What kind of switch will mechanically break a circuit in response to a 12V signal - Page 3
Close
Login to Your Account
Page 3 of 3 FirstFirst 123
Results 41 to 46 of 46
  1. #41
    Join Date
    Dec 2008
    Location
    Vt USA
    Posts
    8,998
    Post Thanks / Like
    Likes (Given)
    1515
    Likes (Received)
    3206

    Default

    A Klixon Thermal circuit breaker would answer .. alas, they a Thermal devices, not 12V.

    They are cheap though....

  2. #42
    Join Date
    Jan 2007
    Location
    Flushing/Flint, Michigan
    Posts
    10,430
    Post Thanks / Like
    Likes (Given)
    603
    Likes (Received)
    8465

    Default

    Quote Originally Posted by dgfoster View Post
    Geez, a button! I should have thought of that. ;-)

    Did you have any particular component in mind that is actuated by that button?

    Denis
    Not sure, in my world it is called a relay or starter since the power not huge here.
    A very few rungs of logic.
    I just do not see the problem or a need for a plug in fix.
    I see kill power if overtemp if all it not cool with the world as the goal and a forced reset to this fault.
    What did i miss here or not get right?
    The hard contact goes open so no SSR leak. The logic want's a hard reset from the trigger.

    Fancy relays, fancy fuses. I see so a simple controls problem.
    Is there a need for a one wire solution?
    I must be missing something in this as it seems I look like an ass.

    What we are talking here is a safety circuit. Not a production make or break cycle.
    Contracts may not be very happy doing it but done rarely.

  3. #43
    Join Date
    Jun 2008
    Location
    Bellingham, WA
    Posts
    4,440
    Post Thanks / Like
    Likes (Given)
    1101
    Likes (Received)
    2515

    Default

    Quote Originally Posted by CalG View Post
    A Klixon Thermal circuit breaker would answer .. alas, they a Thermal devices, not 12V.

    They are cheap though....
    I see these devices are usually used to sense overcurrent applications which heats an internal bimetal and opens the circuit. How would you be using it in my application? On the oven outer surface to sense heat?

    One of those little round metal button thermostats on things like radiant heaters, motors, etc that open the circuit when they reach a preset temp would stop overheating. Seems like that would be the way to go as they are built more or less for the purose I intend. But, they reset themselves I think. So, not ideal for my purposes.

    Denis

  4. #44
    Join Date
    Jun 2008
    Location
    Bellingham, WA
    Posts
    4,440
    Post Thanks / Like
    Likes (Given)
    1101
    Likes (Received)
    2515

    Default

    Quote Originally Posted by CarbideBob View Post
    Not sure, in my world it is called a relay or starter since the power not huge here.
    A very few rungs of logic.
    I just do not see the problem or a need for a plug in fix.
    I see kill power if overtemp if all it not cool with the world as the goal and a forced reset to this fault.
    What did i miss here or not get right?
    The hard contact goes open so no SSR leak. The logic want's a hard reset from the trigger.

    Fancy relays, fancy fuses. I see so a simple controls problem.
    Is there a need for a one wire solution?
    I must be missing something in this as it seems I look like an ass.

    What we are talking here is a safety circuit. Not a production make or break cycle.
    Contracts may not be very happy doing it but done rarely.
    I guess I'd go back to my original post. I was looking for specifics and have gotten some pretty good specific suggestions. You may not agree with or understand my perceived need and that's OK.

    Denis

  5. #45
    Join Date
    Aug 2005
    Location
    Raymond , CA
    Posts
    389
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    285

    Default

    There are two design details that have not been covered.

    The over temperature alarm/furnace shutoff is installed to protect the part from damage due to excessive temperature AND for fire safety.

    Protecting the part is not straightforward. The difficulty is measuring the true temperature in the casting. The ideal situation requires installing the thermal couple into a thermal well drilled into the center of the casting.

    The default TC installation with the probe extending a few inches past the furnace wall will not provide a accurate temperature measurement.

    This PDF has a few suggestions on what to do to minimize the measurement error:
    https://solaratm.com/uploads/2015/08...sm-webinar.pdf

    Fire safety has a different set of requirements.
    The ready made furnace high temperature protection devices use a independent temperature monitor and thermal couple.

    If the process controller is used for alarming there is no redundancy in the system. A partially failed thermal couple, for example, could cause the controller to go to full power in a attempt to raise the furnace temperature. This would occur even though the furnace temperature might already be too high.

    A second, independent, TC is needed. It is unlikely that both thermal couples will fail at the same time. The second TC might be installed in a protected area on the furnace frame where it is less likely to be damaged but can still provide warning of a fault.

    The redundant installation allows either the process controller to shut off the furnace using a programed set point or the safety monitor to open the power contactor using a fixed set point.

  6. #46
    Join Date
    Jun 2008
    Location
    Bellingham, WA
    Posts
    4,440
    Post Thanks / Like
    Likes (Given)
    1101
    Likes (Received)
    2515

    Default

    Quote Originally Posted by Robert R View Post
    There are two design details that have not been covered.

    The over temperature alarm/furnace shutoff is installed to protect the part from damage due to excessive temperature AND for fire safety.

    Protecting the part is not straightforward. The difficulty is measuring the true temperature in the casting. The ideal situation requires installing the thermal couple into a thermal well drilled into the center of the casting.

    .
    I guess I’d have to ask ideal for what situation? I suppose someone somewhere actually drills holes into castings for heat treating—-maybe aerospace or some other super-critical application. But doing so in my case (and nearly all cases) is very impractical as it would damage the casting in a way that would be sure to make a customer reject it. None of the commercial foundries I have visited or used drill castings for any reason. I re-melt any casting that has any void in it that is more than a tiny pock certain to machine out in use. I am aware of no one implanting TC’s in the castings for heat treatment. Tolerances for heat treatment of cast iron for either stress relief or annealing are often quoted +/-25 deg F. The common industrial practical heat treatment routines are non destructive and allow for some less-than-perfect uniformity and precision in temp control.

    Quote Originally Posted by Robert R View Post

    Fire safety has a different set of requirements.
    The ready made furnace high temperature protection devices use a independent temperature monitor and thermal couple.

    If the process controller is used for alarming there is no redundancy in the system. A partially failed thermal couple, for example, could cause the controller to go to full power in a attempt to raise the furnace temperature. This would occur even though the furnace temperature might already be too high.

    A second, independent, TC is needed. It is unlikely that both thermal couples will fail at the same time. The second TC might be installed in a protected area on the furnace frame where it is less likely to be damaged but can still provide warning of a fault.

    The redundant installation allows either the process controller to shut off the furnace using a programed set point or the safety monitor .
    The board I am using senses TC failure, flashes a continuous alarm, and the pin that closes the power relay goes to zero opening the relay. If the argument is made that the board may not properly respond to a failed TC, then I would be more inclined to rely on a simple skin button thermostat or an internal melting link safety fuse. Adding a second TC to a malfunctioning board is not as fail-safe as the latter options.

    Denis


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •