Case 580SR Service Manual page 951

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FUEL LEVEL GAUGE
When a certain low fuel level is reached, the relevant
"low fuel" lamp will be lit according to the following
logic. The filtering of the data read is obtained with a
hysteresis on the resistance value joined to a delay
time of 2 seconds.
Ohmic parameter threshold and delay time value
must be kept in NVM. Lamp activation depends on
values used for needle movement; this means that
at key-on the low fuel level warning is active if the
cluster sees a resistance value greater the table be-
low.
Resistance values used are as follows:
The fuel level gauge will indicate the fuel level of the
vehicle tank. The gauge dial will be divided into two
ranges: red and green. The red range will indicate a
low fuel zone. The green range will indicate a non-
low fuel zone. This gauge will be connected to a sen-
sor that will provide specific a resistance to correlate
to a specific fuel tank level.
Tank size
133 l
Z X = empty. The centerline (CL) of the pointer will be
+0/-2 angular degrees of the centerline of this emp-
ty mark.
Z Y = Red - Green threshold. The CL of the pointer
will be +/-3 angular degrees of the centerline of this
1/2 mark.
Z Z = full. The CL of the pointer will be +4/-0 angular
degrees of the centerline of this full mark.
In case the sender is disconnected, the gauge has to
go down in empty position. Reconnecting the sensor
the gauge has to return to the correct position. Both
the movements have to be uniform.
A stepper motor will drive fuel level gauge. The
gauge accuracy should be less than or equal ± 2%.
Needle calibration has never to be lost for any exter-
nal condition. During cranking, the needle movement
shall be frozen in order to inhibit any spurious move-
ment of it.
SECTION 55 - ELECTRICAL SYSTEM
Empty value (X) Red-green border
320 ohms 186 ohms
Full (Z) value
(Y)
6.5 ohms
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Fuel level
indicated
30% with 18
angular degrees of
gauge motion