The selection of weighing sensors must pay attention to 5 major parameters

The selection of weighing sensors must pay attention to 5 major parameters

When facing a detailed technical specification sheet of a load cell, the numerous parameters can indeed be overwhelming. Selecting a model is not just a simple parameter comparison, but a precise matching based on application requirements.

This article aims to help you get straight to the point, clarify which parameters are the "critical points" that you must understand and focus on, and how to interpret the meaning behind them, so as to make a wiser choice and effectively distinguish the professionalism of suppliers.

### 1. Understanding Load Cell Parameters: Basic Concepts as a Bridge for Communication
The core of "understanding" lies in demand matching: Indeed, you don't need to be a sensor design expert. But having a deep understanding of the core requirements of your own application (such as accuracy, range, environment, installation, service life, regulatory requirements, etc.) is a prerequisite. This enables you to ask precise questions when communicating with manufacturers and understand the rationality of their suggestions.

**Value and Risk of Professional Manufacturers**: Relying on professional manufacturers is a wise move, but the word "professional" needs to be verified:

- **Risk Points**: There are many salespeople in the market who have only a superficial understanding of technical details or make excessive promises. If you are completely unfamiliar with basic concepts, you are easily misled, leading to wrong model selection. At best, the accuracy is not up to standard; at worst, the sensor is overloaded and damaged, equipment shuts down, and even safety accidents are caused.
- **Self - protection Strategy**: The subsequent "key parameter knowledge" in this article is your most powerful "shield" against being deceived. Being able to ask key questions (for example: "In a high - temperature environment, how is the temperature drift parameter guaranteed? ", "What is the OIML R60 error limit for this precision level? ") can quickly distinguish the professional depth of the other party.
- **Verify Professionalism**: Require the manufacturer to provide model selection suggestions for your specific application scenario and explain the basis for their parameter selection; inquire about their production standards (such as whether they follow OIML R60, NTEP, etc.), calibration procedures, and quality control measures.

### 2. In - depth Analysis of Core Parameters of Load Cells: "Hard Indicators" That Must Be Looked at for Model Selection
(1) **Accuracy - related Parameters**: The Golden Standard for Measuring "Accuracy"
- **Nonlinearity**: The maximum deviation of the sensor's output curve from its ideal straight line. It reflects the quality of the sensor's "linearity" throughout the range.
- **Repeatability**: The consistency of the sensor's output when loaded to the same load multiple times under the same conditions. It reflects the stability and reliability of the sensor. This is a very critical indicator for measuring the internal quality of the sensor.
- **Hysteresis**: The maximum difference between the output values of the sensor during the loading process and the unloading process at the same load point. It reflects the energy loss of the sensor material or structure during the force application/unloading process.

- **Clarification and In - depth Interpretation of User Misconceptions**:
The one - sidedness of "the values are probably consistent": Although the values of these three errors in the specification sheet are often close or even the same (for example, all marked as ±0.02% F.S.), this is not an absolute rule, and it does not mean that they are the same concept.
Excellent sensor design will strive to optimize these three indicators to make them all reach a high level and be balanced.
The true meaning of accuracy grade: The comprehensive accuracy (Accuracy/Class) of a sensor is determined by these three core error items: nonlinearity, repeatability, and hysteresis (usually also including creep, zero - point temperature influence, sensitivity temperature influence, etc.).
The accuracy grade on the specification sheet (such as C3, 0.03%) is a comprehensive indicator, representing the upper limit of the overall performance that the sensor can achieve under standard conditions. When checking the specification sheet, be sure to confirm whether the marked accuracy grade includes these core error items.

How to "Understand" Accuracy:
Look for "comprehensive accuracy" or "accuracy class": This is the most intuitive indicator. For example, "Accuracy: 0.05% F.S." or "Compliant with OIML C3 class".
Check error components: If only single - item errors are listed (such as nonlinearity ±0.017% F.S., repeatability ±0.01% F.S., hysteresis ±0.02% F.S.), the comprehensive accuracy is usually equal to or slightly greater than the maximum value of these single - item errors.
A more rigorous calculation requires reference to the formulas defined in relevant standards (such as OIML R60, EN 12640), and each error is synthesized in a specific way (usually Root Sum of Squares, RSS).
Key to model selection: If your application requires an accuracy of ≤0.1% R.O., be sure to choose a sensor with a nominal comprehensive accuracy better than 0.1% F.S. (such as 0.05% or 0.03%). Because there are also additional errors introduced by installation, environment (temperature), signal processing, etc. in actual applications. Leaving a margin is the key to ensuring system accuracy.

