Why Is My Load Cell Inaccurate? 11 Problems and Solutions for Troubleshooting Load Cells

Accurate load cells are critical to get the right mix. There are many different types of load cells for different processes, all of which can become inaccurate for different reasons. In this blog post, we’ll discuss a few of the ways your load cell may become inaccurate, what these problems look like when they occur, and how to troubleshoot load cell problems.

11 Problems and Solutions for Troubleshooting Load Cells

1. Total Combined Error

All measurement devices will have some degree of error that is not preventable. In load cells, this is shown through non-linearity and hysteresis. Since some level of error is unavoidable, there aren’t load cell troubleshooting strategies for this. However, this is acceptable as long as the error is less than the error tolerance of any ingredient. Additionally, non-linearity and hysteresis are less problematic in particular situations.

Non-linearity describes the weighing error over the entire load cell range. Smaller changes will create less error due to non-linearity, while a change from zero to maximum capacity will cause the greatest effect. Hysteresis is the difference in the results between increasing the load from zero and decreasing from maximum. Similar to non-linearity, error due to hysteresis is more noticeable when dealing with larger loads. So, when working with batching, this inevitable error is generally less of a problem compared to larger loading operations.

2. Temperature Changes

Dramatic temperature changes cause metal to warp. Traditional load cells are built using strain gauges, which are delicate metal pieces. Dramatic temperature changes will affect the function of the strain gauge, and therefore the load cell. If the load cell is exposed to cold nights and then hot, direct sunlight, or surrounding equipment heats up the area, this can cause inaccuracy. To troublehshoot this load cell problem, you might take temperature readings at different times, and shield the equipment from the sun if it causing dramatic temperature shifts.

3. Creep

If a load cell remains under pressure for a long period, it becomes susceptible to creep. This isn’t a problem in batching operations at two or three minute intervals, but load cells measuring storage silos or other containment units for extended periods will need to account for creep.

4. Load Cell Response

All load cells require a set time to return to zero before they can accurately measure a new load. If the process begins to refill the vessel before the load cell(s) return to zero, the measurement won’t be accurate within the error tolerance. Allow enough time between measurements for the load cells to stabilize and response time will not be an issue. To troubleshoot this load cell problem, test the load cell response upon installation and with calibration, to ensure it remains stable.

5. Balanced Load

The load must be properly balanced on the load cell, or the load cells must be arranged to accommodate for unbalanced loads. Where multiple load cells are used, they must be mounted so no other part of the vessel or container takes on a part of the load. For a sitting vessel, this generally means the load cells must be situated between the vessel and the floor. For a mounted load, bumpers and checkrods used to stabilize the load cannot also support its weight.

6. Vibration

Excessive vibration, usually from other nearby processes or sometimes from passing trucks or heavy equipment, can disrupt the reading. Troubleshooting this load cell problem might involve moving the source of the vibration or moving the load cells and attached equipment. Dampening devices such as layers of rubber or cork can also absorb the vibration. If the vibration is cyclical, it can also be electronically filtered out by a weight controller.

7. Windforce

Air currents exert force on a load cell that can disrupt the weight of the load alone. Usually, this is not enough to cause significant inaccuracy, but strong, consistent windforce can disrupt the reading. This might come from intense winds outdoors, or from strong air currents used to prevent dust buildup.

8. Noise

When the load cell transmits its electrical signal to the weight controller, interference, or noise, can disrupt it. Radio signals and electromagnetic signals both cause noise, which includes electrical currents, other data transmission signals, even strong wireless signals. Proper shielding around the load cell cables and grounding of the shield can prevent interference from noise. Using a capacitive digital load cell can also help to prevent signal loss due to noise. In a capacitive digital load cell, the signal is converted to digital locally within the load cell, so there is no loss of signal across the cable length or at bad connection point.

9. Moisture

Moisture can also inhibit the signal from the load cell to the weight controller. Moisture, perhaps from steam, excessive humidity, or equipment washing, most often enters the load cell through the cable entry area. Hermetic sealing will prevent moisture from damaging the load cell and internal components.

10. Signal Jitter

A number of factors can cause the weight signal from a load cell to “jitter;” moving unsteadily upward (or downward, as in a loss-of-weight feeder) instead of in a smooth line. The hopper’s or vessel’s movement while weighing, material entering the vessel unevenly, an agitator preventing sticking, or unshielded noise can all cause the signal to fluctuate. A weight controller averages the fluctuation and creates a smooth analog signal, then converts the signal to digital. However, if the weight controller isn’t working properly or isn’t installed properly, signal jitter will disrupt the measurement.

