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Why does the EGT gauge on jet engines require bus power if thermoelectric voltages generated by thermocouples are sufficient to move the needles?

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    $\begingroup$ What do you mean by drive the pointer ? $\endgroup$ – BambOo May 1 '18 at 10:35
  • $\begingroup$ Well if only it's as simple as a thermal couple and a needle. Welcome to 21 century man! $\endgroup$ – user3528438 May 1 '18 at 13:35
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The thermocouple voltage is a DC millivoltage. Presuming you’re talking about an analog gauge, there simply isn’t enough potential to “drive the pointer.” As such, that small voltage is usually amplified. The amplification requires that a larger power supply be used.

For a digital gauge, that millivoltage is capable of being read by a microprocessor, but the rhetorical question of “What powers the microprocessor?” Should be enough to resolve the rest of the question.

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