Programming a Secondary (Safety) Heater

P3 eX, FW o; 5.0.0.11.

Sometimes heaters fail. With my previous controller, I ran 2 heaters for redundancy, each assigned to their own socket. I programmed each heater with a one-degree difference. That way, if heater 1 failed at the assigned set point of 76, then heater 2 would come to the rescue as soon as the tank reached 75... and I would know heater 1 failed simply by looking at the current temp. If the temp was 75 instead of 76, that meant heater 1 had failed and required replacement... yet my tank temp could never become dangerously low. This is how I programmed my old controller:

If Temp < 75.5 Then HT1 ON
If Temp > 75.8 Then HT1 OFF
If Temp < 74.5 Then HT2 ON
If Temp > 74.8 Then HT2 OFF

Is this (or something similar) possible using programmable logic?

it is even simpler: use an virtual sensor

create a virtual sensor as a copy of temp. sensor 1

desired temp1: 75.6°F
desired temp2: 74.6°F
(exact values depend on the hysteresis settings)

then assign socket a - temp1 and socket b - temp2

OK that's amazing. The more I see, the more I'm "getting" it :-)

Hopefully these questions & answers help others too.

question: if I look in PLC 5.0.0.11 and FW o ) I can't see virtual probes anywhere I assume those can only be created on the P3 itself ?

Yes you have to create the virtual sensor first on the controler.

so thinking about virtual probes (and find a use for them :) ) and to avoid playing with hysteresis and coolingdifference (and to test multiple solutions of the same thing with the profilux)

I could use a virtual probe to solve the issues in these threads ?
( same base problem in both theads )
http://www.aquariumcomputer.com/Foru...splay.php?f=18
http://www.aquariumcomputer.com/Foru...ead.php?t=1815

I just set my nominal value x degrees higher on the virtual one and put the cooling socket on the virtual probe 3 ?