The Guide to Scale Service and Repair

Scale maintenance and repair is something that is brought up whenever someone is looking to buy a large industrial scale. Usually it is met with a question like “how often should I have my scale serviced?”, which generally is every 6 months, but depending on environment, frequency and other factors, scale service could be done every 3 months or every quarter.

It is important to consider the number of weigh-ins, climate and the value of the product being weighed, as these can all have an impact on the frequency of maintenance your scale needs.

Aside from the actual calibration, most of the inspection will consist of a visual inspection of the scale, foundation and surrounding area. Depending on the condition of the scale and the surrounding parts will determine what services will be needed.

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Foundation

Like any structure if there is a poor foundation, then the entire structrue will be unstable. A truck scale foundation is no different. No matter how tough and durable a scale is, it will be at risk of failure if the foundation is not good. Cracked foundations can lead to movement or settling which causes chronic calibration errors, which in turn adds more profit loss due to downtime.

If there are any cracks in your foundation, then you should address it asap. Allowing small cracks to become bigger can possibly require you to remove part or all of the foundation, and force you to pour an entirely new foundation.

When a scale tech arrives at your site for service, cleaning or any type of maintenance, then they are going to give the scale a full visual inspection, and cracks in the foundation is one of the things that they search for.

Weighbridge

The weighbridge takes the bulk of the damage when weighing trucks. Generally truck scales are outside and are subject to the elements. It is a good idea to check for rust, on the surface and all around the weighbridge. Rust can cause the structure to not be as stable and can cause a lot of problems if it is not sorted in a timely manner.

Binding is also a common cause of inaccuracies in truck scales. With a lot of trucks being weighed daily, there is a high chance that rocks and other debris can fall off the truck and get itself lodged in between the foundation and the deck. It is a good idea to ask your scale tech about t-stripping. Installing t-strip molding between the two can help keep debris from getting caught or falling down into the scale. This may be a good precaution to take to help decrease binding incidents.

Checking Devices

Other than the foundation and weighbridge, the scale has other parts that need to be checked to ensure your scale is operating properly. Other aspects are the junction box, load cells, cable, indicator, etc. All of these devices need to be operating for the scale to get complete and accurate measurements.

If your scale has checking devices, make sure they are working properly. Inspect check rods to make sure the attachment points are solid. Inspect the bindings and hardware to ensure jam nuts are tight and that rods are level and free of debris.

Load Cells

Load cells are definitely at risk of getting debris and moisture in the electronic section of the load cell. The load cell area may contain dirt and debris that has built up since the scale’s last check. Load cells must have clearance to deflect through their capacity range. The same debris that can bind the scale deck can also keep the load cells and suspension components from moving freely. So it is a good idea to try and keep that area as clean as possible.

You will also want to check load cell cables for damage and if the seal has been degraded. To combat this problem, some manufacturers offer rigid or flexible metal conduit to run the cable through, providing a layer of protection that’s nearly impervious to damage from rodents.

One more thing to note is that during cleaning, if your load cell is electronic then you want to be careful about where you spray. It can cause damage to the internals of the load cell. If you are using a hydrostatic scale then you don’t have to worry since there are no electronics in a hydrostatic scale.

Junction Box

The junction box (J box) is one part of the scale that can surprisingly still get a lot of moisture and debris inside of it. If the J box is not operating correctly then you will get incorrect readings. This occurs from air exchanges, heating and cooling cycles, and over-aggressive washing that damages sealing components that haven’t been properly maintained. If left unchecked, wiring terminals and other components in the enclosure can corrode.

During the visual inspection, the scale tech will follow the aforementioned steps to check and be sure there is no moisture, debris or frayed wires in the J box.

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Closing Words

At American Scale we strive to bring you informed and useful content on all things scale systems related, including products from the top scale manufacturers. Be sure to check out our truck scale articles about truck scale foundation or how much do truck scales cost. We even have a guide to warranties. To learn more about bench scales, it would be good to check out our other articles such as “Bench Scale Basics'' and “How Much Does A Bench Scale Cost?”. These articles will help with the basics of bench scale ownership. Also, take a look at our“Common Problems With Bench Scales'', to help prolong the lifespan on your scale.

