How to Connect a Load Cell to a Data Acquisition System

To connect a load cell to a data acquisition system, the load-cell signal typically passes through a signal conditioner or amplifier before reaching the DAQ, PLC, or data logger.

The basic signal path is:

Load Cell → Signal Conditioner/Amplifier → DAQ/PLC → Software

Load cells produce a very small mV/V output, so amplification and signal conditioning are often required. The conditioner can provide excitation, amplify the bridge signal, filter electrical noise, and convert it into a suitable voltage or current signal.

Finally, the DAQ or software applies calibration and scaling to convert the electrical signal into a meaningful force or weight reading, such as N, kg, or tonnes.

What Is Load Cell Data Acquisition?

Load cell data acquisition is the process of capturing, converting, recording, and analysing the electrical signal produced by a load cell. A DAQ system receives the load cell’s low-level analogue output and converts it into digital data that can be displayed and processed by a computer or software system.

A typical process is:

Load Cell → Signal Conditioning → Analogue-to-Digital Conversion → Computer/Software

The DAQ system can:

• Receive the electrical output from the load cell.
• Convert the analogue signal into digital data.
• Record and display measurements in real time.
• Monitor changes in force or weight.
• Analyse and store measurement data for further evaluation.

This makes load cell data acquisition useful for both laboratory testing and industrial monitoring, where accurate measurement and continuous data recording are required.

What Can You Measure?

A load cell DAQ system can measure and analyse:

• Weight — monitor material, products, tanks, or containers.
• Force — measure applied or reaction forces.
• Tension — monitor pulling or tensile loads.
• Compression — measure pushing or compressive loads.
• Load changes over time — track how force or weight changes during a process.
• Peak load — identify maximum force or weight reached.
• Process trends — analyse measurement patterns to identify changes, variations, or abnormal conditions.

With suitable software, these measurements can also be displayed as live values, graphs, trends, or recorded datasets, making it easier to understand how a load changes during testing or production.

Load Cell Data Acquisition System: Basic Architecture

A load cell data acquisition system combines the load cell, excitation and signal-conditioning electronics, data acquisition hardware, and software to convert a physical force or weight into usable digital measurement data.

Basic Load Cell DAQ Block Diagram

Load Cell
↓
Excitation Supply
↓
Signal Conditioner / Load Cell Amplifier
↓
DAQ / PLC / Data Logger
↓
Computer / HMI / Cloud Software

In practice, the excitation supply is connected to the load cell’s bridge, while the load cell’s output is sent to the signal conditioner or DAQ. Depending on the equipment, the DAQ or signal conditioner may provide the excitation voltage itself, so a separate excitation supply is not always required.

Role of Each Component

1. Load Cell

The load cell is the primary sensing element. When force or weight is applied, its internal elastic element deforms slightly, causing the strain gauges in the Wheatstone bridge to change resistance.

This produces a small differential electrical output, typically specified in mV/V.

2. Excitation Supply

The excitation supply provides a stable voltage to the load cell’s Wheatstone bridge. Common excitation values depend on the load cell and measurement equipment.

A stable excitation voltage is important because changes in excitation can affect the load-cell output. In many systems, the signal conditioner or DAQ provides this excitation directly.

3. Signal Conditioner / Load Cell Amplifier

The load-cell output is usually very small, so a signal conditioner or amplifier prepares it for the acquisition system. It may:

• Amplify the millivolt-level signal.
• Filter electrical noise.
• Provide stable load-cell excitation.
• Provide electrical isolation where required.
• Convert the bridge signal into a standard output such as voltage or current.

Some DAQ devices have built-in bridge excitation and amplification, eliminating the need for a separate conditioner.

4. DAQ / PLC / Data Logger

The DAQ (Data Acquisition) system receives the conditioned analogue signal and converts it into digital data. It can sample the signal at a selected rate and send the measurements to software for recording and analysis.

A PLC can also receive a suitable load-cell signal for industrial automation, while a data logger can record measurements over an extended period.

5. Computer / HMI / Cloud Software

The final stage displays, records, and analyses the acquired data. Depending on the application, software can show:

• Real-time force or weight
• Measurement trends
• Peak loads
• Time-based load changes
• Alarms and process limits
• Historical measurement data

What Do You Need to Connect a Load Cell to a DAQ?

