Page 323 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

12.2 Sensor categories 315
Spring
Mass
Piezoelectric material
Volt meter
FIGURE 12.14
Configuration of a typical accelerometer used in seismic sensing.
The active element is the piezoelectric crystal which allows for a varying electrical signal pass- ing through the crystal as the force applied to the crystal increases or decreases. The voltage is mea- sured as a highly sensitive value allowing for close measurement of the stress applied to the sensor. The sensor can be arranged in various orientations based upon the plane of motion to be sensed.
The piezoelectric sensor can be adapted to several applications including a depth sensor (mea- suring stress on the crystal due to ambient pressure), inertial navigation system sensor (measuring acceleration through all planes of motion), vibration sensing (sensor mounted to the motor housing for sensing mechanical degradation), or other uses.
An example of an accelerometer would be an airbag sensor on a car or a “G-meter” measuring the stresses on an airplane (and the pilot for the old-fashioned manned vehicles) during aerobatic maneuvers. An accelerometer is used on an ROV for sensing momentum change such as through contact or collision with a subsea structure by various vehicle components (e.g., collision with the TMS, subsea structure, or vessel hull).
Typical accelerometer types and characteristics (Table 12.2) are as follows:
• IEPE (internal electric piezoelectric) piezoelectric accelerometers
• Charge piezoelectric accelerometers
• Piezoresistive accelerometers
• Capacitive accelerometers
• Servo accelerometers
12.2.2 Biosensors
Biosensors are used extensively in the medical industry but have a particular application in the subsea industry for scientific applications. In recent years, subsea biosensor applications have