When selecting a load cell for your application, understanding the various specifications is crucial for ensuring optimal performance, accuracy, and reliability. This comprehensive guide to load cell specifications covers everything you need to know about the terms and figures that regularly appear in technical drawings, datasheets, calibration certificates, and other documents.
By grasping these specifications, you can make informed decisions to select the best load cell for your needs. Whether you are dealing with industrial weighing, precision laboratory measurements, or dynamic applications, understanding these parameters will help you ensure accurate and reliable performance.
DEFINITION: Rated Capacity, also sometimes referred to as full scale (FS) capacity, maximum capacity, or Emax, refers to the maximum load that a scale or load cell is designed to measure. This value is specified by the manufacturer and represents the upper limit of the weighing system’s operating range, ensuring reliable and accurate performance without causing accelerated fatiguing, damage, or significant error beyond standard tolerance.
EXPRESSION: Unit of weight (e.g., kilograms, pounds) or force (e.g., Newtons).
FURTHER INFORMATION: It is common for one model of a load cell to be available in multiple rated capacities. This flexibility allows the same basic design to be used across different applications, which may require different load ranges. The variations in rated capacities for a single load cell model can be achieved through primarily through:
DEFINITION: Full Scale Output (FSO), also known as rated output, is the electrical signal output produced by a load cell when the maximum rated load (Emax) is applied.
EXPRESSION: Millivolts per volt (mV/V). This means that for every volt of excitation supplied to the load cell, the output signal will be a certain number of millivolts when the load cell is loaded to its rated capacity (Emax).
Example: A load cell with a rated capacity (Emax) of 10,000 kg and an FSO of 2 mV/V ± 0.25% means that when 10,000 kg is applied, the load cell will produce an output of ~2 mV (plus or minus 0.25%) for every volt of excitation. If the excitation voltage is 10V, the output signal at full capacity would be 20 mV with an error margin of ±0.05 mV. Thus, the output signal at full capacity could range between 19.95 mV and 20.05 mV.
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DEFINITION: Zero Balance, also known as zero offset, is the output signal of a load cell when no load is applied. Ideally, this output should be zero, but due to manufacturing tolerances and environmental factors, there is usually a small non-zero output.
EXPRESSION: Millivolts per volt (mV/V).
For example, a zero balance specification of ±0.02 mV/V indicates that the load cell output with no load can vary by up to 0.02 mV for every volt of excitation.
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DEFINITION: Non-linearity in a load cell refers to the deviation of the load cell’s output from a straight line that represents the ideal response across the entire range of the load cell. It is a measure of how much the actual output curve deviates from the ideal linear curve.
EXPRESSION: Percentage of the full scale output (FSO).
For example, a non-linearity specification of < ±0.017% FSO indicates that the maximum deviation from the ideal linear output is less than ±0.017% of the FSO.
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DEFINITION: Repeatability in a load cell refers to the ability of the load cell to produce consistent output readings when the same load is applied multiple times under the same conditions. It is a measure of the variability in the output signal for repeated applications of the same load.
EXPRESSION: Percentage of the full scale output (FSO).
For example, a repeatability specification of ±0.01% FSO indicates that the output variation for repeated applications of the same load is within ±0.01% of the FSO.
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DEFINITION: Hysteresis in a load cell refers to the difference in the output signal when the same load is applied, depending on whether the load is approached from an increasing or decreasing direction. It measures the lag in the load cell’s response to changes in load, which can cause inaccuracies in the output signal.
EXPRESSION: Percentage of the full scale output (FSO).
For example, a hysteresis error specification of ±0.02% FSO indicates that the difference in output due to hysteresis is within ±0.02% of the FSO.
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Application: Hysteresis error is particularly critical in dynamic applications where loads are continuously cycled, such as in industrial weighing systems, testing machines, and automation equipment.
DEFINITION: Creep in a load cell refers to the change in the output signal when a constant load is applied over a specific period, typically measured in 30 minutes. It is a measure of the load cell’s stability and ability to maintain a constant output under a sustained load.
EXPRESSION: Percentage of the full scale output (FSO) over a specified time period, usually 30 minutes.
