571 The Variable Voltage Map Sensor

The MAP sensor shown in Fig. 5.21 receives a 5 V supply from the ECU. Variations in manifold pressure (vacuum) cause the small silicon diaphragm to deflect. This deflection alters the resistance of the resistors in the sensor's bridge circuit and the resulting electrical output from the bridge circuit is proportional to manifold pressure.

100 200 300 400 500 600 700 (mmHg) D

100 200 300 400 500 600 700 (mmHg) D

A - Vacuum cavity C - Output voltage

B - Silicon diaphragm D - Gauge reading

Fig. 5.21 A manifold absolute pressure sensor

Details of the pressure sensing element are shown in Fig. 5.22. Figure 5.22(a) shows four resistors that are diffused into the silicon. The size and chemical composition of the resistors is accurately controlled during the manufacturing process. Figure 5.22(b) shows how the vacuum cavity permits the silicon sensing diaphragm to flex under the influence of pressure in the induction manifold.

Resistors

Resistors

200 M-m

Vac. cavity

5 volts

5 volts

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