5 things that can affect your weighing systems’ accuracy
In manufacturing, accuracy is required. Every time a product is made, it needs to meet set conditions, such as undergoing outlined procedures, to make sure that the final version fulfils all requirements needed.
A large part of this involves accurate weighing of your products, making sure that the right volumes are used during production, the right mixture of components are included and that your end product meets the set amount as outlined by your packaging and labelling. Due to this, it is essential that your weighing systems are accurate so that you can be confident that your product is meeting the necessary guidelines.
If you are concerned your weighing systems’ accuracy is not at the level it should be, or you are experiencing anomalies during production, there could be many factors at play. In this blog, we have detailed the top five so you can rectify and prevent issues in your weighing accuracy.
Remember that, if you have checked for issues and find that problems are still persisting, you may need to seek expert advice. We can work with you to find the right solution for your weighing system issues.
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Environmental factors
If you are seeing inaccuracy in your weighing systems, it may not necessarily be a problem with the machine, but instead external environmental factors. For example, if your system is outside, it could be affected by wind – similarly, internal systems could be affected by air movement if they are positioned near an air conditioning vent. Wind can place force onto your load cells that are not connected to the product you are weighing, so the affect cells appear heavier and those unaffected appear lighter than they actually should be. If you feel this could be an issue in your production line, it is worth either repositioning the weighing systems to an area less affected or invest in a Plexiglas cover.
Temperature can also affect your accuracy, particularly in the case of temperature changes in your warehouse. If the temperature becomes warmer or colder, it can cause the load cells to expand or contract, thereby leading to inaccuracy when it comes to weighing and the potential for damage to your system. To combat this, you should try where possible to regulate a consistent temperature in your warehouse.
Another environmental factor to consider is pressure differentials. This is where the pressure of the operating environment (e.g. your factory) differs from the calibration of your weighing system – for example, if your weighing system is the air pressure between the two is different. Aim to calibrate your system so that it aligns with the pressure of the environment in which it sits. Where possible, aim for a constant pressure in this area or move the system to area where pressure is constant, so that you can reduce inaccuracies.
Vibration can also create issues when it comes to accuracy, with movement from nearby equipment to your weigher potentially recognising the weight of any vibrations transmitted to it. To prevent this, you should remove the system from any vibration sources.
Accuracy can also be impacted by the way you load your weighing system. If a particularly heavy substance is added onto your load cells that is higher than the system’s capacity, it has the potential to damage your system and make it less efficient. To avoid this, you should either switch to higher capacity load cells if required or use a feeder to control the flow of materials into your system, thereby preventing shock loading.
A final environmental factor is the build-up of substances that comes with prolonged usage. If you use your system regularly, the chances are many different materials will have passed through and each has the ability to leave residue. As this builds up over time, it can cause this residue to be counted towards your future weighing. You can prevent this with regular and systematic cleaning of your machine.
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Accuracy of your load cells
When it comes to your weighing system, your load cells are essential. The load cell takes a mechanical force (such as you placing mass onto the weigher, which bends the load cell) and turns it into an electronic signal. This means that if there is an issue with your load cell, it can have a knock-on effect onto the accuracy of the entire system.
In order to prevent issues, it is important to understand the specification of your load cells. These include:
- The creep of the cell – the change in measurement when a load is left on the cell for a long time.
- Non-linearity – the maximum deviation of a load cell’s calibration curve from a straight line, compared to a zero-weight to the maximum capacity of the cell.
- Response time – the time it takes for a load cell to provide an accurate reading after loading. Best practice is to give the cell time to settle to improve accuracy.
- Hysteresis – the difference in the measured weight when the same load is measured twice. One reading will be taken from the weight increasing from zero as you first load the materials, while the second will be taken using the decrease of the cell’s maximum capacity.
- Non-repeatability – the maximum difference between readings during weighing of the same load multiple times under identical conditions.
Each of these elements have the ability to affect your weighing accuracy, even when working correctly, so it is important to account for the variations they may cause to your recorded weights. Your weighing system supplier should be able to talk you through these.
