Can I change a pressure pad from Normally Closed to Normally Open?

[Rex Kramer]

I have a lovely electric power reclining sofa, and a lovely cute dog that sometimes sits underneath it. We are worried that one day we will recline the sofa and squash the dog! So I want pressure pads on the floor that will kill the power to the chair when activated. I have bought a cheap pressure mat to look at, and it has a "normally open" switch, so it could only turn the power on, not off.
I cannot find a similar mat with a "normally open" default.
Is there some kind of emergency stop switcher I can put between the two, or is there somewhere I can buy a "normally open" pressure mat for a reasonable price?
I am not an electrician so I am looking for the simplest solution!
Thanks

 

[DPG]

Nothing to stop you triggering a relay and use the appropriate normally open or normally closed contacts on it. To be honest you wouldn't want to run the full current through the pressure pad anyway as it no doubt will be insufficiently rated for that.

 

[James]

simplest solution,

recline the seat when the dog is under it, have someone watch to make sure but,
i expect the dog will yelp and run out quick time.
if you do it a couple of times it will be afraid of being under there and find somewhere else to hide.

 

[Rex Kramer]

Nothing to stop you triggering a relay and use the appropriate normally open or normally closed contacts on it. To be honest you wouldn't want to run the full current through the pressure pad anyway as it no doubt will be insufficiently rated for that.

Thanks James. Is there a simple tutorial online explaining how I do that? As I said, I'm not an electrician. I do know that the full current is too much to put through the pad, so this sounds like a good potential solution.

 

[DPG]

Does it operate at 240 volts, or is the motor something much lower? I would be reluctant to assist if it is the former, as it would be too much of a safety risk.

 

[Darkwood]

Technically this would not be fail safe system, there is always the risk it simple won't operate due to a broken wire, faulty relay etc.

If you are happy with the risks and understand that then yes you can achieve this in several ways but I would be inclined (pardon the pun) to look at a more logical solution without any circuitry at all, wire mesh, concertina guards etc to simply stop access in the first place, even a material wrap to block the way would suffice or simply get a flatter dog.

I will add a edit, implementing a system will give you sense of security but if the system is not fail safe or designed badly then the sense of security may give you complacency and you may actually increase the likelihood of an accident IE you won't be conscious about the dog when using the chair because you think you got things covered meaning you will not bother to check, having no preventative measures will keep you aware more, at least that is the general idea until you do forget one day.

 

[James]

Be aware that any technical solution to the problem should be fail safe.

the problem is that if you believe that the system will prevent the possibility of injuring an animal or person, you will not take due care in operating it. i.e. not bother to check if someone or something is in the way.

therefore if you are gong to do it then you should do it right or not at all.

If this was an issue that could injure a person in the workplace, the problem and risks would be assessed and a solution designed and implemented.

this may well include, dual channel redundancy on sensors and control equipment.
i would budget for 1 to 2 thousand pounds for a failsafe solution.

Also, for it to remain as safe as it is when installed and commissioned, i would expect Dailey checks to be carried out to ensure it is working correctly.

Please don't think that I am just being pedantic or argumentative, it is not meant like that at all.
In fact, well done for identifying a potential risk to animals or small children.

however once you have identified a risk, you should be now be morally obliged to reduce it or remove it.

Your options are as I see it.

1. do nothing
2. sell the dog
3. sell the sofa
4. be cautious about operating the device and check before use if any living creature is in the way
5. train or educate the household (and visitors) about the dangers and how to avoid them
6. devise some complex safety system that will prevent an injury, keep it checked for proper functionality
7. do a half hearted safety system that puts your mind at rest but actually increases the risk of injury.

 

[littlespark]

Keep the pressure pad and recliner systems separate. Use the pad to operate a buzzer or light when the dogs goes under.

 

[Rex Kramer]

Does it operate at 240 volts, or is the motor something much lower? I would be reluctant to assist if it is the former, as it would be too much of a safety risk.

I think it's a 29v 2A power supply.