RE POISING THE MOVEMENT
Replace the dial and pointer, locking the dial screws with Paripan Locking
Varnish or a suitable equivalent. Fit the iron core, former and pulse lead
and then proceed to poise the movement and set the basic calibration as
described below.
Connect the impulse tachometer to the ignition pulse simulator and
speedometer test apparatus as described in the Testing Procedure on page S.4.
Switch on the supply to all these units and set the tachometer so that the
pointer rests at the lower calibration mark at the 1750 r.p.m. position on the
dial.
Check the poising by holding the tachometer in a vertical plane and rotating
it at 90
°
intervals, observing the position of the pointer after each turn.
In all four. positions the pointer should be within the limits of the lower
calibration mark. If the pointer does not lie within the
mark the movement is unbalanced and should be re-poised in the following
manner.
On the movement balance arm is fitted a moveable brass counter weight and
at 90 to the counter weight are two extension arms on which is wired two
small moveable coils. With the tachometer reading oppositethe lower
calibration mark proceed to check the tachometer at 90 intervals
in the vertical plane. If the pointer lies to the right or left of the
calibration mark it is possible by moving the counter weight and/or a
coil to bring the pointer into line. Care should be taken to avoid causing
a short circuit as the adjustment is made. This procedure should be carried
out until the pointer shows correct balance in each of the four positions.
If it is found that correct poising cannot be obtained the magnetic circuit
of the tachometer should be carefully checked for correct assembly, and if
further difficulty is experienced the magnet should be changed.
S.
7