For example, a creep specification of ±0.03% FSO in 30 minutes indicates that the change in output under a constant load will not exceed ±0.03% of the FSO over a 30-minute period.
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Application: Creep is particularly critical in applications such as material testing, industrial weighing, and structural monitoring, where loads are applied for extended periods.
DEFINITION: Input resistance in a load cell refers to the electrical resistance measured across the input terminals of the load cell, specifically between the positive excitation (+EXC) and negative excitation (-EXC) leads. This parameter is critical for the proper functioning and compatibility of the load cell with the excitation voltage provided by the signal conditioning electronics.
EXPRESSION: Ohms (Ω).
For example, an input resistance specification of 400Ω ±25Ω indicates that the resistance between the excitation terminals can range from 375Ω to 425Ω. The specified tolerance (e.g., ±25Ω) accounts for variations in the manufacturing process.
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DEFINITION: Output resistance in a load cell refers to the electrical resistance measured across the output terminals of the load cell, specifically between the positive signal (+SIG) and negative signal (-SIG) leads.
EXPRESSION: Ohms (Ω).
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DEFINITION: Recommended excitation, also referred to as the “rated excitation,” refers to the optimal voltage range that should be applied to the load cell for accurate and reliable operation. This voltage powers the load cell’s internal circuitry, particularly the strain gauges, to produce a measurable output signal in response to applied loads.
EXPRESSION: Volts (V), along with a maximum allowable voltage.
For example, a load cell might specify a recommended excitation of 10V with a maximum of 15V, indicating that while 10V is ideal for optimal performance, the load cell can safely operate up to 15V.
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DEFINITION: Insulation resistance in a load cell refers to the electrical resistance between the load cell’s electrical circuit and its metal body or shield. It is a measure of how well the load cell’s electrical components are isolated from the load cell body, preventing unwanted current leakage and ensuring accurate measurements.
EXPRESSION: Giga-ohms (GΩ), with a specified test voltage.
For example, an insulation resistance specification of >2 GΩ (50V DC) indicates that the resistance is greater than 2 giga-ohms when tested with a 50-volt direct current (DC) supply.
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DEFINITION: The compensated temperature range of a load cell refers to the range of temperatures over which the load cell is designed to maintain its specified performance, accuracy, and stability. Within this range, the load cell’s internal temperature compensation mechanisms work to minimize errors caused by temperature variations.
EXPRESSION: Degrees Celsius (°C) and or Fahrenheit (°F).
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DEFINITION: This specification refers to the change in the load cell’s zero output signal (zero balance) or sensitivity due to changes in ambient temperature. It indicates how much the zero balance or sensitivity drifts per degree of temperature change.
EXPRESSION: Percentage of the full scale output (Cn) per degree Celsius (or Kelvin).
For example, a specification of < ±0.0040% of Cn/°C indicates that the zero balance or sensitivity will change by less than ±0.0040% of the full scale output for each degree Celsius of temperature variation.
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DEFINITION: The safe overload capacity of a load cell refers to the maximum load that can be applied without causing permanent damage or significant degradation of performance. It is typically expressed as a percentage of the full scale capacity.
EXPRESSION: Percentages of the full scale (FS) capacity.
For example, safe overload might be 150% of FS, meaning that the load cell can safely handle loads up to 150% of its rated capacity without damage.
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DEFINITION: The breaking overload capacity is the maximum load that a load cell can withstand before experiencing catastrophic failure. This threshold is also expressed as a percentage of the full scale capacity.
EXPRESSION: Percentages of the full scale (FS) capacity.
For example, breaking overload might be 300% of FS. This means that the load cell can withstand loads up to 300% of its rated capacity before breaking.
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DEFINITION:
EXPRESSION: Seal types are described by their specific method of sealing (environmental or welded), while IP ratings are expressed as IPXX, where XX are numerical digits.
For example, IP67 indicates a high level of protection against dust and temporary immersion in water.
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DEFINITION: The cable color code of a load cell refers to the standardized color scheme used for the wiring of the load cell’s electrical connections. This color coding helps identify the function of each wire, ensuring correct installation and connectivity.
EXPRESSION: Each wire color alongside its corresponding function.
