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-   -   I hacked up a P-J diagram, not sure if it will work. (http://www.homebrewtalk.com/f170/i-hacked-up-p-j-diagram-not-sure-if-will-work-369896/)

ajdelange 11-28-2012 03:14 PM

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FWIW here is how I would do alarms. I don't like the idea of being able to turn them off with a toggle/rotary switch as if you forget to turn them back on they are not there next time an alarm condition exists. I'm not telling anyone that they need to do it this way or that they should do it this way. Just throwing out another idea for perspective.

In the circuit below K1 is any NO contact that closes when an alarm condition is detected. It could be one of the alarms in the PID controller itself or a float switch or a ground fault detector... When K1 closes, however briefly, K2 picks up and is latched energized by the NO contact pair in parallel with K1. The only way to release K2 is to push the reset button and that will only de-energize it if the alarm condition no longer pertains (K1 is open).

When K2 energizes the lamp lights and the buzzer sounds. The buzzer can be silenced by pushing the Silence button which latches K3 on thus opening the NC contact pair in series with the buzzer. But the lamp will stay lit until the alarm condition is cleared and the reset button is pressed. This way if you left the room and got an PV+Hy alarm, for example, which only persisted for a few seconds you would know upon your return that something had gone awry.

ajdelange 11-29-2012 02:05 PM

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Per request here's another diagram that separates the two alarm outputs available from these controllers. In this circuit if either alarm is set it latches a light dedicated to it on and sounds the buzzer which can, as before, be silenced. Also as before once an alarm condition is detected its lamp stays on until the alarm condition is reduced and the reset button is pushed.

The situation in which the latching is helpful is the one in which, for example, there is a wild overshoot for whatever reason while you are absent. Without latching you would not be aware of this and if the beer turned out to be less than you hoped for you would be puzzled as to why. With latching you'd would at least have the overshoot as a possible explanation. Of course if you stay in the room that can't happen and it's unlikely that such a situation would occur anyway unless an SSR failed on but it's unlikely that such a failure would heal itself. I guess the controller output stage could 'stick' on and heal itself but again, that's unlikely. So I don't really see the alarm circuit of any kind as necessary and don't use them in my brewery(Edit: Actually I do - if the water level gets low enough in the atmospheric tank of my RO system the pump which empties the atmospheric tank gets latched off until a reset button is pushed even if the water level returns to normal). What I do do, however, is record the temperatures (main and decoction vessel) throughout the brew day. If you look carefully at the Auberin 'manual' you will see that there are menu settings for baud rate etc. This tells me that they sell very similar controllers which communicate (probably Modbus). A temperature profile is the ultimate monday morning quarterback's tool.

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