Compact DWDM laser Temperature

文章摘要：While it is true that with infinite gain the steady state error for the PID loop is zero, in transient cases, such as a system warm up, the loop gain is far less than infinite. This is shown in the thermal plots in Figure 3 below. Figure 3 shows the TEC system's response to a temperature step ch

Compact DWDM laser Temperature,标签：计算机控制技术,工厂电气控制技术,http://www.88dzw.com

While it is true that with infinite gain the steady state error for the PID loop is zero, in transient cases, such as a system warm up, the loop gain is far less than infinite. This is shown in the thermal plots in Figure 3 below. Figure 3 shows the TEC system's response to a temperature step change. For this test the module's internal laser temperature is set to 25°C (Vtherm = 0.75V). The external temperature is changed from 25°C to 45°C in 20 minutes (1°C/Minute) then held for 40 minutes. Finally it is ramped back to 25°C at 1°C/Minute. From Figure 3 we can determine that the thermal error for this transient change is 200µV Pk to Pk, or 15m°C, or ±7.5m°C. At the end of the hold period, the steady state error is less than 50µV Pk to Pk, far less than the transient error. It is important to note that the thermal data in this report shows that the control system can regulate the thermistor's temperature accurately, this may not exactly represent the laser temperature or the light wavelength produced.


Figure 3. Twelve hour strip chart showing thermal performance of control loop.

Figure 4 shows the system's response to three different external temperature ramps (1, 0.7 and 0.3 degrees per minute). In this test the module's internal temperature is set to 35°C (Vtherm = 0.592V). It is important to note that accurate temperature measurements must be given a long time to settle. In fact with enough time to settle, the plot would follow in the center of the three rates of Figure 4. Figure 5 is the same test as Figure 4 with the internal laser temperature set to 15°C (Vtherm = 0.916V).


Figure 4. Thermal loop performance for three different rates of temperature change and the module set at 35°C.


Figure 5. Thermal loop performance for three different rates of temperature change and the module set at 15°C.

When performing thermal tests, it is important to note that water can play a significant role in degrading circuit performance. At 0°C and below water freezes and has no effect on the circuit. When the temperature rises however, the ice melts and the water can cause leakage currents that can reduce the thermal performance. As mentioned above, an acrylic based conformal coating over the circuit can help improve this situation.

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