For example:
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DEFINITION:Combined error, also known as total error, is the maximum deviation of weighing system output, obtained for increasing and decreasing applied loads. EXPRESSION: Percentage of the full scale output (FSO). For example, a combined error specification of 0.03% FSO indicates that the maximum deviation from the true value due to all combined errors will not exceed 0.03% of the load cell’s full scale capacity FURTHER INFORMATION:
DEFINITION: Deflection at Emax refers to the amount of vertical displacement or deformation that occurs in a load cell when it is subjected to its maximum rated load (Emax). This measurement indicates how much the load cell bends or deflects under full load conditions.
EXPRESSION: Millimetres (mm).
For example, a deflection range of 0.04 mm to 0.14 mm at Emax indicates that when the load cell is loaded to its full rated capacity, it will deform by an amount within this specified range.
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DEFINITION: The estimated weight of a load cell, excluding any additional accessories, mounting hardware, or packaging. This weight is a physical property that can impact the installation and application of the load cell, and also helps to inform product fulfilment logistics.
EXPRESSION: Kilograms (kg) or pounds (lb).
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DEFINITION: Minimum Dead Load, or Load Cell Minimum Capacity (emin) refers to the manufacturer’s rating for the smallest load that can be accurately measured by the load cell without exceeding the maximum permissible error as defined by its certified accuracy class (OIML, NTEP, other). It represents the lower limit of the load cell’s effective measurement range.
EXPRESSION:emin is typically expressed in the same units as the load cell’s maximum capacity (emax), such as kilograms (kg), pounds (lb), or Newtons (N).
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DEFINITION: The Minimum Verification Interval (Vmin) is the smallest increment of load that can be accurately measured and verified by a load cell or scale. It represents the minimum weight change that can be reliably detected and is used to determine the load cell’s resolution and precision during calibration and verification processes.
EXPRESSION: Units of weight, such as kilograms (kg), pounds (lb), or grams (g).
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DEFINITION: Y-Value is a calculated value also known as Relative Vmin. Y-value is the ratio of the Maximum Cell Capacity (Emax) to the Minimum Load Cell Verification Interval (Vmin). This ratio describes the resolution of the load cell independent from the load cell capacity.
EXPRESSION: Y-value is expressed as a ratio
It is calculated by dividing the load cell’s maximum capacity (Emax) by its minimum load cell verification interval (Vmin). For example, a load cell with an Emax of 10,000 kg and a Vmin of 1 kg would have a Y-Value of 10,000.
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DEFINITION: The apportionment factor (PLC) is a value used in the context of load cell calibration and verification to distribute the maximum permissible error (MPE) among multiple load cells in a weighing system. It reflects the proportion of the total allowable error that can be attributed to an individual load cell within the system.
EXPRESSION: PLC is typically expressed as a decimal or percentage.
For example, a PLC of 0.7 indicates that 70% of the total allowable error is assigned to a load cell (assuming it is a single cell system).
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DEFINITION: The Maximum Number of Verification Intervals (nmax) refers to the highest number of discrete intervals into which the load cell’s measurement range can be divided while still maintaining the specified accuracy. It is an indicator of the load cell’s resolution and precision.
EXPRESSION: nmax is typically expressed as an integer value.
For example, an nmax of 3000 indicates that the load cell’s measurement range can be divided into 3000 equal intervals, each representing a verification point.
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Different manufacturers and resellers have varied methodologies for providing load cell specifications. As such, there can be significant differences in how the data should be interpreted. Some may rely on theoretical calculations or industry-standard benchmarks, while others might derive information from more rigorous live testing.
At ANYLOAD, we distinguish ourselves by only providing data that we have proven through extensive live testing using our comprehensive array of equipment. This approach ensures that our specifications are accurate and reliable, reflecting more accurately real-world performance rather than theoretical assumptions.
Additionally, in scenarios where there is uncertainty or a high risk of error, we may understate our figures. This conservative approach provides our customers with an added layer of security, ensuring that our load cells perform reliably even in the most demanding conditions. By prioritizing accuracy and reliability, we help our customers achieve precise and dependable measurements in their applications.
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