Truck Scale Cleaning Guide.

The Importance Of Cleaning Your Truck Scale.

Keeping your truck scale well maintained and clean is an important part of truck scale ownership. Not only is it good practice to keep your weighbridge clean, it also helps you to have a productive maintenance schedule for your scale. This will help significantly reduce the risk of downtime and inaccurate weighing.

What it means to clean.

Cleaning your truck scale does not mean simply spraying the deck with some water, it also means visually inspecting the scale for any loose or missing parts that could contribute to an inaccurate weight. When discussing cleaning, it means the areas of the scale where dirt, mud, debris and other things get stuck and thus cause the scale to not work properly. It is fine having a clean deck, but the underside of the truck scale will need the most attention. 

Over time, the build-up of mud and debris can have a negative impact on a weighbridge performance. Compacted mud can set hard and reduce the movement of the weighbridge. This in turn causes reduced accuracy in weighing. Certain types of site environment will suffer more with mud and related issues and weather conditions can also play a part.

Keep in mind, weighbridge cleaning can be a bit tricky. For one you need to remove the mud and buildup so the scale platform can perform correctly. However, the water jet force required to remove dirt and debris from around a weighbridge’s critical weighing points can, if not performed correctly, damage load cells, cables, junction boxes, and summing boards.

When cleaning the scale, the lightest amount of water pressure you can use and still get adequate cleaning, the better.

Building a maintenance schedule

Weighbridge maintenance should take place as part of a daily or weekly routine depending on the type of site. The build-up of debris and water should be monitored and obstructions should be removed from beneath the scale to provide clearance between the weighbridge and the ground. Otherwise, your scale accuracy will suffer.

Pit weighbridges should be checked to make sure clearances are clean and the correct gap between the deck and pit wall are in place. ‘T’ section rubber can be used to help maintain gaps and should be replaced if worn or damaged. Regular end-middle-end tests with a loaded truck should be carried out to review the accuracy of the scale to see if there are any buildup issues. This basic cleaning and maintenance can be carried out by a site foreman or truck scale weighbridge operator.

Closing Words

At American Scale we strive to bring you informed and useful content on all things scale systems related, including products from the top scale manufacturers. Be sure to check out our truck scale articles about truck scale foundation or how much do truck scales cost. We even have a guide to warranties. To learn more about bench scales, it would be good to check out our other articles such as “Bench Scale Basics'' and “How Much Does A Bench Scale Cost?”. These articles will help with the basics of bench scale ownership. Also, take a look at our“Common Problems With Bench Scales'', to help prolong the lifespan on your scale.

The Guide to Scale Calibrations

Understanding the importance of calibrations.

Using a scale for an extended amount of time, especially in a business will require you to get your scale calibrated. Scales are not able to be accurate forever, there are factors that cause it to need calibrations periodically. Normal wear and tear occurs and over time, accuracy slips. It can degrade even quicker if the scale is exposed to electric or mechanical shock or is in a manufacturing environment with moisture, oils, metal chips, etc.

Calibration is the process of testing the scale, to ensure the level of accuracy you require. In a laboratory setting, where results are dependent upon exact weights, scale calibration is of particular importance. An inaccurate scale could significantly hurt your business. In processing and manufacturing, incorrect measurements could result in product quality issues, scrapped batches, or even a product recall. This guide will help  give some insight to scale calibration, helping to create a plan of action and ensure that less issues involving an inaccurate scale.

How Does Scale Calibration Work?

Using a test weight on your scale is the standard to properly calibrating your scale. The test weight reading is recorded, and if the weight readings match the standards applied or fall within the calibration tolerance, the scale does not need any adjustment. If the weight readings do not match or fall within the tolerance, service will likely be needed to restore the scale to the acceptable state of accuracy.

While an instrument may be capable of measuring a particular range of weight, it may or may not be calibrated for that entire range. Instead, there may be a calibration range that’s chosen, which ranges from zero to a maximum weight of your choosing (also known as the span). Once the calibration range is defined, the calibration is done at several points from zero to span to ensure high accuracy.

