JCI unt programing

[doubledose]

I am trying to program a loop presure reset in a unt with hvac pro. I am monitoring a hot water loop and want to open a bypass valve when the pressure gets to high. I can make it work using the ai to ao setup and selecting reset schedule and adding all of the other info. But I would like to add some delay into the logic so it is not hunting or changing constantly. So I have tried to select PI control with reset schedule so I can add some deadband or time to the logic. But I cannot get it to output to my OA point and control any thing. If I do just the reset schedule I can make it work fine. Anyone have any ideas on how to add some delay into a reset schedule?
Thanks
Wayne

[DaveCR]

What you describe is a conventional control loop so a reset schedule is not required. If you set up an AI to AO, PI Control, side loop you'll have what you need.

[Cagey57]

As DaveCR said use a simple PI control loop. The reset will only create problems for you.

Here are some suggestions for your tuning parameters.

Let X = Differential setpoint ((10PSI))

Prop Band will equal 5X ((50PSI))
Dead Band will equal .05X (5% of X), ((1-2 PSI))
Integration... start with 200

Preliminary checkout: get your output to change at a rate of aprox 1-2 % per second for starters. If it changes too fast increase PB by 25%, too slow decrease by 25%.

Also increase the filter value of the Analog Input to about 3 (roughly 4.5 seconds) to keep the loop from spiking.

Good Luck, let us know how it works out O.K.

CCI (Controls Cause Insanity)

[doubledose]

Thanks for the reply's. I have been gone for a couple of days and got time this mourning to work on this.
Ok This is my first attempt at a PI loop programming in a unt. So if I understand this correctly with a PI loop X would = what you want to maintain as a setpoint presure. ( What I was trying to do with the reset schedule was if presure = 25psi then bypass valve would be 100 % open and if presure = 10 psi then bypass would be 0% open. ) With the PI sequence it looks like I would use X=20 (for 20psi)
Does the 50 in your prop band mean it will go up to 50 psi or is that just an intergration number?

X=20 psi setpoint
Prop band =50
dead band=1
Int=200

And also it looks like 20 becomes the middle of the swing, below this closes the valve and above it opens it up. ( I have a test bench with a unt on it with pots on the inputs and an anolog guages on the outputs.) so I am able to download and watch what happens.

[Cagey57]

I am not going to ask why but...

AI to AO
Reset Schedule


Input 1 10 PSI
Input 2 25 PSI
Output 1 0% (0VDC)
Output 2 100% (10VDC)

If that doesn't work you messed something up !

[doubledose]

What my senairio is that I have a DX9100 sitting in a control cabinet now only controling a bypass valve and a pump command . I am wanting to change that Dx out so I can use it elsewhere in my building and put in a unt controler. The reason I was messing with the reset schedule was that I have a couple of loops here using that for tempature reset on hot water loops and I thought I would try and use the same thing for a presure bypass since I have not used any PI loops before. So at this time I am playing with a PI loop and that was why I was asking about the settings. I have been working on the Johnson controls here at the school for about 15 years and like I said this is my first attempt at setting up a PI loop.
Wayne

[Cagey57]

Based on your test results and description you want a simple reset.

If you want to do A PI control loop refer to previous post and "Play with it" on your test setup.

Open the Help inside HVAC-Pro, lots of good stuff there.

And like I said, I didn't want to know why !

[DreamCar]

If you want the valve open at 100% at 25psi, 0% at 10psi, just use a PI loop, with setpoint of 10, prop band of 15 (10+15 = 25psi full open).

If you want more accurate control to a specific number (like 15 or 20psi), make the actual number you want your setpoint, triple the prop band (say 50) and add the integration number (200ish would be a good starting point).

If the valve "hunts" up & down, increase either your prop band or integration. Next step I would probably try would be 75 prop band, 400 integration. Or just one at a time.

good luck!