Technical Guide

Safety Solutions

General Information

Safety Light Curtains

Safety Switches

Emergency Stop Switches

Safety Application Controllers

Safety Relays

Safety Components

Part IV: Safety Circuit Examples

1. Examples of Control Circuits by Safety Category
 

This part provides control circuit (safety circuit) examples grouped by category. These circuits are made up of electric interlocking mechanisms that incorporate protective door and safety switches.

Note 1:
These interlock mechanisms are only part of the safety systems of machines. An appropriate system suitable to the safety of the overall machine must be designed, selected, and constructed after evaluating the risks in the work environment as well as hazardous conditions, such as the frequency of access to hazardous areas and the time required to ensure the hazard has been removed.

Note 2:
Circuit Examples

• Safety Components
  
  The safety components that are used in these circuit examples are equipped with functions such as a direct opening mechanism for switches and a forcibly guided mechanism for relays, as required by standards. These functions are designed to operate correctly within the control system in which they are used. A control system cannot be constructed using only the safety components.
   

• Safety Category

1. Category B applies basic safety rules, such as those regarding the environment that are common to other categories, and it does not apply to interlocking devices that use ordinary safety guards (safety doors).

2. In the simple circuit examples of categories 1 to 4, the safety functions required for each category are included to show circuit concepts. When designing a safety-related control system using safety components, refer to Circuit Diagrams.

(1) Safety Category 1

● Circuit with a Single Limit Switch

(2) Safety Category 2

● Circuit with a Single Limit Switch

Note: Safety functions will be lost by a single failure, such as a short-circuit failure in the input wiring.

(3) Safety Category 3

● Circuit with two Limit Switches

(4) Safety Category 4

● Circuit with a Electromagnetic-locking Safety Door Switch and a Limit Switch

Note: Construct the circuit so that operating lock release switch Sr requires an AND condition for the perfect rotation stop signal.

2. Description of Safety Component-related Standards

The international standards are described below, along with the European EN number and the new JIS number for each set of standards.

(1) General Standards

● Description
This part of these standards defines the basic concepts of machinery safety and stipulates safety design procedures.

● Main Points

(1) Machinery hazards are classified as follows: Mechanical hazards, electrical hazards, thermal hazards, hazards generated by noise, hazards generated by vibrations, hazards generated by radiation, hazards generated by materials and substances, and hazards generated by neglecting ergonomic principles in machine design.

(2) Identify the preceding hazards and apply safety design procedures to reduce risks.
Step 1: Specify the operating range of the machine.
Step 2: Identify the hazards and assess the risks.
Step 3: Remove hazards and reduce risks as much as possible.

Step 4: Design guards, safety equipment, and other safeguards against any residual risks.

Step 5: Inform and warn users about any residual risks.

● Description
This part of these standards describes the safety design procedures stipulated in part 1 in greater detail.

● Main Points
This part of these standards takes step 3 (Remove hazards and reduce risks as much as possible.), step 4 (Design guards, safety equipment and other safeguards against any residual risks.), and step 5 (Inform and warn users about any residual risks.) given in part 1 and describes them in greater detail.

● Description
These standards pertain to risk assessment in the safety design procedures described in ISO12100-1.

● Main Points
Assess risk is performed using the following systematic methodology:
A) Determine how the machinery will be used.
B) Check foreseeable hazards.
C) Identify risk elements based on hazardous events.
D) Assess the risk and design accordingly to reduce the risk.

● Description

These standards apply to control systems where safety is a concern.

● Main Points

(1) These standards consider the anticipated degree of injury (light to serious) and the probability of injury (rare to common) in determining the hazard level of machinery.

(2) These standards classify hazard levels in five safety categories and stipulates safety functions that control systems should have in every category.

● Description

Regarding the verification of the applicability of claims in relation to ISO13849-1 (EN954-1) categories.

● Main Points

In order to verify applicability to the category claims, the following should be specified:
(1) Guidelines for validity testing and inspections
(2) General considerations at time of design
(3) List of failures and failure exclusion criteria
(4) Test and test results or report

● Description
This part of these standards applies to electrical equipment with a rated power supply voltage of less than 1,000 VAC or 1,500 VDC between lines or a rated frequency of less than 200 Hz.

● Main Points
This part of these standards stipulates all elements required in electrical equipment for machines including the control circuits, functions, devices, safety measures, and technical documents related to the installation, operation, and maintenance of electrical and electronic equipment in machines.

● Description
This standard sets out specific requirements regarding visual, audio and tactile methods for providing safety related information to operators and those that may be placed in dangerous situations.

