AUTOMOTIVE INSTRUMENTATION design in automobiles

Automotive Instrumentation

1. AUTOMOTIVE INSTRUMENTATION

2. MODERN AUTOMOTIVE INSTRUMENTATION. Sensors – nonelectrical signal to voltage or current. Electronical signal processor. Display device.

3. General Instrumentation Block Diagram

4. COMPUTER-BASED INSTRUMENTATION SYSTEM.

5. INPUT AND OUTPUT SIGNAL CONVERSION. Analog-to-Digital Conversion

6. DIGITAL-TO-ANALOG CONVERSION.

7. SAMPLING. Only one variable at a time. Sample period < time in which quantity changes. Rapidly changing quantities sample period is short. Variables which change slowly sample period is long. Sequential Sampling

8. ADVANTAGES OF COMPUTER-BASED INSTRUMENTATION. Flexibility. Improved performance compared with conventional instrumentation. More accurate.

9. FUEL QUANTITY MEASUREMENT During a measurement of fuel quantity, the MUX switch functionally connects the computer input to the fuel quantity sensor, as shown in Figure This sensor output is converted to digital format and then sent to the computer for signal processing

10. Fuel Quantity Measurement

11. understanding automotive electronics Fuel quantity sensors use a float within the fuel tank; the float is mechanically linked to a potentiometer that operates as a voltage divider .

12. The sensor output voltage is not directly proportional to fuel quantity in gallons because of the complex shape of the fuel tank. The computer memory contains the functional relationship between sensor voltage and fuel quantity for the particular fuel tank used on the vehicle. The computer reads the binary number from the A/D converter and corresponding sensor voltage used to address a particular memory location. The computer then uses the number from memory to generate the appropriate display signal—either analog or digital, depending on display type—and sends that signal via DEMUX to the display.

13. COOLANT TEMPERATURE MEASUREMENT

14. To measure coolant temperature, the sensor output from a thermistor is converted into a digital signal and compared to a maximum safe value stored in memory Coolant Temperature Sensor

15. OIL PRESSURE MEASUREMENT The simplest oil pressure warning system involves a spring-loaded switch connected to a diaphragm diaphragm is exposed directly to the oil pressure. The force developed on the diaphragm by the oil pressure hold the switch open as long as the oil pressure exceeds the lower limit Whenever the oil pressure falls below this limit the spring force is sufficient to close the switch Switch closure is used to switch on the low oil pressure warning message lamp.

16. One of the deficiencies of this simple switch-based oil pressure warning system is that it has a single fixed low oil pressure limit

17. VEHICLE SPEED MEASUREMENT Digital measurement of vehicle speed is possible using a binary counter and a sensor having an output signal frequency that is proportional to speed.