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Search: Posts Made By: Peter Nachtwey
Forum: LIVE PLC Questions And Answers February 27th, 2021, 04:01 AM
Replies: 15
Views: 1,012
Posted By Peter Nachtwey
Every time there is an interrupt, the interrupts...

Every time there is an interrupt, the interrupts are turned off and all the CPU registers will be used by the interrupt must stored on the stack. When the interrupt is done the original values of...
Forum: LIVE PLC Questions And Answers February 25th, 2021, 08:54 PM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
There is no hope or help until you figure out...

There is no hope or help until you figure out what dead time is.
Forum: LIVE PLC Questions And Answers February 25th, 2021, 08:53 PM
Replies: 15
Views: 1,012
Posted By Peter Nachtwey
If you trigger on a range of counts it will be...

If you trigger on a range of counts it will be possible to trigger more than once. This may be OK but I would use a one shot approach where the trigger is armed until it counts exceed the trigger...
Forum: LIVE PLC Questions And Answers February 24th, 2021, 12:23 PM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
I am talking about the original plots. There is...

I am talking about the original plots. There is huge dead time between the control signal to the valve and when the blue line, the temperature, response.


If you can't get this right there is no...
Forum: LIVE PLC Questions And Answers February 24th, 2021, 07:00 AM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
Did you give up?

Did you give up?
Forum: LIVE PLC Questions And Answers February 22nd, 2021, 07:15 PM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
I shake my head. The PV can never respond to a...

I shake my head. The PV can never respond to a change in the CV that hasn't happened yet.
This is the problem. Until you understand what you are controlling you will need to be lucky to get it to...
Forum: LIVE PLC Questions And Answers February 22nd, 2021, 06:38 PM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
Dead time is measured from the time the control...

Dead time is measured from the time the control output changes, the orange line, to the time the system responds.
You have the wrong definition of dead time.
There may be multiple dead times in a...
Forum: LIVE PLC Questions And Answers February 22nd, 2021, 08:17 AM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
I don't see how anybody can say the dead time is...

I don't see how anybody can say the dead time is close to 0.
From the plots above I see the orange output start to increase before 3:17PM There are 6 hours between the vertical markers so the...
Forum: LIVE PLC Questions And Answers February 20th, 2021, 11:00 PM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
Another trick that can be used to free a sticky...

Another trick that can be used to free a sticky valve is to super impose maximum or minimum output for one scan when the control output changes direction. The problem with this method is if the...
Forum: LIVE PLC Questions And Answers February 19th, 2021, 10:34 AM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
That use to be a problem with hydraulic valves. ...

That use to be a problem with hydraulic valves. The answer was to super impose dither signal. This could be as much as adding or subtracting 20% of the full range of the control signal on top of...
Forum: LIVE PLC Questions And Answers February 19th, 2021, 09:38 AM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
Why does the CV change in 1% steps in post #98? ...

Why does the CV change in 1% steps in post #98?
If the calculations are done in floating point, the output should have much finer resolution.


I can see the control output changing in steps if...
Forum: LIVE PLC Questions And Answers February 18th, 2021, 07:18 PM
Replies: 32
Views: 1,646
Posted By Peter Nachtwey
Usually the LSB is bit zero so if no bit is set...

Usually the LSB is bit zero so if no bit is set then a -1 is returned.
Forum: LIVE PLC Questions And Answers February 18th, 2021, 01:05 PM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
So how does that work for the non-linear ball...

So how does that work for the non-linear ball valve?
Forum: LIVE PLC Questions And Answers February 18th, 2021, 10:23 AM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
Non-linear system identification

Non linear valves should not be a problem.
The differential equation part of the system identification program can be modified to take into account non-linearities....
Forum: LIVE PLC Questions And Answers February 17th, 2021, 01:05 AM
Replies: 32
Views: 1,646
Posted By Peter Nachtwey
Slap Bubba's hand for even thinking about...

Slap Bubba's hand for even thinking about changing code that already works.
Forum: LIVE PLC Questions And Answers February 16th, 2021, 08:35 PM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
Ok, I was reading the plots 180% out of phase. ...

Ok, I was reading the plots 180% out of phase.
I normally use a negative gain for cooling operations so the error is always SP-PV.
Forum: LIVE PLC Questions And Answers February 16th, 2021, 08:15 PM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
@drbitboy, the dead time must be much longer than...

@drbitboy, the dead time must be much longer than 1.0
Forum: LIVE PLC Questions And Answers February 16th, 2021, 08:10 PM
Replies: 32
Views: 1,646
Posted By Peter Nachtwey
I have posted the link to this many times in over...

I have posted the link to this many times in over 20 years.
https://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
Forum: LIVE PLC Questions And Answers February 16th, 2021, 01:33 PM
Replies: 32
Views: 1,646
Posted By Peter Nachtwey
I would rather use Ron's method than the log...

I would rather use Ron's method than the log method. Log functions are very compute intensive especially of the PLC doesn't have floating point processor. Using two log functions is a crime. There...
Forum: LIVE PLC Questions And Answers February 16th, 2021, 05:48 AM
Replies: 32
Views: 1,646
Posted By Peter Nachtwey
Ron's method is the brute force method. There...

Ron's method is the brute force method. There are better ways.
Forum: LIVE PLC Questions And Answers February 15th, 2021, 02:06 PM
Replies: 8
Views: 1,239
Posted By Peter Nachtwey
A trend showing the command, target, actual...

A trend showing the command, target, actual positions and control output would avoid a lot of guessing.
Forum: LIVE PLC Questions And Answers February 15th, 2021, 12:39 AM
Replies: 25
Views: 1,370
Posted By Peter Nachtwey
That is because they don't have "The Knack" ...

That is because they don't have "The Knack"
https://www.youtube.com/watch?v=TvGYIALoKRk
You must really understand the significance of the doctor in this cartoon. He is not just a doctor or...
Forum: LIVE PLC Questions And Answers February 14th, 2021, 10:26 PM
Replies: 25
Views: 1,370
Posted By Peter Nachtwey
You are assuming you are working for a big...

You are assuming you are working for a big company. They assume you can't work on your own. The best will leave then contract with their former employer because they can solve problem the others...
Forum: LIVE PLC Questions And Answers February 14th, 2021, 09:34 PM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
Ooop, sorry about that. I really hate when I ask...

Ooop, sorry about that. I really hate when I ask a question and I don't get an answer.

The units are minutes for the time constants and dead time.
I used the standard ISA PID.
The gain is...
Forum: LIVE PLC Questions And Answers February 14th, 2021, 10:00 AM
Replies: 139
Views: 7,426
Posted By Peter Nachtwey
Yes, SSE is the sum of errors squared. The...

Yes, SSE is the sum of errors squared.
The problem that sometimes occurs is that there are local minimums. I used two minimization routines in hopes of not getting stuck in a local minimum. The...
Showing results 1 to 25 of 500

 
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