Connecting a load cell to a DAQ requires compatible sensing, signal-conditioning, power, acquisition, and software components. Before installation, check the specifications of each component to ensure they work together correctly.

1. Load Cell

Choose a load cell based on the required capacity, output sensitivity, resistance, and wiring configuration. Most strain gauge load cells provide a low-level output measured in mV/V and are available in 4-wire or 6-wire configurations.

The recommended excitation voltage should also be checked in the manufacturer’s specifications. Selecting the correct capacity is important because the load cell must safely handle the expected maximum force or weight.

2. Load Cell Amplifier or Signal Conditioner

Because the load-cell output is usually only a few millivolts, a signal conditioner or amplifier may be required before connecting it to the DAQ. It amplifies the bridge signal and can also provide filtering, stable excitation, and electrical isolation.

Depending on the application, the conditioner may provide a standard voltage or current output, such as 0–10 V or 4–20 mA. However, some DAQ devices have built-in bridge excitation and signal conditioning, so a separate amplifier may not be necessary.

3. DAQ Device

The DAQ must be capable of measuring the signal produced by the load cell or signal conditioner. Check whether it provides a suitable analogue input or dedicated bridge input, along with the required input range, resolution, and sampling rate.

For slowly changing weight measurements, a lower sampling rate may be sufficient. Dynamic force measurements may require a much higher sampling rate.

4. Power Supply

The system requires suitable power for the load cell, signal conditioner, and DAQ. The load cell needs a stable excitation voltage, while the amplifier or conditioner requires its specified operating supply.

The excitation supply may be built into the DAQ or signal conditioner, meaning a separate power source is not always required.

5. Software

The software receives the digital data from the DAQ and converts it into useful engineering measurements. It can handle scaling, calibration, data recording, graphing, and alarms.

For example, software can convert the DAQ signal into kilograms, newtons, or tonnes and display the load as a real-time value or trend graph.

How to Connect a Load Cell to a Data Acquisition System

Connecting a load cell to a data acquisition system requires more than simply connecting wires. The load cell, excitation supply, signal conditioner, DAQ input, and software must all be electrically compatible. Follow these steps to establish a reliable measurement system.

Step 1: Check the Load Cell Specifications

Before making any connections, review the manufacturer’s datasheet. Confirm the rated capacity, rated output in mV/V, recommended excitation voltage, number of wires, wiring configuration, and environmental specifications such as IP rating and operating temperature.

The load-cell capacity should be suitable for the expected measurement range, while the rated output determines the size of the electrical signal available to the DAQ system.

Important: Never assume wire colours. Wire colours can vary between manufacturers and models. Always follow the manufacturer’s wiring diagram.

Step 2: Identify the Load Cell Wires

A typical four-wire strain gauge load cell has two excitation wires and two signal wires:

A six-wire load cell additionally includes Sense+ and Sense− wires. These sense wires monitor the excitation voltage at the load cell and can compensate for voltage drops in longer cables when used with compatible instrumentation.

Before connecting the sensor, identify each wire from the manufacturer’s documentation rather than relying on colour alone.

Step 3: Provide Excitation

A strain-gauge load cell requires an excitation voltage to energise its internal Wheatstone bridge. The excitation supply should be stable and within the voltage range specified by the manufacturer.

The excitation voltage directly affects the available load-cell output. For example, a 2 mV/V load cell supplied with 10 V excitation can produce approximately 20 mV at rated load.

Using an incorrect excitation voltage can result in incorrect measurements, unstable operation, or potentially damage the sensor or connected electronics. Depending on the equipment, excitation may be provided by the DAQ, signal conditioner, or a separate power supply.

Step 4: Connect the Load Cell to the Signal Conditioner

The basic connection is:

Load Cell → Signal Conditioner

The signal conditioner acts as an interface between the low-level load-cell bridge and the DAQ. It can amplify the millivolt signal, filter unwanted electrical noise, provide excitation, and prepare the signal for the acquisition system.

Depending on the equipment, the conditioner may provide outputs such as:

• 0–10 V
• ±10 V
• 4–20 mA
• Digital output

The correct output should be selected according to the input requirements of the DAQ or PLC.

Step 5: Connect the Conditioner to the DAQ

The next connection is:

Signal Conditioner → DAQ Analogue Input

Make sure the signal conditioner output falls within the DAQ’s specified input range. For example, a 0–10 V conditioner output should be connected to a DAQ input capable of measuring that range.