11. Damaged Load Cell Connections

Often, multiple load cells are used to measure a load. When these load cell signals are not combined and summed properly at the weighing instrument, it can cause noticeable error. This can occur due to faulty connections between the load cells and the instrument. Corrosion from acids or salts can cause connections to corrode, thereby disrupting the signal.

One of these load cell problems alone will probably not create a noticeable problem, unless it is extreme. However, several of them occurring at once can cause measurements to be noticeably inaccurate. Careful attention to the environment around the load cell and the equipment, as well as the installation and use of the load cell itself, can prevent many load cell problems.

Hermetically Sealed Load Cells Explained

hermetically sealed digital load cell

Though they’re often used in highly durable scales and heavy equipment, load cells themselves are somewhat delicate, and can easily be damaged by surrounding elements. This is what makes hermetic sealing so important. Hermetically sealed load cells are air- and water-tight, protecting the delicate measurement components inside from damage. In this blog post, we’ll explain further what hermetically sealed load cells are, why they’re important, and how you can ensure that your load cells are sealed properly.

Hermetically Sealed Load Cells Explained

What is a Hermetically Sealed Load Cell?

A hermetically sealed load cell is an air- and water-tight weighing instrument. The load cell is contained by a welded seal around the gauge, which prevents dust, moisture and other materials from disrupting it. The connecting cable also uses a welded header to maintain the seal.

Hermetic sealing is slightly different for a capacitive load cell compared to a strain gauge load cell, which we will explain later in the blog post, however the principal of completely sealing the weighing elements remains the same.

Are Hermetically Sealed Load Cells Necessary?

strain gauge load cell
A simple diagram of a strain gauge load cell

Load cells, including both strain gauge load cells and capacitive load cells, can be disrupted by changes in conductivity. This means that any conductive element can contaminate the load cell, and disrupt the measurement, or cause the cell to stop working all together. The load cell may be exposed to many different conductive materials, the most common being simply water. The inner workings of the load cell are very delicate, and can be damaged by water from washing down equipment, contact with other liquids used in the process, or even changes in humidity.

Other conductive materials such as metallic dust or salt can also disrupt the load cell. Finally, corrosive chemicals and vapors can erode the exterior and damage the load cell. Hermetically sealed load cells made from laser-welded stainless steel offer the best protection from all of these threats.

If you are washing your equipment, or it is exposed to salt, metallic dust, notable changes in humidity, corrosive chemicals or chemical vapors, hermetically sealed load cells are necessary. The load cell will last longer, and it won’t need to be recalibrated or replaced as often as a non-sealed cell. The additional cost of hermetic sealing will be lower than the costs associated of repeated maintenance and replacement of a non-sealed cell. A non-sealed cell is also at much greater risk of sudden failure, which can cause expensive downtime.

Hermetically Sealed Load Cell Technology: Strain Gauge vs Capacitance

a strain gauge
A closer look at the delicate strain gauge

In a strain gauge load cell, the strain gauges themselves are comprised of arrangements of thin, conductive metal and an insulated backing, which are very delicate. The fine interconnecting wires and electrical circuits measuring resistance are also very fragile. These components depend on electrical conductance to work, so any conductive material can contaminate the load cell and disrupt the measurement. This includes water and moisture in the air, as well as conductive dust. If the load cell is not hermetically sealed, water, dust, and even changes in humidity can damage it. The external output must also be directly connected to the load cell, so this connection area must also be hermetically sealed. This is the most common area where a hermetic seal might fail.

capacitive load cell diagram
A simple example of how a capacitive load cell works.

A capacitive load cell uses capacitance instead of conductance to measure the load. In a capacitive load cell, a change in charge between two metal places and a dielectric material in between measures the load. These elements can also be disrupted by conductive materials. The capacitive load cell, however, can be more easily self-contained, since it does not require complex circuits, namely a Wheatstone bridge, to measure resistance. A capacitive load cell also uses a coaxial cable for an external output, which is separated from the hermetically sealed load cell itself. This means seal around the external output does not endanger the hermetic seal of the load cell. A coaxial cable connection is also less prone to connection interruption and damage. For these reasons, hermetically sealed capacitive load cells offer more advantages in many risky environments.

Learn more about digital capacitive load cells » 

How to Detect an Low-Quality Hermetic Seal

As previously discussed, the best type of hermetically sealed load cell is made from laser welded stainless steel. Some believe that a stainless steel load cell is adequately sealed and protected by itself, but only hermetic sealing will completely protect the load cell.

