This article we will discuss the different errors that can occur in a load cell. This is slightly technical and best understood in consultation with your weighing engineers.
The more you understand your load cell the better you can determine the dynamics of weighing.
This article will help you to understand different load cell errors and in turn help you choose the right components and manage the environment that determines the final weight output displayed by your weigh bridge.
Here we will be considering different factors that determine the final output from your load cell. It will be a good idea to consult with your weighing engineers to understand these factors better. As this is going to help to zero down the right load cell that would fit your requirement.
The more you understand your load cell the better you can determine the dynamics of weighing.
Factor-1 – Error amplification
Load cells may amplify an error with increase in weight. This is termed as non-linearity issue.
The impact of this issue can be best understood with an example. When you weigh a load of 200 kg let’s say the error of 10 kg is encountered. We at times assumethat this error is constant. But to our surprise we may find that when we weigh 2000 kg the error is also amplified 10 times. We may have calibrated the weighbridge to nullify 10kg but with 2000kg measurement the error of 90kg still remains in the measurement. This is surely not an error to be neglected.
There are load cells that are pre-calibrated to tackle such non-linearity errors. This is one of the major factor that differentiates load cells based on cost.
As a consumer you may be startled by the price difference of load cells in the market. One major factor that drives the price of the load cell is determined how good a load cell is handling such linearity issues.
Linearity issues is a major factor that determines the cost of load cells
Factor 2 – Hysteresis
Do you know that your load cell may have different reading for the same weigh applied to it? This difference is encountered when the load is increased to a specific weight and second when the weigh is being decreased to that weight. Technically it is called Hysteresis.
This comes in affect when we need to fill a shipment to a particular weight or empty a container toa certain weight.
Most of the load cells are calibrated against hysteresis and linearity issue together and called as combined error.
Factor 3 – Error with time and frequency
Load cells may display some error while repeatedly measuring weight. This is one factor that must be accounted for as well to mitigate any error in the final output.
Load cell also shows difference with time, when the load remains on the cell for a long time. This is called creep effect.
Factor 4 – Temperature changes
Temperature changes the sensitivity of the load cell. Most of the load cells are temperature-compensated to reduce errors.
But if the weighing cycle exposes the load cells to low temperature (at night) and high temperature at day time is wise to account for errors due to temperature change.
Your weighbridge is a huge machine. It can take the load of heavy trucks for your business needs. But what needs to be understood is that at the end of the day, your weighbridge is a precision instrument. The core functionality of the weighbridge of providing the correct weight is possible due to the load cells present in it. This article will serve you as the load cell maintenance guide.
Load cell maintenance and why do you need it –
We have talked a lot on how weighbridge errors can steal away your business profitability earlier. Faulty load cells can be a major reason for the same. So for your weighbridge to perform uniformly, your load cells need to be serviced and calibrated periodically from a competent company.
What are the safety tips for load cell maintenance –
- Keep the weigh bridge clean – Your weighbridge will age faster if it is not relieved of the dust and mud. Make it a point to keep the weigh bridge clean. Use an air blower to keep the area across load cell free of dust.
- No flooding – Make sure that you have an efficient drainage system to get rid of the water from the pit. Water and moisture poses threat to your load cell.
- Welding is not cool – Just let us know in case you need any welding repairs to be done on your weighbridge. Do not try to do electric welding on your weighbridge by a welder. As the welder may not know how to get the welding done without destroying the load cell. Welding requires high current and that can destroy the load cell easily.
- No compromise on electric source – Weighbridge needs a stable and a good quality power source. Providing a dedicated and stable power source will be a good idea to provide a long life for your machine. One better way is to avoid sharing the power source which is attached to machinery that destabilises power.
- Do not avoid servicing – Servicing is insurance towards getting quality output from your weighbridge. Tie up for an annual maintenance with a competent company and be assured of good health of your weighbridge.
- Calibration – Calibration is an important aspect of your weighbridge. In fact you are legally obliged to maintain accuracy of your weighbridge in case you are using it for business purposes. You can also go through our article which deals with calibration and maintenance of your weigh bridge. As a rule of thumb calibrate your weighbridge in case you have repaired or replace components like load cells or weight indicator.
NOTE: It is usually a trend in organization to calibrate their weighbridges against a common weighbridge. Let’s call it the mother calibration for the organization. It is advised to calibrate that weighbridge against light, medium and heavy categories of weight.
