SLVAFK1 January 2025 INA228 , INA232 , INA234 , INA236 , INA237 , INA238 , MSPM0C1103 , MSPM0C1103-Q1 , MSPM0C1104 , MSPM0C1104-Q1 , MSPM0C1105 , MSPM0C1106 , MSPM0G1105 , MSPM0G1106 , MSPM0G1107 , MSPM0G1505 , MSPM0G1506 , MSPM0G1507 , MSPM0G1518 , MSPM0G1519 , MSPM0G3105 , MSPM0G3105-Q1 , MSPM0G3106 , MSPM0G3106-Q1 , MSPM0G3107 , MSPM0G3107-Q1 , MSPM0G3505 , MSPM0G3505-Q1 , MSPM0G3506 , MSPM0G3506-Q1 , MSPM0G3507 , MSPM0G3507-Q1 , MSPM0G3518 , MSPM0G3518-Q1 , MSPM0G3519 , MSPM0G3519-Q1 , MSPM0H3216 , MSPM0L1105 , MSPM0L1106 , MSPM0L1117 , MSPM0L1227 , MSPM0L1228 , MSPM0L1228-Q1 , MSPM0L1303 , MSPM0L1304 , MSPM0L1304-Q1 , MSPM0L1305 , MSPM0L1305-Q1 , MSPM0L1306 , MSPM0L1306-Q1 , MSPM0L1343 , MSPM0L1344 , MSPM0L1345 , MSPM0L1346 , MSPM0L2227 , MSPM0L2228 , MSPM0L2228-Q1 , TPS62866 , TPS62868 , TPS62869 , TPS6286A06 , TPS6286A08 , TPS6286A10 , TPS6286B08 , TPS6286B10
6 Results
Figure 6-1 shows the measured, steady-state temperature of a 1.5Ω nominal load resistor for different values of applied constant power. The linear response shows that constant power can be used as the control method to set the temperature in the resistive heating element.
Figure 6-1 Load Resistor Temperature Versus Applied Constant PowerFigure 6-2 shows the measured power for 1W steps from 1W to 9W with a 1.5Ω nominal load resistor. The loop is held running in constant power at each level for 50 seconds and the power measured every 1 second. The absolute variation in measured power increases as the requested power level increases but the percentage variation stays pretty constant as can be seen in Table 6-1 which shows the measured levels and variation for each power level from nominal. The constant power control loop maintains the power applied to the load within ±3.0% of the set level.
Figure 6-2 Constant Power Control Steps. 1W to 9W in 1W Steps. 50 Seconds at Each Power Level| Requested Power (W) | Average measured power (W) | Minimum measured power (W) | Maximum measured power (W) | Negative variation (%) | Positive variation (%) |
|---|---|---|---|---|---|
| 1.0 | 1.0008 | 0.971 | 1.029 | -2.90 | 2.90 |
| 2.0 | 2.0073 | 1.942 | 2.059 | -2.90 | 2.95 |
| 3.0 | 2.9913 | 2.911 | 3.081 | -3.00 | 2.70 |
| 4.0 | 4.0123 | 3.898 | 4.116 | -2.55 | 2.90 |
| 5.0 | 5.0108 | 4.864 | 5.145 | -2.72 | 2.90 |
| 6.0 | 6.0146 | 5.840 | 6.174 | -2.67 | 2.90 |
| 7.0 | 6.9999 | 6.796 | 7.204 | -2.91 | 2.91 |
| 8.0 | 8.0209 | 7.764 | 8.235 | -2.95 | 2.94 |
| 9.0 | 8.9982 | 8.752 | 9.251 | -2.76 | 2.79 |
Figure 6-3, Figure 6-4, and Figure 6-5 show more detailed plots of the measured power values for 1W, 5W and 9W constant power operation.
Figure 6-3 Measured Power at 1 Second Intervals for 1W Constant Power Operation
Figure 6-5 Measured Power at 1 Second Intervals for 9W Constant Power Operation
Figure 6-4 Measured Power at 1 Second Intervals for 5W Constant Power OperationAs an additional test of the robustness of the constant power control, the load was driven at constant 4W across a temperature range from around -18°C to +23°C. As the temperature increases the resistance of the nominal 1.5Ω load increases from around 1.33Ω at -18°C to 1.75Ω at +23°C. Figure 6-6 shows the measured current, voltage and power across this temperature range. The constant power control algorithm adjusts the voltage as the resistance changes to successfully keep the power constant across the temperature range. The variation in measured power across this temperature range is +1.5% and -2.1%.
Figure 6-6 Measured Current, Voltage and Power Across -18°C to +23°C Temperature Range