Dry contacts, analogs, serial, IP—what to use when.
Define the electrical “languages” your system speaks. This page clarifies when to use dry contacts, 24VDC I/O, analog signals, or simple supervisory protocols so automatic HVM bollards interoperate with fire/BMS/SCADA (346, 533). We outline Ethernet/serial options, fiber vs copper, and isolation methods that survive harsh sites (347, 337). Acceptance tests tie into the interlock matrix (352), I/O list (523), and SAT steps (634–638) to preserve crash rated bollard safety intent. Include one-sentence context that naturally links upward to the parent hubs (this section and the chapter hub). Add SIRA context with a link to SIRA Bollards (UAE) when relevant. Link installation pages only if helpful: What to Expect and Installation Guide.
Important: This is a general guide. For live projects we develop a tailored
Method Statement & Risk Assessment (MS/RA) and align with authority approvals (e.g., SIRA) where in scope.
531.1 Dry contacts/relays
Simple, robust for interlocks and fire drops. Use where HVM bollard behavior must be deterministic and independent of network noise (352, 532).
Dry contacts are the lowest-risk way to assert critical inhibits, emergency drops, or permit signals. They’re immune to protocol versions and can be supervised with end-of-line resistors if needed. For life-safety tie-ins via PLC/Controller, define contact state at rest, debounce, and fail-safe orientation in the I/O list (523).
Where deterministic response matters (e.g., fire alarm → bollards down), map hardwired contacts into the interlock matrix (352) and verify with point-to-point tests. Keep wiring routes and contact ratings aligned with enclosure and cabling practices (347, 528).
| Aspect | What matters | Where to verify |
|---|---|---|
| Determinism | Known states on loss of power/comms | Modes of Operation |
| Safety | Hardwired inhibits & E-stops | Safety circuits |
531.2 24VDC I/O
Standardize levels and polarity. Clean 24VDC signaling keeps a crash rated bollard lane responsive and testable (523).
Use 24VDC sourcing/sinking I/O for local status and permissives, with clear polarity, common return policy, and surge suppression at coils. Adopt a single color/ferrule scheme (Panel Wiring Standards, 527) and segregate power vs control (Cables & Routing, 515). Document normal/abnormal logic in the I/O list and prove each point during Power-On & Controls Health (632).
531.3 4–20mA/0–10V
Use for analog status (pressure/position). Scale and filter so HVM bollard thresholds are reliable (519).
Analog channels are ideal for HPU pressure, EM drive load, or position feedback. Prefer 4–20 mA for noise immunity and open-circuit detect; use 0–10 V for short local runs in clean environments. Define scaling, alarm bands, and filtering in the controller and show acceptance thresholds under Power Test Points (519). Where critical, add local displays and record values into counters/health telemetry (541–542).
531.4 Modbus/BACnet (plain)
Lightweight supervision to BMS/SCADA (533). Keep it read-mostly so crash rated bollard control remains local (521).
Plain SCADA/BMS links (e.g., Modbus RTU/TCP, BACnet MS/TP/IP) suit dashboards, alarms, and counters. Expose read-only points for states, KPIs, and health pings; restrict commands to non-safety functions or require dual-channel authorization. Describe registers and priorities in the Integration Documentation (539) and align alarm semantics with the Alarm Philosophy (536). Core motion control must remain at the local controller (521).
531.5 Ethernet/serial
Choose media per distance/EMI; document ports. Stable links prevent HVM bollard comms faults (535).
Serial (RS-485/232) is simple and robust for device buses; Ethernet offers speed, segmentation, and tooling. For outdoor panels, specify industrial connectors, screened cables, and proper earthing/segregation (347, 516). Assign fixed port roles, VLANs where applicable, and time sync for logs (NTP; see 542). Capture addressing and connector pin-outs in the Interface Control Document (ICD) and label clearly in the panel (528, 527).
531.6 Fiber/copper choices
Fiber for noise/long runs; copper for local panels. Media choice preserves crash rated bollard uptime.
Use fiber for distances, galvanic isolation between buildings, and high-EMI corridors; copper for short intra-panel links and where PoE accessories are needed. For fiber, specify single-mode vs multi-mode, connector type, and patch discipline. For copper, enforce surge protection and bonding, and avoid shared containment with power (515). Reflect choices in drawings and site test sheets so SAT teams can fault-isolate quickly (638).
531.7 Protocol converters
Use gateways sparingly and document maps. Converters shouldn’t become hidden HVM bollard failure points (539).
Gateways (e.g., Modbus↔BACnet, serial↔IP) add complexity and single-point risks. If required, choose industrial units with watchdogs, clear fallback states, and logged configuration. Freeze firmware versions (537), export a tag map, and include a converter-bypass test in commissioning so the lane can still fail-safe without the gateway. Keep a spare pre-configured unit in the common spares policy (734, 854).
531.8 Isolation methods
Opto/galvanic isolation between domains. Isolation protects crash rated bollard safety IO (343).
Break fault paths between domains: use opto-isolated input cards, relays, or dedicated signal isolators. Provide surge protective devices at panel entries (514) and maintain separate returns to avoid ground loops. Isolation strategy should be visible in the Control Architecture (521) and verified with induced-fault tests where safe. Record isolation notes in the ICD and panel door card (528).
531.9 Acceptance tests
Point-to-point checks and timeout/failover trials (634). Tests prove HVM bollard interfaces behave as specified.
For each interface, test the happy path and loss-of-signal behavior: contact open/short, 24VDC polarity reversal, analog wire-break/out-of-range, serial bus disconnect, IP link flap, and converter failure. Timeouts and retries must match the interlock matrix (352) and alarm policy (536). Capture evidence per point in the Witness Procedure (638), with COS (change-of-state log) entries and annotated photos (716).
Related
External resources
- FEMA 426 / DHS — Reference Manual
- ASIS — Security Risk Assessment Standard
- NPSA — Hostile Vehicle Mitigation Guidance
531 Interface Types — FAQ
Should bollard motion be controlled over BMS/SCADA or kept local?
Keep motion control local at the PLC/Controller for determinism and safety. Use BMS/SCADA for read-mostly supervision (states, alarms, counters), and require dual-channel authorization or physical interlocks for any remote commands.
When do we choose dry contacts instead of a protocol?
Use dry contacts where fail-safe states and immediate response are critical (e.g., fire drop, E-stop, permissives). Contacts are protocol-agnostic, simple to test point-to-point, and immune to version or network issues.
How do we test a Modbus/BACnet link during SAT?
Verify addressing and register maps, then simulate state changes and communication loss. Check timeouts/retries, alarm translation, and that the bollard lane remains safe if the supervisory link fails.
Fiber or copper for outdoor links between panels?
Use fiber for long runs, high EMI, or building-to-building links (galvanic isolation). Use copper for short local runs or where PoE is required, adding surge protection and proper bonding.