Timer example – Watlow Series SD31 PID with Optional Countdown Timer User Manual
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Wa t l o w S e r i e s S D 3 1
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C h a p t e r 8 Ti m e r
Timer Example
Convection Oven Application
A master chef bakes bread at 350 F for 30 minutes. She wants the oven at the proper temperature with an indica-
tion when it is ready to begin baking. She isn't concerned if the oven is 10 degrees cool at first. After she loads the
oven, the chef wants to start the countdown time by pressing a key. When the baking time is complete, she wants a
10-second audible indication that the bread is done. She would also like to easily be able to monitor both the count-
down time and the temperature during the baking process.
Recommended Controller
Series SD31 controller part number of SD31-HCJA-AT0R.
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Output 1 is a switched DC output connected to a Din-A-Mite solid state power controller to control the oven's
heaters.
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Output 2 is an electromechanical relay connected to an audible indicator to provide the completion indication.
In the Setup Page, program the following parameters:
[~C-F] = [~~~F]
Set the controller to Fahrenheit
[ti;En] = [~~On]
Enable the Timer Function
[hour] = 0
Set the hours of countdown timing to 0.
[Min] = 30
Set the minutes of countdown timing to 30.
[~Sec] = 0
Set the seconds of countdown timing to 0.
[ti;St] = [rdyA]
Configure the timer for Ready with Acknowledge.
[ti;SP] = [Pre;S]
Use the preset set point for the timing sequence.
[~rdY] = 10
Set the ready band at 10 .
[rdY;L] = [~~On]
Enable the ready light for the "begin baking" indication.
[~Ot2] = [TiM]
Configure Output 2 as a timer output.
[ti;F2] = [sg;On]
Select "signal on" to provide the completion signal.
[S;M2] = 0
Set the signal time minutes to 0.
[~S;S2] = 0
Set the signal time seconds to 0.
[~dsp] = [to;tt]
Set to toggle between countdown time and process temperature using
ß key.
[Ct;SP] = 350
Set the timer sequence set point to 350 .
[CC;SP] = Off
Set the set point to Off when not timing.
Operator/Control Actions
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With the oven "off", the chef starts the preheat cycle by pressing the Down
¯ key. The RDY LED is off. Series
SD31 begins to control to the 350°F bake set point.
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The chef can press the
ß key to toggle between the process temperature and the timer countdown. Viewing
the temperature, the chef should see it progressing up toward 350°F. Toggling over to the countdown time, she
should see the countdown paused and the colon having a steady indication.
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When the actual oven temperature increases to within the Ready Band at 350°F ±10°F, the RDY LED turns on.
The chef loads the oven and presses the Down
¯ key to acknowledge the Ready Band, starting the bake cycle.
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Time starts counting down. The countdown time displays a flashing colon.
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If the temperature deviates out of the Ready Band (less than 340°F or more than 360°F), timer countdown will
pause, but will continue as soon as temperature re-enters the Ready Band.
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When time reaches 00:00, Output 2 turns on for 10 seconds sounding the audible indicator. The chef can stop
the audible indicator by pressing the Up
¿ key. The Series SD31 then automatically shifts to the idle set point,
Off .