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07

2023-06

What is a safety relay?

2023-06-07

25

2022-01

Comparison of Active Isolators and Passive Isolators

2022-01-25

25

2022-01

Main application areas and features of Parokon Technology’s signal isolators

2022-01-25

25

2022-01

Answers to Common Questions About Isolators

2022-01-25

25

2022-01

Applications of PA-Series Signal Isolators in Industrial Environments

2022-01-25

25

2022-01

Classification of Explosion-Proof Ratings and Introduction to Relevant Parameters

2022-01-25

10

2022-01

Operating principle, wiring diagram, and illustrated instructions for safety relays

Safety Relay: Working Principle, Wiring Diagram, and Usage Instructions – January 13, 2021 A "safety relay" is composed of multiple relays and circuits working together to compensate for each other's potential defects, ensuring reliable operation with minimal false activations. This design reduces the likelihood of errors and failures, thereby enhancing safety. It is important to note that a safety relay is not a "fault-free relay"; rather, it performs predetermined actions when a fault occurs. Featuring a forced‑guide contact structure, it ensures safety even if contacts become welded shut—something typical relays cannot guarantee. Parokon safety relays are an essential control component in safety circuits. They receive safety inputs, process them internally, and then output deterministic switching signals to the equipment’s control circuitry. Simply put, safety relays operate on a dual-channel principle: they only function properly when both channels deliver normal signals. If either channel fails, the relay immediately ceases output until both channels return to normal and reset. Working Principle of Parokon Safety Relays 1. Electromagnetic Type An electromagnetic relay typically consists of an iron core, coil, armature, contact springs, and other components. When a voltage is applied across the coil terminals, current flows through the coil, generating an electromagnetic field. Under this magnetic force, the armature overcomes the spring tension and moves toward the core, closing the normally open (NO) contact and opening the normally closed (NC) contact. Once power to the coil is removed, the electromagnetic attraction vanishes, and the spring returns the armature to its original position, disconnecting the contacts. Through repeated cycles of attraction and release, the relay achieves on/off switching within the circuit. The distinction between NO and NC contacts is as follows: the stationary contact that remains open when the coil is de-energized is called the NO contact, while the stationary contact that remains closed when energized is called the NC contact. 2. Thermal‑Sensitive Dry Reed Relay A thermal‑sensitive dry reed relay is a novel type of temperature‑sensing switch that uses thermally sensitive magnetic materials to detect and regulate temperature. It comprises a temperature‑sensitive magnetic ring, a permanent magnetic ring, a dry reed switch, a heat-conducting mounting plate, a plastic substrate, and several auxiliary components. Unlike conventional relays that rely on coil excitation, this device operates via magnetic forces generated by the permanent magnetic ring. Whether the permanent magnet can exert sufficient force on the reed switch depends on the temperature‑control characteristics of the temperature‑sensitive magnetic ring. 3. Solid-State Type A solid-state relay is a four-terminal device with two terminals serving as inputs and the other two as outputs. An isolation element separates the input and output circuits electrically. Wiring Diagram for Safety Relays Internal Circuitry of Parokon Safety Relays: Two application-specific wiring diagrams for Parokon safety relays are shown below: Usage Instructions for Parokon Safety Relays In everyday operations, such relays are commonly found in electrical control systems, particularly in imported foreign equipment. Especially during sudden equipment malfunctions, the system must remain inactive until the fault is resolved or confirmed. This precaution prevents hazardous situations arising from unexpected equipment startup after a failure. Consider a specific safety relay model; its internal control circuitry is illustrated below: Key Points for Using Parokon Safety Relays: 1. Power Connection: In the diagram, A1 and A2 represent the power terminals, with A1 connected to +24V and A2 connected to 0V. 2. Control Input Circuit: During normal operation, appropriate switching conditions must be connected between S11 and S12, as well as between S11 and S22. These are typically contact switches or push-button contacts. 3. Reset Circuit: Between S33 and S34, corresponding reset conditions must be established. Simultaneously, the conditions between Y1 and Y2 also form part of the reset circuit; both sets of conditions must be satisfied concurrently. How Do They Operate? A. For the safety relay to engage (i.e., K1, K2, K4, and K5 become energized), simply having power at the input terminals (S12 and S22) is insufficient. To ensure all these contacts close, in addition to power at S12 and S22, the condition requiring K3 to be energized must also be met. B. If K3 is energized, the prerequisite is that K1, K2, K4, and K5 are all de-energized, while the reset circuit must also be powered (i.e., terminal Y2 must have power). Specifically, this means S33 and S34 must be conducting, and both Y1 and Y2 must simultaneously be energized. Example: Consider the control circuitry of a certain piece of equipment, which includes the following configuration: According to the wiring diagram above, if the external emergency stop button is pressed, K11 will lose power. Even after resetting the external emergency stop switch—meaning the input circuit already has power—the internal relay K11 will only regain power once the fault confirmation button on control box 190SP1 is pressed. In summary, upon releasing an emergency stop, the machine must not restart unexpectedly. Instead, the operator must first confirm the fault by pressing the designated fault‑confirmation button before power can be restored, thus ensuring personal safety and protecting the equipment. Parokon Safety Relay Models The Parokon PASR series safety modules primarily serve as protective components between safety devices (such as safety door switches, emergency stop buttons, and light curtains) and start/stop control elements (including relays and hydraulic solenoid valves). Their role is to verify critical safety inputs—for example, whether a safety door is fully closed, whether a light curtain is obstructed, or whether a safety valve spool is jammed. PASR‑9000A: Suitable for monitoring emergency stop switches and safety doors. PASR‑9000B: Suitable for monitoring safety mats or edge sensors. PASR‑9000N: Suitable for monitoring NPN-type light curtains. PASR‑9000P: Suitable for monitoring PNP-type light curtains. PASR‑9000S: Suitable for two‑hand start controls. PASR‑9002T: Suitable for monitoring emergency stop switches and safety doors.