Use appropriate signal wiring and connect the signal reference correctly. Shielded cable can help reduce electrical interference, particularly in industrial environments. Load-cell and signal cables should also be routed away from high-voltage power cables, motors, drives, and other major sources of electrical noise.

Step 6: Connect the DAQ to the Computer or PLC

Once the analogue signal reaches the DAQ, the system converts it into digital measurement data. Depending on the application, the DAQ may communicate with a computer through:

DAQ → USB/Ethernet → Computer

For industrial automation, the arrangement may instead be:

Signal Conditioner → PLC Analogue Input → HMI/SCADA

The computer, HMI, or SCADA software can then display the measured force or weight, record data, generate trend graphs, monitor peak loads, and trigger alarms when predefined limits are reached.

Can a Load Cell Connect Directly to a PLC?

Usually not to a standard PLC analogue input.

A conventional strain-gauge load cell produces a very small millivolt-level differential signal, typically specified in mV/V. Standard PLC analogue inputs, however, commonly accept industrial signal formats such as 4–20 mA, 0–10 V, or ±10 V rather than a raw load-cell bridge signal.

For this reason, a signal-conditioning device is normally required:

Load Cell → Load Cell Transmitter → 4–20 mA / 0–10 V → PLC

The load-cell transmitter provides the required excitation, amplifies and conditions the low-level bridge signal, and converts it into a standard analogue output that the PLC can read.

When Can a Load Cell Connect Directly to a PLC?

A load cell can be connected directly when the PLC has a dedicated load-cell input or weighing module designed to accept strain-gauge bridge signals. These modules may provide load-cell excitation, high-resolution analogue-to-digital conversion, filtering, and calibration functions.

Therefore, always check the PLC or input module specifications before connecting a load cell. A standard analogue input should not be assumed to support a raw mV/V load-cell signal.

Load Cell Signal Conditioner Explained

A load cell signal conditioner is an electronic interface that prepares the low-level electrical signal from a load cell for connection to a DAQ, PLC, display, or data acquisition system. Since strain-gauge load cells typically produce only a small mV/V bridge signal, conditioning is often required for reliable measurement.

Key Functions

A signal conditioner can perform several functions depending on the model and application:

• Bridge excitation: Provides a stable excitation voltage to energise the load cell’s Wheatstone bridge.
• Signal amplification: Increases the small millivolt signal to a more usable measurement level.
• Filtering: Reduces electrical noise and unwanted signal fluctuations.
• Electrical isolation: Provides isolation between the load cell and connected control equipment where supported.
• Zero/span adjustment: Allows the measurement range and zero point to be configured or calibrated.
• Signal conversion: Converts the load-cell bridge signal into a standard analogue or digital output.

Common Outputs

Depending on the conditioner, the output may be provided as 0–10 V, ±10 V, 4–20 mA, or a digital interface. The appropriate output should match the input requirements of the DAQ, PLC, or other receiving equipment.

Why the Correct Conditioner Matters

Choosing the correct signal conditioner is critical because it directly affects the quality and accuracy of the measurement. The conditioner must be compatible with the load cell’s mV/V sensitivity, excitation requirements, bridge resistance, required accuracy, and operating environment.

An unsuitable conditioner can introduce excessive noise, incorrect scaling, signal saturation, or measurement errors. A properly matched conditioner provides stable excitation, appropriate amplification and filtering, and a compatible output, helping the DAQ or PLC produce reliable and repeatable force or weight measurements.

Load Cell Data Logger vs DAQ System

Both load cell data loggers and DAQ systems can capture measurements from load cells, but they are designed for different levels of monitoring, analysis, and automation.

Which One Should You Choose?

A data logger is a practical choice when the main requirement is to record load or weight measurements over time without needing a complex control system. It is useful for field measurements, periodic monitoring, and applications where stored data can be analysed later.

A DAQ system is generally better when you need higher sampling flexibility, real-time analysis, computer-based monitoring, or integration with PLCs and industrial automation systems.

Load Cell Data Acquisition Sampling Rate

The sampling rate determines how frequently a DAQ system measures the load-cell signal. Choosing the correct sampling rate is important because the system must capture changes in force or weight quickly enough to represent the actual measurement without missing important events.

