Industrial Safety Controls: An Overview Modern automation environments demand rigorous control measures to ensure machinery operates within defined safety parameters. Industrial safety controls—including standstill monitoring,…

Industrial Safety Controls: An Overview

Modern automation environments demand rigorous control measures to ensure machinery operates within defined safety parameters. Industrial safety controls—including standstill monitoring, speed monitoring safety relays, and protective devices like proximity switches—form the foundation of these systems. Whether for safe detection, direction of rotation, or speed window monitoring, safety relays provide real-time safeguards across a wide range of applications.

Importance of Industrial Safety Controls

Uncontrolled movement during maintenance, start-up, or failure events poses a severe risk. Industrial safety controls enable precise monitoring of motion applications, ensuring machinery adheres to safety functions such as standstill detection, overspeed protection, and unexpected running prevention.

By deploying devices like sensorless speed monitors, zero-speed safety relays, and compliant interlocks, facilities can prevent damage to machinery, protect workers, and meet functional safety standards with confidence.

Key Elements of Standstill and Speed Monitoring

The Role of Proximity Switches

Proximity switches are a reliable tool in standstill monitoring and safe speed detection systems. When mounted near rotating parts or shaft assemblies, they provide non-contact feedback about motion presence or absence. Their use is especially effective in:

3-phase motor applications
Machine tools and spindles
Conveyor systems and rollers

Paired with speed monitoring safety relays, proximity switches help ensure that gates or guards only open after full stop—enhancing both operator safety and machine integrity.

Sensorless Techniques for Monitoring

For environments where external sensors like encoders or proximity switches aren’t viable, sensorless standstill monitoring becomes essential. These systems derive speed or stop conditions from indirect data such as:

Motor winding frequency
Remanence voltage
Signal track variation within the motor

Sensorless approaches reduce installation complexity and cost while maintaining compliance with standards like DIN EN 61800-5-2. They’re especially effective in larger machines, hazardous locations, and drives without sensors.

Understanding DIN EN 61800-5-2 Standards

Safety Functions Compliance

The DIN EN 61800-5-2 standard governs safety functions for adjustable speed electrical drives, covering aspects like:

Safe stop (SS1, SS2)
Safe operating stop (SOS)
Safely-limited speed (SLS)
Safe direction (SDI)
Safe standstill (SSM)

Compliance ensures that safety relays and drive systems correctly handle motion-related hazards and react promptly during failure or fault conditions. The standard outlines performance metrics, response time, and safety-related detection expectations for OEMs and integrators alike.

Technical Insights into Sensorless Standstill Monitoring

Under DIN EN 61800-5-2, sensorless techniques must demonstrate consistent performance in detecting zero motion. Technical considerations include:

Input frequency resolution and response accuracy
Use of frequency windows and time delays to confirm standstill
Analog output integration for real-time diagnostics
Safe speed range validation through test routines

Combining these techniques with external device monitoring and modular safety relay systems provides a layered safety strategy—one that supports both legacy equipment and next-gen automation platforms.

Safety Gate Monitoring and Solenoid Interlocks

Integration with SAFEMASTER STS System

Modern safety relay applications often require more than simple start/stop logic—they need comprehensive safety functions integrated into larger control frameworks. The SAFEMASTER STS system combines safety gate monitoring, solenoid interlocking, and key transfer systems into one cohesive platform. When combined with speed monitoring safety relays, this integration ensures machines only grant access when the motor has reached a safe standstill.

By preventing the opening of gates before the machine has fully stopped, the SAFEMASTER STS system reinforces maximum safety and reduces the risk of hazardous movement or mechanical entrapment.

Key Transfer Systems

Key transfer systems offer a mechanical safeguard to ensure that access to dangerous zones is only permitted under safe conditions. These systems can be configured with standstill monitors or safe detection relays that release the key only when a safe speed range is verified.

Commonly used in machine tools, packaging lines, and automated warehouses, key transfer systems remain a robust, tamper-proof alternative to fully electronic monitoring, especially where power interruptions or external sensor failures could compromise operator safety.

Safe Drive Monitoring Systems

Sensor-Free Over-Speed Safety Relays

Not all applications can rely on encoders or speed sensors. That’s where sensor-free speed monitoring relays come into play. These devices allow for safe speed monitoring using input signals directly from the motor windings, evaluating parameters such as frequency, direction of rotation, and standstill—without requiring additional sensors.

These systems are ideal for drives without sensors, linear movement equipment, or 3-phase and 1-phase motors where additional sensors are not viable due to cost, space, or environmental limitations.

Cost-Effectiveness and Reliability

Speed monitoring safety relays offer a cost-effective interface between electric motors and safety controls. By ensuring fail-safe detection of under-speed, over-speed, or standstill conditions, these relays reduce the need for expensive encoder-based systems and limit exposure to unexpected running of machines.

Products such as the PSRmotion series enable full safety-related detection with built-in external device monitoring, safe standstill functions, and support for standstill detection via frequency or remanence voltage analysis.

Ease of Commissioning

Unlike complex PLC-based safety controllers, standalone speed monitoring relays are designed for ease of commissioning. Most models feature:

Rotary switches or pushbuttons for speed window setup
Standard push-in connection or screw terminals
USB or software configuration ports (e.g., PSRmotion software)
Built-in diagnostics and status LEDs

These plug-and-play capabilities reduce wiring time, simplify testing, and accelerate deployment in both new systems and retrofit projects.

Evaluating Safety Relay Options

Omron’s SR1 Safety Monitoring Relay

The Omron SR1 series is a highly versatile speed monitoring safety relay capable of monitoring rotation, direction, and standstill without external sensors. Its compact design supports applications with safely-limited speed, and the unit integrates directly with light curtains, safety mats, and safety gate interlocks.

With options for analog output, frequency monitoring, and USB interface, the SR1 meets a wide range of safety applications across multiple industries.

Diverse Product Series Overview

Manufacturers now offer a diverse portfolio of speed monitors and zero-speed safety relays, including models with:

Sensor inputs for encoder-based detection
Analog outputs for speed signal tracking
External device monitoring for fail-safe control
Time delays and window range functions

Popular options include:

PSRmotion series (Phoenix Contact)
Sentry series (ABB, e.g., 2TLA010061R0001)
SAFEMASTER series (DOLD)

These devices are often certified to PL e, SIL 3, or other safety levels, ensuring compatibility with international safety criteria.

Key Features and Price Points

When selecting a speed monitoring relay, consider these core factors:

Speed detection method: sensor-based vs. sensorless
Monitoring capabilities: standstill, overspeed, underspeed, direction
Installation ease: push-in or screw terminal wiring, DIN rail mounting
Diagnostics: LED indicators, USB interface, or software tools
Compliance: Certified to IEC 61508, ISO 13849, or EN 62061

Price points vary based on capabilities, but most standalone speed monitoring relays range from cost-effective basic models to high-end units with extended diagnostics and multi-signal processing.