Timing circuit issue

Discussion in 'The Projects Forum' started by Rockhopper, Jan 28, 2015.

  1. Rockhopper

    Thread Starter New Member

    Jan 28, 2015
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    I am working on a project that will sound an audible alarm when a liquid reaches a particular level. I need a timed "alarm off" that can be initiated by a momentary 'on' switch so more liquid can be pumped into the vessel manually. If no liquid is pumped in the set time, the alarm should re-sound.

    The circuit is 24VDC.

    I have tried a number of commercial timers used for refrigeration compressors (ICM102, ICM206, ICM253). The work on the bench but not when I put a load on them. Any thoughts?
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Do you have details about what worked? Shouldn't be hard to fix the load problem.
     
  3. #12

    Expert

    Nov 30, 2010
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    Refrigeration timers are designed to work with AC.
     
  4. Rockhopper

    Thread Starter New Member

    Jan 28, 2015
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    All I can say to that is the catalog I ordered them from shows the specs as both AC and DC. Also, look at your first picture. The Interstate Electric relay states 12-256 AC/DC for the input. If that's the case, it should work.
     
  5. Rockhopper

    Thread Starter New Member

    Jan 28, 2015
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    WayneN - I'll scan a sketch to send shortly. Trying to get through lunch without giving myself any more of a headache from this. LOL!
     
  6. Rockhopper

    Thread Starter New Member

    Jan 28, 2015
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    I have attached the circuit I am working with. Low-3 alarm is the alarm I need a delay for. I have a momentary on switch that I can use to trigger the time delay and three commercially available delay timers as mentioned above. The ICM253 works on the bench, checking the load voltage with a meter, but once I put the load on (either the buzzer directly or through another relay), it activates but does not deactivate.
     
  7. #12

    Expert

    Nov 30, 2010
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    One of my timers says, "DC", but not the ICM brand.
    Best for me to double check this.
    Specs
    Voltage:
    ?
    18/30 VAC
    Frequency: 50-60 Hz
    Amperage:
    ?
    1 amp (max)
    Holding Current: 40 mA (minimum)
    Amp Inrush: 10
    Adjustable Time Delay: 12-390 Seconds
    Dimensions: 2" x 3"

    NOT DC
     
  8. Rockhopper

    Thread Starter New Member

    Jan 28, 2015
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    [/QUOTE]
    So, chances are, the commercial delay timers I have won't work. Any ideas what might?
     
  9. #12

    Expert

    Nov 30, 2010
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    Can your sensors ground an AC signal? Just change the supply wiring.

    Otherwise, this seems like a job for some LM555 timer chips.
     
  10. Rockhopper

    Thread Starter New Member

    Jan 28, 2015
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    I already have a job box outfitted with a 24VDC supply and all the relays. Pictures attached.

    BTW: OMRON S8VK-G03024 power supply
    finder 20 Series relays (20.21.9.024.000) to drive each alarm
     
  11. Reloadron

    Active Member

    Jan 15, 2015
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    OK, maybe I can help with this. The timer you reference (The ICM253) is a delay on break timer. In the wiring diagram it is shown with a T stat. So for example in a furnace system when the T stat calls for heat the contacts close. Those contacts remain closed during the heating cycle, they are closed. When set point temperature is achieved the heating stops (be it gas off or electric off or whatever) but we want the fan to continue running for a period of time to cool the plenum or whatever. That time period is a Delay on Break. I don't think that is what you want.

    I believe what you want is when an alarm condition exist, Low 3 Alarm in your case you want an audible alarm to sound for a given period.

    So Low 3 alarm sounds (which relay is that in the drawing?) and when Low 3 Alarm condition exist, exactly what do you want to happen?

    Ron
     
  12. Rockhopper

    Thread Starter New Member

    Jan 28, 2015
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    All the relays are the same, so which one is sort of immaterial (it is Low 3 Alarm on the print). What I actually want is for an alarm to sound when the Low 3 Alarm relay is triggered, but to have the capability to silence it (open the circuit) for a set time period so that the level in the vessel can be changed (pump more liquid in). After the set period, the alarm circuit needs to close. If liquid was pumped in and the level has changed, the Low 3 Alarm relay will have been deactivated so the alarm buzzer will no longer sound. If no liquid was added, then the alarm will reactivate. I don't want people to be able to permanently silence the alarm.

    Does that make any sense?
     
  13. Reloadron

    Active Member

    Jan 15, 2015
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    Yes, think I have the idea. I'll draft what I think will work. May take awhile as I have some things to do. The timer you wanted was a one shot, let me see what I can come up with.

    Ron
     
  14. Rockhopper

    Thread Starter New Member

    Jan 28, 2015
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    I appreciate any help you can provide. This thing has been driving me crazy for a few days now.
     
  15. KMoffett

    AAC Fanatic!

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  16. Reloadron

    Active Member

    Jan 15, 2015
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    Sorry, got busy this afternoon. The type timer you want I believe would be a One Shot. More on that later. The below circuit isn't exactly what you want as it lacks the timer function at this point. This is an alarm circuit I used quite a bit for general applications. The circuit is somewhat stripped down basic.

    Alarm Audible Latching.png

    Low 3 Alarm is your alarm relay, it closes on an alarm condition. Power is passed through the normally closed contacts of K1 and the horn (audible alarm sounds). Additionally the alarm lamp illuminates. As long as low alarm 3 is in an alarm state the lamp will be lit. To silence the alarm (audible) you push the normally open alarm silence push button. This causes K1 to pull in and with the normally open K1 contacts across the alarm silence push button K1 will latch on removing power from the alarm horn. The lamp however remains lit. What I need to do is work a timer into the scheme and I am thinking a One Shot. This based on your post #12. Let me think about the timing function.

    Ron
     
  17. Rockhopper

    Thread Starter New Member

    Jan 28, 2015
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    Thanks for the help. Unfortunately, my electronics education from 30 years ago has all but escaped me. I never thought about a One-Shot until it was mentioned here. Makes sense.
     
  18. Reloadron

    Active Member

    Jan 15, 2015
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    Just to be clear, your relays are 24 VDC and switching 24 VDC correct? For example in the drawing I posted above I show your Low 3 Alarm, the PWR would be 24 VDC correct?

    Ron
     
  19. Rockhopper

    Thread Starter New Member

    Jan 28, 2015
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    Correct. Everything in the box is 24VDC
     
  20. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Last edited: Jan 29, 2015
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