1. Introduction
The Farringdon RCA50 Series of tachometers are believed to be the first available with stepper
motor driven main and tell-tale hands. The tell-tale hand is a very useful feature especially when
used in its auto-reset mode and not just an extra hand to make it look more like historic
chronometric types.
Please read these instructions carefully and make sure that the tacho displays the correct rpm—if
set up incorrectly, it is likely to show double or half the rpm but it is possible to set it up so that it
shows 4/5th of the true rpm which might be very expensive!
Outline Specification
7 to 16 volts DC. Below 10
volts hand speed is reduced
5 to 100 volts. Pulse width
greater than 10
microseconds
Less than 100 mA without
shift lights, less than 150 mA
with shift lights
2. Fitting Your Tachometer
2.1 Mounting the Tachometer
The RCA50 tachometer is 80 mm in diameter, the RCA51 is 100 mm in diameter and the RCA52
120 mm and the hole in your dash should accept this diameter. It will require 60 mm behind the
dash to accommodate the depth of the instrument and the clamping studs.
An ‘O’ ring is supplied that may reduce vibration a little if it is fitted behind the bezel. Also it will
provide a compliance for the clamp to work against. If the dash is wood, then it is probably
unnecessary and will prevent the bezel from seating on the dash neatly.
In order to keep the overall depth of the instrument as small as possible, the mounting studs are
relatively short and therefore the U shaped clamp may have to be trimmed to accommodate thick
dash boards. The U clamp is steel but is easy to cut.
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