Fuel Tank Sender Linearisation Network

Why Have a Linearisation Network?

The MM2000 has a standard Morris Minor fuel gauge, positioned at the bottom of the speedometer in the central dashboard.  That gauge takes its electrical input from the fuel sender in the petrol tank in the car's boot.  The sender unit is essentially a variable resistor which changes its resistance from a high value when the fuel tank is full to a low value when the fuel tank is empty.

Since the petrol tank is larger than a standard Morris Minor tank and it comes from a Volvo 340, it has the sender unit of a standard Volvo 340.  This is not directly compatible with the Morris Minor's fuel gauge.

To overcome the mismatch between the sender and the gauge, a simple resistor network is employed which approximately linearises the curves of the two devices.  That means that the 'E' on the gauge then corresponds to a low fuel reading on the sender and the 'F' on the gauge corresponds to a high fuel reading on the sender.  Without the benefit of the linearisation network, neither of these fuel readings would be reliable.

The Linearisation Network

The linearisation network used is shown below.  It can be seen that the Volvo fuel tank sender unit forms part of the network and terminals A and B are attached between the fuel gauge and ground.  Orientation is not important.