Choosing the right type of scale for your weighing operation
Today's hydraulic truck scales combine state-of-the-art electronics with virtually indestructible hydraulic load cells for a weighing system with no electronics in the scale platform, which is the area of greatest potential problems and failures. The design of a hydraulic truck scale allows the weight signals from the load cells via pressure transducers to be totalized and converted to a single data signal which, in turn, is sent to the indicator for viewing and further system processing by the operator.
When selecting scales or upgrading your weighing operation, there are many advantages to choosing a hydraulic truck scale, including the fact that hydraulic scales are considered to be extremely accurate in high-capacity applications. They also have several advantages over a traditional truck scale which uses analog strain gauge or digital load cell technology.
Lightning strikes and power surges
In locations subject to lightning strikes and power surges, hydraulic truck scales perform better than both digital and analog scales because the load cells are immune to damage resulting from transient voltages.
Unlike traditional truck scales, which use digital or analog strain gauge load cells, hydraulic load cells do not require power in the scale and also don't have strain gauges or wiring. They will not be affected by lightning strikes or power grid changes - one of the most common reasons for load cell failures.
Hydraulic truck scales use hydraulic tubing from the load cells and are terminated at the scale totalizer by a non-conducting rubber line. This creates a barrier of protection which prevents lightning from travelling into the scale house where the digital weight display is located.
Water and high-pressure washdowns
If your weighing operation is in an area that frequently floods and the scale is continuously submerged in water for an extended period of time, then a hydraulic scale will prevent the water from damaging the weighing components in the scale. Hydraulic truck scales use hermetically sealed load cells that are welded together and then pressure tested to ensure there are no leaks. By keeping the hydraulic fluid inside the load cell, water is kept out, preventing damage that would shut down a traditional truck scale using digital or analog strain gauge load cells.
Another benefit of a hydraulic truck scale is that the scale's weighing components will not be damaged by the high-pressure washdown that is routinely performed on scales used in the solid waste industry to remove dirt and grime.
Operations subject to shock loading
In any operation, there will be times the scale is subjected to shock loading or vibration. Hydraulic truck scales perform well when this happens due to the design of the load cells. Both analog and digital load cells use a steel spring element to sense the load. Applying a shock load, even one less than the capacity of the load cell, can and will cause permanent damage to the load cell rendering it unusable. Hydraulic truck scale load cells, on the other hand, act much like a shock absorber on your automobile, dissipating the shock load or vibration in the hydraulic fluid and preventing damage to the scale that would result in costly downtime.
Extreme temperatures can affect a traditional truck scale's circuit boxes and cause problems with the load cells. Fortunately, there are no electronic components in hydraulic truck scales, allowing them to operate over a wide range of temperatures.
Instead of using electronic components, hydraulic truck scales have load cells that use aircraft-quality hydraulic fluid. This type of hydraulic fluid allows a hydraulic truck scale to continue to operate accurately and efficiently in environments with temperatures as low as -65 degrees F (-54 degrees C) and up to 275 degrees F (135 degrees C) resulting in a truck scale that will never stop working because of weather extremes.
Usage in hazardous areas
Hydraulic truck scales are ideal for any hazardous environments where explosive materials are present and where a spark could potentially set off an explosion. Furthermore, hydraulic truck scales are a safer alternative in any operation with a pit-type scale, where fuel or other flammable materials leaking from a vehicle and collecting in the scale pit can be ignited.
Traditional truck scales using analog or digital load cells must take extra precautions and use barrier strips to limit the energy to the scale or explosion-proof enclosures to contain the explosion. Those steps are not necessary when you use a hydraulic truck scale. Because hydraulic truck scales contain no electrical circuitry, there are no electrical currents, and therefore, no chance of an explosion-causing spark when used in an explosive atmosphere.
With all the components that require power located in the scale house and absolutely no power in the scale itself, hydraulic truck scales are inherently safe and highly recommended for hazardous environments.
Load cell output
Digital truck scales have the ability to display weight data from each load cell and can alert the scale operator or service technician of a potential problem before the scale weights are affected. Some hydraulic truck scales are available with the same type of load cell controllers that perform the same functions as found in digital truck scales. These controllers digitize each hydraulic load cell output independently allowing the operator or technician to view the outputs of each load cell.
Software is also available to alert the operator when an excessive shift in the no-load output of one or more cells is detected prior to affecting the accuracy of the scale. Another advantage of a hydraulic truck scale with this type of load cell controller is quick and easy calibration.
Legal and metrology standards
Scales used in commerce, where money is exchanged based on scale weight, must have a National Type Evaluation Program Certificate (NTEP) to verify that they comply with the requirements for use in trade. Just like their digital counterparts, today's hydraulic truck scales have been thoroughly evaluated and comply with the National Institute of Standards and Technology (NIST) Handbook 44 requirements for Class IIIL scales for use in commerce.
Cost of ownership
The technology used in hydraulic truck scales has a long history of being used in scales, much longer than either the strain gauge or digital technology used in traditional truck scales.
Although hydraulic truck scales have not been as popular as the less expensive traditional truck scale, when the costs of ownership are figured in, the hydraulic truck scale is clearly less expensive to own and maintain.
Hydraulic truck scales are easy to maintain as there are very few moving parts. It's also easy to spot any leakages and therefore easy to know if there are any maintenance issues. With virtually no moving parts, the life expectancy of a hydraulic truck scale can be 30 or more years.
Most manufacturers of hydraulic truck scales offer a lifetime warranty on the primary components (the hydraulic load cells) against damage from voltage surges and water damage, which are the two most common reasons for the failure of strain gauge and digital load cells.
With a lifetime warranty on the primary components of the hydraulic truck scale, components that are waterproof, shockproof, explosion-proof, and resistant to both caustic and corrosive environments, you will never have out-of-your-own-pocket expenses to replace these due to damage or malfunction.
Steve Hosp is a technical writer at Cardinal Scale Manufacturing Co.