Latching using momentary switch and relay

Discussion in 'The Projects Forum' started by Lanz, Oct 30, 2008.

  1. Lanz

    Thread Starter Active Member

    Oct 30, 2008
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    Hi,im new to this forum.
    I have been assigned a project at my workplace.
    Its about a sensor that will trigger an alarm when the pressure is low in a canister.
    There are 12 canister and i had made 1 sensor and 1 relay for 1 canister.
    I had designed very well the circuit for that and my project is powered by 24VDC.
    Now they ask me to add a momentary push button to stop the alarm.
    The problem is,i dont know how to make a circuit that can switch off the alarm when the push putton pressed using normal DPDT relays.
    Can anybody help me?
     
    Last edited: Oct 30, 2008
  2. Wendy

    Moderator

    Mar 24, 2008
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    I've actually done something very similar using an SCR. The sensor triggers the SCR, which stays conducting until the button breaks the alarm current. The catch is, the sensor has to be off for the reset to work. Interested in the schematic? I'll need a rough schematic of your setup to work with.


    ----------------------

    No reason we can't do it with a relay either, thinking about it. But we still need a schematic to be able to help.
     
    Last edited: Oct 30, 2008
  3. mik3

    Senior Member

    Feb 4, 2008
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    Here is a circuit i designed with paint!!

    The NO push button is to trigger the relay and the NC push button is to reset the relay.
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    This must be to simple for the solution. Assume that the ALARM ckt. latches relay,buzzer sounds; Pushing NO sw. resets relay buzzer stops assuming again ALARM ckt self reset.
     
  5. Lanz

    Thread Starter Active Member

    Oct 30, 2008
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    Here i had attached the circuit picture.
    The circuit on the picture is for 1 canister only.
    Each canister has the same circuit.
    So,i want to control all sensors alarm by one switch.
    Hope u guys can get a picture now.
     
    Last edited: Oct 31, 2008
  6. mik3

    Senior Member

    Feb 4, 2008
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    I guess your sensor will output a signal while the pressure in the tank is low until it gets high again, so you cant use just a simple relay to do it. You need to add a circuit after the sensor which will output a brief pulse when the sensor is activated. With that brief pulse you will latch the relay (like the circuit i gave you) and then use the NC push button to reset it.
     
  7. Lanz

    Thread Starter Active Member

    Oct 30, 2008
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    Thanks for the reply.
    It would be easy for me to understand if you can draw the circuit that u mention n upload here mik3.
    Im not that expert on electronics.
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    One sensor and one relay for each of 12 canisters; must be just one alarm for all 12 ? How do you determine which canister tripped ?
     
  9. mik3

    Senior Member

    Feb 4, 2008
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    Here is a circuit i designed for you. When the sensor gives a high on its output it will activate relay 1 and 2. Thus relay 1 will give a short pulse to relay 3 and it will latch because of the NC push button. Then relay 1 will turn off because the capacitor in series with it will charge but relay 2 will remain on. Relay 2 will turn off when the output signal of the sensor goes low and it will discharge the capacitor as relay 1 can give a pulse again when the sensor output goes high. To reset the alarm you need to push the NC push button.
     
  10. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Lanz,

    Do you have a link to a datasheet on your "sensor"? The schematic symbol doesn't make sense as drawn. Is this a "module" with +24v and Common IN, and an output that is 0v or +24V?

    Ken
     
  11. Lanz

    Thread Starter Active Member

    Oct 30, 2008
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    Sorry guys.What KMoffett said is true.Actually i copied the sensor and relay picture from another circuit for my ease.I forgot to change some properties.I had attached the corrected picture and the sensor built-in circuit.I had tested my circuit and its working perfectly.I only forgot to change some properties in the circuit.For more details about the sensor,u can visit its homepage here Keyence.


    To Bernard,this sensor have two colour display.One is green and one is red.When in normal pressure,it will display in green while in low pressure it will display in red.So,from the display colour we can trace the tripped canister.
    It looks like this

    [​IMG]
     
    Last edited: Oct 31, 2008
  12. mik3

    Senior Member

    Feb 4, 2008
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    You can use the circuit i posted in my last post and connect it to the blue wire out of the sensor and to the black or white wire out of the sensor. This will do the job but i guess you can use just one relay to drive the alarm and use pink wire as an input (you have to select as an input) to reset the alarm with a simple NO push button by programming the sensor. I cant get the datasheet so if you attach it it would be helpful.
     
  13. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Another way to do it.

    Ken
     
  14. Lanz

    Thread Starter Active Member

    Oct 30, 2008
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    Sorry mik3,I had try to attach it but the file size is above 2MB.So,download from the link below.
    http://www.ziddu.com/download/2547064/apc_30w_40w_v40w_ks.pdf.html

    Thanks for the reply guys.I appreciate it very much.
    If got any other suggestion,please post it.
    Meanwhile,i will try the given circuit by the senior members.

    Is it possible if i want the alarm to be ON once per minute untill the pressure back to normal again and the time can be adjusted?
     
    Last edited: Nov 1, 2008
  15. mik3

    Senior Member

    Feb 4, 2008
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    I saw the datasheet but i cant see anything about how to program the device by using the buttons on it. You have to 'play' with it and find out how to do it and what are the functions when you select the pink pin as an input. For this input you dont have to apply a voltage but just connect a switch between the pink and blue wire.
     
  16. Lanz

    Thread Starter Active Member

    Oct 30, 2008
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    Yeah mik3.Thats why im also blurrrr.No detailed datasheet.
     
  17. mik3

    Senior Member

    Feb 4, 2008
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    Then you have to go to more complicated circuits, I suggest you to use a PLC to make your life easier. I have used Crouzet PLCs and they are very easy to learn and program (by using function blocks and connect them by wires on the PC screen). Also, they have a tutorial which explains you what each function block does. Visit them here:

    www.crouzet.com

    Or maybe you can program the sensor to do it. Check it.
     
  18. Lanz

    Thread Starter Active Member

    Oct 30, 2008
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    Thanks mik3.But i just joined this company for practical purpose.I want to finish this project as simple as can.Anyway,thanks for ur suggestion.

    From what i know,PLC is a program that controls some device rite.This PLC only use simple program to run without a computer or CPU.

    Then,i can see that some machine using computer(CPU) to control some devices using software.What is the term called?I mean if using program its called PLC.And whats its called if using software?
     
  19. mik3

    Senior Member

    Feb 4, 2008
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    The PLC needs to be programmed by using a computer and a cable. If you use a computer to directly control a machine then its called Computer Aided Manufacture (CAM).
     
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