Overview of Safety Technology
What Is Industrial Safety Technology?
Safety technology in industry comprises technical systems, measures and procedures for the protection of persons, machines, systems and data. It is divided into industrial safety, i.e. the protection of employees against hazards caused by machines, and industrial security, which covers the protection of assets and data against attacks. The aim is to minimize risks and ensure the safe operation of the plants.
What Tasks Does Safety-Oriented Sensor Technology Perform?
Personal Protection and Hazard Zone Monitoring
Electro-sensitive protective equipment monitors working ranges and detects unauthorized intervention or entry of persons into hazardous machine movements. Intelligent diagnostic tools also detect and transmit faults at an early stage. Downtime can be avoided and system availability maximized.
Highly Efficient Logistics Solutions in Optimized Space
Safety light curtains in combination with pre-assembled muting sets enable safe material transport to protected plant areas without interrupting the material flow. This allows goods to be fed in and out at the same time, while ensuring personal protection at all times. The space-saving integration supports efficient use of space and increases material throughput.
Downtime Optimization
Automatic restart combines reliable personal protection with high system availability. As soon as the danger zone is cleared again, the safety light curtain automatically switches to safety operating mode and allows the machine to restart. This reduces downtime and supports efficient workflows. However, this function is only permitted under certain conditions.
Process Safety Through Position Monitoring and Locking of Movable Protective Devices
Guard locking devices allow the electromagnetic or electromechanical locking of security doors. They provide a door locking mechanism to protect workers from potential hazards from machine movements or hidden hazards. At the same time, unintentional intervention in the process can be avoided. Higher process safety therefore ensures that there is less downtime.
Secure Communication Between Man and Machine
Command devices, in combination with suitable safety relays, enable the safe control of machines and automated processes. This means that applications can be reliably set up, started, stopped or terminated with maximum personal protection.
What Makes Safety Sensors Different from Standard Sensors?
Safety sensors must be designed and used in such a way that no danger arises even in the event of a failure. The applicable standards and safety requirements must be taken into account. The safety outputs carry 24 V DC in normal operation. The safe state is the OFF state (0 V). Wire breaks or voltage failures therefore also automatically lead to a safe state.
This level meets the industry standard to ensure high immunity to interference, reliable signal security over long distances, and protection against faulty circuits and against people and equipment. This standard also enables easy interoperability of components from different manufacturers. For maximum safety, the safety functions are retained even in the event of a fault. Permanent comparison and read-back detects errors as early as possible.
Legal Basis
| Responsible | Central task | Legal basis | That is extremely important |
|---|---|---|---|
| Machine manufacturer | The machine must be designed and constructed in such a way that it can be operated, set up and maintained safely. Both the intended use and reasonably foreseeable misuse must be taken into account in this process. | Machinery directive/Machinery ordinance |
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| Machine operators | Work equipment may only be used after hazards have been assessed, suitable state of the art protective measures have been implemented and safe use has been established. | Ordinance on industrial safety |
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How Is the Required Performance Level Determined?
Performance Levels (PLr)
The required performance level – PLr (Performance Level required) for short – is determined as part of the risk assessment. It defines the necessary reliability of the safety function and thus forms an essential basis for the selection and design of suitable protective devices.
The following risk parameters are taken into account in the assessment:
Severity of possible injury
Frequency and duration of exposure to danger
Possibility to avoid the hazard or limit the damage
Determination of the PLr for Machine Manufacturers
Safety Integrity Level (SIL)
The safety integrity level (SIL) describes the reliability of electrical, electronic and programmable safety-related systems. It indicates to what extent a safety function reduces the existing risk or how likely a dangerous failure is.
Classification takes place according to IEC 61508 or IEC 61511 in four stages – from SIL 1 to SIL 4. SIL 1 stands for the lowest and SIL 4 for the highest required risk reduction.
SIL is used in particular in the process industry as well as in complex process and process engineering systems. In some international markets, functional safety requirements are also often specified using SIL instead of the performance level (PL) or required performance level (PLr) commonly used in the machine industry.
How Does wenglor Determine the PL?
The PL of a sensor is determined based on its safety-relevant architecture and reliability parameters. The following factors are taken into account:
Mean time to dangerous failure of the component used.
Secure Communication and Signal Processing
Why Is Secure Communication in Machine Safety Necessary?
A safety light curtain detects when a person enters a hazard zone. However, the safety function only becomes effective when the signal is reliably transmitted to the safe machine control system, correctly evaluated there and the intended protective reaction – for example the safe stop of the machine – is triggered.
Secure communication does not always prevent every error, but ensures that communication and system errors are detected and controlled in good time. This includes line interruptions, short circuits, corrupted or lost data telegrams, device failures and impermissible delays in signal transmission. If such a fault is detected, the safety system must bring the machine to a safe state within the specified response time.
What Are OSSD Outputs and How Do They Work?
OSSD outputs, also known as safety outputs, are the outputs of electro-sensitive protective equipment connected to the machine control. They transmit the current protection status to a safety controller or a safety relay.
If the safety field is clear, the OSSD outputs are in the ON state. If the safety field is interrupted or a safety-relevant fault is detected, they switch to the OFF state. The connected control system then triggers the intended protective reaction and brings the machine to a safe standstill, for example.
