Skip to Content

SiePortal

The integrated platform for your product selection, buying and support workflow - bringing together Industry Mall and Online Support.

SiePortalDeutsch

Search

Home
Support Support
{{(apiData.Support | filter:{'rank':1}:true)[0].title}} Support
- Menu temporary not available
- Menu temporary not available
- Menue temporary not available
- {{item.title}}

Products & Services
- Menu temporary not available
- Menue temporary not available
- {{item.title}}
Support Support
{{(apiData.Support | filter:{'rank':1}:true)[0].title}} Support
- Menu temporary not available
- Menue temporary not available
- {{item.title}}
MySiePortal MySiePortal
{{(apiData.MySiePortal | filter:{'rank':1}:true)[0].title}} MySiePortal
- Menu temporary not available
- Menue temporary not available
- {{item.title}}
Cart ({{apiData.CartCount}})

Navigation

Ratio Control in S7 1200?

Created by: JasD at: 7/14/2014 9:52 PM (9 Replies)

Rating (1)

Thanks 10

10 Entries

7/14/2014 9:52 PM	Rate (0)
JasD Posts: 2 Rating: (0)	Hi, I am controlling Acid to Water ratio. Water has to be added to Acid, so as to get desired Acid cutting. Water needs to follow Acid flow, so as to make it easy to control the Acid-water ratio from HMI by entering the desired cutting ratio set piont.
JasD Posts: 2 Rating: (0)
Suggestion To thank Quote Answer

7/14/2014 10:01 PM	Rate (0)
William_B Posts: 5225 Rating: (1195)	Welcome to our community! What is your question?.. The S7-1200 is a programmable device. It can do whatever you can make a program for. My questions back to you is rather.. 1. What type of process control method do you wish to use? Lead-lag / PID / Fuzzy control / Rule based / ++? 2. What do you want to measure and what do you want to control? 3. What sensors do you have that can handle the conditions to measure what you need to measure? Yes the PLC is capable to handle it.. but you will need to know how it should be done.. you will need a design strategy. PLUS the safe factors needs to be engineered as well. Please consider these thing and ask a bit more detailed questions. Best regards. w
William_B Posts: 5225 Rating: (1195)
Suggestion To thank Quote Answer
This contribution was helpful to 2 thankful Users dchartier Kahl

7/14/2014 10:22 PM	Rate (0)
JasD Posts: 2 Rating: (0)	Hi Williams, Thanks for replying. answers to your questions are: 1. It is a PID process control. 2. The process has Acid and water involved in it. The final mixture will have 90 - 98 % of Acid. I am controlling the Valves to control the flow. e.g. a) if output is to be 93% then acid flow valve is 63% open and water flow valve is 7.5 % open. b) if output is to be 96% then acid flow valve is 63% open and water flow valve is 3.5 % open. 3. I have flow transmitter gigving me the flow value as feedback. I basically wanted to know if it possible to use something like Ratio block (didn't found Ratio block in S7 1200), or I have to write down a program to make water following acid flow. I want the Water flow SP to be adjusted automatically if there is any variation in Acid flow. Please consider these thing and ask a bit more detailed questions.
JasD Posts: 2 Rating: (0)
Suggestion To thank Quote Answer

7/14/2014 11:12 PM	Rate (0)
William_B Posts: 5225 Rating: (1195)	JasD Hi Williams, Thanks for replying. answers to your questions are: 1. It is a PID process control. 2. The process has Acid and water involved in it. The final mixture will have 90 - 98 % of Acid. I am controlling the Valves to control the flow. e.g. a) if output is to be 93% then acid flow valve is 63% open and water flow valve is 7.5 % open. b) if output is to be 96% then acid flow valve is 63% open and water flow valve is 3.5 % open. 3. I have flow transmitter gigving me the flow value as feedback. I basically wanted to know if it possible to use something like Ratio block (didn't found Ratio block in S7 1200), or I have to write down a program to make water following acid flow. I want the Water flow SP to be adjusted automatically if there is any variation in Acid flow. Please consider these thing and ask a bit more detailed questions. touché! [smile] It is difficult to have this conversation.. it is a bit of a guessing game to know what your background is. You will have to develop the background coding yourself. You could however try something from OSCAT [LINK] and convert it to SCL. Process control is not my field of practice for a long time. I do however remember that flow through a valve is not always linear in relation to how big the valve is open and that pressure in the system play a big role. Measuring flow of water is easy in comparison to measuring the flow of acid. -- I can not help but being concerned about these factors. There is also the case of how the system reacts on a power outage / PLC failure / PLC error and such things. In my book the writing of code is easy when compared to engineering the process well. If I may leave the engineering in your hands.. my opinion for the PLC side is that the S7-1200 will be able to handle the process control, but you will have to much of the coding to do yourself (excluding the PID loop(s) ). The S7-1200 is capable of handling the maths and the analogs. I recommend you to refrase this question and ask the forum's opinion which PLC is best suited for the job you have in mind. The "SIMATIC S7 general" would be the best place for this question. If you could state what sensors and actuators you plan to use and signal type (analog/communications), this will be most helpful. Good luck w
William_B Posts: 5225 Rating: (1195)
Suggestion To thank Quote Answer