(2) **Capacity/Range**: The Cornerstone of Safety and Accuracy
- **Selection Iron Law - Redundancy**: The 30% redundancy you mentioned is an industry consensus and best practice. For example, if the maximum weight to be measured is 1000kg, a sensor with a capacity ≥1300kg should be selected.
- **In - depth Interpretation and Expansion**:
- **Prevent Accidental Overload**: Material impact, operational errors, equipment vibration, etc., may cause the instantaneous load to exceed the design maximum. Redundancy is the last line of defense to prevent plastic deformation (permanent damage) of the sensor's core elastic body.
- **Protect Measurement Accuracy**: When the sensor is close to its full range, errors such as nonlinearity and creep usually increase. The best performance can be obtained when operating within 70 - 80% of the range.
- **Extend Service Life**: Avoid long - term operation under extreme stress to reduce fatigue damage.
- **Dynamic Load Consideration**: If the application involves frequent impact or vibration (such as batching scales, dynamic weighing), a larger safety factor (such as 50% or even higher) is required, or a sensor specially designed for impact/dynamic response should be selected.
- **Minimum Load**: Specifications often mark the minimum measurable load. If your application needs to measure very small weights (such as no - load or tare weight), pay attention to this parameter, as it is related to sensitivity and signal noise.

(3) **IP Rating**: Armor Against the Environment
- **Interpretation of IP Code**: IPXX (e.g., IP67)
- The first digit (X): Solid foreign object intrusion grade (0 - 6). For example: 6 represents complete dustproof.
- The second digit (X): Waterproof grade (0 - 9K). For example: 7 represents short - term immersion in 1m deep water without water ingress for 30 minutes; 8 represents continuous water immersion, and the depth and time are specified by the manufacturer; 9K represents the ability to withstand high - pressure/high - temperature water jet cleaning.

### Key Points for Model Selection:
- **Matching the Environment**: Select an appropriate IP rating based on the dust, moisture, flushing (especially high-pressure and high-temperature flushing in food, chemical, and pharmaceutical industries), oil contamination, etc. at the sensor installation location. IP65/IP66 are basic requirements for common industrial environments; IP67/IP68/IP69K are strongly recommended for humid and flushing environments.
- **Sealing Material**: Sensors with high protection ratings typically use special sealing rings (such as fluororubber FKMI) and sealing processes. Ask the manufacturer whether the sealing material can withstand possible chemical corrosion or high temperatures in your field.
- **Cable Inlet**: The protection rating also includes the sealing at the cable inlet. Ensure that the selected cables and connectors (or potting treatment) can meet the same IP rating requirements.

### (4) Excitation Voltage and Rated Output/Sensitivity: The Source and Intensity of Signals
- **Excitation Voltage (V exc)**: The input voltage supplied to the sensor bridge. The common range is indeed DC 5V - 15V (a typical value is 10V).

### Notes for Model Selection/Use:
- **Matching the Instrument**: Ensure that the excitation voltage provided by your weighing instrument (or signal conditioner) is within the allowable range of the sensor.
- **Stability Requirements**: The stability of the excitation voltage directly affects the stability of the output signal. The ripple of the excitation voltage provided by the instrument should be small.
- **Power and Temperature Rise**: A higher excitation voltage can bring a larger output signal (with better signal-to-noise ratio), but it also means an increase in the internal resistance power consumption of the sensor, which may lead to an increase in temperature drift. In occasions with extremely high accuracy requirements, trade-offs need to be made (sometimes using constant current source excitation is also a solution).
- **Rated Output/Sensitivity (Sensitivity/Rated Output - RO)**: Defined as the millivolt-level (mV) output change generated by the sensor per unit excitation voltage under the rated load (full range). The unit is mV/V. Values of 1 - 3 mV/V are most common (such as 2 mV/V).