However, if one malfunctions, it can cause greater inaccuracy, so take time testing your load cells on its specifications until you can identify where the issue is coming from. A way to reduce the risk of such malfunctions is to ensure you are using high quality load cells from reputable sources that are created to work with the rest of your system.
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Other load issues
It isn’t just issues with your load cells which can cause trouble with your accuracy – there are many other load issues that could have an effect.
One of the key ways to avoid load issues is to spend time getting to know your system and its accompanying instructions so that you can load it efficiently. Incorrect loading can cause additional strain onto your cells, which can impact the signals being sent and give you inaccurate readings. Make sure that you only apply load in the proper way, as outlined by your system manual.
Proper loading should include making sure that the load is entirely contained with the designated load cell area. If materials are resting elsewhere, such as on check rods or other connections, it may lead to error in your weight measurements.
You will also want to ensure your load points and mounting hardware are correctly aligned. Misalignment of these elements can prevent the load from taking the necessary direction it needs to through the system and stop it from being directly applied to the load cell, creating potential for inaccuracy. To prevent this, check your alignment and make sure that each load cell is level so that they can share the load equally. Part of this may include make sure the weighing system is placed on a level and stable floor or mounting structure, where it can hold the entire system without movement.
You should also ensure that any cross braces you use have lightweight support legs. This means that side loads are reduced when the legs move in accordance with any strain placed upon them, and will help you to get a consistent reading.
Most load issue can be eliminated by ensuring your system is set up correctly, in an appropriate location, and that any staff using the system have received adequate training. This means you can remove the room for error and enjoy accurate readings of your loads.
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Interference
Digital weighing systems work through load cells transmitting electronic signals. As such, interference of these signals can lead to inaccurate readings appearing on your digital indicator. There are many causes of interference, including:
- Condensation and moisture can build up over time on the load sensor, or moisture can enter the system’s junction box and affect cables. This can cause the electrical input and output to get coupled together and result in inaccurate readings. A waterproof system can eliminate this risk.
- If your weighing system sees temperature increasing, this can lead to increased wire resistance. This resistance causes voltage to drop, which then lead to the system to show incorrect readings.
- RFI/EMI. RFI and EMI are types of electrical noise that can come from radio, lightning, power lines and static electricity. This noise can affect the electrical signals transmitted to your weighing system, leading incorrect measurements to be displayed. You can use shielded cable to isolate the voltage of your system and reduce the impact of outside electrical noise.
Regular maintenance of your systems can help to reduce some interference, particularly in the case of moisture, as can ensuring a controlled environment where the impacts of temperature and moisture is less severe.
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Maintenance
Machines in your production line will likely see a lot of use, leading to general wear and tear. All the issues detailed above could be associated with use over time, such as build-up of substance or moisture in load cells, or misalignment of system parts. As you continue to use the system, these issues may continue to grow, leading to ineffectiveness and more complex problems. This means that, if you are seeing continual issues with your weighing system, it may need more than re-calibration to address the problem.
Regular maintenance of your systems is recommended to prevent issues from worsening and this maintenance should be planned in on a regular basis to ensure your consistent performance. Any maintenance that is undertaken on your weighing system should contain an assessment of the system in its entirety to make sure that everything is in functional order. The assessment might even include the area around your machinery, as the environment and other machinery have the potential to prevent your system from working at full capacity.
Maintenance and repairs are best provided by the manufacturer of your weighing system, as opposed to a third-party provider. This is because your manufacturer’s engineers are likely to have expert knowledge of the machine, its specifications and how to optimise it, so are best equipped to handle any issues.
Further guidance to improve accuracy in your weighing system
The key to ensuring accuracy in your weighing system is to know how they work, what guidelines to adhere to and being able to check and identify malfunctions when they occur. This can be provided by comprehensive training for your staff, setting up the system correctly and spending time maintaining your equipment.
For further guidance on how to improve accuracy, have discussions with your system supplier, who can provide you with their insight into how the system should be set up and used. Yamato can offer detailed information on each of our checkweighers, and can also install them into your production line so that you can ensure correct set up. Get in touch today to find out more.