The type of cable, power source, network structure, and number of connected devices are some of the variables that affect the greatest distance that FOUNDATION Fieldbus (FF) can travel. An in-depth explanation is provided below:
Maximum Cable Length in FOUNDATION Fieldbus
Main Trunk Length:
- The main trunk length refers to the primary cable running from the power supply to the junction boxes.
- The maximum length for a FOUNDATION Fieldbus H1 segment (with a typical cable) is 1,900 meters (6,233 feet).
Spur Length:
- The spur length refers to the cable running from the junction box to individual field devices.
- The maximum length of each spur is 120 meters (394 feet).
Combined Length:
- The total cable length (including trunk and all spurs) must not exceed 1,900 meters (6,233 feet).
Factors Influencing Cable Length
Cable Type:
- FOUNDATION Fieldbus typically uses Type A cable (twisted shielded pair), which provides the best performance for long distances.
| Cable Type | Maximum Segment Length (meters) | Maximum Segment Length (feet) |
|---|---|---|
| Type A | 1,900 | 6,233 |
| Type B | 1,200 | 3,937 |
| Type C | 400 | 1,312 |
| Type D | 200 | 656 |
Voltage Drop:
- Voltage drop across the cable can limit the distance. Proper calculation of the power supply voltage and load is necessary to ensure all devices receive sufficient power.
Network Topology:
- FOUNDATION Fieldbus uses a bus topology where devices are connected along a common cable (trunk), with spurs leading to individual devices.
Number of Devices:
- The segment supports up to 32 devices, but the actual number may be limited by power and signal strength.
Signal Integrity:
- High resistance, interference, or poor shielding in the cable can reduce the maximum length.
FOUNDATION Fieldbus Distance Table
| Parameter | Specification | Details |
|---|---|---|
| Maximum Trunk Length | 1,900 meters | Using Type A cable with proper power supply. |
| Maximum Spur Length | 120 meters | Distance from junction box to the device. |
| Total Cable Length | 1,900 meters | Combined length of trunk and spurs. |
| Maximum Devices Per Segment | 32 | Limited by power and communication requirements. |
| Recommended Cable Type | Type A | Twisted shielded pair for optimal performance. |
| Cable Resistance (Type A) | 22 ohms/km | Low resistance ensures better signal transmission. |
| Cable Capacitance (Type A) | 100 nF/km | Low capacitance minimizes signal degradation. |
Practical Considerations for Designing FOUNDATION Fieldbus
- For longer distances, repeaters can be used to extend the segment length. Each repeater allows an additional 1,900 meters.
- Ensure the power supply provides adequate voltage and current for all connected devices.
- Avoid electromagnetic interference by using proper cable shielding and grounding.
- Maintain proper spacing between fieldbus cables and high-voltage power lines.