3 thermostat temperature(average of 3) need to control one motorised valve actuator

what would be the output range of the rtd?
is it analog current or vlotage(4-20mA or 0-10V).

An RTD is a positive temperature coefficient element that changes resistance with temperature. The controller pumps a constant current through the resistor which develops a voltage (IR) drop which the controller 'reads' and converts to a temperature value. The Platinum Pt100 is the most common industrial RTD.

A 2 wire RTD ALWAYS as a positive error due to the resistance of the copper lead wires. Always use a 3 wire RTD because a UDC can handle a 3 wire and the 3rd wire allows the controller to compensate for lead wire resistance.

how can i loop the rtd to honeywell loop controller? directly can i connect the (3 wire or 2 wire) from pt100 rtd to UDC3500 controller or in between i need to use any temperature transmitter?

You connect a 3 wire RTD to the controller with 3 copper wires of equal length. The cable is called Triad for 3 conductor. Sometimes people use two twisted pair cables for a total of 4 conductors and don't use one of the conductors. RTD cable should always have twisted shielded conductors because it is a very low level signal.

There is no external power needed for an RTD. The controller does what it needs to do to 'excite' the RTD and read the IR value.

can i use pt1000 rtd instead of pt100 rtd? pt1000 is available in honeywell.
No, PT1000 is HVAC, PT100 is industrial. The UDC is an industrial controller designed for a Pt100.

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attached the schematic i made for your kind info sir. please see the link. http://i64.tinypic.com/2cwlyzm.png
1) Use a 3 wire RTD, and say "3 wire RTD". No choice for 2 wire . Bad Juju.

2) 'Feedwater' is a term usually associated with boilers. If the control is cooling control, why not call it cooling supply line, or something like that? The arrow might point to the rooms, because that's where it is presumably used, since that's the temperature you're measuring.

3) "Position feedback" is not the same as a 4-20mA control signal. The controller generates a 4-20mA control signal which is position demand signal. Some actuators have an optional 4-20mA feedback with the actuator generates and the controller reads, but I doubt that's the case here.

It should read: A1) Use a 3 wire RTD, and say "3 wire RTD". No choice for 2 wire. Bad Juju.

2) 'Feedwater' is a term usually associated with boilers. If the control is cooling control, why not call it "cooling supply line", or something like that? The arrow might point to the rooms, because that's where the cooling is presumably used, since that's where you're measuring and controlling the temperature.

3) "Position feedback" is not the same as a 4-20mA control signal. The controller generates a 4-20mA control signal which is position demand signal. Some actuators have an optional 4-20mA feedback with the actuator generates and the controller reads, but I doubt that's the case here.

It should say: Actuator with a 4-20mA control signal

4) Get rid of the word "feedforward". The math option is a summer. There is no feedforward control.
 
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thanks mr.danw.. your kind suggestions and technical guidance helped a lot and i learnt many new things from you.. will get back to you once i use this hardware, will post the pic of the installation once it gets successful :)
thanks a lot Mr.Danw
 
+1 for Robertmee and briancr

If you are taking an average of three rooms, you may not necessarily be able to cool a room at 34 degrees as you stated you wanted to do in your earlier post. If Room 1 = 26, Room 2 = 30, and Room 3 = 34, then your average is still 30 so your cooling valve would not modulate. If you looked at each room individually you could use a compare instruction so that if any of the temperatures is greater than 30 you modulate your valve. However, this will cool the temperature of your other two rooms as well. The whole system just seems inefficient.
 
UDC3500 isn't going to have the brains to do selective control based on conditions or ranges of inputs.

Ideally three control valves, one for each room would be a better solution. If that's not possible and it's important to not let a room get too hot or too cold then you're back to a PLC. With a PLC you can make decisions on what do...for example if any one room gets too cold shut off valve. Or if any one room gets too hot open valve. And maybe limit the operation of the valve in attempt to cool a room gradually if other rooms are already cool. Alot depends on the thermal characteristics of the rooms individually and as a whole. And we don't know enough about those properties.
 
just guess

thanks @osmanjdt,
as per my observation from your solution: air from the (FCU or AHU's) rotary damper is controlled by using the temp controller individually according to the pv and sp of each temp controller.

so in this, temperature controller is actually a PID controller? what options that a temp controller should have in it from the below?
CONTROL OUTPUTS
Analog Output: Non-isolated, programmable for control or retransmission; Voltage Output 0-10V output. 500Ohms Min. Accuracy 0.1%(1); Current Output 0-20mA output. 500Ohms Max. Accuracy 0.1%(1)(2); Step response time 100ms(3)
DC Pulse: Non-isolated; 10 Vdc at 20 mA
SPST Relay: Single pole, single throw mechanical relay, 250 Vac or 30 Vdc at 3 A (resistive load)
SPDT Relay: Single pole, double throw mechanical relay, 250 Vac or 30 Vdc at 3 A (resistive load)
SSR: 20 to 265 Vac at 0.05 to 0.5 A (resistive load)
Isolated Analog: 1.5kV Isolation(4), programmable for control or retransmission; Voltage Output 0-10V output. 500Ohms Min. Accuracy 0.1%(1); Current Output 0-20mA output. 500Ohms Max. Accuracy 0.1%(1)(2); Step response time 100ms(3)
Isolated DC Pulse: 1.5kV Isolation(4); 10Vdc at 20mA
(1) At 25C.
(2) Output scaling required for stated accuracy. Refer to Platinum Current Output Application Note.
(3) Filter setting of 1.
(4) Isolated outputs not individually isolated.
 

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