Load Cell Wiring 101
Proper load cell performance depends significantly on the electrical system, including cables, connectors, and mating connectors. Wire colors and pin assignments are essential when assembling your load cell using connectors, cables, and instrumentation. Wiring mishaps are a source of electrical connection errors, leading to inaccurate readings, equipment damage, or even safety hazards.
Signals define the electrical system in force measurement. Load cells often refer to this as millivolt, voltage, or current output. The signal is transmitted from the strain gage sensor through a connector or cable with a series of pins or colored wires matched to a cable assembly.
For example, many Interface load cells offer four wire colors: red, white, black, and green. These wires function for positive excitation and signal output and negative excitation and signal output. Interface’s 6-axis multi-axis sensors have 24 pins and 24 wire colors, each with a function to transfer the measurement data output via a connector and cable to an instrument, such as a data acquisition system.
TIP: Use our Electrical Wiring and Diagrams for reference.
Interface provides a detailed connector pin diagram by model for our load cells, torque transducers, multi-axis sensors, load pins, tension links, and instrumentation online and in product specifications. The connector pinout and integral cable models are defined by pinout, wire color, and function by individual model. The following is the connector pin diagram for the 1000 Fatigue-Rated Universal LowProfile® Load Cell.
1000 Series Connector Pin Diagram
Essential Electrical Wiring Support Guide
Interface provides a detailed electrical wiring support reference with cable and connector wire color coding diagrams. The thorough online resource is a must-have for anyone who needs a quick reference to the color configurations. Download a copy here.
Interface Electrical Wiring Diagrams Resource includes:
- Electrical Selection Chart by Model Number
- Load Cell Cable Wiring Diagram
- Load Cell Connector Wiring Diagram
- Load Cell Wire Color Coding
- Torque Transducer Wire Color Coding
- 3-Axis Wire Color Coding
- 3-Axis Round Wire Color Coding
- 6-Axis Wire Color Coding
The Importance of Consistent Color Coding
While there are standard conventions, it is critical to always consult the specific load cell’s datasheet. Adherence to standards reduces errors and simplifies troubleshooting, especially in complex setups. Proper color coding drastically reduces the time spent troubleshooting connection issues.
Understanding Wire Systems
The four wires in a typical load cell are related to a Wheatstone bridge circuit.
- Excitation (+/-): The voltage supplied to the bridge.
- Signal (+/-): The millivolt output is proportional to the force applied.
Many cables are also shielded to reduce noise. The shield wire, often bare or in a separate color, is typically grounded.
Six-wire systems add two “sense” or “remote sense” wires. These wires compensate for voltage drops in the excitation wires, improving accuracy. They are connected back to the instrumentation to provide feedback on the actual voltage at the bridge.
Multi-axis sensors are inherently complex, and accurate wiring is essential. Each axis has its own set of excitation and signal wires. Always refer to Interface’s online pin diagrams and our electrical reference.
Nine Practical Wiring Tips
1 – Always double-check all connections before applying power.
2 – Ensure proper color matching by reviewing the pinouts in your specifications.
3 – Check if you have acceptable input to data acquisition.
4 – Examine noise immunity and requirements for shielded cables.
5 – Use an appropriate cable length as the effect of long cable lengths on signal integrity.
6 – Determine proper grounding.
7 – Use appropriate crimping tools and connectors for reliable connections.
8 – If the load cell is in a harsh environment, use cables and connectors rated for that environment.
9 – The load cell may need to be recalibrated after wiring changes.
Common problem areas are loose or dirty electrical connections or incorrect connections of color-coded wires.
Expert Advice Related to Wiring, Cables, and Connectors
Interface partners with Rob Fuge, CEO and founder of Epsilon Laboratory, a strain gage, load cell, and cable expert. He provides tremendously useful references and support in Minimizing Error in Load Cell Cables.
“If you add length to the cable by extending the lead wires without taking the proper steps to correct it, you will see a decreased signal. This is because the voltage drop between the DAQ and the load cell is increased due to the added resistance of the lead wires.” – Rob Fuge
Rob offers this respected tip: check the number of pins. Loading cells with integral cable terminated to a connector is extremely important. Rob’s suggestions:
Pins Tip #1—If there are 4 pins, your load cell does not have sense leads. They can be added to the mating connector and extension cable without altering the calibration, but cable temperature effects will persist in the 4-conductor portion.
Pins Tip #2 – If there are 6 pins, your load cell may have sense leads. Consult the data sheet for the assignment of each pin and see if any pin pairs have much lower resistance than the rest. By way of example, if pins 1 and 3 measure 350 ohms, but pins 1 and 6 measure 1.2 ohms, then either pin 1 or 6 is likely the intended sense lead. Once you have confirmed that your load cell has sense leads, you can extend all 6 conductors via a mating cable. Any time a solder joint is reflowed, it may slightly impact the calibration. Ask a load cell expert for help designing your measurement for the highest possible accuracy.
Get more insights and load cell instrument-specific cable references from Epsilon Laboratory’s Rob Fuge here.
Cable Assemblies and Connectors
The Interface Sensor Interconnect Cable Assemblies Guide provides wire information for connecting transducers to Interface indicators and other instrumentation.
A cable assembly transmits signals and ensures accurate measurements. Features like shielding to protect against interference, twisted pairs to reduce noise, and durable jackets to withstand environmental factors are important considerations.
Utilize the Interface Cables and Connectors Brochure when pairing a sensor with an instrument, whether using an Interface instrumentation device or another product you use to gather and analyze data. You will get a full review of cable assemblies, connectors, and electrical details, including load cell integration cables type, wire size, number of wires, shield, description, load cell cable wiring diagrams, and connectors.
Cable Effects on Performance from Interface’s Load Cell Field Guide
Cable Length Effects: If the Interface load cell is sold with cables of any length, the sensitivity is determined by the installed cable during calibration. For load cells with connectors, there will be a loss of sensitivity of approximately 0.37% per 10 feet of 28 gage cable and 0.09% per 10 feet of 22 gage cable. This error can be eliminated if a six-wire cable is run to the end of the load cell cable or connector and used with an indicator with sense lead capability.
Temperature Effects: Since cable resistance is a function of temperature, the cable’s response to temperature change affects the thermal span characteristics of the load cell cable system. For 6-wire systems, this effect is eliminated. For 4-wire cables, the effect is compensated for in the standard cable lengths offered with the load cells if the load cell and cable are at the same temperature simultaneously. For non-standard cable lengths, there will be an effect on thermal span performance. The impact of adding 10 feet of 28 gage cable is to cause a decrease in sensitivity with a temperature equal to 0.0008%/°F (an amount equal to the standard Interface specification).
Adding 10 feet of 22 gage cable decreases the sensitivity by 0.0002%/°F. Customers can often tolerate the degraded performance since our standard specification is extremely tight. However, this can be a significant factor for long cable runs or high-accuracy applications. In such cases, the best approach to the problem is to run six wires to the end of the standard cable length and sense the excitation voltage, eliminating the problem. For a copy of Interface’s essential Load Cell Field Guide, go here.
Understanding load cell wiring is paramount for accurate and reliable force measurement. Correct connections ensure the signal transmitted from the strain gauge through the cabling to the instrumentation is precise and error-free. Incorrect wiring can lead to inaccurate data, equipment damage, and safety hazards.
By adhering to specifications and understanding colors, connectors, and cables, load cell users can minimize errors, streamline troubleshooting, and maximize the performance and longevity of their load cell systems. A thorough grasp of load cell wiring is essential for obtaining trustworthy and consistent measurement results.
