Closed loop Sensor monitoring

[Rocboni]

Hello,

How are closed loop sensors like the below and monitored integrated into a control system, isolation switches/switch amplifiers? These are typically used on explosion panels where when they blow off it snaps the cable or ceramic plate causing an open circuit.

(I’m Prepared for the onslaught of atex approval etc)

 

[buzzlightyear]

 

[Bobster]

Failsafe wiring.

Circuit breaks once a vent explodes.

 

[Rocboni]

Always liked Michael Caine

 

[Rocboni]

Failsafe wiring.

Circuit breaks once a vent explodes.

Yes Rob, can this be done with a standard relay held closed?

 

[Spoon]

Yes Rob, can this be done with a standard relay held closed?

This will depend on the 'risk assessment' of the function. A safety device may be needed.

 

[Rocboni]

A “safety device” as in a safety relay?

The use of switch amplifiers is required when a intrinsically safe system is required, I cannot see the point of a instricically safe device being used when nothing else is rated for zone 2 and the fact that sensor is not actually in the zone, I would not class the environment as potentially explosive or the motors lighting etc would be required to be explosion proof? I understand this is a specialised field.

 

[Spoon]

A “safety device” as in a safety relay?

Yes a safety relay or safety plc. All depends on the 'risk assessment' if one is needed.

 

[Bobster]

Yes Rob, can this be done with a standard relay held closed?

You can get sil rated I.S barriers.

Dependent on risk assessment, that alone may be good enough.

Of course there are the atex calculations involved, but going through a barrier it should comply. Just need to fill the calculation forms out to satisfy the regs.

 

[Rocboni]

Yes I noticed some has sil ratings in the spec.
I guess what I was asking was is there any situation where a standard relay would be sufficient bearing in mind these are high leve, I have used a safety relay in the past but thinking larger scale where there are multple elevators each would require an SR or IS barrier as they obviously don’t have auxiliary n.o contact for indication purposes like many safety switches where they have two Nc and a NO

 

[Bobster]

A normal relay could be used if the explosion vent is not in a hazardous area. Say a bursting disc on a pressurised air line. A bursting disk on an atomized coal line and no barrier will result in a fire ball when the burst disc membrain fails due to the spark created.

Just series up a few of the explosion vents to one barrier. Doesn't require a relay per explosion vent.

Also bear in mind these are a last defence mechanism. Other sensors in the process should prevent explosions first. An you're going to see a broken explosion vent from a distance so I wouldn't worry about NO contacts for indication.

 

[Rocboni]

Not when they are on the top floor and there’s a few of them. The main reason is to shut the elevator down. Traditionally no sensors were used and they were a paper like membrane, now they are stainless.

Specifically this would be on an bucket elevator carrying grain, which have extraction to minimise dust but they still have the vents, surly the explosion has already occurred when the sensor is “cut”

 

[Rocboni]

I suppose it would shut the plant down if one barrier was used and you could just have one explosion vent indicator and they would have to walk round to see what one, no big deal just handy if they can indicate what one from the panel.

 

[Bobster]

Then use more than one barrier.

Your supervisor should be giving you this information anyway.

 

[netblindpaul]

You need to identify the safety function required then design it to the relevant standard, 13849, 62061, 61508, 61511 etc. then get the design validated.
Once that is done, implement the design and verify the performance meets the requirements.
However, functional safety is a last resort.
The danger of explosion, must be designed out utilising first principles in accordance with 12100.