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I’m building a test bench for some aircraft instruments and I was testing a Bendix 1964771-3 inverter (24 VDC) bought from eBay.

The inverter should have outputs of 129VAC at 370Hz and 12VAC/18VAC at 1110 Hz. The inverter was marked as untested but I was told it was removed from a working aircraft.

I powered up the inverter and checked the outputs with a Unit-T UT33C multimeter, but I did not get any output.

I suspect maybe only the expensive like Fluke, Omega, etc. can measure such high frequency voltages. Could this be the case? Just as a precaution I tried using a neon voltage tester and it immediately lit orange light.

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  • \$\begingroup\$ Rectify to DC and measure on DC with your meter as an alternative proof of voltage presence. \$\endgroup\$
    – Andy aka
    Aug 6 at 14:02
  • \$\begingroup\$ I measured the 3dB bandwidth on a 20 dollar generic DMM and got about 1.5 KHz. Yours could be anything but I doubt the drop off is so sharp that you would measure 0V at 370 Hz. \$\endgroup\$ Aug 6 at 14:06
  • \$\begingroup\$ You are basically asking us what reads in your multimeter manual what AC frequency range it can measure. Have you read your multimeter manual? \$\endgroup\$
    – Justme
    Aug 6 at 14:09
  • \$\begingroup\$ @Andyaka I'm going to try this now. Thanks for the suggestion. \$\endgroup\$
    – RSB
    Aug 6 at 14:15
  • \$\begingroup\$ Make sure you add a light load so that maybe a few milliamps are taken but, calculate the resistor load power dissipation with what you might expect to see if the voltage is present. \$\endgroup\$
    – Andy aka
    Aug 6 at 14:17

1 Answer 1

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The Unit-T UT33C user's manual says it can handle AC up to 400Hz and 500V.

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It can probably manage the 400Hz (if it meets its specifications.) It will give totally wrong results for the 1110Hz - either nothing or way too low.

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