PID Programming Delta DT320 temperature controller

4 posts in this topic

Hello ! 

The idea is to heat greenhouse with stable temp at 13*C. 

Heating method is with circulating hot water(80*C) true pipe, and open/close three-way valve.

Output 1 is for open big circul

Output 2 is for close big circul

valve is 50 mm , step is 10 mm per minute

In theory water heater start at temp 15*C to be prepear and for about 40 min is ready with 80*C . 

Temp is continue droping and at 14*C three-way valve start to open circul 1(big one) and need to open 10 mm 
After 0.2*C drop down open 10mm again ... 
and when temp is drop to 13*C 3-way valve need to be open at all 50mm ... 

So the greenhouse is big ( arount 10.000 sq.m. ) 

And temp continue drop(or not) but in fact is drop to arount 12,5*C to 12*C and stop. 

When greenhouse start heating. Temp is start to go up. 

3-way valve need to start closeing,and at temp 13*C need to be fully close. 

Problem is that : when temp is going up  Delta DT320 is operating at the same time OUT1(because temp is lower then 13) and the same time OUT2 is try to close, so the 3-way valve stay at the same place and not closing because is have "line" on open and "line" for close. 

setting from Delta DT320

Ctrl Method : PID
Heat/Cool : Heat(out1)/Cool(out2)
Com Write : enable
Lock status : normal 
AT : Stop
SV control : Const SV

Type : 4-20mA
Unit : EU
SV : 13.0
Range Hi : 50
Range LO : -20
Pointer : 1 

PID Parametyer 
Pb : 0.2 
Ti : 787
Td : 196
Ctrl Period : 20 
I offset : 0.0 
PID set : AUTO
PID SV(auto) : 100.0


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Let me suggest you introduce temp and lasttemp variables.  From these create tempdroping and temprising variables.  IF you're less than 14C and tempdropping then open valve.  if the temp is greater then 12c and temprising then close valve.  this should maintain your 13C +/-1 if your system is capable of it.

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1. valve/actuator


a. A 3 way valve has 3 ports, either one inlet and two outlets or two inlets and one outlet.

Why are you using a 3 way valve for steam?  How does that work?  Do you waste steam when the valve is in the 50% position?

Normally a heat-only application uses a 2 way valve, one inlet, one outlet.

b. On/off or modulating

Depending on the actuator a valve can be controlled as either
- open or closed, or on-off, or
- modulating, where the actuator partially opens or closes the valve over the range of 0% (closed) or 100% (open).


Is your valve/actuator that you are working with an on/off valve actuator or a modulating valve?

What input signal does it expect?

Is it driven by 4-20mA, one relay or two relays?

2. Control modes

a. heat (reverse action)

Heating action uses only one control output, either
- a single relay or
- a single 4-20mA,
- the special application of driving a modulating electric actuator with two relays, where one relay drives the electric motor to a closed position, and the other relay drives the electric actuator to an open position. Honeywell calls this position proportional when there is slidewire feedback from the actuator or "Three position step control (TPSC)", an open loop control mode with no feedback for motor position. TPSC uses timing to estimate the motor position.  

The controller's output for PID Heating action is 0% is closed, 100% is open.  

b. Heat/cool control mode uses 2 control outputs.  One output is dedicated to the heating loop.  The other output is dedicated to the cooling loop.  

When the PV (temperature) is below setpoint, the heating output is controlled and the cooling output is OFF, closed, at 0%.

When the PV (Temperature) is above setpoint, the cooling output is controlled adn the heating output is OFF, closed, at 0%.  There is a setting, typically called deadband, which is a range around the setpoint where both heating and cooling are disabled (at 0%) because there is rarely an application where heating and cooling are needed to maintain setpoint.
3. All that said,

what's going on?

a. it isn't clear whether your valve is modulating or on-off:

>"valve is 50 mm , step is 10 mm per minute"  An electric actuator takes time to close or open a valve but what is the intended design of your valve/actuator?  on/off or modulating?

b.  I suspect that what you call a 3 way valve has an actuator that expects to be controlled with two relays, one to drive the motor open, one to drive the motor closed.  Is your term '3 way' related to the number of wires on the actuator or the number of ports on the valve?  

c. >"when temp is going up  Delta DT320 is operating at the same time OUT1(because temp is lower then 13) and the same time OUT2 is try to close,

This sounds like your are trying to drive an electric actuator with two relays, one relay to close the valve, the other relay to open the valve, which is the position proportional or 3 position step action described above.

That's not the action that the relays are performing - the action that the relays are performing is heat/cool action: the heat relay is enabled (on a time proportional (a form of pulse width modulation) basis while the cooling relay is OFF.

The control of two relays to drive an electric actuator is a special function.  Only one relay is enabled at a time.  The ON time must be calculated and controlled.  That motor control function is not mentioned in Delta DT3 instruction sheet, at least, I could not find it.

Page 8 of the instruction sheet describes the control outputs and their allocation as Heat, Cool or Heat/Cool control outputs or as alarm outputs.  No mention of actuator control.



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I'd suggest you look at the Blog at the link below, Understanding Control Signal Jargon, aimed at the control of electric actuators.


I suspect that your actuator is in the group called "3-point, Tri-State, Floating Control" (to which I can add: position proportional, Three position step control, PAT, valve motor)


You need to understand exactly which control mode your actuator requires.

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