For strain gauge load cells, the output should also have a welded cable header. In some cases, the cable may be sealed using foam, adhesive, or epoxy. While these may provide adequate protection for a time, they will eventually break down and expose the load cell to dust and moisture. A welded cable header and seal will not break down prematurely and it will prevent dust and moisture from building up in cracks or pockets.

Hermetically sealed load cells are requirements in many facilities, and advantageous in most others. There are many different types of load cells that can be hermetically sealed, including many different designs, configurations, weights and tolerances. With a high-quality hermetically sealed load cell included in your weighing system, you can extend the life of your machine and reduce maintenance and risks. Download the brochure to learn more about hermetic load cells.

8 Advantages of Capacitive Digital Load Cells

In our previous post, we discussed problems engineers and scale dealers often face when working with traditional strain gauge scales and load cells, and solutions that can improve accuracy and durability. In many cases, utilizing capacitive digital load cells can help to avoid problems posed by the strain gauge. In this post, we’ll explore the capacitive digital load cell, how it works, and advantages it provides to scale dealers and their customers.

How Do Capacitive Digital Load Cells Work?

While strain gauge load cells use resistance to change voltage and therefore measure weight, capacitive load cells use changes in capacitance. Inside a capacitive digital load cell, two plates with opposing charges stand a small distance apart. When a load is applied, it forces the plates closer together. As this happens, current moves between the negatively- and positively-charged plates in an effort to establish equilibrium. A charge is then stored between the plates, creating capacitance. This then produces voltage output which can be transferred to a reading on a digital scale.

Capacitive digital load cells are simpler to construct than strain gauge load cells, and this simple design makes them less susceptible to many of the issues that often disrupt strain gauge load cells. Other advantages also make capacitive digital load cells easier to use, and more affordable to manufacture.

8 Advantages of Capacitive Digital Load Cells

1. Fewer Start-Up Costs

Capacitive digital load cells are already calibrated at the factory, and do not need to be recalibrated when they are installed. To install in the field the engineer or operator must only zero off the dead load of the system and check for binding.

2. More Sensitive

For strain gauge load cells, detecting small changes and measuring small loads means utilizing very small changes in resistance. This requires the load cell to be more sensitive, which also makes it more susceptible to damage and requiring more frequent recalibration. Thanks to their simple design and versatile materials, capacitive digital load cells retain their durability even at high sensitivity. Since a smaller amount of movement can be easily sensed with a capacitive cell, then the metal can be thicker and able to withstand more load, with the same amount of sensitivity. This makes the cell less susceptible to overload.

3. Simple Maintenance

The delicate cables and wires that interconnect strain gauge load cells are not required with capacitive digital load cells. This means field wiring of small connections in difficult arrangements is a thing of the past. The only cables needed are communication and power transfer cables, which can be replaced in the field without the need for recalibration.

4. Versatility

Capacitive sensors can be built from a wide variety of materials, and in many different shapes and sizes. They are also suitable for very large and very small loads, with many levels of accuracy. This makes it easy to design and manufacture a capacitive digital load cell for any application. Digital capacitive load cells may be designed in beam, compression buck, tension or single point configurations, as well as specialty configurations like on-board weighing, tensioning, force measurement and more.

5. Less Noise

Capacitive load cell output is completely digital. Since it does not use DC signals in milliVolts, which are easily disrupted by ambient noise, the signal is less susceptible to interference. This also means there is no need for an analog to digital converter to convert the signal to a digital format.

6. More Affordable

Reducing the noise levels, eliminating the need for an analog to digital converter, and utilizing a wider range of materials with a simpler design allows manufacturers to produce capacitive digital load cells that are more affordable, when comparing feature for feature.

7. Durable and Hygienic

Many capacitance digital load cells are ATEX certified for hazard zones 1, 2, 21 and 22. These load cells can also be hermetically sealed (rated at least IP 68 and some at IP67) without significant additional expense, unlike the strain gauge load cell, which can be difficult to completely seal. This makes it suitable for hygienic applications such as food and pharmaceuticals.

8. Additional Features

The reduction in noise, simpler design, and digital output makes it easy to augment the capacitive digital load cell with additional features. Ethernet IP, EtherCAT, Profibus DP, ProfiNet, DeviceNet, Serial outputs and analog outputs are all available in neat compact packages.

