FB58 Auto Tuning Problem

[Edric]

Dear All,

Now I'm in the commissioning with a heater exchanger using saturated steam as a hot source. It will heat up the water in a tank. I use the FB58 as the PID temperature control, during the auto tuning process, the tuning always stay at the phase 1(according to the manual, this phase 1 only lasts nearly 1 minute, but now it always stays more than 20 minutes even after the PV which at the begining is 50 oC reaches the SP 65 oC), guys who have the experience for the auto tuning of this block, it will be a greatly appreciated any hint providing to me.



Please see the attached pictures for the parameter setting and the status of the tuning process.

 

[nightline]

When do you start tuning?
You should start tuning in cold condition, or you can manual puss it to the next fase.
In the FB58 manual you'll find how to do this..

Jack

 

[nightline]

What kind of data format do you use for the PV and SP ?
These should be from the REAL data type.
The manual "says" they can be any data type, but INT or DINT for example does not work.

Jack

 

[Edric]

When do you start tuning?
You should start tuning in cold condition, or you can manual puss it to the next fase.
In the FB58 manual you'll find how to do this..

Jack

Dear nightline,

Thank you for your reply!

what do you mean manual push it to the next phase, it is to set the TUN_ST to 1 from the VAT? But what is the right time to set this bit to 1. As I set it to 1, I get the result as the following(seeing the attachment).

Does it means I should wait for until the manipulated variable change >5%（it should be from 100 to <95) then I can trigger the TUN_ST then get to the phase 2, is it right? Today I don't try this.

For the data type, I use the REAL as the SP and PV.

 

[nightline]

That's right: set TUN_ST to 1 and you will see the fase jumps to fase 2.
I do this as soon as the PV is about 50% of SP, but this is not criticall...

 

[Edric]

That's right: set TUN_ST to 1 and you will see the fase jumps to fase 2.
I do this as soon as the PV is about 50% of SP, but this is not criticall...

Hay Jack

But you see from my second picture, my SP is 55 C and my PV is 49 C, I set the TUN_ST to 1, it shows that tuning stopped as the MV difference<5%, this I cannot understand. From the manual of the FB58, P3-7, mentioned as the attached picture. Then it is the time to change to phase 2,(around 1 minute later)

 

[nightline]

The tuning stopped... hmmm... I've seen this before, but can't remember what it was...
I've to dig in my memory...

You're using the tuning wizard if I'm right.
Most of the tunings I did was from inside the DB / VAT table.
Maybe you can try it this way.. I'm not sure if it works.

The last time I performed tuning an FB58 was in a bag making machine with 3 zones.
Tuning of 2 zones worked perfect, the 3th didn't, while there all exact the same.
Maybe there is something inside this function what keeps the tuning in fase 1. It has to detect some temperature rise change to trigger fase 2.
Have you tried to adjust a higher temperature for SP?
The 60 deg. is the default in the wizard, if I remember it right.

 

[Edric]

The tuning stopped... hmmm... I've seen this before, but can't remember what it was...
I've to dig in my memory...

You're using the tuning wizard if I'm right.
Most of the tunings I did was from inside the DB / VAT table.
Maybe you can try it this way.. I'm not sure if it works.

The last time I performed tuning an FB58 was in a bag making machine with 3 zones.
Tuning of 2 zones worked perfect, the 3th didn't, while there all exact the same.
Maybe there is something inside this function what keeps the tuning in fase 1. It has to detect some temperature rise change to trigger fase 2.
Have you tried to adjust a higher temperature for SP?
The 60 deg. is the default in the wizard, if I remember it right.

Hey Jack,

Today I test the tuning again at the jobsite, using the VAT table, but the result is the same. I read the manual again, find that:

The tuning manipulated variable (LMN0 + TUN_DLMN) is applied by changing the
setpoint (transition Phase 1 -> 2). The setpoint, however, becomes effective only
when the point of inflection is reached (the controller switches to automatic only
when this point is reached).

From my screen print, I fond that my LMN0=99.9999, and the my TUN_DLMN=80 which I set, so the MV will be >100, how it can be.

I don't know what's wrong with my operation, and I also don't understand that the meaning of the point of inflection is reached?

 

[Edric]

The tuning stopped... hmmm... I've seen this before, but can't remember what it was...
I've to dig in my memory...

You're using the tuning wizard if I'm right.
Most of the tunings I did was from inside the DB / VAT table.
Maybe you can try it this way.. I'm not sure if it works.

The last time I performed tuning an FB58 was in a bag making machine with 3 zones.
Tuning of 2 zones worked perfect, the 3th didn't, while there all exact the same.
Maybe there is something inside this function what keeps the tuning in fase 1. It has to detect some temperature rise change to trigger fase 2.
Have you tried to adjust a higher temperature for SP?
The 60 deg. is the default in the wizard, if I remember it right.

I find some new information in the manual for the description of phase 1:

Set the parameter TUN_ON = TRUE. This makes FB 58 "TCONT_CP" ready for
tuning (Phase 1). The TUN_ON bit must only be set in the steady state or during
aperiodic settling to the steady state.
If the quasi steady state changes after setting the TUN_ON bit, this must be reset
and the new quasi steady state must be signaled to FB 58 "TCONT_CP" by
setting the TUN_ON bit again.

So for my understanding, for the phase 1(set TUN_ON=1), the SP should equal PV, otherwise, the PV will always increase just like my case, at the beginning I set the SP=75 at the same time the PV is 68.5. So I get LMN0=99.99999.

Hopefully my understanding is right, this PID tuning waste of my such long time.