● Main Points

(1) Separate signals into passive and active

(2) Visual spectrum, brightness, and contrast ratio

(3) Meaning of colors and the shape of markings, and examples of forms that can be discerned by touch alone

(4) Operating switch symbols

(5) Shape, color and dimensions of safety markings (Prohibitions, warnings, information etc.)

● Description
This standard sets out the identification of machines, and markings to ensure safe use and the reduction of danger from incorrect connections.

● Main Points

(1) Regulations regarding manufacturer information (manufacturer name, address etc.), and rating information (power supply range, maximum speed etc.)

(2) Regulations regarding necessary markings such as for AC, DC and grounding etc.

● Description
Specifies safety issues for actuators that are operated by hand or by human control.

● Main Points

(1) Set up away from dangers, and avoid ambiguous operations. Also, be sure that operation does not create alternative risks.

(2) Design to increase the clockwise rotation of handles and lifting action for levers, so that the operator is better aware of the resulting operation.

(3) Two-handed operating controls and enabling devices where necessary.

● Description
This standard specifies those matters applicable to the machinery portion of the industry as included in the IEC 61508 Series Functional Safety Standards.

This standard applies to the design and verification of safety related control systems that use electric, electronic, or programmable electronic control systems.

● Main Points

Standards, including the following, for the allotment of SIL (Safety Integrity Level) and in order to achieve the allotted SIL, for safety functions performed by safety control systems.
(1) Functional safety management
(2) Create specifications for safety controls
(3) Control system design
(4) User information (Manual)
(5) Check Validity

(2) Standards for Safety Switches

● Description
These standards stipulate general design and selection principles for equipment that uses interlocking devices for safety.

● Main Points

(1) There are two types of interlocking devices: those with and those without a guard lock.

(2) The guard must not allow machinery to operate until it is closed and it sends a stop command if it is open.

● Description
This part of these standards applies to control circuit devices and switching elements that are produced to control, signal, and interlock switching and control devices. It applies to control circuits with a maximum rated voltage of 600 VDC or 1,000 VAC (a maximum frequency of 1,000 Hz).

● Main Points

(1) This part of these standards consists of Chapter 1: General Requirements, Chapter 2: Special Requirements for Indicators, and Chapter 3: Special Requirements for Positive Opening.

(2) It contains provisions such as switching capacity, temperature rise, terminal strength, protective structures, and positive opening.

● Description
An IEC 60947-5 Series standard that stipulates 3-position enabling switches, for enable devices under the IEN60204-1 standard. This does not apply to devices that employ teaching pendants or grip switches etc., but only to those devices with built-in enable switches.

● Main Points

(1) Stipulates electrical properties such as withstand voltage and insulation, and operating characteristics for operating stroke and load etc.

(2) The 3-position enabling switch verification mark has been changed.

● Description
These standards stipulate safety requirements related to the design and selection of two-hand control devices.

● Main Points

(1) Stipulates dimensions for prevention of defect.

(2) Output signal shall be designated only when both control actuating devices are actuated less than or equal to 0.5 s.

(3) Classify devices by type (type I, II, IIIA, IIIB and IIIC) and risk assessment results as the basis for selecting devices.

● Description

These are German labor safety standards that were enacted to prevent industrial accidents. They apply to testing on positive opening position detector switches that are installed for safety.

● Main Points

(1) Limit and door switches are classified in two categories according to function.

(2) The switches must have a positive opening mechanism, a mechanical service life of 1,000,000 operations, and an enclosure rating of IP54, and must not operate with any tool except a special operation key.

● Description
These are also German labor safety standards. They apply only to devices that have a lock monitoring mechanism in door switches that use a key lock for safety.

● Main Points

(1) The switches must use a mechanism like a solenoid for locking and unlocking.

(2) They must have a locking strength and positive opening mechanism, a mechanical service life of 1,000,000 operations, and an enclosure rating of IP54, and must not operate with a tool other than a special operation key.

(3) Standards for Emergency Stop Device

● Description
These standards stipulate principles used to design emergency stop devices.

● Main Points

(1) Devices must have a positive opening mechanism.

(2) Devices must have a latching mechanism.

(3) The operative parts must be structured to allow easy access to the mushroom-shaped pushbuttons, wires, and ropes.

(4) The operative parts must be red on a yellow background.

(4) Standards for Safety Sensors

● Description
These standards apply to devices, such as safety sensors/safety light curtains, that detect the presence of workers electrically and output a control signal for their protection. They stipulate items like fault detection performance, software design policy, heat resistance performance, EMC performance, vibration and shock performance, indicator colors, labeling details, and the content of operating manuals.

