To enhance the service of motor vehicle tires it is proposed to measure tire pressure continuously or intermittently and automatically warn the vehicle operator when a low tire pressure is detected. This is accomplished by an electronic pressure transmitter unit including a battery, a pressure sensor and a circuit board including a radio transmitter, and a radio receiver and warning means within the vehicle to effect a warning when the transmitter issues a warning signal. The transmitter is on the wheel inside the tire so that the unit is constantly subject to the tire pressure,
The transmitter is mounted on the outside diameter "drop center" of the wheel rim and is inside the tire. AM transmissions are broadcast from the device on a speed transition and on a low tire pressure threshold transition. The device is battery powered for a design life of several years. During this period, the transmitter will encounter the environment of 125.degree. C., three axis 100 G shock, 1000 G centrifugal force loading, and extremes of humidity. The substantial mass of the battery under these conditions could impose substantial stress on the circuit board which could result in failure of solder joints.
One design approach for such transmitters is to mount the circuit board and battery radially, but experience with this configuration has led to reliability problems; it is suspected that the problem stems from the centrifugal force loading on the solder joints. Another approach has been to pot the unit in epoxy. This hard substance introduces several potential problems. The epoxy has a high coefficient of thermal expansion and can add stress to solder joints. The epoxy also adds substantial mass which is undesirable for an application with such large G forces.