2022-01-10

31

2014-10

Six Key Aspects to Know for the Safe Use of Safety Barriers

The safety barrier isolates and converts voltage and current signals from the hazardous area into either a single‑channel or two mutually independent current/voltage signals for transmission to the safe area. It also supports serial communication networking in the safe area via a configurable communication interface. As an intelligent safety barrier, this product allows users to configure the input signal type and output range using a dedicated programmer or a computer.

2014-10-31

12

2013-07

The function of a safety barrier

Currently, the main types of safety barriers in use are resistive, Zener, relay‑amplifier, and isolating barriers. Among these, Zener‑type and isolating‑type barriers are the most widely applied. Zener‑Type Safety Barrier A Zener‑type safety barrier operates based on the reverse breakdown (conduction) characteristics of Zener diodes. (1) When the supply voltage is normal—typically rated at 24 V with a maximum of 28 V—the Zener diodes VDW1 and VDW2 remain non‑conducting, and the loop current is determined by the transmitter within the 4–20 mA range. In the event of a short circuit on-site, the presence of resistor R limits the short‑circuit current to below the safe rated value, thereby ensuring safety. (2) When the barrier terminal voltage V1 exceeds the safe rated voltage V0 but remains below the discharge voltage Var of the spark gap—that is, V0 ≤ V1 ≤ Var—the Zener diodes break down (conduct), causing the current through fuse F1 to increase. Once this current rises above 125 mA, the fast‑acting fuse F1 blows first (within microseconds), instantly isolating the potentially hazardous high voltage from the field. Prior to F1 blowing, the voltage‑regulating action of VDW1 and VDW2 continues to maintain safety in the hazardous area. (3) If V1 reaches or exceeds Var, the spark gap discharges immediately, reducing the terminal voltage to a very low level (below 10–20 V). At this point, the current through fuse F2 rapidly increases; when it reaches 1 A, F2 blows, cutting off the dangerous high voltage and safeguarding production safety. Under normal operating conditions, thanks to the current‑limiting effect of resistor R and the voltage‑regulating function of the Zener diodes, fluctuations in current and voltage on the hazardous side are effectively contained, minimizing frequent blowouts of fuses F1 and F2. Zener‑type safety barriers are compact, lightweight, highly accurate, versatile, and more affordable than isolating‑type barriers. They also offer relatively high explosion‑proof ratings. However, their key component—the fast‑acting fuse—is extremely difficult to manufacture, requiring stringent process controls and high‑quality materials. The fuse must blow at least ten times faster than the Zener diode could burn out. Zener‑type safety barriers require a separate intrinsically safe grounding system. Isolating‑Type Safety Barrier This type employs a circuit architecture that electrically isolates the input, output, and power supply circuits from one another, while simultaneously meeting intrinsic safety requirements for energy limitation. Compared with Zener‑type barriers, although slightly more expensive, isolating barriers offer distinct advantages that deliver greater benefits to users: 1. Due to their three‑way isolation design, they eliminate the need for a common ground connection, greatly simplifying both system design and on‑site installation. 2. Instrumentation requirements in hazardous areas are significantly reduced, removing the necessity for intrinsically safe instruments on site. 3. With no shared ground required for signal lines, the stability and noise immunity of sensing and control loops are markedly improved, enhancing overall system reliability. 4. Isolating barriers provide superior input‑signal processing capabilities, capable of accepting and handling thermocouple, RTD, frequency, and other signals—functions beyond the reach of Zener‑type barriers. 5. They can output two mutually isolated signals, enabling simultaneous use by two devices sharing the same signal source while preventing cross‑interference and improving electrical insulation between connected equipment. Thus, comparing the features and performance of Zener‑type and isolating‑type safety barriers reveals that isolating barriers possess notable advantages and broader applicability. Although their price is slightly higher than Zener‑type barriers, when considering design, installation, commissioning, and maintenance costs, their total cost may actually be lower. In demanding industrial environments, isolating barriers have almost universally replaced Zener‑type barriers as the primary intrinsically safe explosion‑proof instrumentation, gradually gaining widespread adoption in the field of explosion protection.

2013-07-12

17

2013-04

Explosion-proof Knowledge for Safety Barriers

2013-04-17

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Liaoning Advance Foundation Semiconductor Materials Co., Ltd.

Address: No.89, Shendong 4th Road, Wanghua District, Fushun City, Liaoning Province

Telephone: +86 24 56856688

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