Question
What effect does the D term have on system response?
Answer
The D term can amplify system noise, so we wanted to see its affect on time to temperature. To demonstrate the differences, we compared the 23.5°C to 15°C step response tests with D term OFF (Figure 1) and with a load-optimized D term (Figure 2).
To illustrate the differences, we used a 3 A load with a 10 kΩ thermistor while characterizing IntelliTune® performance.
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| Figure 1. | Tuned, 57.1 seconds to stable temperature |
| First crossing of setpoint: 21.3 seconds | |
| P=8.214; I=0.685; D=OFF | |
| Setpoint Response |
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| Figure 2. | Tuned, 39.9 seconds to stable temperature |
| First crossing of setpoint: 19.9 seconds | |
| P=14.081; I=1.408; D=1.594 | |
| Setpoint Response |
Turning the D term off significantly increased overshoot and extended time to temperature. The D term roughly acts as a brake to offset the accelerator (P).
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