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TDC1000PW Datasheet(PDF) 19 Page - Texas Instruments |
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TDC1000PW Datasheet(HTML) 19 Page - Texas Instruments |
19 / 60 page RTDx REF REF RTDx t t R R K START STOP tREF tRTD1 tRTD2 TRIGGER td1 td2 Reference RTD2 RTD1 CLKIN O 8 O 2 TX_FREQ_DIV+1 ¦CLKIN 0x00[7:5] ± TX_FREQ_DIV ¦TEMP TTEMP = ¦TEMP 1 0 1 0x03[4] ± TEMP_CLK_DIV TDC1000, TDC1000-Q1 www.ti.com SNAS648B – OCTOBER 2014 – REVISED AUGUST 2015 Figure 24. Timing Source for the Temperature Measurement 8.3.8.1 Temperature Measurement with Multiple RTDs The temperature measurement mode is selected by setting the MEAS_MODE bit in the CONFIG_2 register to 1. A temperature measurement is started by sending a trigger pulse. After the temperature measurement is complete, the TDC1000 returns to SLEEP mode. To return to TOF measurement mode, reset the MEAS_MODE bit to 0. The temperature sensor measurement can be performed without the need of an external ADC. The temperature sensor block operates by converting the resistance of a reference, RREF, and up to two RTDs into a series of START and STOP pulses. The interval between the pulses is proportional to the measured resistance, and therefore, the temperature. As shown in Figure 25, the TDC1000 performs three measurements per trigger event and generates the corresponding pulses on the START and STOP pins. Figure 25. Temperature Measurement Output Timing The resistance of RTD1 and RTD2 can be calculated from the time intervals in Figure 25 as follows: (3) With a 1-k Ω reference resistor, the tREF interval is approximately 200 μs. The following intervals, tRTD1 and tRTD2, will depend on the resistance of the RTDs. The time delay between measurements, td1 and td2, can be approximated as follows: td1 = (51 × TTEMP) + ( tRTD1 × 0.55 ) (4) td2 = (51 × TTEMP) + ( tRTD2 × 0.55 ) (5) For example, two PT1000 sensors at 0°C will have an approximate resistance of 1 k Ω; the same as the reference resistor in this example. Given an external 8-MHz clock and the default temperature clock divide-by-8 from the TEMP_CLK_DIV bit, the overall measurement time between the START pulse and the last STOP pulse is approximately 922 µs. Copyright © 2014–2015, Texas Instruments Incorporated Submit Documentation Feedback 19 Product Folder Links: TDC1000 TDC1000-Q1 |
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