Factory Calibration                

When you purchase a scale, it often comes with factory calibration, which means that it was calibrated at the facility before you got the scale. In the few days that have passed since it left the factory, you might assume that your scale is delivered calibrated and ready for use, right? Wrong. The location of the factory and your location are two different places – with two different elevations and therefore, the on-site calibration is the only way to ensure your scale is accurate where you intend to use it.

If you do decide you want to have your scale calibrated once it arrives, then a third-party scale company is your best option. Your ultimate goal is to restore your scale to its original, optimal accuracy state, so the details matter. Some scale dealers will also offer calibration services, like American Scale, will not only calibrate the scale, but also make adjustments and perform repairs as needed to get the deviation from the mass standard back within tolerance.

How Often Should You Calibrate Your Scales?

How often you calibrate your scales depends on a few different factors; manufacturer’s recommendations, how often you use the scales, the environment they’re in, and how essential an exact weight is to your business. Some are calibrated once per month, others are only calibrated once per year, while some are even spot checked daily for accuracy.

After considering these factors, it’s determined that somewhere in the middle —certified calibration once per quarter with a weekly user spot check is ideal to ensure quality control of scales that are used fairly often. However, your needs may vary based on the information below.

Always consult the manufacturer’s recommendations first. Manufacturers should have a recommendation for the frequency of calibration, and since all scales are made differently, it’s usually safe to assume the manufacturer knows best.

If your scales are used multiple times throughout the day, every day of the week, normal wear and tear will occur faster than in scales that are used a few times per week. Therefore, if you use these scales more frequently, they should be calibrated more frequently.

The surrounding environment also plays a role. For example, if your scale is in an area that contains dust, fluids, or other substances, your scale could have a buildup of these substances that interfere with the performance of the scale. If you have the scale located in a place where there are vibrations, static electricity or mechanical shock, scale accuracy can suffer.

In general, you should also consider a more frequent calibration to ensure these substances and other work environment factors are not getting in the way of getting a precise weight.

Calibrations are done at a variety of frequencies, depending on a variety of factors. It’s important to note that if your equipment is frequently calibrated and almost always needs adjustment or repairs, it could be a sign of a bigger issue.

While the frequency of calibrations depends upon use, the rapid deterioration of accuracy warrants additional troubleshooting.

Once you’ve determined the appropriate frequency for your scales, you should look into signing a service plan with a calibration company. Many companies, like American Scale will work with you to learn more about your process and then create a maintenance plan tailored to you and your equipment

What Is Calibration Tolerance?

Calibration tolerance is defined by the International Society of Automation (ISA) as “permissible deviation from a specified value; may be expressed in measurement units, percent of span, or percent of reading.“ When it comes to scale calibration, tolerance is the amount the weight reading on your scale can differ from the nominal value of the mass standard that has optimal accuracy. Of course, ideally, everything would match up perfectly. Since that’s not the case, tolerance guides ensure that your scale is measuring weights within a range that will not negatively affect your business.

While the ISA specifically states that tolerance can be in measurement units, percent of span or percent of reading, it’s ideal to calculate the measurement units. Eliminating the need for any percentage calculations is ideal, as those additional calculations only leave more room for error.

The manufacturer will specify accuracy and tolerance for your particular scale, but you should not use this as your only source to determine the calibration tolerance you will use. Rather, in addition to the manufacturer’s specified tolerance, you should consider:

• Regulatory accuracy and maintenance requirements

• Your process requirements

• Consistency with similar instruments at your facility

What Is Legal-for-Trade Calibration?                

Commercial scales require legal-for-trade calibration. That means the scale needs to be calibrated according to the standards found in “Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices” — also known as “Handbook 44.” This comprehensive list of requirements is mandatory for all scales used for commercial purposes. A new version is published every year by the National Institute of Standards and Technology (NIST).

Do I Need Legal-for-Trade Calibration?