Capacitive digital load cells are replacing strain gauge load cells in a number of applications. If your strain gauge load cells are making processes more difficult or less efficient, or if you’re looking for a competitive advantage as a scale dealer, consider the digital alternative. Learn more about capacitive load cells and talk to an expert to find the right load cell for your application.

5 Strain Gauge Scale Problems and Solutions

Load cells are essential devices used in many processing systems, though we seldom think about them. Only when the load cell malfunctions and the scale is inaccurate do we think about the workings behind the measurement. When it comes to measuring ingredients, from fine pharmaceutical powders to silos full of grain, understanding how strain gauge scales and traditional load cells work, and common strain gauge scale problems, can help prevent inaccuracies.

How do Strain Gauge Scales and Traditional Load Cells Work?

Strain gauge scales use traditional load cells, also called resistive load cells or strain gauge load cells, to measure weight. Strain gauge load cells operate on the principle of piezoresistivity. When voltage is applied to the strain gauge within the strain gauge scale, and then a weight is applied, the strain gauge senses changes in piezoresistivity, and this creates a change in voltage output. For this to work, several strain gauge sensing elements are often used throughout the load cell, and these are connected with wires. For the sensing elements and the strain gauge scale to be accurate, the wires must be able to transmit small changes in voltage, so the wires can be very delicate.

A strain gauge scale relies on mechanical forces to change piezoresistivity and voltage output. When a load is applied, the conductive material within the strain gauge is deformed, causing changes in resistance, and therefore changes in voltage output. This can introduce a number of challenges to both large and small loads. If your scale is repeatedly inaccurate, and you have determined that other aspects of the system are not to blame, look for the following issues with the load cell.

5 Traditional Strain Gauge Scale Problems and Solutions

Low-Quality Manufacturing or Construction

Small mechanical changes within the strain gauge are responsible for changes in voltage, which creates the reading on the scale. If flaws in the strain gauge’s construction prevent the material inside from moving properly, the reading will not be correct. For this reason, the process to manufacture an accurate strain gauge-based load cell is delicate. If this isn’t done correctly, the load cell won’t deliver adequate readings. This can be particularly problematic when working with discount scale dealers, who rely on fast manufacturing and testing. Working with a reputable scale dealer with references can help you to avoid load cells with faulty construction.

Temperature Changes

Temperature changes effects the conductivity of metals, which will change the output of the strain gauge. Once the load cells are built, they need to be tested at different temperatures in order to ascertain their drift with temperature. When the traditional strain gauge is needed to measure particularly small amounts, temperature changes can be especially problematic. Thermistors installed prior to the final test and calibration stage will reduce the temperature effect.

Wrong Type of Load Cell

There are many types of load cells using traditional, strain gauge technology, and certain types are better suited to certain applications. Capacitive load cells, which use changes in capacitance instead of resistivity, can also be used in many different applications. Finding the right load cell for your application can make significant differences in accuracy, longevity and efficiency.

  • S-Beam Load Cell: Instead of a load sitting on top of the load cell, an S-Beam load cell hooks the load on one side and uses the pulling force to measure the load.
  • Beam Type Load Cell: The beam type load cell uses compression to measure weight, and it is often used in tank weighing and platform scales.
  • Single Point Load Cell: The single point load cell works similarly to the beam load cell, except it is ideal for loads that are not centered.
  • Button Load Cell: The button load cell also uses compression, but measures load applied axially.
  • Pancake Load Cell: These load cells are used for high-capacity loads up to 500 tons, such as silo weighing or structural loads.
  • Capacitive Load Cell: Since capacitive load cells operate on a different principle, they are not as affected by noise and interference as strain gauges, and they can be more sensitive with less need for delicate manufacturing. Capacitive load cells are highly effective for a variety of applications, and are also available in all of the above configurations.

Exceeded Sensitivity

Smaller, more precise strain gauge load cells are much more delicate than their larger counterparts. The nature of strain gauge technology requires that the strain gauge be much smaller, and its components more delicate, to be more accurate. This makes the strain gauge and the load cell much more susceptible to disruption from physical impacts, electromagnetic interference, dust, temperature changes, and other issues. More frequent calibration of traditional load cells can help them to maintain their accuracy. Capacitive load cells can also be used in lieu of strain gauges for these applications.

Improperly Sealed

If your traditional load cell must operate around water, dust, or other debris, it must be hermetically sealed. For traditional strain gauge load cells, hermetic sealing raises the price significantly, and some scale dealers may cut corners in this area. If your traditional strain gauge is significantly cheaper than other comparable models, it might not be properly sealed.

