Omega Owners Forum
Chat Area => General Discussion Area => Topic started by: Lazydocker on 18 August 2015, 21:38:12
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After some suggestions to save myself a few pennies... I need to replace some switches in my vans because I want a higher standard. I'm after sealed, intrinsically safe switches. Some are just on-off, some are on-off-on. They can be in an enclosure if the price is right.
Anyone got any suggestions?
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It would help to know what voltage & current is being switched and what the present switches are and why they are not good enough :-\
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Opti link any use?
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Farnell, etc. are bound to have something, I'd have thought?
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It would help to know what voltage & current is being switched and what the present switches are and why they are not good enough :-\
12V. Switching milliamps. Currently plain old toggles but, as stated, I want sealed, intrinsically safe units :y
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http://www.durite.co.uk/
automotive allsorts.
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any use? :-\ http://www.carbuildersolutions.com/uk/electrical-switches
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It would help to know what voltage & current is being switched and what the present switches are and why they are not good enough :-\
12V. Switching milliamps. Currently plain old toggles but, as stated, I want sealed, intrinsically safe units :y
If they are for use around flammable materials, see what TB recommends, but you probably don't want Chinese made ones. ::) ::) ::) ::)
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Ive fitted some Explosion Proof / IS rated PTT toggle switches to IS Radio Comms gear in the past when it was specified on certain Trucks, Vehicles, the Motorola PTT ones where quiet flimsy and cost mega bucks, around $200+ each, we managed to source some others more heavy duty ones from Germany (about 20 euros), they were ratted around 10amps from memory, they also came with a screw on rubber cover that fitted over the toggle making them Dust and Waterproof.
I'll try a work out where we got them from, as I can't for the life of me remember the name of them.
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Switch sealing is usually specified by an IP rating - https://en.wikipedia.org/wiki/IP_Code
The first digit of the number is the sealing against solid particles like dust, and ranges from 0 to 6 - higher is better - 6 is dustproof. The second digit is for moisture sealing, and ranges 0 to 9. Again, higher is better, and 8 is waterproof to a depth of greater than 1m.
Switches in the with ratings like IP65 and IP67 are relatively easily available. However, if you're using them in a potentially explosive atmosphere, then you also need to consider ATEX ratings. https://en.wikipedia.org/wiki/ATEX_directive. This is a pain in the bum.
And don't mention ITAR.
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Not sure if an IP67 switch would necessarily be OK in this application as it says nothing about its' susceptibility to vapour, which would be the hazard here. Unless the contacts are sealed such as in a reed switch type of design, vapour could find its' way to the contacts and be ignited by a spark.
You could take an IP67 rated pushbutton with a rubber sealed button, put it in a suitably sealed enclosure and hope for the best. I personally would also ensure that it's only switching a low energy control signal.
To make a design intrinsically safe you really want to take the switching function that presents a hazard out of the hazardous environment completely. I'm assuming you're talking about switching motors and valves in the presence of fuel vapour, so high currents, inductive loads and the potential for sparks.
You need to perform the load switching and any protection, circuit breakers, etc elsewhere, and ideally with a solid state relay, and switch only a low energy control signal in the hazardous environment, with a protection circuit that ensures that a fault can't cause a large enough current to cause an arc to flow in the circuit.
You can take this as far as you like. Hot tubs and spa baths, for example, often have pneumatically actuated switches that are operated by plungers mounted on the bath via a length of air line.
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Not sure if an IP67 switch would necessarily be OK in this application as it says nothing about its' susceptibility to vapour, which would be the hazard here. Unless the contacts are sealed such as in a reed switch type of design, vapour could find its' way to the contacts and be ignited by a spark.
You could take an IP67 rated pushbutton with a rubber sealed button, put it in a suitably sealed enclosure and hope for the best. I personally would also ensure that it's only switching a low energy control signal.
To make a design intrinsically safe you really want to take the switching function that presents a hazard out of the hazardous environment completely. I'm assuming you're talking about switching motors and valves in the presence of fuel vapour, so high currents, inductive loads and the potential for sparks.
You need to perform the load switching and any protection, circuit breakers, etc elsewhere, and ideally with a solid state relay, and switch only a low energy control signal in the hazardous environment, with a protection circuit that ensures that a fault can't cause a large enough current to cause an arc to flow in the circuit.
You can take this as far as you like. Hot tubs and spa baths, for example, often have pneumatically actuated switches that are operated by plungers mounted on the bath via a length of air line.
The high load switching is already dealt with. We are talking about ultra low current switching. It doesn't have to be Atex approved but I want to take it somewhere near to Adr Spec. I think I may have found a suitable switch but it isn't supplied in the UK ::)
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I found this explanation of intrinsic safety circuit design (http://www.omega.com/temperature/z/pdf/z131-148.pdf) interesting (if a little long)
If the energy available is insufficient to create a spark (or heat anything up to its flashpoint) then it is intrinsically safe - you can safely use any switch you like in that case (assuming the solvents don't dissolve the switch of course.......)
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I found this explanation of intrinsic safety circuit design (http://www.omega.com/temperature/z/pdf/z131-148.pdf) interesting (if a little long)
If the energy available is insufficient to create a spark (or heat anything up to its flashpoint) then it is intrinsically safe - you can safely use any switch you like in that case (assuming the solvents don't dissolve the switch of course.......)
Yep. This is allegedly the situation I'm currently in but a requirement of a contract I am negotiating requires safe switches ::)
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Ive fitted some Explosion Proof / IS rated PTT toggle switches to IS Radio Comms gear in the past when it was specified on certain Trucks, Vehicles, the Motorola PTT ones where quiet flimsy and cost mega bucks, around $200+ each, we managed to source some others more heavy duty ones from Germany (about 20 euros), they were ratted around 10amps from memory, they also came with a screw on rubber cover that fitted over the toggle making them Dust and Waterproof.
I'll try a work out where we got them from, as I can't for the life of me remember the name of them.
Any Joy?
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Watcha want I might be able to help
I`ll talk to our design guru & see if we have supplied / utilised a similar switch in the past :-\
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Watcha want I might be able to help
I`ll talk to our design guru & see if we have supplied / utilised a similar switch in the past :-\
Excellent... I've found something suitable at a sensible price (previous option was over £1000 per van!) but will await further suggestions. The circuit is Intrinsically Safe due to low switching current so really this is a box ticking exercise, hence why I don't want to be spending fortunes.
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A switch that meets the requirement as a standalone will be in an explosion proof sealed enclosure, usually with an additional front plate, with a lever that actuates the internal switch.
Whoever is asking for a specific clearly has no idea of what 'intrinsically safe' is as its quite possible to design the circuit such that any switch utilised is intrinsically safe, this is exactly what we do at work for systems associated with drilling in offshore applications.
Also have a look for reed switch switches, these have a low current reed which is actuated by a magnet on a lever.