Refrigeration control with S 1200

Hello
I would be grateful if someone could help me with a project that I'm working.
I am using an S1200 PLC to control two cold chambers. I have the PLC functions programmed thermostats, running times, defrost .... etc. I only need two  electronic expansion valves  installed in the evaporators (Carel or Danfoss supplier or the like along with their own controller). My question is whether there is some kind of expansion valve Siemens destined to cold chambers designed to be controlled directly by the PLC S1200 my intention is to control the electronic valve exansion from the PLC but I don't know if Siemens manufactures this type of valves for industrial  refrigeration to be controlled by PLC.

Thank you very much and regards

yes,the process is really on / off because the compressor stops and starts but however what is the need to control valve allowing varying gas coolant passage according to the need of cold inside the chamber (while the compressor this "on". Depending on the value of the temperature valve opens more or less (but is not a PID control). it is an electronic expansion valve. It's an analogic control. The valve Works by steps

In image you can to see a electronic expansión valve but its used with a controller of the same firm.  I don't know if Siemens Works with a similar thing to connect to a PlC.

Thank you very much

I see.  I know nothing about refrigeration or air conditioning other than from a user standpoint .  However, the valve itself is nothing special.  Your problem is to develop the algorithm that determines opening vs. condition.  This may be a PID or a step control.

I did a quick search and found this.

"Standard calculations of superheat are all the same, whether done by a technician in the field or an electronic controller. The pressure in the suction line, just after the evaporator, is measured. This pressure is converted to a saturation temperature by the use of a pressure-temperature chart for the refrigerant used. This saturated temperature is compared with the actual temperature measured on the suction line, also near the outlet of the evaporator. The difference between these two temperatures is the operating superheat."

Your problem, as I see, it, is not some magic compatible valve, but understanding how the system works and how to control it.  I'm sure there are ASHRAE and other papers that you can read that describe this in detail.

If it were me, as I know nothing about it, I would start searching for "How Does an Air Conditioner Work" so I understand the system and then "How To Control an Expansion Valve" for more details.

Hi Cesarinko,

I use the S7-1200, Carel EVD and Danfoss stepper drivers in my refrigeration applications frequently.

Siemens do not manufacture a native driver for the 4 wire stepper motor but as a say you can indeed use Carel or Danfoss' own drivers as an interface.

The options you have are to provide the Carel or Danfoss stepper drivers with a digital input to enable their own internal PID function, or you can set them to Analog proportioners and give them a 0-10v signal from the S7-1200 scaled to how ever many steps you require the valve motor to drive.

Either of the above methods work really well. I like to add a Modbus connection too so that the control values on the stepper driver can be displayed and altered via the Siemens HMI.

The attached picture of one of my projects is for your interest...

Good luck!

Plazz

Thank you very much. I'm going to try to do my proyect with Carel's controller

.Thank you

You can use anythink valve, analog example ALCO EX4-8 with external Module with analog input 0-10 V and control under Siemens, Digiltal example EX2.

You need make a map of superheating the Refrigerant.

This can you make from a saturation table. 

When you need i can send you the link to this table. 

I understand. thank you
I have a question, I could control an electronic expansion valve (stepper) only with the PLC s 1200 or will I need valve + controller. I could program a single algorithm to control the valve without using driver.

if this is not possible, as it could make the connection to the Modbus PLC controller Carel (as Plazz previously said)?

Thank you and regards

Hi Cesarinko

If you are using the Carel stepper valve its a four wired motor that the S7 hardware cannot natively drive. I don't think you have any choice but to use the Carel driver as an interface.

Plazz