Example. For a 60 ton weighbridge –
Light weight is: 5to 10 ton
Medium: 20 to 30 ton
Heavy: 50 to 60 ton
This is recommended to avoid linearity problems. if you do get your weighbridge calibrated with only one vehicle because of unavailability at site it will cause weight difference later and it will trouble you. Though the best way is to perform with right test weights for the whole procedure but is rarely possible as it’s not available.
We have been helping organizations to weigh accurately since 5 decades. You can write to us or comment us below and we will be glad to help you.
How to choose a load cell?
A good load cell can determine the performance of your weighbridge. If you are thinking of purchasing a load cell, you should consider some important points.
Your choice of load cell guarantees optimum performance of your weigh bridge. To achieve weighing accuracy and proper weighing data, one should consider the choice of load cell. To choose a good load cell the factors responsible are-
• System capacity- The capacity of your weighbridge determines what load cell you
choose. It is also responsible for determining accuracy.
• The brand of load cell- Make sure you choose a good quality load cell. In the recent
times, many local vendors have started producing load cells. Even the production of duplicate load
cells has led to inaccurate weighing measurements. A good brand with good quality is worth the price.
• Type- Analog/Digital as per the requirement. Each type has a price attached. But, for
proper accuracy selecting a type irrespective of its price would be advisable.
Hence, selecting a good load cell with proper consultation can help you achieve weighing accuracy.
Analog or Digital Load cell?
Load cell also known as a load sensor or transducer converts mechanical force into electrical signal. However, there is always a lot of confusion pertaining to the choice of load cell. An analog load cell functions differently when compared to digital load cells.
The performance of your weighing machine is determined by various components. One such vital component for any weigh bridge is the load cell. It is considered to be the heart of your weighing machine.
We do not say that analog is better than digital or vice versa. Yet, this comparison just aims to highlight the pros and cons of analog and digital load cell.
In analog load cells, analog to digital (A/D) conversion is performed at the indicator, whereas; in digital load cells perform A/D conversion using an internal A/D converter.
In analog load cells, indicators from different manufacturers can be freely combined, but, it is highly recommended to use digital load cells and indicators from the same company if you choose digital load cells.
In case you are facing calibration issues, it would be better to choose digital load cells as they are lab tested (pre-calibrated) and hence requires no site calibration. Hence, digital load cells from Tulsi Weigh Solutions are pre-calibrated.
For example, if you purchase a 60 ton weighbridge you will have to arrange for 25% of test weights (as per the Rules and Regulations by Legal Metrology Department) for calibration. But, if you purchase digital load cells you do not have to worry about calibration. But, not to forget all the requirements as per the Legal Metrology Department has to be provided depending on the State.
Thus, digital load cell reduces your problem of calibration, which is not the same with analog load cells.
Furthermore, digital load cells provide you with an added advantage. Digital load cells are capable of transmitting the weight on the load cell in digital form. This prevents any kind of manipulation and secures your weighing data. It fortifies your weighing measurement from any kind of theft.
Yet, in case of analog load cell, the signal input is received by the indicator, where it is converted to digital form. In comparison, digital load cell is more stable than analog load cell.
Corner correction is normally not required when the weigh bridge is designed using digital load cell. Nevertheless, in case of exceptional structure deformity or mounting assembly defects, the corner errors can be removed with minimal effort.
Note: You have to comply with all the rules and regulations as stated and required by the Legal Metrology Department.
How placement of your vehicle determines your weighing data?
Are you gloomed due to the difference in weighing data? Is your weighing machine causing deadly accuracy issues? Have you been constantly criticizing your weighing measurements?
There are many reasons that can lead to such differences in weighing data. However, few important factors can be considered to receive proper measurements. These factors include-
• How you apply the load on your weighing system.
• Equal load should be distribution on load cells.
• Do not miss on the placement factors.
• On a weighbridge, ensure that equal pressure applied on the load cells for
proper weighing data.
For long lasting weighing systems and better reading of the measured data, here are few simple concerns that needs to be kept in mind-
• Placement of the vehicle is imperative.
• Corner difference should not be present.
As such, your vehicle should not be placed outside the weighing scale. For accurate weighing data maintaining the placement of your vehicle is highly advisable.