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And spaal correlaon of sensors singlenode processing

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Unformatted text preview: ut less stable crystals AT ­cut, BT ­cut, Tuning Fork, Ceramics, and etc. •  Measure Behavior of the Crystals Directly –  Use frequency to correct for the frequency drio –  Does not rely on other materials or sensors •  Digital Compensa;on –  Does not alter the source –  Opportunity for other algorithms 3/2/11 USC  ­ PTE587 49 AT ­Cut Quartz Crystals •  Majority of clocks for digital logic are AT ­Cut Quartz Crystals •  Frequency stability is a cubic curve dependent on the cut angle 3/2/11 USC  ­ PTE587 50 Frequency Calibra;on ΔF12(T) = ΔF1(T) - ΔF2(T) for a given Temperature Reference Frequency 3/2/11 ΔO1(T), ΔO2(T) Freq. offsets from Ref. USC  ­ 51 PTE587 Frequency Compensa;on •  Addi;onal Considera;on –  –  Es;ma;ng the sampling frequency For AT ­Cut quartz, using one of two as reference is effec;ve ΔF12(T) = ΔF1(T) - ΔF2(T) for a given Temperature Timer Register Value Reference Frequency ΔO1(t), ΔO2(t) Freq. offsets from Ref. Clk1 Clk1_Count = c Clk2 Temp ≈ T Ref. Clock ≈ ΔO2(T) Time 3/2/11 USC  ­ 52 PTE587 XCXT Prototype •  Hardware –  –  –  –  –  Telos mote with MSP430 µC Two crystal inputs for the ;mers An extension board for the crystals One exis;ng 8MHz AT ­cut crystal Replaced 32kHz clock with AT ­cut 8MHz •  Sooware –  SOS opera;ng system –  Calibra;on and compensa;on modules •  Calibra;on –  Temperature chamber:  ­10°C to 60°C 3/2/11 USC  ­ PTE587 53 XCXT Calibra;on/Compensa;on •  Kyocera HC49SFWB and FOX HC49SDLF •  8.000 MHz fundamental frequency with +/ ­50ppm stability 3/2/11 USC  ­ PTE587 54 Experimental Results Stability: A mean stability of 0.47ppm with a sample standard devia;on of 0.31ppm Current: average of 474 μA at 3V Power: average of 1.4 mW (about 1/4 of a typi...
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