Pressure transducers control of a VFD
Hey everyone
I'm working on a project that I have one pressure transducers and two VFD and I have AC500 ECO PM564 ETH As main CPU .
And of course analog input , output modules .
So I need to know what is the difference between PD and PID function block and in my case I need to control the speed of the vfd according to the pressure value , so what should i use pd or pid control ?
I'm thinking to send the output speed to the vfd using modbus not analog output, is that ok or I will face some problems like losing modbus connection due to the noise of the vfd (5.5kw) , which I really faced but the vfd was 160 kw .
And the most important question did pm564 have an auto tuning function block or not ?
If not how to make the perfect tuning for pid I made a many search about tuning but it's not clear 100% .
So is there any documentation from abb for tuning a pid for a pressure application.
Thanks in advance.
Ps: the consultant or the owner refused to use the built in pid of the vfd and he need it from plc direct .
I'm working on a project that I have one pressure transducers and two VFD and I have AC500 ECO PM564 ETH As main CPU .
And of course analog input , output modules .
So I need to know what is the difference between PD and PID function block and in my case I need to control the speed of the vfd according to the pressure value , so what should i use pd or pid control ?
I'm thinking to send the output speed to the vfd using modbus not analog output, is that ok or I will face some problems like losing modbus connection due to the noise of the vfd (5.5kw) , which I really faced but the vfd was 160 kw .
And the most important question did pm564 have an auto tuning function block or not ?
If not how to make the perfect tuning for pid I made a many search about tuning but it's not clear 100% .
So is there any documentation from abb for tuning a pid for a pressure application.
Thanks in advance.
Ps: the consultant or the owner refused to use the built in pid of the vfd and he need it from plc direct .
Asked 4 months ago
Answers
1
PD is "Proportional Derivative"
PID is "Proportional Integral Derivative"
A pressure Process typically requires "Proportional Integral" ( ie Gain and Reset ) So program a PID, and set the "D" value to off or zero.
Use hard wired 4..20mA signals because there's zero programming and every technician in the plant will understand it and can fix it when it breaks.
PID Tuning has a long and complicated history. Its not a simple subject. Much of what you read on the internet ( and even a lot of old text books ) are basically junk. Some guide lines ....
- There is no such thing as "perfect". The harder you try to reach perfect, the worse your results become. PID tuning is a compromise.
- The AC500 does not have an "Auto Tune" PID, and in any case, Auto Tune PIDs will often produce rubbish results. Without the skills to recognize this, your search for "perfect" ends in disaster.
- The best compromise tuning will be Robust - ie it will continue to work even when things change in the process. It wont be the "fastest" - it will be the tuning that works best under all circumstances.
- You cannot make the process respond faster that it is capable of moving. Trying to make a PI loop work faster is like trying to drive a truck round a corner at full speed. It won't do it - it will crash.
- For 95% of control loops the PI action works just fine. Don't use D and dont try to add complicated and "clever" programming to override the output / limits / gain / reset etc. You will make it worse. Just tune it properly.
The simplest form of Robust tuning is "lambda tuning". Its a compromise between easy and "perfect".
https://www.controleng.com/articles/f...
Do this often enough and you will find that similar processes tend to come up with similar tuning numbers. They aren't perfect but they are robust ....
For a Fluid Pressure Loop, the Time Constant will be short - typically 3 to 5 seconds. The Process Gain should be about 1 if your pump is properly sized. And the Deadtime should be very short. Lambda tuning will tell you to set the Gain to 0.3 and the Integral to 3 to 5 seconds.
The best way to learn PID tuning is to pay someone who knows what they are doing and take a training course using a proper PID tuning software package. Trying to learn PID tuning from google is generally worthless.
PID is "Proportional Integral Derivative"
A pressure Process typically requires "Proportional Integral" ( ie Gain and Reset ) So program a PID, and set the "D" value to off or zero.
Use hard wired 4..20mA signals because there's zero programming and every technician in the plant will understand it and can fix it when it breaks.
PID Tuning has a long and complicated history. Its not a simple subject. Much of what you read on the internet ( and even a lot of old text books ) are basically junk. Some guide lines ....
- There is no such thing as "perfect". The harder you try to reach perfect, the worse your results become. PID tuning is a compromise.
- The AC500 does not have an "Auto Tune" PID, and in any case, Auto Tune PIDs will often produce rubbish results. Without the skills to recognize this, your search for "perfect" ends in disaster.
- The best compromise tuning will be Robust - ie it will continue to work even when things change in the process. It wont be the "fastest" - it will be the tuning that works best under all circumstances.
- You cannot make the process respond faster that it is capable of moving. Trying to make a PI loop work faster is like trying to drive a truck round a corner at full speed. It won't do it - it will crash.
- For 95% of control loops the PI action works just fine. Don't use D and dont try to add complicated and "clever" programming to override the output / limits / gain / reset etc. You will make it worse. Just tune it properly.
The simplest form of Robust tuning is "lambda tuning". Its a compromise between easy and "perfect".
https://www.controleng.com/articles/f...
Do this often enough and you will find that similar processes tend to come up with similar tuning numbers. They aren't perfect but they are robust ....
For a Fluid Pressure Loop, the Time Constant will be short - typically 3 to 5 seconds. The Process Gain should be about 1 if your pump is properly sized. And the Deadtime should be very short. Lambda tuning will tell you to set the Gain to 0.3 and the Integral to 3 to 5 seconds.
The best way to learn PID tuning is to pay someone who knows what they are doing and take a training course using a proper PID tuning software package. Trying to learn PID tuning from google is generally worthless.
Answered 4 months ago
0
Hi
Honestly, you can't find a better answer than Rob's!
I can only add that not wanting to use the PID integrated in the drive by the consultant or the final customer is to waste a good opportunity to optimize the system. Also because if you're using ABB drives, you could use the signal monitor which is really useful in commissioning. Perhaps the customer's doubts are related to the fact that if you need to replace the drive, you will have to redo a PID tuning?
Or do you not need to use the PID of the drive because you want to learn how to do it from the PLC?
In both cases, it is preferable to make experiences on your own without "copy" solutions on google. The best suggestion remains that of Rob: get help from those who are more experienced and remember that there is no routine that solves all situations, every process has its peculiarities and every time you have to carefully analyze the variables involved.
BR
Flavio
Honestly, you can't find a better answer than Rob's!
I can only add that not wanting to use the PID integrated in the drive by the consultant or the final customer is to waste a good opportunity to optimize the system. Also because if you're using ABB drives, you could use the signal monitor which is really useful in commissioning. Perhaps the customer's doubts are related to the fact that if you need to replace the drive, you will have to redo a PID tuning?
Or do you not need to use the PID of the drive because you want to learn how to do it from the PLC?
In both cases, it is preferable to make experiences on your own without "copy" solutions on google. The best suggestion remains that of Rob: get help from those who are more experienced and remember that there is no routine that solves all situations, every process has its peculiarities and every time you have to carefully analyze the variables involved.
BR
Flavio
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