Digital load cells, like FUTEK's LSB206 miniature digital sensor, provide fully digital output in an all-in-one solution. These load cells feature embedded electronics that convert the analog signal directly into a digital output, eliminating the need for separate amplifiers and analog-to-digital converters.

How does a Digital Load Cell Circuit work?

Understanding load cell circuits begins with the principle of the strain gauge, the key component in strain gauge load cells. A metal foil strain gauge is a resistive element that changes its electrical resistance when subjected to forces like tension, compression, torque, or weight. This resistance change, triggered by mechanical force, translates into a measurable electrical signal.

A load cell is built around a metallic structure, or “flexure,” to which strain gauges are precisely bonded. Typically made of durable materials like aluminum or stainless steel, the flexure provides two essential properties: (1) robust strength to endure high loads and (2) elasticity to deform under force and then return to its original shape.

When a load is applied, whether in tension or compression, the flexure behaves like a spring and deforms slightly. This deformation alters the strain gauge’s electrical resistance, resulting in a differential voltage change within a Wheatstone Bridge circuit and generating an output voltage proportional to the applied force.

The raw output from the Wheatstone Bridge is usually a low mV/V signal, which is insufficient for direct use with most PLCs, data acquisition systems, computers, or microprocessors. A signal conditioner is often needed to provide regulated excitation to the bridge and amplify or convert this output into a more usable format, such as 4-20mA, VDC, or digital USB.

In traditional setups, Wheatstone Bridge outputs require external signal conditioning. However, modern strain gauge sensors now feature embedded digital signal conditioners, allowing them to output digital signals like SPI and UART directly.

The difference between Analog and Digital Load Cells

In strain gauge-based load cells, a Wheatstone bridge circuit is commonly employed. This circuit generates an output signal in millivolts per volt (mV/V) based on several factors, including the excitation voltage, the number of strain gauges, and the resultant bridge resistance. The key difference between analog and digital load cells lies in how this Wheatstone bridge output signal is processed and interpreted.

Analog Load Cells

With an analog load cell, the mV/V output signal from the strain gauge bridge is first amplified by a signal conditioner. This conditioner amplifies the low-level mV/V signal into a higher, more usable output—typically voltage (VDC) or current (mA). Analog signal conditioners are valued for their straightforward amplification and transmission of the signal without converting it to a digital format. However, as analog load cells depend on stable external factors, like consistent excitation voltage, any variation in power supply or environmental conditions can impact accuracy. For instance, if the excitation voltage fluctuates, the analog output signal will change proportionally, making stable voltage conditions essential for precise measurement.

Digital Load Cells

Digital load cells stand apart from their analog counterparts by integrating an analog-to-digital converter (ADC) and embedded signal conditioning circuitry. These components amplify, filter, condition, and digitize the low millivolt-per-volt (mV/V) signal generated by the Wheatstone bridge, converting it into a digital output format such as SPI, UART, or USB. This process often includes real-time compensation for excitation voltage fluctuations, ensuring consistent and accurate measurements. The onboard processing circuitry reduces susceptibility to noise and enhances signal stability, making digital load cells particularly suitable for precision-critical environments like automation, robotics, and industrial machinery.

In summary, analog load cells output a low mV/V signal that is then amplified by either an external or embedded analog signal conditioner, producing an analog voltage (VDC) or current (mA) output. Due to their sensitivity to excitation voltage changes, analog load cells require stable power conditions for accurate measurements. Digital load cells, on the other hand, convert the mV/V signal directly to a digital value using an internal analog-to-digital converter (ADC). With embedded or external signal conditioners to amplify, filter, and stabilize readings, digital load cells deliver consistent, stable output across various environments, unaffected by excitation voltage fluctuations. Additionally, digital load cells offer versatile digital outputs such as SPI, UART, or USB, making them ideal for microcontroller integration in machine or robotic applications.

Learn more about LSB206

Advantages of Digital Load Cells

Digital load cells provide key benefits over traditional analog load cells, particularly in terms of performance, integration, and cost-effectiveness. Some of the primary advantages include:

• Improved Signal Stability: Digital output maintains signal integrity over long distances, resulting in accurate and reliable data.
• Noise Reduction: Digital signals are less affected by electrical noise, which is critical in environments with significant electromagnetic interference.
• Embedded Electronics: With built-in signal conditioning and analog-to-digital conversion, digital load cells eliminate the need for external signal conditioners, saving both setup time and space.
• Cost Savings: The all-in-one design reduces equipment costs by consolidating multiple functions within the load cell itself, eliminating the need for additional signal conditioning hardware.
• Direct Compatibility with Digital Systems: Digital load cells connect seamlessly with microcontrollers, PLCs, and computers, simplifying data acquisition and control processes.

These advantages make digital load cells, like FUTEK’s LSB206, a practical choice for precise, streamlined, and cost-effective measurement solutions.

FUTEK's Digital Sensor Solution

For applications that demand precision and reliability, we recommend LSB206 Digital S Beam Jr.® Load Cell 3.0. This compact, high-performance sensor combines the accuracy of FUTEK’s miniature S Beam Jr.® design with embedded digital electronics, eliminating the need for external amplifiers and A/D converters. Its features include:

• Embedded digital signal conditioner - SPI and/or UART available.
• Digital output of up to 1,300 samples per second (SPS) and up to 15 Bits of Noise-Free Resolution (NFR).
• Low power consumption of 78mW.
• High-performance tension and compression load cell with nonlinearity and hysteresis of ±0.1% of R.O. (Rated Output).
• Lightweight with 14 grams only and miniature size in a compact package of 0.75in [19.05mm] height and 0.38in [9.5mm] width.
• Integrated overload protection of impressive 1000% of Rated Output.
• Notable non-repeatability of ±0.05% of R.O.
• Shock resistant: 500 g per IEC60068-2-2.

Learn more about LSB206