P.I.D questions?

grasshopper

When using the PID object I want to know when do I set Δt to zero.

An exaggerated example [noparse][[/noparse]If running a PID program that is controlling a system; after a full day of keeping track Δt the number would become so huge.]

Leon

I can't see deltat anywhere in the code, just IT which is a constant. Are you using the PID code in the Obex?

Leon

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

grasshopper

Leon said...
I can't see deltat anywhere in the code, just IT which is a constant. Are you using the PID code in the Obex?

Leon

No that object seems lacking. I am using Andys PID object listed below

[code]

{{
┌──────────────────┬────────────────────────┬────────┬────────────────┬────────┐
│ PID.spin │ (C)2007 Parallax, Inc. │ V0.92 │ by Andy Lindsay│ Aug 24 │
│ │ │ │ │ │
├──────────────────┴────────────────────────┴────────┴────────────────┴────────┤
│ │
│ Relies on Cam Thompson's Float32 object, which is available for download │
│ from the Propeller Object Exchange. │
│ │
│ Includes HyperTerminal diplay code for viewing calculation iterations. │ │
│ In HyperTerminal, use 57600, 8, N, 1, no flow control. │
│ │
│ │
│ Performs PID calculations: │
│ │
│ P + I + D │
│

---

---

---

│
│ E + Ep ΔE │
│ out = kp

Leon

That code is completely different from that I mentioned. I don't think that Deltat should be increasing continuously, should it not stay at roughly the same value?

Leon

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Post Edited (Leon) : 6/24/2008 8:23:42 PM GMT

John Abshier

Delta is calculated each call and will not grow. If you set it to zero, that will cause an error when you calculate dedt in the Derivative section. I have read of people resetting the integral term I to zero. Note what integral windup is capped by Amax and Amin

John Abshier

Leon

Deltat is current time - previous time. The OP must be using the time when the program starts instead of the current time, for Deltat to keep increasing.

Leon

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

grasshopper

Thanks for pointing this out for some reason I figured that the delta t would keep adding up.