Every racing car engine produces a digital electronic signal that
is proportional to the engine rpm. Inherently robust and fairly immune
to noise, vibration etc, digital signals are highly suitable for use
in racing car environments. Electronic tachometers convert the digital
signal into analogue, which moves the analogue needle. This inherently
inaccurate conversion makes the needle movement an inaccurate and
fragile part of the system.
Stack had the idea to marry this digital signal to a display mechanism
- effectively giving a display of digital accuracy driven in a way
to give an analogue reading. The key element in the product is a
stepper motor which drives the needle. Driven by electrical signals,
the motor does not continually rotate, it "steps" to a specific position
and is held firm. A change in the signal will cause it to step again.
(The positions are predefined in the motor). So when the electrical
signal from the engine, (proportional to the revs) changes, the motor
steps forward or back, causing the needle to move forward and back.
Advantages of the stepper motor:
- It drives the needle to a position and holds it there, ensuring
no needle waver. [This, combined with solid state electronics and
a lightweight aluminium casing renders the tachometer very robust
and unaffected by vibration, g forces or indeed hurling the instrument
across the track].
- The motor driving the needle can be run at a very fast speed to
give a fast response. Readings from the Intelligent Tachometer are
given every tenth of a second, considerably faster than older instruments.
A microprocessor is used in the tachometer to make all the necessary
calculations. Using quartz timing, it measures the period in between
the engine's ignition pulses to work out the rpm. A microprocessor
is not essential for this task, but its degree of accuracy, to 0.16
per cent, IS essential to match the accuracy required by drivers of
their instruments. It also works out how to drive and control the
stepper motor for the display.
The stepper motor also ensures robustness of the needle.
The aluminium casing and tough, shatter-resistant glass render the
whole unit very tough and crash-proof. (Plastics are not appropriate
for racing cars as they react with fuel and often cloud over).
Stack's innovation has given users tachometers that give results that are rapidly updated, highly accurate rpm indication with absolutely no needle waver and a build quality able to withstand the rigours of harsh enviornments..