Static Weighing

For static weighing, the load changes slowly and remains relatively stable. Therefore, a lower sampling rate may be sufficient. Applications such as platform scales, tank weighing, and inventory measurement generally do not require extremely fast data acquisition.

Filtering can also be used to reduce small fluctuations and provide a stable weight reading.

Dynamic Weighing

Dynamic weighing involves loads that change continuously, such as conveyor weighing, filling systems, or moving products. These applications may require a higher sampling rate so the DAQ can capture changes in the load accurately.

The required rate depends on how quickly the load changes and the desired measurement accuracy.

Impact or Rapid Force Measurement

For impact, vibration, or rapidly changing force measurements, the DAQ must sample fast enough to capture short-duration events and peak loads. If the sampling rate is too low, important peaks may occur between samples and be missed or underestimated.

Key Factors to Consider

• Sampling frequency: The number of measurements taken per second, usually expressed in Hz or samples per second.
• Filtering: Reduces noise and unwanted fluctuations but must be selected carefully because excessive filtering can remove or reduce genuine load changes.
• Signal bandwidth: The measurement system must have sufficient bandwidth to capture the frequency content of the force being measured.
• Peak capture: A sufficiently high sampling rate and suitable signal bandwidth are essential when maximum or impact loads need to be detected accurately.

How to Improve Load Cell Data Quality

Accurate load-cell measurements depend not only on the sensor itself but also on wiring, signal conditioning, mechanical installation, and calibration. The following practices can help improve measurement stability, repeatability, and overall data quality.

Use Proper Signal Wiring

Use shielded signal cable where appropriate to reduce electromagnetic interference. Keep load-cell and signal cables separated from high-voltage wiring, motors, variable-frequency drives, and other sources of electrical noise.

Maintain Stable Excitation

A stable excitation supply is important because the load-cell output depends on the excitation voltage. Use the excitation voltage recommended by the manufacturer and ensure the power supply is suitable for the complete measurement system.

Select the Correct Amplifier and Filtering

Choose an amplifier with an appropriate gain and input range for the load-cell mV/V output. Filtering should reduce unwanted noise without removing genuine load changes, particularly in dynamic or impact measurements.

Ensure Correct Mechanical Installation

Mechanical installation has a major effect on load-cell accuracy. Mount the sensor according to the manufacturer’s instructions and ensure the applied force follows the intended load direction.

Avoid side loading, twisting, mechanical binding, vibration, and uneven mounting, as these can introduce measurement errors.

Check Grounding and Electrical Isolation

Proper grounding can help reduce electrical interference and unstable readings. Where required, use suitable electrical isolation between the load-cell circuit, signal conditioner, DAQ, and control equipment to minimise ground-loop problems.

Perform Regular Calibration

Regular calibration helps maintain measurement accuracy and identify changes caused by mechanical wear, overload, temperature effects, or electronic drift. Calibration intervals should be based on the application, operating conditions, and manufacturer’s recommendations.

FAQs

How do I connect a load cell to a DAQ?

Connect the load cell to a compatible bridge input or load-cell signal conditioner. The conditioner can provide excitation and amplify the low-level mV/V signal before sending it to the DAQ. The DAQ then converts the signal into digital data for measurement, recording, and analysis.

Do I need an amplifier for a load cell?

An amplifier is usually required when the DAQ or controller cannot directly measure the load cell’s low-level millivolt output. A suitable amplifier increases and conditions the signal so it matches the input range of the DAQ. However, a separate amplifier may not be necessary if the DAQ already has a dedicated load-cell or bridge input.

Can a load cell connect directly to a PLC?

Not normally to a standard PLC analogue input. Conventional load cells produce a low-level mV/V bridge signal, while standard PLC inputs commonly expect signals such as 0–10 V or 4–20 mA. A load-cell transmitter or dedicated weighing module is typically used to provide a compatible interface.

What is a load cell signal conditioner?

A load cell signal conditioner is an electronic device that interfaces between the load cell and the measurement or control system. It can provide bridge excitation, amplify the load-cell signal, filter electrical noise, and convert the signal into a standard output such as 0–10 V or 4–20 mA.

Conclusion

A reliable load cell data acquisition system requires correct wiring, signal conditioning, compatible DAQ equipment and proper calibration. The typical setup is:

Load Cell → Amplifier/Signal Conditioner → DAQ/PLC → Software

Choosing the right components ensures accurate, stable and reliable force or weight measurements.