Guardian ODS vs Istec SpeedSys® 300
In turbomachinery, overspeed protection is critical to preventing failure and ensuring compliance. To help you come to the best decision in choosing the right system, we’ve put out a comparison. In this comparison, we’ll be looking at the Guardian ODS and the SpeedSys 300.
Why forward-thinking OEMs, integrators, and end users choose SpeedSys® 300
Established brands often continue to build on existing architectures for many years, leaving limited room to incorporate user feedback or modern application requirements. Istec, however, has developed its latest systems from the ground up, with a clear focus on today’s needs in machine protection and monitoring.
As a result, SpeedSys® 300 not only covers the core overspeed protection functions traditionally expected from established solutions, but also extends them with a compact modular design, support for multiple sensor types, configurable outputs, modern communication options, and clearly specified response characteristics. This allows users to implement proven protection concepts while benefiting from additional flexibility and transparency that are increasingly important in both new installations and retrofit projects.
Guardian ODS
Istec SpeedSys 300
Proven in use
Guardian ODS is designed for critical turbomachinery applications and has extensive operational use in compressor and turbine overspeed protection systems, including API 670‑based installations.
Certified by design
SpeedSys® 300 is designed with functional safety embedded directly into the system architecture. SIL 2 and SIL 3 capability are integral to the product design and depend on the applied redundancy configuration, rather than being added as an external system layer.
(Background on this approach: Het verschil tussen SIL-certificering door ontwerp en proven in use)
System‑integrated protection concept
Overspeed (and optional acceleration) protection is implemented within a single, integrated system architecture, combining sensing, internal voting, trip logic, logging, and testing functions in one system.
Standalone protection concept
Each SpeedSys® 300 module performs a complete overspeed protection function independently, clearly separating protection functionality from control and monitoring systems.
Internal redundancy approach
Guardian ODS uses a fixed triple‑modular redundant design with three independent speed monitoring modules and integrated 2oo3 voting. Redundancy and voting are inherent to the system architecture.
Modular redundancy approach
Redundancy is achieved by combining multiple SpeedSys® 300 modules, supporting flexible 1oo1, 1oo2, or 2oo3 voting architectures at system level.
Integrated safety outputs
The system provides internally voted shutdown relay outputs, individual alarm relays per module, and 4–20 mA speed outputs for direct connection to trip valves and monitoring systems.
Integrated safety I/O
Safety relays and a safety‑related 4–20 mA analog output are available directly on each module, reducing the need for additional external safety hardware.
Backplane‑based system design
Guardian ODS is built around a shared backplane with plug‑in modules, enabling hot‑swappable replacement of individual modules while the machine remains in operation.
Compact and practical design
The compact footprint supports space‑constrained installations and retrofit projects, while maintaining full overspeed protection functionality within a single module.
Communication for diagnostics
Serial communication interfaces (RS‑232, RS‑422, RS‑485) using Modbus are provided for diagnostics, monitoring, logging, and system integration.
Communication for diagnostics
Modbus RTU over RS‑485 is provided for monitoring and diagnostics, without making communication part of the safety function.
System‑level protection architecture
Guardian ODS operates as a complete, self‑contained overspeed protection system, with protection, voting, and trip functions implemented at system level rather than as independent standalone modules.
Standalone and distributed installation
SpeedSys® 300 is installed as an individual DIN‑rail mounted device. Multiple units can be mounted side‑by‑side to implement redundancy concepts without requiring a shared rack, backplane, or central baseplate.
Lifetime Support
SpeedSys 300 delivers a clean architectural separation between control and trip logic ensuring uncompromised protection compared to integrated systems.
SIL3 by Design
Adapt as needed: from single-channel setups to fully redundant 2oo3 architectures, SpeedSys 300 supports stepwise scalability at every stage.
Compact Footprint and Seamless Integration
Engineered for space-limited panels and demanding environments, it’s ideal for both retrofits and new installations.
FAQ
Yes, it’s an independent overspeed protection system, aligned with the requirement that overspeed protection be separate from the control system.
Yes, both systems support 2oo3 redundant architectures, but they implement redundancy in different ways. SpeedSys® 300 supports up to 2oo3 architectures through external hardwired voting, where multiple independent SpeedSys units are combined to form the required voting logic without relying on a central backplane or CPU. This allows flexible deployment of redundancy tailored to the application. Guardian Overspeed Detection System (ODS) supports 2oo3 voting through a triple‑modular redundant (TMR) architecture, consisting of three independent, hot‑swappable modules with internal 2‑out‑of‑3 voting for shutdown relays and protection functions.
Neither system supports Profibus‑based DCS integration.
SpeedSys® 300 uses Modbus RTU over RS‑485 for communication and diagnostics, while the Guardian Overspeed Detection System provides serial Modbus communication (RS‑232, RS‑422, or RS‑485). Profibus is not part of the communication interfaces of either system.
Accuracy disclaimer
All of our comparison pages have been filled in to the best of our knowledge, using publicly available sources. However, we cannot guarantee that they are fully up-to-date or completely correct.
Istec ensures the availability and safety of your rotating machinery by providing the most convenient and accessible hardware solutions, delivered by the world’s leading vibration and speed sensing experts.
| Aspect | Guardian ODS | Istec SpeedSys 300 |
|---|---|---|
| Key features | Triple‑modular redundant design, internal 2oo3 voting, online testing and repair, integrated logging, API 670 compliant | Overspeed, underspeed and acceleration detection, modular redundancy, compact standalone design, Modbus diagnostics |
| Number of relays | 2 voted shutdown relays + 3 alarm relays (1 per module) | 2 safety relays per module plus additional signal outputs |
| Frequency range | MPU: 100–32,000 Hz; Proximity probe: 0.5–25,000 Hz | 0.0025 Hz – 35 kHz |
| Hardware response time | 12 ms response time (0.5–80,000 rpm) | < 8 ms (relay output) |
| Number of inputs (active) | 1 speed input per module; 3 modules total (2oo3 voting) | 1 input per module (only one sensor input active at a time) |
| Voting system | Integrated internal 2oo3 voting across three modules | 1oo1 (single module); 1oo2 or 2oo3 using multiple modules (external voting) |
| Outputs | • 3 × 4–20 mA analog outputs (speed) • Alarm relays • Shutdown relays • Modbus via RS‑232 / RS‑422 / RS‑485 | • 1 × safety‑rated 4–20 mA analog output • 1 × binary output • 1 × frequency output • Modbus RTU (RS‑485, diagnostics only) |
| Input voltage | Dual-redundant power supplies: 88–264 VAC / 90–150 VDC or 18–32 VDC | 24 VDC (18–36 VDC), dual-redundant power supply |
| Functional safety | TÜV‑certified SIL 3 (IEC 61508); API 670 compliant | SIL 2 / SIL 3 capable; functional safety embedded in system design |
| Stand‑alone protection | Yes – complete overspeed protection within one integrated system | Yes – each module performs a complete overspeed protection function independently |
| Relay information | Shutdown relays: 2oo3 voted, 8 A @ 220 VAC or 24 VDC; Alarm relays: 2 A @ 24 VDC | 2 × safety relays (DPST); max. 30 VDC / 2 A (resistive) |
| Rack / backplane mounting | Yes – shared backplane with plug‑in modules | Optional 19‑inch rack for mechanical mounting only; no shared backplane or internal bus |
| Reserve scalability | Fixed triple‑modular (3‑module) architecture | Scalable from single module (SIL 2) to redundant multi‑module SIL 3 configurations |