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.
Scales and Bezels The RCA50 is available with both
linear and compressed scales. The standard scales are 0 to 8,000, 0 to 10,000 and 0 to 12,000 rpm with linear scales as copies of historic types and 0 to 12,000 rpm with a compressed scale. Various styles of bezels
can supplied. Copies of the chronometric types, both in chrome and black anodised finish are available. Also chrome or brushed alloy bezels rounded to meet the requirements of SVA can be provided 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. Push Button The tacho is supplied with a small electrical push button to be mounted by the customer. Apart from resetting the tell-tale needle or the maximum rpm value, the button is used to set up the number of cylinders and other
adjustments. 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 Input The tacho requires 12 volts and a pulse from the ignition system or a crank or cam sensor. A special user adjustable filter function in the tacho software allows a wide
variety of electrical inputs to be accepted. Accuracy 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. Set Up Holding the button pressed while power is applied puts the tacho in set up mode. The tell-tale needle shows
the set up stage and the main needle shows the value of the set up parameter. The following adjustments can be made: a) Number of pulses per two engine turns from ignition or sensor
b) Mode – trigger pulse edge, tell-tale mode. c) Filter value d) RPM for shift light 1 e) RPM for shift light 2
