Common Gauge Types

Bi-Metallic Strip

The bi-metallic gauge operates using heat. Inside the gauge is a small piece of bimetallic material that is connected to the needle. Wrapped around this strip is some thin wire which gets warm when electrical current flows through it. This material is created using two different metals bonded together. These metals expand at different rates when they are heated. This causes the material to bend as one metal expands to a greater length than the other.

Moving Coil

This type of gauge uses magnetism to move the needle. Inside the gauge is a coil which is connected to the supply terminals. When a voltage is applied to the terminals current flows through the coil creating a magnetic field. This field causes the needle to be moved by a varying amount. As the field increases the needle will move toward the maximum value indicated by the gauge. The field is linked directly to the voltage applied and the current flowing through the terminals. This value will depend upon the state of the sensor that is being used.

How stuff works
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Fundamentals of Motor Vehicle Technology
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