Farringdon has developed  a tachometer movement which allows two needles to be driven by separate stepper motors. Although the main  purpose of this development was to produce a replacement for older chronometric  types, the tell-tale needle remains an important engine monitor and a useful feature in any tachometer.

Sizes and Bezels

There are three sizes; the RCA50 which is fits into an 80 mm diameter hole, the RCA51 which fits in a 100 mm hole and the RCA52 which fits into a 120 mm hole.  Various scales and ranges are available - please call for the latest availability.  All three types are available with chrome or black anodised bezels.  The commonest types are pictured below:


The Tell-Tale Needle

The tell-tale needle can operate in one of two modes. The  first is conventional where the tell-tale  needle appears to be pushed by the  main needle and sticks at the highest  position reached. In this mode, the  needle is reset by pressing the small  button supplied with the tacho.
The second mode, called auto-reset,  automatically resets the needle after  a period of two seconds. This is a  useful driving aid as it allows the  driver to monitor the maximum revs  reached by the engine at each gear  change without having to keep his  eyes on the tachometer at the very  instant of the change.

After power is applied to the tacho,  the tell tale needle is driven to  the maximum rpm it has seen. If the  tell tale is in auto-reset mode, this  shows the value that a normal tell-tale  would have shown. This value can be  reset at any time by simply pressing  the push button.


Shift Lights

The tacho provides  two separately adjustable shift light  outputs. When both shift lights are lit, they flash as an additional alert.  Two special LED shift lights are supplied  with the tacho.


The tachometer is quartz  crystal controlled and will show the  rpm to an accuracy better than 1% +  or - 100 rpm on the main part  of the scale. The resolution and therefore  the accuracy of the compressed scale  is reduced in proportion.


The tacho is powered from the car’s 12 volt supply.  (As the case is isolated, it can be used with positive earth cars)

The trigger can be from any reasonable source although contact breaker type require the fitting a small filter box which is supplied with every instrument.   By far the best form of trigger is from a separate sensor which will not be affected by odd ignition spikes or rev. limiters that always give a false reading when reached.  Call us to discuss the options....

Click for Tacho Wiring Diagram      Click for Data Sheet

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