Expert tips for important load cell specifications

Selecting the right load cell requires a detailed understanding of its specifications and how they interact with the specific requirements of your application.

The webinar from Interface entitled “Demystifying specifications"" offers a series of tips to help you make informed decisions about the type of sensor that will meet your test and measurement needs. By focusing on key metrics related to capacity range, accuracy, temperature, calibration, and system-level considerations, you can develop realistic expectations regarding the performance and longevity of your measurement equipment investments.

Five tips for specifying load cells and their impact on performance

Selecting a load cell is about more than just choosing a measurement range; it's about understanding how the sensor will perform in your specific system. Below are top tips from force measurement interface experts to help you understand the five most important load cell specifications so you can get the most accurate and reliable measurements.

#1 – Capacity range

A load cell's capacity is often the first consideration, but its impact extends far beyond handling the maximum expected load. Proper sizing of the capacity is critical for both signal quality and product longevity. An oversized load cell may provide a weak signal, while an undersized load cell risks physical damage.

For applications with external loads, composite load calculations are essential to determine a capacity that can accommodate all forces without compromising signal integrity or causing premature failure. For cyclic loading, distinguishing between standard and fatigue-resistant load cells is crucial. Standard cells are suitable for a few hundred thousand cycles. However, for millions of cycles or fatigue testing, a load cell with fatigue characteristics or a standard load cell with significantly higher capacity is required. Even for cyclic loading, unidirectional applications (compression only or tension only) with a lower percentage of capacity often allow for non-fatigue cells. Read more here: Fatigue-rated load cells 101.

The biggest challenge in determining load cell capacity is ensuring the load cell is sufficiently sized to provide a sufficient signal for quality measurements while avoiding physical damage. Incorrect sizing can significantly impact product quality and service life.

CAPACITY TIP: Always compare load cells based on the consistency of their signal output across different capacities, not just the stated capacity, to avoid misinterpretation of measurement quality.

#2 – Accuracy Metrics

Accuracy isn't a single, fixed number. It's a dynamic concept influenced by the details of your measurement's use case. Different accuracy specifications are relevant depending on factors such as temperature profile, load profile, and calibration data. If your test environment has a constant temperature, temperature-related accuracy specifications are less important. Likewise, hysteresis is irrelevant for simply increasing load tests. The quality of the excitation supplied to the sensor is also crucial, as any noise in the excitation is directly reflected in the measurement signal. Here's a white paper on this topic: Factors contributing to the accuracy of load cells.

ACCURACY TIP: To achieve a certain level of accuracy, the entire system must be considered, not just the load cell itself.

#3 – Temperature influences

Temperature significantly influences both the zero point and span of a load cell. While these effects can be characterized and often compensated for, it is critical to ensure that the temperature around the sensor is as standardized and consistent as possible. It is strongly recommended to bring the entire system, including the mounting and wiring, up to temperature without applying force. This allows you to observe the thermal behavior and ensure that all mechanical elements stabilize. Read here: Understanding cable length and temperature effects

TEMPERATURE TIP: Focusing exclusively on the temperature behavior of the sensor without considering the rest of the system can lead to other error influences that make the temperature performance of the sensor almost irrelevant.

#4 – Calibration

Proper calibration is essential for optimal load cell performance. Calibration should closely match the actual test conditions, taking into account whether tension, compression, or multi-point data is required. It is important to understand the type of calibration described in the load cell specifications and the Calibration certificate In addition to the calibration method, the uncertainty of the calibration itself is a critical, often overlooked factor. To compare the performance of a load cell, you need to know the calibration uncertainty (e.g., 0,04% vs. 0,02% for deadweight calibration). A load cell with seemingly good specifications but a high or unrecognized calibration uncertainty poses a significant risk to your measurements.

CALIBRATION TIP: Always prefer calibrations with low, traceable uncertainties, such as dead weight calibration.

# 5 – System Level

Achieving the specified load cell performance requires a systems-level approach. This means considering all components that interact with the load cell, including the measuring devices, cabling, and fixtures. How will you connect your load cells to the measuring device? What size cable will you need to reach the measuring devices? Are you considering wireless signals? What type of connector will you use? What does the pinout diagram indicate about sensor connection and wiring?

Measuring instruments, cables, connectors, accessories, signals, gauges, and fixtures are all elements that can cause errors, such as electrical noise from measuring instruments, signal degradation from long or unshielded cables, or extraneous loads from inappropriate fixtures. The way a load cell is mounted and calibrated directly impacts its ability to meet datasheet specifications. By following best practices for load cell integration and calibration, you can ensure that the entire measurement system functions harmoniously and achieves the desired performance. Understanding the unique requirements of your application allows you to focus on the few basic specifications and simplify sensor selection and integration.

SYSTEM-LEVEL TIP: It's important to follow best practices for connecting and correctly using the load cell. Interface strongly recommends system-level calibration when purchasing a sensor and measuring devices together. This is the best way to avoid performance errors. Verification: System-level calibration.

Expert tips on load cell specification

Listen to what Brian Peters and Keith Skidmore have to say about these 5 key considerations for specifying load cells.