If you use your scale for commercial purposes, you need legal-for-trade calibration. For example, at the grocery store, your lunch meat and cheese is weighed on a scale and is sold to you at a price determined by that weight. That grocery store scale is an example of a commercial scale.

Commercial scales require legal-for-trade calibration. A state weights and measures inspector will follow up to ensure that your commercial scale has proper calibration.  A device found to be out of tolerance by a state inspector is generally tagged and taken out of service.  To avoid the problems associated with a device being found out of calibration by a state inspector, owners of commercial scales should have them calibrated and adjusted periodically to keep them in proper operating order.

Do I Need to Register My Weighing Device?

Yes. Many states require that you register commercial scales with the state. Also, you must make sure that the state you plan to use the scale in approves of the purchase. Most states accept scales that are National Type Evaluation Program (NTEP) approved. NTEP-approved scales get a Certificate of Conformance (CC or CoC), showing its approval. This document is usually in the form of a metal plate or tag on the scale with the make, model and capacity information.

The state will inspect and test the scale then review the results.  As long as your scale has the Certificate of Conformance, and the scale performs to all of the relevant standards and tolerances in Handbook 44, you will pass inspection. If your device is out of tolerance, the state weights and measures official will not adjust it to bring it back within tolerance. Rather, you will be required to repair and adjust the scale. Only a licensed and professional scale calibration and repair company like Precision Solutions can do this.

Closing Words

Acuuracy is paramount when it comes to scales and weighing, an innaccurate scale can really cuase you a lot of lost time and money, if not remedied quickly. Remeber that in the long run if you have an innaccurate scale then you will lose a lot of potential profits. Consider how important an accurate weight is to your business. If your company can’t afford to have even the slightest inaccuracy in weight, it’s likely that more frequent calibrations will be necessary.

At American Scale we strive to bring you informed and useful content on all things scale systems related, including products from the top scale manufacturers. Be sure to check out our truck scale articles about truck scale foundation or how much do truck scales cost. We even have a guide to warranties. To learn more about bench scales, it would be good to check out our other articles such as “Bench Scale Basics'' and “How Much Does A Bench Scale Cost?”. These articles will help with the basics of bench scale ownership. Also, take a look at our“Common Problems With Bench Scales'', to help prolong the lifespan on your scale.

10 Reasons To Get A Hydrostatic Scale

10 Reasons To Get A Hydrostatic Scale

The Advantages of Hydrostatic.

Scales are as essential to our lives more than we realize. If it is sold then at some point in the production process then it was weighed. When coming to accuracy of weighing, there are several options that are considered. Analog and electronic load cells seem to be the main options, but the one not mentioned as much is hydrostatic scales. This post will go over the 10 reasons why hydrostatic scales should be considered.

What is a 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.

Lightning and Power Surges.

Lightning strikes and power surges plague large industrial scales more than realized. When this happens with electronic load cells installed, then there usually will be some downtime when lightning strikes. Hydrostatic load cells are unaffected by electrical surges, power failures, stray voltages or even lightning strikes. Electronic load cells are highly susceptible to these common industrial occurrences and are often damaged requiring replacement. Outdoor tank scales or truck scales often lose all load cells from a lightning strike, even with surge protectors.

corrosion

Hydrostatic load cells are available in grade 304 and 316 stainless, with improved life and performance over the more common aluminum and carbon steel. Most electronic load cells are made of nickel plated tool steel, or at best 17-4PH grade stainless steel, which is far less corrosion resistant that that of 304/316. Many electronic load cell manufacturers avoid stainless steel completely due to performance deterioration. In environments that are washed down, this can be bad for electronic load cells due to the moisture getting into the wiring and boards on top of potential corrosion from the type of steel used.

durability

Durability is essential to separating the good scales from the bad. A scale that is unable to handle the amount of measurements it receives will eventually cost more money than it earns, this also includes downtime for the repairs.Hydrostatic scales are a lot more durable compared to their electronic counterparts. They are able to last for decades without any sort of parts replacement. Whereas mechanical scales require periodic replacements of pivots and bearings. Electronic load cells will have to be replaced numerous times throughout the life of the scale.In harsh environments the hydrostatic scale will definitely be up to the task. Less moving parts with a design to handle the harshness of the environment places hydrostatic above electronic and analog.