Careful attention to detail and working with a reputable scale dealer can help traditional scale gauges to maintain accuracy. Utilizing the right load cell designs, as well as newer technology like capacitive load cells, can also help to solve many common load cell problems.

Cattle Pro: The Cattle Feed Micro Machine Saving Time and Money

cattle pro

Finding the right cattle feed micro machine for your dry and liquid micro ingredient additives can save you time and money. However, it’s important to find a balance between price, ROI, maintenance costs, ease of use, and functionality. Understanding the challenges facing feedlots, APEC developed the Cattle Pro with flexibility, durability, and cost-savings in mind. The Cattle Pro enables feedlot owners to precisely add  the best combination of antibiotics and nutrients for optimal quality.

8 Benefits of the Cattle Pro Micro Ingredient Scale

cattle micro machine mixer 1. No Commitment, Better Prices

Many liquid and dry weighing machines for cattle come with an unspoken agreement; a long-term ingredient supplier’s  contract. The Cattle Pro does not have fine print. The Cattle Pro micro machine is suitable for any of the typical micro ingredients used in a feedlot, and is programmable for any amounts you specify. You can continue to purchase from any suppliers, so you are free to shop around for the best price.

Our Cattle Pro Micro Ingredient System means you no longer need to sign a contract with your micro ingredient distributor. It allows you to reduce costs by shopping for the micro ingredients without being locked into a contract. The Cattle Pro Microingredient System is fully accepted and compliant with government regulations.

Learn more about the Cattle Pro micro machine for dry and liquid micro ingredients »

2. Fewer Processes

The Cattle Pro allows you to add dry and wet micro ingredients in exact amounts.  The system delivers the ingredients as a slurry that is pumped directly to your feed mixer.  This means no more time-consuming separate weighing and adding of nutrients and antibiotics. The Cattle Pro also weighs ingredients in a fraction of the time compared to manual weighing. You and your staff can save time, energy, and manpower.

3. Faster, Easier, Safer

Weighing and adding micro ingredients by hand not only takes time, energy and extra staff, but it also introduces error. A moment’s distraction means feed is not properly formulated and cattle are exposed to nutrient deficiencies and the possibility of disease. The Cattle Pro eliminates this uncertainty with a pre-programmed, precise weighing system and automatic delivery into the feed mix. Liquid and dry ingredients are weighed and added exactly, every time, in a few quick minutes.

4. Lot and Ingredient Tracking

For organization and quality assurance, it’s important to know where your ingredients come from and where they go. The Cattle Pro can conduct barcode tracking on ingredients automatically, so you can see exactly what nutrients, antibiotics and other additives went into the feed. Lot tracking takes this visibility a step further, showing you where the feed went, and when it was used.  Every transaction is stamped with the exact time and date, so there is no guesswork involved.

5. Accurate Measurements Support ROI

Adding too many minerals or antibiotics means paying for extra you don’t need. Not adding enough means cattle don’t get the nutrients they need for optimal production or disease resistance. Exact feed measurements and mixing allow you to pinpoint the optimal amounts, and perfectly balance inputs and outputs.

6. Low Maintenance

Investing in an automated micro machine for cattle feed additives means weighing the costs against the benefits. Maintenance plays an important part here. The Cattle Pro is easy to clean and maintain, giving it a long life and minimal down-time. The flush hopper and conveyor can be separated from the machine, so it is easy to completely clean. The modular construction makes it easy to access any areas that require maintenance. Made from industrial-grade stainless steel with off-the-shelf components, it can easily be maintained.

7. Reduce Waste

The Cattle Pro automated cattle feed micro machine is completely enclosed.  This keeps the additives contained and eliminates housekeeping problems from water mist escaping from the machine.  The heavy duty construction and precision load sensors mean that you will have accurate results time after time. This also makes it more durable and less susceptible to jamming or environmental damage. Finally, the ingredient conveyor and water pump combination is designed for optimal efficiency, requiring less water than comparable models.

8. Start Right Away

Set-up is also an important consideration when investing in an automated cattle feed micro machine. It shouldn’t take a team of experts to get it up and running. The Cattle Pro is pre-wired and pre-plumbed, so the startup takes less time.  

The Cattle Pro simply makes cattle feed mixing easier. When you save time, money, and benefit from consistent feed quality, you can focus on growing your business. Learn more about the Cattle Pro micro machine  online or contact us for more information.