● Main Points

(1) Electro-sensitive protective equipment (ESPE) is classified as either type 4, which complies with category 4 requirements in EN954-1, or type 2, which complies with category 2 requirements in that same standard.

(2) The provisions in these standards stipulate that equipment displays the fault mode for electronic components in the equipment and they demonstrate that safety characteristics for the type of equipment are maintained in all fault modes.

● Description
This part of these standards applies to the type of ESPE protective equipment that in principle detect emitted or received light. They stipulate items such as detection performance for the minimum size object detected, effective aperture angle, extraneous light resistance performance, and mutual interference resistance performance.

● Main Points

(1) Directional angles are stipulated separately for type 4 and type 2 according to the distance between the emitter and receiver.

(2) Conditions that maintain ordinary operation and conditions that permit incorrect operation safely are stipulated for all extraneous light sources.

● Description
This part of these standards applies to electro-sensitive protective equipment that diffuse or reflect light. They stipulate items such as detection performance for the detection range, allowable errors, response time, detection capacity, resistance to extraneous light, and reflective detection capability as well as the influence of background interference.

● Main Points

(1) Only stipulated for Type 3. (not specified for types 1, 2 and 4)

(2) Conditions that maintain ordinary operation and conditions that permit incorrect operation safely are stipulated for all extraneous light sources.

● Description
These standards stipulate the minimum distance that must be provided between hazardous parts of machinery and protective equipment. Referred to as the safe distance, this distance is calculated from the worker entry direction, protective equipment response time, machine response time, and minimum object size detectable by the protective equipment.

● Main Points

(1) These standards apply when individual machine standards do not prescribe the method used to calculate safe distance.

(2) Protective equipment must be selected with a detection performance level capable of maintaining a safe distance so machines can be stopped before they pose a hazard to workers.

(5) Standards for Safety Relays

● Description
These standards apply to control circuit relays that are installed for safety and its provisions are for self-monitoring relays that have a forced guided mechanism that prevents normally open and closed contacts from operating simultaneously.

● Main Points

(1) If a normally open contact of a relay with forcibly guided (linked) contact is welded shut, the coil switches OFF and all normally closed contacts must maintain a gap of at least 0.5 mm. Even if a normally closed contact is welded shut, the coil switches ON and all normally open contacts must maintain a gap of at least 0.5 mm.

(2) Ideally, contact load switching must comply with the AC-15 (AC electromagnetic load) and DC-13 (DC electromagnetic load) utilization categories.

(3) The forced guide contact mark may be used on all class A relays (all relays with forcibly guided (linked) contacts).

3. Terminology

(1) General Terminology

● Pollution Degree (IEC60664-1)

Pollution degree is the most important factor in deciding clearances (determined by the pollution degree and overvoltage categories) as well as creepage (determined by the pollution degree and CTI value), and it is classified into four degrees depending on the air pollution of the equipment used.

● Overvoltage Category (IEC60664)

The overvoltage category classifies overvoltages into categories I, II, III and IV depending on whether the rated voltage is the rated impulse voltage or the rated voltage of the equipment as shown in the table below. Rated impulse voltage levels are set individually with respect to the rated voltages as shown in the figure below.
The overvoltage category is one of the factors that decide spacing (determined by the overvoltage category and pollution degree).
 

● CTI (Comparative Tracking Index) Value (IEC60112)

Measurement of CTI Value

(The value is measured using method A from the CTI/PTI value measurement methods stipulated in IEC60112.)

The CTI value of an insulation material is the maximum possible voltage that does not cause tracking when 50 drops of 0.1% ammonium chloride solution are dripped onto the material at a rate of 30 seconds per drop.

Materials Classified with CTI Value Range (IEC60664-1)

Group I: CTI value greater than 600
Group II: CTI value greater than 400 but less than 600
Group IIIa: CTI value greater than 175 but less than 400
Group IIIb: CTI value greater than 100 but less than 175

Standard limit switches use group IIIa or better insulation material

● PTI (Proof Tracking Index) Value (IEC60112)

Materials that conform to CTI values of 175, 250, 300, 375 and 500 are called PTI-175, PTI-250, PTI-300, PTI-375 and PTI-500 respectively. IEC60335 and IEC60065 stipulate that electric household appliances and consumer electronic appliances such as TVs, VTRs and radios must use PTI-175 or PTI-250 materials.

(2) Switch/Relay Terminology

● Rated Operating Voltage (Ue) (IEC60947-1)

The rated operational voltage (Ue) of equipment is the voltage applied to equipment, and is combined with the rated operational current (Ie) as references for utilization categories (i.e., AC-15).

