Understanding the output signal of load cells

2021-11-12 11:03

　　A load cell is a type of force sensor used in weighing instruments. This article introduces the concept of the output signal from a load cell, as well as the principle behind resistive strain-gauge load cells, which convert the gravitational force acting on the measured object into a measurable output signal according to a specific proportion. Additionally, it discusses how variations in gravitational acceleration and air buoyancy at different locations can affect the conversion process. Key performance indicators of load cells include linear error, hysteresis error, repeatability error, creep, zero-point temperature characteristics, and sensitivity temperature characteristics.

　　A weighing sensor outputs a measurable electrical signal; essentially, it’s a device that converts a mass signal into a measurable electrical output. When selecting a sensor, the first consideration should be the actual working environment in which the sensor will be used. This is crucial for choosing the right weighing sensor, as it directly affects whether the sensor can function properly, as well as its safety, service life, and even the overall reliability and safety of the entire weighing system.

　　The new and old national standards differ significantly in their fundamental concepts and evaluation methods regarding the key technical specifications of load cells. Common types include S-type, cantilever-type, spoke-type, plate-ring type, diaphragm-type, bridge-type, and cylindrical-type sensors, among others.

　　Traditionally, load sensors are referred to as weighing sensors. Force Measurement Sensor A general term used to describe its metrological characteristics evaluated by individual parameters. The previous national standard treated two distinct types of sensors—those designed for "weighing" and those intended for "force measurement"—as a single unified category, despite their vastly different application scenarios and environmental conditions, and failed to differentiate between their respective testing and evaluation methods. The old national standard included a total of 21 indicators, all tested under ambient temperature conditions. Furthermore, the maximum error among six key metrics—nonlinearity, hysteresis error, repeatability error, creep, zero-point temperature-induced error, and rated-output temperature-induced error—was used to determine the overall performance. Weighing sensor Accuracy classes are represented by 0.02, 0.03, and 0.05, respectively.

　　A force sensor used in weighing instruments. It converts the gravitational force acting on the object being measured into a measurable output signal according to a specific proportion. Taking into account how gravitational acceleration and air buoyancy at different locations can affect the conversion, Weighing sensor The key performance indicators include linear error, hysteresis error, repeatability error, creep, zero-point temperature characteristics, and sensitivity temperature characteristics. In various weighing instruments and mass measurement systems, a comprehensive error band is typically used to collectively control the accuracy of sensors, linking the comprehensive error band directly to the instrument's tolerance range. This ensures that the appropriate weighing sensor is selected for a specific accuracy class of weighing equipment.

　　The International Organization of Legal Metrology (OIML) stipulates that the sensor's error band δ should account for 70% of the weighing instrument's total error band Δ. Additionally, the combined errors of the load cell—including linear error, hysteresis error, and any temperature-induced sensitivity variations within the specified temperature range—must not exceed the error band δ. This allows manufacturers to fine-tune each component contributing to the overall measurement error, ensuring the desired level of accuracy is achieved.

The principle and application environment of weighing module sensors

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