If you have not seen this thread, take a look at it.
Also here is a much better TA4 configuration manual.
PIDInstructionManualupdated11-2013.pdf 688k .pdf file
That being said, as I read your post, I'm a little confused. Is the kettle tracking temp correctly and you are having issues when the alarm lights illuminate or is the kettle temp swinging more than 3 degrees and you want to tighten the band up? To control the actual temp tighter, you will need to fiddle with the P, I, and D settings. Have you set up the kettle in operating conditions (at least with water to simulate normal load) and run an AUTOTUNE session? If you autotuned previously and did not simulate the normal load in the kettle, it will be off. Let it run until the AT light is out.
To autotune the PID controller:
For the Mypin, press and hold the AT button until the green AT light illuminated. Should take 5 seconds to get into AT mode, and at least 5 minutes to do the autotuning. Then the AT light will turn off. I start with my process material at room temp when I run autotune sessions.
Otherwise, you will be manually editing the PID settings to dial it in tighter.
Now if the actual temp in the kettle is tracking correctly and you are asking about the alarm light, that's different. To have AL1 light when the kettle is over temp and AL 2 light when it is under temp, try this:
ALARM 1 = desired temp variation over set point
ALARM function 1 = 0 (0 sets that function to deviation high or over your set point)
ALARM 2 = desired temp variation under set point
ALARM function 2 = 1 (1 sets that function to deviation low or under your set point)
You could also go another route and use the "section outside" function and a single alarm LED. That function activates the alarm when the process value is over or under the set value by a designated amount. I don't recall the TA4 having a decimal value for alarm vale settings, so you might have to use a 2 or 4 degree band. To set alarm 1 for 2 degree band (+/- 1 degree) band, use this setting:
ALARM 1 = 1 (for 2 degree band, use a value of 2 for a 4 degree band)
ALARM function 1 = 4 (alarm if process value is outside the 2 degree band)
Hope this helps
Edited by dward51 - 1/30/16 at 6:11pm