Hvac

Hi all i have burner control as per rung below.uSING rslOGIX 5000. My problem is the set point(AHU.Temp_SP), because it is inputed via RSView 32 engineers tend to change unnecessarily. Secondly when the temperatures change in the room the set point remains until changed.I am trying to remove the human error here. I want to look at the ambient temp add a factor move into set point. I have initially done this (ADD 5 AHU.Control_Temp AHU.Temp_SP _) the problem with this is keep going up. In short i want to be able to look at the ambient calculate my setpoint when it get too hot go the other way.
Code
XIC AHU.Burner_Start XIC M_001.I.Run BST CMP AHU.Control_Temp<(AHU.Temp_SP-AHU1.Setpoint_DeadBand) NXB XIC AHU.Burner_Req LEQ AHU.Control_Temp AHU.Temp_SP BND OTE AHU.Burner_Req

Please help

Secondly when the temperatures change in the room the set point remains until changed.

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Yes, the Set Point should not change except manually, and then rarely. The purpose of a Temperature SetPoint is to allow your control function to increse or decrease the ambient temperature until it is equal to the Temperature SetPoint. It seems that you are trying to change the Setpoint to match the ambient! (your horse is trying to push the cart). What you are doing will really screw up what little control you have now.

Try it the other way. Increase or decrease the ambient temperature until it equals the set point, then stop until there is an error larger than the deadband setting. If there is too much delay before the temperature increases, then your gain factor is too small. Adjust this in your thermostat or PID function, not by changing the Set Point. If you are using a themostat, you may need a better, more accurate unit, or the sensor needs relocating.

(If the engineers are changing the Set Point too often, it is most likely because your temperature control is not working correctly). Examine that carefully and try to refine it so that you achieve better control. Temperature control usually needs to be within +/- 1 degree accuracy to satisfy most people's comfort level.

If I can add a little note here. Not related to the PLC.

It is very common to change the ambient temperature SP with the outside temperature, IE a low outside temperature would increase the inside temperature slightly.

I don't think he is basing the Set Point change on the outside ambient.

In short, I want to be able to look at the ambient, calculate my setpoint when it gets too hot, then go the other way.

Click to expand...

In other words, trying to control the temperature by mostly automatically adjusting the Set Point. If you do this, why even have a Set Point (that is no longer a Set Point, but simply a number that gets overridden by the PLC)?

I agree !

You just stated that it wouldn't change except for manually

Yes thank you all. Yes set point becomes useless. I see let me put some meat to what i am trying to achive. The room i am trying to control temp is difficult. At wrong temps the condensation builds on ceilings or fogs rendering the cameras looking at the product useless, they start to fail. we have to raise the temp to clear all that. The is a problem in winter. So was thinking of a code either looking at the room temp or outside temp thereby increase temp when outside is low vice versa when its worm.

It seems that a humidstat in that room would be the best solution.

Otherwise you probably will need a Summer/Winter switch to make the temperature control work correctly.

If your PLC has a built-in clock/calendar, you might use that instead of a Summer/Winter switch. Decide what days of the year you need to switch from Summer to Winter and Winter to Summer control. Use those time-of-year days to turn on or off a Summer/Winter bit. Then add rungs that adjust the Setpoint (by a fixed additional amount) based on the Summer/Winter bit. You could call it "High Humidity Season = ON" if that makes more sense.

Thanks Lancie 1 and Boneless, the summer/winter time in the plc will be preferred as an early fix then move to install humidity sensor.So that means i will have a set humidity compared against the sensor humidity and the output to temp set point.

hvac

Hi again i have programmed as follows COP AHU_Temp_SetPoints[AHU_No_Select.1,Clock_Quarter] AHU1.Temp_SP 1 and i am getting
Error: Rung 6, COP, Operand 0: Invalid array subscript specifier. I have tried all sorts struggling any help