7/14/2014 11:30 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 11/8/2024 Posts: 15388 Rating: (2443)	I have as my current development project something that is mixing up various things, one being acid, one being water, and one being oil, and also, some items are being dumped in dry in a more manual way at a specified point in the batch according to a recipe. If you are comfortable with SCL and want to continue converting the OSCAT library for the process controls you want to use, you will save a lot of time, but may also find it very frustrating learning what is possible in other Siemens plc families as compared to the s7-1200's. As for the safety aspects, you have to think about how all the valves fail. Some may need to fail normally open and some may need to fail normally closed. If you already have that figured out, that's great, just make sure your plc failure mode is to apply the right output signal if it faults. Same applies to your analog output signals.Just be sure to consider the proper response on loss of power as well as a plc crash or stop mode. As to the ratio control, if you calibrate your controls based on the density of the liquids they are controlling, you can get good flow controls if you have very stable pressure. However, if you simply open your valve and vary the pressure to get the desired flow, you might find better results. Really is something you need to find out for your specific process needs and go from there. Post how far you have progressed in your plc programming and process/controls design and what is keeping you from moving forward.
	science guy
Suggestion To thank Quote Answer
This contribution was helpful to 2 thankful Users William_B Kahl

7/17/2014 10:59 AM	Rate (1)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	It seems very straigtforward, why complicating with OSCAT and SCL conversions, etc.. If you have flowmeters on water and acid then the acid flow multiplied by ratio factor is the setpoint value for water flow. Now all you have to do is to add one regulator (P, PI, PID). The process value is water flow, setpoint is acid flow * ratio, outputhas to be limited 0-100% and it goes to analog output and then to valve amplifier.

Suggestion To thank Quote Answer

7/24/2014 1:07 AM	Rate (0)
Jas D Posts: 3 Rating: (0)	Thanks Williams.
Jas D Posts: 3 Rating: (0)
Suggestion To thank Quote Answer

7/24/2014 1:12 AM	Rate (0)
Jas D Posts: 3 Rating: (0)	Hi Huggy, first of all thanks a lot for your reply. Its a very very small project. I have decided to use individual PID's for both Acid and water. Process just needs that water should follow acid fluctuations. So, i am using a divide blockfrom acid PV to water SP. Which has solved my problem.
Jas D Posts: 3 Rating: (0)
Suggestion To thank Quote Answer
This contribution was helpful to 2 thankful Users 0_Einstein William_B

7/25/2014 6:18 PM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	I think, what you didis the only right implementationofratio controller. You could use a PI for acid or even P with bias: Yacid = (SP_acid-PV_acid)*Kp + Y_bias AnaOut= UNSCALE(HiLim, LoLim, Yacid) // convert to anlog and limit the signal 0 to 100% A PI would respond slightly slower ( which is not bad for your project). I think PID, can react too fast, since the water regulator has to follow the acid, the water regulator should be faster than acid regulator. A very good idea would be tomake a ramp function for acid setpoint. You could havein tottaly higher gains and smaller integrating times, because if you simply open the valve at initialization you will get a big step of acidflow that is your SP for the water, thus water regulatorwould react very emotional. To avoid this you are forced to decrease the gain, then to react slower in the stability bounds. However if you ramp up, you will apply less stress and you can increase gain and the whole system will be morefaster.

Suggestion To thank Quote Answer
This contribution was helpful to 3 thankful Users dchartier Kahl tony311

7/25/2014 7:00 PM	Rate (0)
Jas D Posts: 3 Rating: (0)	Hi Mark, That's really helpful. Thanks for the explanation. I am trying to make it work in this direction.
Jas D Posts: 3 Rating: (0)
Suggestion To thank Quote Answer
This contribution was helpful to 1 thankful Users S_Moderator

|

Share this page:

Share this page on...

Follow us on