gage transducer, generating a millivolt output proportional to the sum of the Hydrostatic load cell pressure output.

Sketch #7 illustrates four (4) Hydrostatic load cell inputs to a Summing Totalizer:

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Assuming a 70,000 lb. weigh system; each receiver cell in the Summing Totalizer accepts the output pressure from its Hydrostatic load cell; the sum of the four (4) producing a force used to calculate the value of the weight on the receiving element (weighbridge or platform) of the scale. The design of the Summing Totalizer directs all the forces vertically, with zero side loading to disturb readout accuracy.

And finally, the electronic transducer is sized to maximize output voltage - providing maximum signal strength for high resolution and sensitivity. It makes no difference how the loading is distributed among the four (4) Hydrostatic load cells. For instance, cell A1 could be loaded to 60,000lbs, cell B1 and C1 at 3,000lbs and D1, at 4,000lbs - and the system would still read 70,000lbs just as accurately as in Sketch #7's weight distribution.

Finally, the Summing Totalizer offers a significant advantage over an electronic load cell system should a load cell be damaged and in need of replacement. In the rare occurrence of a Hydrostatic load cell failure, a replacement load cell can often be installed with no need to recalibrate. Sketch #7 illustrates that the Summing Totalizer mV output senses no change should a load cell be replaced with another cell of equal acting area. This can be particularly important in process control operations where material already "on stream" could be lost if a load cell fails.

Outdoor Environment

Lightning, rain, flooding, snow, barometric changes, temperature extremes, hurricanes and tornadoes, seismic effects and other natural causes are all elements that affect outdoor weighing systems. When these conditions occur in severe form, the effects on unprotected weighing systems can be catastrophic.

By far the most effective way to prevent catastrophe from striking an outdoor weigh system is to utilize scale devices that have total immunity to these natural events. The most damaging natural forces are lightning and water. These two natural forces account for the destruction of tens of thousands of electronic load cells annually. The great Mississippi flood of the early 1990's destroyed hundreds of electronic load cell truck scales and railroad track scales. The Hydrostatic™ truck and track scales were unharmed. When the water receded, the scales performed as if there had been no water. All that was necessary was to wash away the mud and silt and the Hydrostatic™ scales were back in business.

Outdoor tank/hopper vessels, truck scales and railroad track scales are often the first to be struck by lightning.

In addition to damaging electronic load cells, the effects of lightning frequently damage summing boards and instrumentation via electrical cable that electrically connects the load cells to the rest of the system.

Not so in Hydrostatic™ systems. Lightning that strikes the vessel or weighbridge WILL NOT damage the Hydrostatic load cells nor the Summing Totalizer nor the Instruments. Sketch #8 illustrates how a Summing Totalizer is inexpensively isolated from the damaging effects of a lightning strike.

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Much less frequently, but still a possibility, lightning damage to scale instruments via the power source lines can occur. Although damage cannot be 100% prevented, lightning resistors are nevertheless recommended.

The most common outdoor scales in terms of numbers are:

Tank and Hopper Scales
Truck Scales
Railroad Track Scales

Whenever an installation is located outdoors, Hydrostatic™ is clearly the better choice.

Indoor Environments

Some indoor environments are benign and friendly to weighing systems. However, there are indoor environments that are hostile and unfriendly to weighing systems and these applications cause greatest harm to scales.

Indoor environmental conditions of concern are:

Where washdown with water or high temperature disinfectant solutions is common.
Where hazardous gases or explosive dusts pose the threat of an explosion.
Where corrosive conditions demand metals such as grade 304 or grade 316 stainless steel, titanium, Monel, Hastelloy, aluminum or even exotic plastics.
Where vibration and shock loading is part of the process.
Where lightning or electrical abuse occurs, or where electrical surges from arc welding is a possibility.
Where RFI/EMI electrical noise is extreme.
Where temperature variations are extreme.

With such indoor environmental conditions, Hydrostatic™ is a better and more cost effective solution for the following reasons:

All Hydrostatic load cells have 100% immunity to water. All Emery Winslow Hydrostatic load cells carry a Lifetime Guarantee against failure from water.
All Hydrostatic load cells have 100% immunity to explosive gases and dusts.
All Hydrostatic load cells can be manufactured from a material of choice to overcome severe corrosion.
Hydrostatic™ weigh systems inherently perform well in environments of shock and vibration.
All Hydrostatic Guarantee against failure from lightning or electrical abuse.
All Hydrostatic load cells have 100% immunity to RFI/EMI noise.
All Hydrostatic load cells have 100% immunity to failure from rodents.
Select Hydrostatic load cells function in temps ranging from -50 degrees F to 450 degrees F.

Indoor scale types available with Hydrostatic™ technology are:

Bench and Floor Scales
Tank and Hopper Scales
Blender/Mixer Weigh Systems
Monorail Weigh Systems
Crane Scales
Custom Engineered Weigh Systems

Industries

Food and Chemical Industries are common users of Hydrostatic™ weigh systems. Transportation, Agriculture, Fertilizer, Steel and Metals, Highway Vehicle Control, Airplane Industry and many more use Hydrostatic™ technology. These industries typically have environmental factors that "strain" electronic load cell technology, frequently exceeding their limit of endurance. The result is a costly replacement or retrofit.

With Hydrostatic™ technology the toughest environmental factors are neutralized. Because Hydrostatic load cells have all but eliminated wear points, life expectancy is very high. A ten (10) year warranty on the Emery Winslow truck scale Hydrostatic load cell against failure from defects in material and workmanship speaks to the reliability in high usage installations.

Summary

Hopefully, we have increased your curiosity about Emery Winslow Hydrostatic™ Weighing Technology. Although we wish Hydrostatic™ were the solution to all weighing problems, we fully understand its limitations. Perhaps its severest limitation is the cost of Hydrostatic™ versus electronic equivalents. It is a more costly technology and thus cannot effectively compete on a cost of purchase basis.

However, when the cost of a Hydrostatic™ product is compared to an electronic equivalent on the "cost of ownership" basis, it clearly becomes a best buy.

Emery Winslow has manufactured many thousand Hydrostatic™ weigh systems utilizing tens of thousands of Hydrostatic load cells over many decades of activity. Emery Winslow does not "enjoy" a load cell replacement market, whereas the electronic load cell replacement market is tremendously large and extremely profitable to the manufacturers of electronic load cell scales, Emery Winslow is content to make profit on Hydrostatic™ weigh systems sold to an increasing number of new customers.

We customize any scale to meet your needs!

Call: (800) 891-3952

Learn About Emery Scale’s Hydrostatic Load Cell Advantages