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Study Overview. Purpose: Explore the effects of shielded & twisted vs. non-shielded wires for remote diode Hardware details: Used TMP51xEVM+USB Dig board as main board Both EVM and USB Dig were in default configuration Used board obtained from customer as remote power supply
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Study Overview • Purpose: Explore the effects of shielded & twisted vs. non-shielded wires for remote diode • Hardware details: • Used TMP51xEVM+USB Dig board as main board • Both EVM and USB Dig were in default configuration • Used board obtained from customer as remote power supply • The wires were cut to 18” in length • Non-shielded wire: standard solid 22 AWG • Twisted and shielded (braided): standard stranded 24 AWG • Used 2N3906 PNP diode-connected as temperature sensors • Tests: • Compared loaded vs. unloaded supply. Used 4.4ohm, 250W power resistor connected to a 12V supply • Also compare the rotation of the power supply • “Not rotated” refers to best-case wire routing, “Rotated” refers to worst-case wire routing • Compared standard filter (50ohm/50pF) with no filter (shorted) and a filter with large valued components (1.3kohm/1nF)
Results STDEV=0.35 STDEV=0.06
Results STDEV=1.02 STDEV=0.06
Results STDEV=1.57 STDEV=0.16
Results STDEV=0.75 STDEV=0.24
Results-Filtering STDEV=1.42 STDEV=1.17 STDEV=0.62
Results-Filtering STDEV=0.17 STDEV=0.28 STDEV=0.19
Observations • Twisted and shielded wires displayed less perturbations than standard wires in all tests • Routing of wires has an observable effect on precision • Loading of supply has an observable effect on precision • Please note that accuracy was not measured here, only relative precision. Also note that very little information is known about the customer’s power supply (for example, we don’t know the switching frequency). Therefore the filtering test results may not correlate with results using other power supplies.