HLT Control

[rmcghie]

A couple of simple questions about HLT control. My HLT is propane fired and so I need to monitor the level in the HLT to prevent the burner from coming on if the level is below the temperature sensor. My idea is to connect a float switch to Din0 to accomplish this. State0 would then test Din0 as a exit condition. If Din0 was on, this would mean that the water level was above the Temp0 sensor and the process should exit from State0 to State 1. However, State0 should insure that Output0, which controls the furnace valve feeding gas to the burner is off. State1 would then turn on Output0 if the temperature was below 170F and turn it off once the temperature reaches 170F. State1 would test Din0 and exit to State0 if it was off. As described, can this be done with two states or do you need three or more. How do I force Output0 off in State0 independent of temperature or other inputs?

Once I have solved this problem, the next steps will be to add dough in and HERMS using a heat exchanger and two pumps.

[rabeb25]

Keep me updated, as I want to do floats on my HLT also, For the exact same reason (though mine is electrical)

[ECC]

State0 would then test Din0 as a exit condition. If Din0 was on, this would mean that the water level was above the Temp0 sensor and the process should exit from State0 to State 1. However, State0 should insure that Output0, which controls the furnace valve feeding gas to the burner is off. State1 would then turn on Output0 if the temperature was below 170F and turn it off once the temperature reaches 170F. State1 would test Din0 and exit to State0 if it was off.

Yes, it sounds like 2 states will work for what you want to accomplish. So you want State0 to be an Idle state, while the HLT is filling? In State1, if the float is tripped (Din0=0), do you want to go back to State0, or exit the process? If you're done in this case, I'd exit to "Proc Off" which will automatically disable the process, and turn off any outputs controlled by that process. Or, you could go back to the idle state like you wrote, where the system is still running, but not asserting any outputs. Both would work.

Exitting to "Proc Off" is also a great way to add safety checks. Test for things that should never happen, and turn off the process if they do.

How do I force Output0 off in State0 independent of temperature or other inputs?

If you don't want Output0 to be asserted, just don't check the "Control" box for Out0 in State0 in Add/Edit States. Some people will control the output, with Direct Off to force it off, but this isn't necessary.

[rmcghie]

ECC,

Thanks for the reply. Got that working. Now I have a question about the operation of the Win Input Buttons. What are the default conditions or settings for the Win Input buttons? If I use Win0 ON as an exit condition in a step, will its setting change when I exit the step or return to the step or will the setting remain the same? That is, once set to ON or OFF will the setting of Win0 remain the same as the controller moves from one step to the next?

[ECC]

Yeah, that should be documented better. When using a Win, the condition field is ignored. So you can set it to On, Off, or leave it at -- (default). All Wins are momentary, so it doesn't matter.

This has a little history, during early stages of the beta testing, Wins were sticky. They were implemented as a checkbox instead of a button, so they could either exit if the Win was on or off. But the beta testers and I agreed that they should be buttons, momentary inputs, so that's what we have today.

[rmcghie]

ECC,

I do not have a problem with momentary push buttons, but this leaves the question. Are there any sticky values that may be set in one step and then checked in another step or process. What would it take to make some of the Win Input buttons momentary and some sticky. Or better let, an option to allow the user to select whether each of the Win Input buttons would be sticky or momentary.