Ramp setpoint profile in PID controller suddenly jumped to later (wrong) steps

[Erene123]

This is a heating test labview program.

The power source heats the sample and is controlled by a PID controller per the desired setpoint profile. 

The setpoint profile is a ramp and hold profile: 5C increase per step in 5 mins, then hold the temperature for 15 mins, until eventually the temperature goes to 320 C. 

However, when the setpoint temperature was at the step where the sample was held at 90 degree C, the set point temperature suddenly went to 190 C, then continued (see below). Has anyone met a similar problem before? 

[GerdW]

Hi Erene,

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@Erene123 wrote:

However, when the setpoint temperature was at the step where the sample was held at 90 degree C, the set point temperature suddenly went to 190 C, then continued (see below). Has anyone met a similar problem before? 

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I don't think so - most probably the problem is in your VI or in your profile definition…

[Erene123]

Hi GerdW, 

   I have confirmed the defined profile is correct. One column is the elapsed time, the other column is the desired temperature. I wonder what could be the problem in the VI. I thought the VI was standard by NI. 

[GerdW]

Hi Erene,

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@Erene123 wrote:

I have confirmed the defined profile is correct. One column is the elapsed time, the other column is the desired temperature. I wonder what could be the problem in the VI. I thought the VI was standard by NI. 

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The problem probably is in your VI, where you call the RampProfile function.

As you did not attach your VI we cannot debug it!

When the profile output (your setpoint) changes so much, then the profile input (most probably time) has also changed that much…

[Erene12345]

Hi GerdW,

   Please see attached the VI. Thank you.

[JensG69 · Accepted solution]

I assume you have to work on the values in your setpoint profile control from your VI:

Regards, Jens

[ravitejaboyana]

Hi Jens,

I just verified the profile again. I still could not trace those values in my profile that have caused the sudden jump to 190 degrees. Can you please suggest a way to resolve it? 

Also, I have created a new setpoint profile in a different VI. Can you please help in checking if this issue happens here as well? 

[GerdW]

Hi Ravi,

now the setpoint array is empty…

[ravitejaboyana]

Sorry about the trouble.

Please find the new file below.

It has the same jump in temperature problem.

[JensG69]

Still exactly the same, and I just copied your setpoint profile to a new VI and connected to an XY-graph for visualization:

Regards, Jens