### In - depth Interpretation and Calculation:
- **Signal Magnitude Calculation**: Actual output signal (mV) = Excitation voltage (V) * Sensitivity (mV/V) * (Current load / Full - range load). For example: With 10V excitation, 2 mV/V sensitivity, and measuring 500kg (full range 1000kg), the output signal ≈ 10V * 2 mV/V * (500/1000) = 10 mV.
- **Estimation of Minimum Detection Limit**:
- **Sensor End**: Theoretically, the minimum weight change that a sensor can distinguish is limited by its noise level (it may be marked as "resolution" or "minimum static load output recovery" in the specification sheet, or reference to repeatability error may be required).
- **High - sensitivity sensors** output larger signals under the same excitation, which helps improve the signal-to-noise ratio (SNR), thereby possibly distinguishing smaller weight changes.
- **System End**: The minimum detectable weight of the actual system is determined by sensor noise + signal conditioning circuit noise + ADC resolution.
- **Simplified Estimation Formula**: Min Detectable Weight ≈ (Comprehensive accuracy error % * F.S. * 1000) / (Sensitivity mV/V * Excitation voltage V * System gain * uV corresponding to ADC resolution). This requires knowing the details of the entire signal chain.
- **A more practical approach**: Choose sensors with higher sensitivity (such as 2 mV/V or 3 mV/V) and excellent repeatability/noise indicators, and select high - resolution ADCs (such as 24 - bit) and low - noise amplifiers for the instrument.
- **Matching Instrument Range**: The measurement range (mV input) of the instrument needs to cover the output signal range of the sensor under the maximum and minimum loads. Sensors with high sensitivity output larger mV under the same excitation and load, making it easier to match the input range of the instrument and make full use of the resolution of the ADC.

### (5) Other Key Parameters to Focus on as Needed
- **Temperature Influence**:
- **Zero Temperature Drift**: The change in the sensor's zero - point output when the temperature changes. The unit is usually %F.S./10°C.
- **Sensitivity Temperature Drift**: The change in the sensor's sensitivity (output signal magnitude) when the temperature changes. The unit is the same as above.
- **Key for Model Selection**: If the temperature change in the working environment is large (> ±10°C), these two parameters are crucial! Select sensors with small temperature drift coefficients (such as < 0.002% F.S./10°C), or confirm whether temperature compensation has been performed inside the sensor and whether the compensation range covers your working conditions (such as -10°C ~ +40°C). High - precision applications may require external temperature sensors for real - time compensation.
- **Creep**: The amount by which the sensor output slowly changes over time under constant load and environment. The unit is %F.S./xx min (such as 30 min). It affects long - term weighing or process control.
- **Material**:
- **Elastic Body**: Alloy steel (economical and commonly used), stainless steel (corrosion - resistant, necessary for food and pharmaceutical industries), aluminum alloy (lightweight). Select according to environmental corrosiveness.
- **Cable**: PVC (general - purpose), PUR (abrasion - resistant, oil - resistant), Teflon (high - temperature resistant, corrosion - resistant). Select according to mechanical wear, chemical contact, and temperature.
- **Mounting Type**: Column type, cantilever beam type, S - type, shear beam type, bellows type, compression type, tension type, etc. It must match your mechanical structure and force - bearing method perfectly! Choosing the wrong mounting type will greatly affect accuracy and even cause damage. This is the top priority when communicating with the manufacturer's engineers.
- **Safe Overload and Ultimate Overload**: After safe overload (such as 150% F.S.) and internal loading, the sensor performance should be recoverable; ultimate overload (such as 300% F.S.) is the load at which the sensor may suffer permanent damage. The redundancy is mainly aimed at safe overload.

### Summary and Golden Suggestions
- **Demand is King**: Clearly define your application scenario (range, accuracy, environment, installation, regulations).
- **Accuracy Core**: The comprehensive accuracy grade is the primary indicator. Understand that it is composed of nonlinearity, repeatability, hysteresis, etc. Ensure it is better than your system requirements.
- **Range Iron Law**: Be sure to reserve a redundancy of ≥30%, and a larger redundancy is needed in dynamic impact environments.
- **Protection Matching**: Select the IP rating according to the severity of the environment (IP65/IP66 for basic industry, IP67/IP68/IP69K for humid and flushing environments), and pay attention to the sealing material.
- **Signal Foundation**: Understand the excitation voltage range and match it. Use the output sensitivity (mV/V) to estimate the signal magnitude and evaluate the minimum detection potential (combined with system noise and ADC).
- **Environmental Adaptability**: Pay attention to temperature influence (zero - point and sensitivity drift) and material selection (corrosion resistance, wear resistance).
- **Installation Matching**: The mounting type is the basis for physical implementation, so be sure to confirm it correctly.
- **Professional Communication**: For special requirements (extreme temperature, strong corrosion, high dynamics, special installation, regulatory certification such as OIML/NTEP), unconfirmable parameters, or complex applications, be sure to have direct and detailed technical communication with the application engineers of the sensor manufacturer. Provide as many application details as possible.