Special materials

Hydrostatic load cells can be manufactured out of many special alloys, with no loss of accuracy. They are available in 304 stainless, 316 stainless, titanium, monel, as well as teflon and hastelloy. Electronic cells require a certain hardness, and therefore can only be made with aluminum, steel, or 174PH stainless, which are less corrosive resistant.

Shock loading

Hydrostatic load cells have a natural inherent quality of shock absorption. Electronic load cells have no inherent energy absorbing qualities. In the event of severe shock loading resulting in load cell damage, the hydrostatic load cell can be easily repaired. Due to the simple design nature of hydrostatic load cells, it is very easy to repair them on site. Electronic load cells have to be rebuilt at a repair shop. They are unable to be repaired on site and almost always require a full replacement.

Calibration

In the unlikely event that a hydrostatic load cell ever needs to be replaced, the scale rarely needs to be recalibrated. Hydrostatic load cells with identical acting areas have matched outputs, whereas electronic load cells have variations in millivolt output, requiring the scale to be recalibrated whenever a load cell is replaced.

Temperature

Hydrostatic load cells are available with a 500 degree operating range, from -50 degrees F to 450 degrees F. Electronics operate at less than half this range. The adhesives used in electronic cells deteriorate in high temperatures and become brittle in cold temperatures, causing total failure or inaccurate readings, frequently resulting in load cell replacement.

high capacity

Hydrostatic load cells have been manufactured with capacities exceeding 1 million lbs. There was actually a 12 million pound load cell that has been operating in a testing machine at the National Institute of Standards and Technology since 1968. In addition, high capacity hydrostatic load cells require a minimum expense in mounting hardware, while the hardware for high capacity electronic load cells can cost more than the cell itself and often must be made of specialty hardened steel.

Installation

Hydrostatic load cells are “dead” until activated with fluid. Therefore, the load cell is almost impossible to damage during installation. While electronic load cells frequently require “dummy” load cells during installation, hydrostatic load cells never do. An electronic load cell is “live” from the time it leaves the factory. It can easily be damaged beyond repair by being dropped, when placed under a tank leg, overloaded, left exposed to weathering, etc. Many are replaced before ever being used.

Cost of ownership

With all these advantages listed, it should be easy to see that scales with hydrostatic load cells have the lowest cost of ownership of any scale on the market today. The fact that hydrostatic load cells are a lot less to maintain, it dramatically reduces your overall cost and keeps you from losing money due to downtime for repairs. Any product that can save you money while being of superior quality is always a plus.

closing words

At American Scale we strive to bring you informed and useful content on all things scale systems related, including products from the top scale manufacturers. Be sure to check out our truck scale articles about truck scale foundation or how much do truck scales cost. We even have a guide to warranties. To learn more about bench scales, it would be good to check out our other articles such as “Bench Scale Basics'' and “How Much Does A Bench Scale Cost?”. These articles will help with the basics of bench scale ownership. Also, take a look at our“Common Problems With Bench Scales'', to help prolong the lifespan on your scale.

Weight Indicator Issues.

Weigh Indicator Issues.

Understanding the environmental factors that can contribute to indicator issues.

Weigh Indicator Issues.

Mechanical and operational issues can and will occur during the life of scale ownership. Scale manufacturers have certain standards when it comes to scale care and scale calibration. When operating your legal for trade scale and indicator, there are factors that will add to potential issues but can be prevented with an understanding of which issues can arise. This will help you prolong the lifespan of your scale system and also help you avoid other common problems. You can ensure that your weighing system performs accurately by choosing components suited to your application and taking steps to control environmental and other forces acting on the system. This article discusses the factors that can affect your weighing indicator’s accuracy and provides advice and DIY fixes for potential issues. 

