Bently Nevada 3500/53 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 Bently Nevada 3500/53 and the SpeedSys 300.
Why forward-thinking OEMs, integrators, and end users choose SpeedSys® 300
Established brands usually work with what’s already there for many years, not taking into account customer feedback and improvement points. Istec however, has built new systems from scratch to fulfill all your current day needs in machine protection and monitoring.
Bently Nevada 3500/53
Istec SpeedSys 300
Certified-by-design
The Bently Nevada 3500/53 is certified-by-design.
Certified-by-design
The SpeedSys® 300 is certified-by-design, with functional safety requirements embedded directly into the system architecture. SIL 2 and SIL 3 capability are integral to the product design rather than added later.
(Background on this approach: The difference between SIL certification by design and proven in use — Istec)
Standalone protection concept
The Bently Nevada 3500/53 is able to carry out a complete overspeed function independent of other modules or systems.
Standalone protection concept
Each SpeedSys® 300 module performs a complete overspeed protection function independently, clearly separating protection functionality from control and monitoring systems.
Modular redundancy approach
The 3500/53 is able to achieve a modular redundancy approach through its lack of reliance on other systems or modules.
Modular redundancy approach
Redundancy can be implemented using multiple SpeedSys units, supporting flexible 1oo1, 1oo2, or 2oo3 architectures.
Separate voting and safety outputs
The 3500/53 separates its voting and safety outputs, which introduces external safety hardware to the process.
Integrated safety I/O
Safety relays and a safety‑related analog output are available directly on the device, reducing external safety hardware.
Rack/ baseplate‑based modular design
The 3500/53 is intended to be mounted either in a rack or on a baseplate, which makes it less fit for space-constrained installations or confined spaces.
Compact and practical design
Its compact footprint fits space‑constrained installations and retrofit projects, while maintaining full overspeed protection functionality within a single module.
Communication for diagnostics
The 3500/53 does not support any Modbus or similar programme integration. This increases the reliance of communication on the safety function.
Communication for diagnostics and integration
Modbus RTU over RS‑485 is provided for monitoring and diagnostics, without making communication part of the safety function.
Centralized installation concept
The 3500/53 requires other Bently Nevada modules or systems to perform its complete function as an overspeed protection device.
Standalone and distributed installation
The SpeedSys® 300 is installed as a standalone device, mounted individually in a control or protection panel. Multiple SpeedSys units can be installed 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
Engineered for space-limited panels and demanding environments, it’s ideal for both retrofits and new installations.
| Aspect | Bently Nevada 3500/53 | Istec SpeedSys® 300 |
|---|---|---|
| Key features | Redundant tachometer-based overspeed protection, rack-based architecture integrated into a full machinery protection system | Overspeed, underspeed, and acceleration protection, SIL2/3 capability, safety relays and safety analog output, external voting, Modbus RS-485 |
| Number of relays | 4 relay outputs | 2 safety relays (DPST), 2 non-safety relays (SPST) |
| Frequency range | Up to 20 kHZ | 0.025 Hz to 35 kHz |
| Hardware response time | < 30 ms above 300 Hz | < 8 ms |
| Number of inputs (active) | Several inputs, exact number not listed | 1 input per module (only one sensor input active at a time) |
| Voting system | Modules can be combined to form 2oo2 or 2oo3 | Modules can be combined to form 2oo2 or 2oo3 |
| Outputs | 4 relay outputs | • 1 × safety‑rated 4–20 mA analog output • 1 × binary output • 1 × frequency output • Modbus RTU (RS‑485, diagnostics only) |
| Input voltage | Supplied via the 3500 rack power supplies | 24 VDC (18-36 VDC, with two redundant power inputs) |
| Functional safety | The 3500/53 requires the rack and associated modules to form SIL protection, unable to perform as a stand-alone SIL device | SIL 2 / SIL 3 capable; functional safety embedded in system design |
| Stand-alone protection | Complete overspeed protection, performed independently | Each module performs a complete overspeed protection function independently |
| Relay information | 4 SPDT relay outputs, buffered transducer outputs, 4 - 20 mA, 250 VAC / 30 VDC maximum switching capacity | 2 safety relays (DPST), 2 non-safety relays (SPST), 1 safety 4-20 mA analog output, 1 frequency output, up to 30 VDC maximum switching output. Binary input/output and Modbus RS-485 |
| Rack / backplane mounting | The 3500/53 only functions as part of a rack mounted solution, in combination with other modules | Optional 19‑inch rack for mechanical mounting only; no shared backplane or internal bus |
| Reverse scalability | Not listed in available documentation | Scalable from single module (SIL 2) to redundant |
FAQ
Yes, it’s an independent overspeed protection system, aligned with the requirement that overspeed protection be separate from the control system.
No, only the SpeedSys 300® supports redundant architectures.
Both the SpeedSys 300® and the Bently Nevada 3500/53 are fit for API 670 environments.
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.