Tag Archives: safety relay

Differences between ESD and F&G Safety Relays

From |
Leave a reply

There are 2 main applications of safety relays in the process industry. Phoenix Contact describes them as the Emergency Shutdown (ESD), and Fire & Gas (F&G) applications. Across the industry, there are many terms used to describe these 2 applications. In this article, we will have a look at the different terms and understand the uniqueness of each application.

Application AApplication B
Emergency Shutdown (ESD)Fire & Gas (F&G)
De-energized To Safe (DTS)Energized To Safe (ETS)
De-energize To Trip (DTT)Energize To Trip (ETT)
Normally Energized (NE)Normally De-energized (ND)
Terms to describe the 2 applications

Emergency Shutdown Application

Under normal operating conditions, a load like an electrical motor, must be continuously powered. The ESD safety relay which is used to power up a load must also be continuously powered and is described as Normally Energized (NE).

During a safety incident (e.g. the electrical motor is overheated), the load needs to be switched off to achieve a safe state. As the power status of the safety relay and load has a direct relationship, switching off (de-energizing) an ESD safety relay, will result in the load being switched off as well. Thus, the terms, De-energized To Safe (DTS) and De-energize To Trip (DTT) are used to describe this phenomenon.

Example of ESD relay application drawing

Fire & Gas Application

Under normal operating conditions, a load like a sounder and a beacon is not powered. The F&G safety relay is only required to be powered up during a safety incident and to allow the sounders and beacons to sound off the alarm and provide light signals. Under normal operating conditions, the F&G safety relay is Normally De-energized (ND).

During a safety incident (e.g. a gas leak or fire incident), the load needs to be switched on to achieve a safe state. As the power status of the safety relay and load has a direct relationship, switching on (Energizing) an F&G safety relay will result in the load being switched on as well. Thus, the terms, Energized To Safe (ETS) and Energize To Trip (ETT) are used to describe this phenomenon.

Some people might be confused by the term, Energize To Trip (ETT). This is because the word “Trip” is commonly used on circuit breakers, where “Trip” here refers to power down. However, the word “Trip” has a deeper meaning and can be used to describe the powering up and down of a load. A similar word for “Trip” is “Trigger”, and you can think of it as “Energize To Trigger”.

Example of F&G relay application drawing

Summary

The key differences between the ESD and F&G safety relays are the type of load they are connected to, the definition of a safe state and the energy state under normal operating conditions. For ESD, the loads are usually machines used in production; the definition of the safe state is to switch off the relay / load and is normally energized under normal operating conditions. For F&G, the load are usually sounders and beacons, the definition of the safe state is to switch on the relay / load and is normally de-energized under normal operating conditions.

In Phoenix Contact, we provide smart solutions for functional safety, from non-contact safety switches to complex controllers. Our applications range from machine building, the automotive industry, and the process industry. Our products are also SIL certified, which allows you to meet your project requirements easily.

Example of PxC Functional Safety Products

Safety Valve Interlocking System

From |
Leave a reply

The Problem:

In a chemical process plant, emergency situations can be extremely costly, both in terms of equipment and human life. However, under such extreme circumstances, it is rare that operators are able to effectively shut down all of the valves and pumps in the process line.

The Task:

We were given two weeks to install an upgrade to their existing system, along with the programming. The idea was simple – interlock the whole system so that no matter which part of the line the operator was, he/she would be able to shut down the entire system from his/her location.

The Solution:

Human-Machine Interface (HMI)

Human-Machine Interface (HMI)

We integrated Phoenix Contact’s Smart PLC Logic Relay and Human Machine Interface (HMI) into their system, splitting all of their valves and pumps in the process line into three zones. In the event of an emergency situation, the operator need only trigger the relay in one zone to shut down the whole process line.

Why it’s awesome:

Instead of having to run to separate parts of the process line to shut them down individually (and quite possibly realising how much more they need to train their running stamina and cardio over the weekends), all the operators have to do is to trigger the nearest zone. This not only saves time and effort, but more importantly equipment repair costs and human lives. This one-touch-kill-switch also reduces the risk of the operator forgetting to shut down some of the more remote areas of the process line in the heat of the moment, which would undoubtedly lead to higher repair costs.

In addition, our solution boasts the following features:

  • Easy troubleshooting on HMI with clear indication of which zone the emergency button was activated.
  • Easy maintenance work with interchangeable plug-in elements.
  • Reduced risk of system failure.
  • Allows greater flexibility for future system modifications.
  • Traceable data logging of system information.

Interested to find out more? Feel free to contact us!

Why Use Safety Relays?

From |
Leave a reply

Let’s say you are asked to be a Design Engineer for a day and are tasked to come up with a Process Control Safety System. What are the questions you should ask? 

  • What happens to the Safety Instrumented Systems (SIS) when the relay contact is welded?
  • When did it happen?
  • Where can you find this faulty relay?
  • Why did this happen?
  • Who will be responsible for monitoring this fault?

Safety Relays are devices that implement safety functions. In the event of a hazard, a safety relay must work to reduce risk to an acceptable level. The safety relay must initiate a safe and reliable response as well as monitor the integrity of its function.

The Process Automation Fire & Gas System is always on standby mode and it becomes more important to have multiple diagnostics to make sure the relays used in the Fire and Gas System Safety remain functional with all wiring connected.

7 Functions the ideal safety relay should have for Fire & Gas Systems:

  1. Power loss diagnostics to field devices such as the Beacons, Solenoid Valves and Fire Sounders.
  2. Field devices disconnection diagnostics.
  3. Alerts when Field Devices short circuit.
  4. Welded relay contacts diagnostics.
  5. Able to Proof Test relay points without the use of external power.
  6. Diagnostics via the same cable to the relay coil by the use of test pulse filtering. This also saves money as there is no need for additional DI cards and cables for monitoring function.
  7. Option for redundant connection to the relay coil.

Safety Relay Connections

Safety Relay Connections

PSR-PC50 Series SIL Coupling Relay

PSR-PC50 Series SIL Coupling Relay

The Phoenix Contact PSR-PC50 series SIL Coupling Relay has the 7 functions you are looking for and it can also be used for power adaptation and electrical isolation in Safe-State-ON applications up to SIL 3 according to IEC 61508 as well as IEC 61511.

This category 3 device is designed for installation in zone 2 potentially explosive areas. By filtering the controller test pulses, premature failure of the safety relays is prevented. The contact side is fully monitored for open circuits and short circuits as well as load and diagnostics supply voltage. If an error occurs, the internal device input impedance is affected. As such, the test pulses sent from the controller are disrupted and the error is reported to the corresponding digital output without additional wiring effort.

If you have any questions or want to know more about this product, please feel free to send us an enquiry at marketing@phoenixcontact.com.sg and a product representation can be arranged to discuss in more detail.