This text is about testing and calibrating a Smiths RVI style tacho, a type of tachometer commonly used in 1970s UK classic cars. The author provides a simple test circuit using a Field Effect Transistor (FET), resistors, and a 12V car bulb to test the tacho’s accuracy.
Circuit Description
The circuit is designed to use the fact that the mains frequency from most networks is very carefully controlled, allowing for a stable source of pulses to calibrate the tacho.
Test Results
The author tested the tacho on a RVI 2417/00 (used in a MG Midget) and found it to be accurate and stable, displaying a constant RPM value at varying supply voltages.
Modifications and Recommendations
The author suggests making modifications to the circuit for better performance, and recommends using a 0.5A fuse for the tacho’s supply and a 2A fuse for the battery charger output.
Manual:
Download: Simple Test for an Smiths RVI Tacho
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