● Rated Operating Current (Ie) (IEC60947-1)

The rated operational current (Ie) is the current applied to equipment.

● Conventional Free Air Thermal Current (Ith) (IEC60947-1)

The conventional free air thermal current (Ith) is the maximum test current used by the manufacturer for temperature-rise tests on unenclosed products in free air.

● Conventional Enclosed Thermal Current (Ithe) (IEC60947-1)

The conventional enclosed thermal current (Ithe) is the test current stated by the manufacturer to be used for temperature-rise tests on products mounted in a specified enclosure. The value of the current must be greater than that of the rated operational current (Ie).

● Rated Impulse Withstand Voltage (Uimp) (IEC60947-1)

The rated impulse withstand voltage (Uimp) is the peak value for an impulse voltage of prescribed form which equipment is capable of withstanding without failure and to which clearance values are referred.

● Rated Insulation Voltage (Ui) (IEC60947-1)

The rated insulation voltage (Ui) is the maximum operating voltage that can be withstood without damage. It is the reference voltage for dielectric strength tests and creepage distance for insulation material. The maximum value of the rated insulation voltage (Ui) must be greater than that of the rated operating voltage.

● Switching Overvoltage (IEC60947-1)

The switching overvoltage is the maximum reverse voltage that occurs with load switching. It must never exceed the rated input withstand voltage (Uimp).

● Rated Conditional Short-circuit Current (IEC60947-1)

The rated conditional short-circuit current is the current stated by the manufacturer that a product can withstand provided the product is protected by a device (10-A fuse model gI or gG/IEC60269 for the D4BL) that is designated by the manufacturer under conditions specified by related product standards.

● A600 Ratings (IEC60947-1)

A600 is the contact rating for a utilized category that expresses the following:

● Utilization Category for Switching Capacity (IEC60947-1)

Utilization Category for Switching Elements (Classified by switching path and current.)
 

● Safety Switch Categories

According to GS-ET-15, safety switches equipped with positive opening mechanisms are classified in category 1 or 2 according to functional differences.

Category 1

Category 2

(3) Sensor Terminology

● Type 4 (IEC61496-1)

Type 4 safety devices satisfy category 4 requirements prescribed in EN954-1.

● Electro-sensitive Protective Equipment (ESPE) (IEC61496-1)

ESPE equipment electrically detects people and outputs a control signal for their protection.

● Active Opto-electronic Device (AOPD) (IEC61496-2)

AOPD protective devices are electro-sensitive protective devices that operate on the principle of detection by emitted and received light.

● Protective Height (IEC61496-2)

The protective height is the range within which objects can be detected. The height is the length from the first optical beam to the last optical beam.

● Response Time (IEC61496-1)

The response time is the maximum amount of time it takes from the moment someone is detected in the detection zone until the output turns OFF. The time it takes to turn output ON again once it goes off is also listed in catalog specifications mainly for system design.

● Muting Function (IEC61496-1)

The muting function temporarily disables the detection function. In that case, the protective equipment remains ON regardless of whether someone enters the detection zone or not. F3SN-A models do not have the muting function.
The muting function can be added by connecting the F3SP-U2P Muting Controller. The muting function can also be added to the F3SJ-A by mounting the F39-CN6 Muting Cap.

● Test Rod or Test Piece (IEC61496-2)

A test rod is an opaque rod equivalent to the smallest detectable object. It is an accessory that is used to check the detection performance of area sensors.

● Minimum Distance from the Detection Zone to the Danger Zone (EN999)

The safety zone is the minimum distance that must be allowed from hazardous parts of machinery to the protection equipment. It is prescribed so that machinery will turn OFF before someone entering the detection zone of the protection equipment reaches hazardous parts of the machinery.

● Light Beam Axis (IEC61496-2)

The imaginal line that top beam and bottom beam of light curtain is connected. It is the reference line that is used to measure the Safety distance from hazardous parts of machinery to the light curtain. The axis is marked by the light beam axis line mark on the indicator section of F3SN-A models.

● Effective Aperture Angle (IEC61496-2)

The effective aperture angle is the angle to which area sensors must be rotated to switch the output from ON to OFF. Measurements can be taken in two directions with lateral rotation as long as the rotation follows the axis formed by the light beams.

● Lock Out (IEC61496-1)

A lock out disables normal operation and it occurs when the output is forced OFF. When F3SJ/F3SN control output remains OFF because self-diagnosis results have determined that operation cannot be resumed as a result of a fault, this is called a lock out.

(4) Other Terminology (Markings)

● Safety Switches

● Safety Relays

● Safety Light Curtains

Emitter:

Receiver: