LabVIEW
PID with controlled ramp Options
I spot welded a K-Type Thermocouple on the surface of platinum foil (0.007mm thickness) I want to heat up from 20K-300K by Kepco power supply by using DC current from 0-6A.
I don't have any heater behind my target just by DC current ( by using Kepco Power supply) , platinum foil has very low resistance so I need initial current 5.12A for start heating from 20K I need to use Ramp heating for example 10 degree/minute et...
I used PID tool kit from Labview to drive kepco power supply and also I have linearized amplifier for thermocouple with 0-10v output. I attached a copy of my labview programme.
Anybody can help me to add an ramp voltage to PID toolkit ?
thanks
at first you should get rid of all (or most) DDT wires...
Then add a Ramp function to change your setpoint automatically...
Hi Ela,
What do you mean "get rid of all (or most) DDT wires"
Get rid of DAQ assistent and use simple DAQmx functions as you do with the AO.
Btw. create the AO task just once before the loop and delete it also just once after the loop!
and you mean ramp to setpoint vi ?
Yes.
many thanks for your guidance ,
please look at my code I add PID to setpoint but when I turn on the system the thempereture is jump very fast and the set point profile does not work.
sorry this is my first time with Labview
sincerly
Hi Ela,
as long as you only attach images here we will not provide much help. Why don't you attach your VI (LV2014 preferred)?
when I turn on the system the thempereture is jump very fast and the set point profile does not work.
- When the temperature is "jumping" either the reading is wrong or your heater has too much power…
- "does not work" is no LabVIEW error message: please explain in which way something "does not work"…
You still use ExpressVIs and DDT wires…
Hi Ela,
see attached VI, simplified to show just the behaviour of PID functions.
Right now the PID reacts as soon as the (simulated) temperature values is greater then the current setpoint. You still need to work out the correct PID gains - in your VI you used the default values…
I attach the VI as 7 zipped because "The attachment's TPD ramp.vi content type (application/x-labview-vi) does not match its file extension and has been removed."
See this lengthy thread and the solution provided there at the end…
Hi Ela,
using a proprietary Office file format to show two images is usually "bad behaviour". Those office file formats could contain viruses, macros, and other bad stuff. Next time please use simple image file formats, PNG preferred!
Unfortunately it is not reproducible please look at Fig 2. Do you have any idea about this problem?
Disturbances?
Unoptimized PID gains?
1. PID Gain Schedule
You should make your gain values as Default of that cluster array…
2. PID output Rate Limiter because for start heating from -238 Celsius I need 5A dc current with this vi I selected initial output in 4 volt.
The "initial output" is zero, as you don't have set any other value as default…
This functions limits the change of rate of the PID output, not the range limits! The output limits of the PID is set with the PID function itself…
3. Another problem is when I push Stop bottom in programmer the analogue output is still in 5 volt I would like to be 0
When you want to output a zero you need to program this behaviour!
THINK DATAFLOW: output zero after the loop…
4. The maximum current of programmable power supply is 7 A .
Ok. You have limited the PID to a range of [0, 4.5]…
please make correction.
- You still create and clear the AI task with each iteration. Don't do THIS!
- Init before the loop, set the timing to "continuous", clear the task after the loop. Read 1000 samples in the loop and DELETE the wait function!
- When you want to have an array of samples you should read the samples as "1D array", not as waveform!