For reliable signal transmission, safety sensors have two separately monitored OSSD channels. The signal status and matching are checked by the analysis module. Short test pulses also enable diagnosis of the connected signal paths.
This can detect the following faults, among others:
- Short circuits
- Cross-circuits between the channels
- Line breaks
- Faulty or contradictory switching states
Dual Channel Wiring
With two-channel wiring, the safety signal is transmitted redundantly to the safe control system. The continuous comparison of both channels ensures that deviations and individual errors are reliably detected and enables higher performance levels to be achieved.
Feedback Circuit Monitoring (EDM)
EDM stands for External Device Monitoring and describes the monitoring of external switching elements. After a shutdown command, the safety function checks whether the connected contactors have actually dropped out.
Welded or faulty contacts are thus detected. If a contactor does not reach the expected state, the system prevents the machine from restarting.
What Are the Advantages of Cascading?
Cascading means connecting several safety devices in series to monitor different safety fields. This allows all of these to act on a safety output. Cascaded safety devices demonstrate the same performance characteristics as a single safety device, enabling extensive protection concepts to be implemented with less wiring effort and flexible expansion.
Benefits
Reduced wiring effort
Lower installation expenses
Fewer inputs needed on the safety controller
Flexible extension of the safety system
Solutions and Key Terms
What Is the Difference Between Finger, Hand and Body Protection?
| Finger protection |
|---|
| Resolution up to 14 mm |
| Detection of fingers |
| Extremely small safety clearance |
| Usage locations include presses, punching machines, bending machines, semi-automated manual workstations |
| A special feature is the positioning relatively close to the hazardous area, as the high resolution removes the need for an additional safety margin |
| Hand protection |
|---|
| Resolution up to 30 mm |
| Hand/arm detection |
| Medium safety clearance |
| Locations of use are e.g. welding robots, pallet feeding devices, unwinding stations |
| The special feature is the greater minimum required safety distance to the danger zone compared to the finger protection |
| Body protection |
|---|
| Resolution from 300 to 500 mm |
| Detection of body/person |
| Large safety clearance |
| Usage locations are, for example, access points and hazardous areas, such as robot cells |
| One special feature is that only a small number of light beams are usually required |
How Is the Safety Distance Calculated?
The safety distance is calculated from: S = (K × T) + C
S = Safety clearance
K = Approach speed
T = Total system response time
C = Additional safety margin
Safety Clearance for Vertical Approach to the Safety Field
Expanded Functions of Safety Light Curtains and Safety Light Arrays
Muting Safety Functions
During muting, the protection function is bypassed in a targeted manner. Additional functions ensure that no one enters the danger zone unnoticed.
- Muting time function
- Belt stop signal function
- Muting enable function
- Direction setting function
- Partial muting
- Gap suppression
- Override function
Blanking Functions
Blanking functions suppress the light beams within a specified portion of the safety field. As opposed to muting, bypassing is permanent in the case of blanking.
- Fix blanking
- Fix blanking with edge tolerance
- Floating blanking
What Does Reduced Resolution Mean for Safety Light Curtains?
The reduced resolution of a safety light curtain is a function that increases the response threshold of object detection. The light curtain no longer evaluates every interruption of individual light beams, but only triggers the safety function when a defined number of adjacent beams are interrupted simultaneously.
This increases the effective detection size from, for example, 14 to 50 or 90 millimeters. Thin materials such as sheet metal can remain in the safety field, while larger objects or body parts can still be reliably detected.
Area of Use:
The function is suitable for applications where materials or workpieces, for example, must be guided through the safety field without interrupting the production process. Personal protection is maintained as long as the changed detection size is taken into account in the risk assessment and calculation of the required safety distance.
Safety Guards
What Is the Difference Between Process and Personal Protection with Guard Locking Devices?
Process and Personal Protection
- The locking device is monitored
- The door remains locked until there is no longer any danger
- Suitable for machines with dangerous overtravel
Process Safety
- The actuator is monitored
- The locking device protects against unintentional opening
- Suitable if there is no immediate danger after switching off
Coding of Safety Switches and Guard Locking Devices
A coding makes it possible to assign a sensor to the associated actuator. A coded safety switch system provides simple protection against tampering and bypassing.
| Coding type | Allocation | Operating principle |
|---|---|---|
| Low coded | Standard |
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High coded | Individual, multi-teachable |
|
High coded | Individual |
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What Is the Difference between the Power to Lock Principle and the Power to Unlock Principle?
Power to lock principle: locking through energy
With the power to lock principle, the locking device is activated by energizing the locking magnet. Without power, the safety door is unlocked and can be opened.
Solenoid activation 0 V: Safety door unlocked
Solenoid activation 24 V: Safety door closed
Power to unlock principle: unlocking with energy
With the power to unlock principle, the locking device is activated mechanically by spring power. The safety door therefore remains closed even without voltage. It is only unlocked when the magnet is energized.
Solenoid activation 0 V: Safety door closed
Solenoid activation 24 V: Safety door unlocked
Note: For personal protection, special standard requirements must be met, see DIN EN ISO 14119.