UNDERSTANDING THE FLOW OF COMMUNICATION

A weighing system and weighing application can take any of several forms but typically includes one or more load cells that support (or suspend) a weigh vessel or platform, a junction box, and a weight controller. Sometimes you will see certain setups with a remote display or scoreboard. When a load is applied to the weigh vessel or platform, a portion of the load is transmitted to each load cell. Each cell sends an electrical signal proportional to the load it senses via a cable to the junction box. The load cell signals are summed in the junction box and sent via one larger cable to a weight controller, which converts the summed signal to a weight reading. This weight reading's accuracy can be affected by the system components' quality and the system's installation and operation in your environment.

INTERFERENCE WITH INDICATOR

Weigh indicators communicate with the Load cells by receiving an electrical signal, which is processed by some type of weight controller that then outputs the weight onto the scale’s digital indicator. If it is an analog or electronic load cell there are factors that can add to inaccurate weight measurements. Interference occurs during any part of the process can lead to inaccurate weight readings between the load cell and scale indicators.

Below are just a few of the more common types of interference that we see when operating your scale and indicator. 

• Temperature – As temperatures increase wire resistance increases as well, causing voltage to drop, which can lead to the scale controller displaying results that are actually different from the load cell’s output.

• Moisture – From time to time, condensation or moisture can build up on the load sensor, which can affect electrical outputs and cause interference in the signals being sent from the load cell to the display indicator.

• RFI and EMI – These can create additional input signals, or noise that can also cause the scale controller to display an incorrect weight.

Temperature: A factor that some can overlook is the impact temperature has on your indicator. A load cell cable conduit that's subject to large temperature changes or that runs more than 50 feet from the junction box to the weight indicator can be affected by temperature fluctuations, which cause resistance changes in the cable. This can cause excitation changes, in turn causing load cell signal changes. To prevent these temperature problems, use six-wire load cell cable, which allows the weight controller to make ratiometric readings of the load cell signal that ignore excitation-change-induced changes. Essentially the extreme temperature changes can cause a chain reaction from the cable to junction box, thus sending an inaccurate signal to the indicator. 

 INTERFERENCE WITH SIGNAL TRANSMISSION

In addition to ensuring that the load cells measure only the desired weight, it's equally important to ensure that the weight controller measures only the load cell electrical signal. Radio frequency interference (RFI), electromechanical interference (EMI), moisture, and temperature can all interfere with this electrical signal.

RFI and EMI. Just as vibration is mechanical noise (that is, interference) to a load cell, RFI and EMI are electrical noise to the load cell signal sent from the cells to the weight controller. RFI and EMI sources include lightning, portable two-way radios, large power lines, static electricity, solenoids, and electromechanical relays. One major step toward preventing these electric noise sources from affecting your weighing accuracy is to isolate the load cell low-voltage signal (typically equal to 1 millionth of a penlight battery's output) in a shielded cable and then route the cable in a conduit separate from other cables. But be aware that the load cell cable shield can also be an open door for electrical noise. To prevent the noise from affecting your load cell function, properly ground the shield by tying it at only one end to a true ground, which will prevent the shield from forming a ground loop.

Moisture. Moisture that enters the weighing system's junction box can wick itself into the cables to each load cell and reduce the capacitance between signal lines. This causes the load cell excitation lines (the lines carrying electrical energy to the cells) to couple with the signal lines (the lines carrying the cells' signals back to the junction box), creating electrical noise that can affect the weighing accuracy. To avoid this, use a waterproof NEMA 4-rated junction box and plug any unused junction box holes. If moisture is present in your environment, also use load cells that are hermetically sealed at both the strain gauge area and the cable entry. The strain gauge area should be welded shut. The cable entry, which is the most vulnerable to moisture because moisture can wick up through the cable, should have a welded fitting that includes a glass-to-metal hermetic header.

At American Scale we strive to bring you informed and useful content on all things scale systems related, including products from the top scale manufacturers. Be sure to check out our truck scale articles about truck scale foundation or how much do truck scales cost. We even have a guide to warranties. To learn more about bench scales, it would be good to check out our other articles such as “Bench Scale Basics'' and “How Much Does A Bench Scale Cost?”. These articles will help with the basics of bench scale ownership. Also, take a look at our“Common Problems With Bench Scales'', to help prolong the lifespan on your scale.