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I need to integrate some airflow alarms we are installing…

I need to integrate some...
I need to integrate some airflow alarms we are installing with the fan motor controllers, so that there is no alarm when the fans have stopped.
I was told to connect the relay coil in parallel with the fan controller M coil. Then put an NO contact in parallel with the NO airflow sensor so that when fan is turned off, the relay contact will close and bypass the sensor input. I have a sketch of what I believe should be happening if someone could review, I would really appreciate it.
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Answered in 5 minutes by:
3/19/2018
Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 976
Experience: I have been an HVAC/R mechanic/technician for 30+ years.
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Hi I'm Brian and I'll be happy to help with this!

Yes, by all means attach your sketch using the "Attach Files" button in your reply dialog window (next to the send button).

Thanks.

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Customer reply replied 1 month ago
thanks and dont laugh at me

No, no worries at all! I get the jist of your plan but for me, there's one piece of the puzzle missing. What specifically is the 'alarm'? Is it in input to some type of building control or automation system? Is it just a local audible or visual alarm?

Also, in the picture with of your fan motor with a circle around it and a coil or winding inside, is that representing the coil of the fan motor contactor or starter and not the fan motor itself?

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Customer reply replied 1 month ago
its a dynalec airflow sensor

Thanks for that. Let me research it a bit and I'll be back shortly with more info. Thanks for your patience!

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Ok, having read through the IO manual for that Dynalec control, it is designed to monitor airflow in a system that runs at all times and alarm if the airflow drops below a level set in an alarm trip setpoint in the control itself. The control receives inputs from a temperature sensor and an airflow sensor. Both of these sensors are analog inputs and vary their input to the control based on air temperature and air volume in feet per minute. The sensors are logic level varying inputs and specific to the controller. The airflow sensor is not a contact type signal, it is an analog signal and as such can't be overriden with any type of contact closure across its signal to the control.

Further, the control doesn't offer any type of external input to it to stop the alarm trigger when desired. Again, the control is meant for continuous operation of the monitored airflow.

It appears to me, the only way to stop this alarm panel from outputting an alarm when the system airflow is purposefully stopped is to remove the 115Vac input power to the controller itself. This could be done with the relay you reference that would have its coil in parallel with the fan motor contractor or starter. Then the added relay, through one of its normally open contacts, would interrupt power to the Dynalec controller.

I don't really see any other way to prevent an alarm from that control beside cutting the power to it. Let me know if you have questions about this.

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Customer reply replied 1 month ago
couldn't I just alter my sketch to run wire from NO contact of relay to the NC of the air flow indicators "run relay" or whatever cuts its power

If by "airflow indicator" you mean the Dynalec alarm control itself, then yes. You would select a relay like perhaps a 90-290Q or if you wanted a simple to install relay a RIB-U1C relay in a box type. Note, these are both 24Vac coil relays, if your motor contactor has a different coil voltage you would select a relay with the same coil voltage. Then you would wire the added relay in parallel with the coil of the blower contactor so it energizes every time the blower is called to run. Then with the NO contact points on the added relay, run the input power hot wire through that relay contact so the controller shuts down if the blower contactor is deenergized.

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If you need me to, I can draw up a quick diagram to show the wiring. Let me know...

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Customer reply replied 1 month ago
please

Very good, this will take a bit of time but I'll have it done today. Thanks much!

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Customer reply replied 1 month ago
thank you

You're very welcome!

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Ok, Click Here for a schematic of how to wire your system as we discussed. Let me know if you have problems viewing it or any questions about it. You don't need to sign up for Dropbox, just click the view now button at the bottom of the dropbox window. If you have no further questions, please remember to rate positively (3 stars or better) before leaving as it's the only way I get paid for helping you.

Thanks much,

Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 976
Experience: I have been an HVAC/R mechanic/technician for 30+ years.
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