To enable Alarm Disable, wire an external element (in this case a switch, button or key switch) into one of the relay inputs. Then, when a user flips the switch or pushes the button, it sends a signal to the relay to switch from open to closed. That will disable the audible alarm and the LCD screen will read “ALARM DISABLE.” The activation process is identical to Night Setback (above), except that in Step 5 Alarm Disable is chosen as the function. This method most often is deployed at times when the sash must be open for extended periods for loading materials in or out of the hood or during service work. Also like Night Setback, the feature may be daisy-chained to other monitors using the output relay of the lead monitor and the input of a follower.
5. "Link" power
The idea here is for someone to wire the monitor so that when the power to an external source (say, the room or hood lights) is shut off, the monitor powers off as well. You can either do that electrically, by connecting wires, or you can do it the “layman's way,” by making sure the outlet that powers the monitor loses power whenever the hood itself loses power (kind of how a TV, DVD player, etc., all shut off as you turn off the surge protector/power strip).
A note on input relays
The AFA 1000 has 3 inputs — these are digital, meaning open or closed, two-wire relays. They are dry contacts; they need no external voltage on them because the monitor itself provides the voltage that is then switched back in. The inputs have two terminals, + & SW. The + is internally connected to the + of the power supply on the AFA (there are some EMC components connected but we can consider them directly linked). As the power supply is 15VDC there is then 15VDC (approximately) on each + input terminal. When the + terminal is connected to the SW terminal (input closed) we are simply connecting the 15VDC back into the SW terminal, this then is indirectly fed to the microprocessor to activate the assigned input function.
In other words, you can fit a simple link wire to the two terminals; this will activate the input.
Typically the link wire is a micro switch (mechanical switch) or signal from the building automation system (dry relay contact) in the field. If you put any external (other source) voltage into the inputs it will damage the AFA — it uses its own voltage.
In the UK it is fairly commonplace to have a blower switch with an auxiliary (spare) isolated contact, a switch with two sets of contacts.
Another solution is to fit a remote 120V relay that is switched from the blower switch, then use a dry contact from the relay to connect to the monitor.
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