Wiring and hardware reduction, compact machine design are the benefits of integrating power, signal and diagnostics in a single sensor cable in industrial automation. These multi-core sensor cables provide power to sensors and actuators, and transmit measurement signals as well as diagnostic information, in a single compact, multi-core bundle. If you’re a cable engineer tasked with selecting cables for robotics, machine tools or control systems, it makes all the difference in terms of reliability, EMC performance, and overall system cost.
At Hulk Electric, we’ve assisted OEMs and system integrators around the world to optimise these combined cables for the stringent application requirements. This guide discusses important design considerations and tradeoffs to help you choose or specify the appropriate sensor cable solution.
Why Combine Power, Signal and Diagnostics in One Cable?
Fewer, smarter connections are favored by modern automation. It is obvious that it is advantageous to bring all the functions together in a single multi-core sensor cable but care will need to be taken in the design aspects.
Fewer Cables, Cleaner Routing and Lower Hardware Count
Conducts power, signal, and diagnostics in the same cable, which reduces cable trays, connectors, and harnesses. This is particularly beneficial when working in restricted machine sided spaces such as around robotic arms or valve islands, where each additional cable contributes to potential failure points, weight and expense.
Smart Sensors and Diagnostics Channels
Most of today’s intelligent sensors provide primary measurement data as well as status, condition monitoring and alarm data. These richer data streams, in turn, are supported by a well-designed combined cable, which also provides power delivery; this means that predictive maintenance and Industry 4.0 are possible without adding any extra wiring.
Core Functions in a Combined Sensor Cable – Power, Signal, Diagnostics
Knowing how each function works will aid in the proper conductor allocation for engineers.
Power Conductors
These cores provide voltage and current to the sensors and/or small actuators. When cross sectional area (CSA) is correct, the current capacity is greater and there is little voltage drop, particularly for longer runs. Oversized power wires will provide better performance but may lead to a decrease in overall flexibility of the cable.
Signal Conductors
Signal lines output analog (eg 4-20 mA) or digital output. Signal integrity can be maintained by paying attention to resistance, capacitance and isolation from power lines to prevent distortion.
Diagnostics and Auxiliary Conductors
Extra cores are used for status signals, secondary measures or superimposed data. These low-level lines tend to be more susceptible to noise in industrial environments and may require additional protection for accurate measurements.
Electrical Design Considerations – Resistance, Capacitance and Current
Real World performance is determined by physical properties of cable.
Conductor Resistance and Voltage Drop
Larger conductors result in lower resistance and heat generation, which can be used for longer cable runs and stable sensor operation. When shopping for combined cables, choose the power cores, but do not forget to keep the diameter to a sensible level.
Capacitance and Signal Fidelity
Higher capacitance in dense multi-core layouts can attenuate signals or slow digital edges. Balanced twisting and proper insulation materials help preserve fidelity for both analog and high-speed digital communication.
Current Capacity vs Flexibility
When designing a dense multi-core layout a high capacitance can cause signal or digital edge attenuation. Balanced twisting and the use of appropriate insulation materials ensure fidelity of analog and high-speed digital communication.
EMC and Routing – Power vs Signal in the Same Bundle
When EMC and Routing are combined in the same bundle, they don’t work together.If EMC and Routing are packaged together, they are incompatible.
Risk of Interference When Combining Power and Signal
Noise may be induced in signal conductors by changing fields produced by power lines. Long parallel runs exacerbate crosstalk, especially in cases of sensitive analog signals.
Shielding, Twisting and Layout Choices
Careful grounding, twisted pairs and overall shielding reduce interference. Natural resilience is provided by differential signaling (e.g. in industrial Ethernet or CAN). Avoid running combined cables parallel to power drives wherever possible and cross perpendicularly where cables must be combined.
When to Separate Power and Signal Cables
For high-EMI environments or for long distances with high-current loads, then separate cables can provide better performance, although they may be more complicated. Measure your noise level to make sure you don’t make the wrong choice.
Power + Data Concepts from Other Domains – Lessons for Sensor Cables
Power-over-Coax or Power-over-Dataline are examples of these kinds of solutions, which represent the old style compact/performance compromise. The combined sensor cables are also based on the same principle: by integration, space is saved, but filters, shielding and conductor allocation are the terms that must be precisely designed.
Machine-Side Sensor/Actuator Cable Solutions – Combining Functions in Practice
The sensor and actuator cables that make up Hulk are designed for use in these types of machine-side applications.
Multi-Core Sensor/Actuator Cables on Machine-Side Routes
Our multi core designs are fully flexible, ensure the power, feedback and diagnostics are organised in one path, perfect for IO-Link, Fieldbus or other sensor configurations.
Jacket and Shielding Choices Based on Route Conditions
Choose PUR jackets that are oil and abrasion resistant or high flex with shielding for areas where motion occurs. Hulk has custom solutions for UL, CE and other requirements.
Termination, Cable OD and Connector Compatibility
Use the correct diameter of cable and correct conductor mapping of your connectors/glands for the longest service life and reliable field installation.
Sensor Wiring Patterns – 2-Wire vs 3-Wire vs Multi-Wire
2-Wire Loop-Powered Sensors
Simplest way with power and signal on the same pair, best for simple applications, but not so good for rich diagnostics.
3-Wire Sensors – Separate Power and Signal
Common configuration that gives dedicated paths making it easier to add diagnostic lines to a combined cable.
Multi-Wire Configurations for Smart Devices
When combined cables make sense and when they don’t, there’s a technique known as Trade-Off Analysis.
Trade-Off Analysis – When Combined Cables Make Sense vs When to Split
Advantages of Combined Cables
- Reduced material and installation costs
- Cleaner machine layouts
- Comprehend how to integrate with modern smart devices, making them easier to use.
Disadvantages and Risks
- Potential EMC issues
- For very small designs, limited power capacity.
- More complicated fault isolation
- More complex fault isolation
Design Rule of Thumb
Combined cables work best for low to medium power, medium to moderate EMI, short to medium runs. If the conditions are very demanding, you may want to use a segmented shielding or separate runs.
Practical Example Scenarios
Machine-Side Valve Island: A multi-core cable with solenoid power, feedback signals and diagnostics to an IO module that is shielded pairs and PUR jacket reliable near the drives.
Smart Sensor with Diagnostics: Power supply and twisted shielded pairs for measurement and condition data in the end-effector of a robot.
High Emi Long Run: Extra care taken to shield and route away from interference from nearby motors.
Design Checklist – Combining Power, Signal and Diagnostics in One Sensor Cable
- Sizing of conductor for current, distance and voltage drop?
- Enough capacitance and shielding to ensure signal integrity?
- EMC risk assessments carried out in accordance with the proper twisting and routing?
- Chemical, temperature, flexible and oil resistant jacket material?
- Comprehensive pin mapping, testing and maintenance documentation?