0
\$\begingroup\$

Could anyone explain to me how electrical tachometers work? I know how mechanical ones do, with cable and drag cup. But i can't find any info or illustration what components drive the electrical tachometer needle?

Asfar as i know, is that tachometer gets a signal from ECU and ECU gets the signal from ignition coil or generator. So ECU sends square wave signal to the Tachometer. Now, how does the tachometer move the needle? There can't be just electric motor, becuase when you apply voltage to the motor, then the motor would just spin around and also the needle. Regardless of the voltage.

Or am i missing here something. Thanks in advance

\$\endgroup\$
2
  • 1
    \$\begingroup\$ Have you invested any time looking for answers on the internet such as these: Electrical Tachometer and A Complete Guide to Tachometers. \$\endgroup\$
    – Andy aka
    Commented Apr 7, 2023 at 12:52
  • 1
    \$\begingroup\$ Hi, yes i have and these still speak about drag cup and are mechanically rotated around. Also no conctact "remote" tachometer isnt that. Sorry i meant about car/engine tachometers. They look exactly the same as mechanical, but just are missing the cable and assumably "drag cup". They make square signal waves to make the needle rotate somehow, but how they do it. I couldnt only think of stepper motor. \$\endgroup\$
    – wtknow
    Commented Apr 7, 2023 at 13:02

1 Answer 1

Reset to default
2
\$\begingroup\$

Seems like you’re asking about the actuator for the needle rather than all the rest of the system.

There are a few ways that will work in an automotive environment.

One indeed is small stepper motors. The steppers are incremental actuators so they need to establish a zero position at power-up. They’re just like their larger cousins, just small and light since they don’t have to drive much of a load.

Another is to use an air-core meter movement, which is driven with analog sin/cos currents for absolute positioning.

You can find specific ICs designed for those two cases, with application notes and detailed datasheets. Finding the actuators may be more difficult, however GM steppers apparently fail frequently enough that low-cost replacements can be found.

\$\endgroup\$
2
  • \$\begingroup\$ Thank you so much! Didn't know nothing about air-core meter untill now (Google is bad sometimes when im forming my sentences) But can you tell me, how does these gauges go back to their resting spot when ignition is turned off? Does these have a return spring, because i cant see any spring on them on google. \$\endgroup\$
    – wtknow
    Commented Apr 7, 2023 at 13:56
  • \$\begingroup\$ Yes, that’s an issue. They may sit by gravity or have a hairspring (air core) or depend on firmware to return them if the system is shut down gracefully (steppers), \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Apr 7, 2023 at 14:21

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.