Making Sense!

1

In ThIs Issue ■ Outline ■ Construction ■ Operation

nexT Issue ■ Wheel Speed Sensor

Outline

There are many types of pressure sensors to detect the pressure placed upon liquids and gasses. In this session the H1 type refrigerant pressure sensor will be used as an

example to explain sensor construction, and detection principles.

■ Pressure Sensor Examples

Pressure Sensor

Construction

The H1 type pressure sensor is constructed primarily from a housing, O-ring, and sensor chip. The sensor chip measures 3 mm on each side, with a sensor element located in

the center.

■ Sensor Construction

2009sensor Fundamentals #009

SensorName/Type

ApplicationExample

• Rail Pressure (Diesel Vehicles Use)

• Fuel Tank Internal Pressure

• Engine Intake Manifold Pressure • Atmospheric Pressure (EMS Use)

• A/C Refrigerant Pressure• Engine Oil Pressure• Power Steering Oil Pressure• Continuously Variable Transmission (CVT) Oil Pressure• Compressed Natural Gas (CNG) Fuel Pressure

• Direct-Injection Engine Fuel Pressure• Suspension Oil Pressure• Brake Oil Pressure (Master Cylinder, Accumulator)

Pressure Range

5 MPa

H1

H1-20

H3

180 MPa

H2

100 kPa

MAPS

BAPS

10 kPa

TAPS

20 MPa

3 mm

Sensor Chip

Sensor Element

Encased Oil

Metal DiaphragmHousing

O-Ring

Connector Case

Sensor Chip

LA990009-2390

© 2009 DENSO Sales California, Inc. All rights reserved. This document may not be reproduced or copied, in whole or in part, without the written permission of the publisher. DENSO Sales California, Inc. reserves the right to make changes without prior notice. 9/2009

■ Sensor Element ConstructionThe sensor element is made from single-crystal silicon with a thickness of 300 μm, forming a diaphragm shape. In addition, a bridge circuit is created on the sensor element from four diffusion resistors.

Pedestal

Diffusion Resistors(Bridge Circuit)Diaphragm

Vacuum Chamber

Pressure

300 µm

Operation

If pressure is applied to the inside of the sensor, a metal diaphragm depresses, transmitting the pressure through

the enclosed oil to the sensor element on the chip. When the sensor element diaphragm changes shape due to the applied pressure, the value of the diffusion resistors forming the element also changes due to the Piezoelectric resistance effect*. As a result, the sensor outputs the pressure change as a change in voltage.

* The Piezoelectric resistance effect is a phenomenon under which electric resistance changes due to an applied stress.

■ Pressure sensor usage example in a car A/C cycleThe pressure sensor used in car A/C cycles is known as a refrigerant pressure sensor, and is positioned in the piping between the condenser and the expansion valve. The refrigerant pressure sensor detects refrigerant pressure, and then outputs the value to the A/C ECU as a voltage change. The A/C ECU uses the pressure information to control items such as the discharge volume for variable capacity compressors, and electric fan rotational speed.

Sensor Chip

Output

PressurePressure

Encased Oil

Metal Diaphragm

High

Low

Low HighRefrigerant Pressure

Voltage

Sensor Output Characteristics (Example: Refrigerant Pressure Sensor)

Expansion Valve

Compressor

Condenser

Evaporator

RefrigerantPressure Sensor