LVITs (Linear Variable Inductance Transducers) are contactless linear position sensors that offer high reliability, durability, and performance, particularly an excellent stroke-to-length ratio, at reasonable cost. These features make them suitable for various internal systems functions within many Remotely Operated Vehicles (ROVs) for subsea activities.

Typical ROV system functions include maneuvering controls, rudder and directional positioning controls, stability augmentation, and tool gripper or robotic arm operation. LVITs can also be used with interactive manual controls in a ROV’s remote control console. 

In most ROV applications, an LVIT position sensor is a feedback element in a closed-loop servo system. In a typical example, LVIT sensors may be mechanically connected to gimbals on the propeller shaft to provide feedback to the ECU that is operating the gimbals’ servos. When used in ROV steering systems, LVITs can give position feedback about the vehicle’s rudder and diving planes orientation that comports with the algorithms being used within the ROV’s position control system. 

One style of LVIT position sensors that works very well with ROV tool grippers is ASG’s SSx-7 series of subsea sensors, available for SAE or ISO O-ring port mounting to function within the hydraulic actuators operating the ROV’s grippers. The SSx-7 series are very robust sensors that can be used directly in sea water to depths of 11,000 ft (3,300 m) or in PBOF environments up to 5,000 psig (350 bar). ASG also offers the MHE-7 series of internally-embedded cylinder position sensors. All in-cylinder sensors use a gun-drilled blind hole down the center of the hydraulic cylinder rod to measure the actuator position. The SSx-7 and MHE-7 in-cylinder LVITs are available in ranges from 1 in. (25 mm) to 36 in. (900 mm). 

The contactless inductive nature of LVITs is a standout feature of these low cost, high reliability position sensors. Being contactless means there is no internal electrical contact that can wear out, particularly from vibration. Also, the fact that LVITs are DC in, DC out devices minimizes the need for any auxiliary electronics. LVITs are also available with various bus-ready digital outputs to connect to many common microcontrollers. And their low input power requirement makes LVITs well suited to subsea operation. 

As noted above, an important advantage for LVIT position sensors in ROVs is their very favorable stroke-to-length ratio, which reflects the sensor’s measurement range compared to its overall length. This feature, their 316 stainless steel construction, and the availability of LVIT sensors with swivel rod ends, make them relatively easy to fit into an ROV’s internal mechanical systems with limited space availability. 

Summarizing the benefits of LVIT position sensing technology for ROVs: 

• Outstanding stroke-to-length dimension ratio, especially in longer ranges. 
• High reliability position sensing at low installed cost. 
• 316 stainless steel construction throughout for subsea units. 
• No internal electrical contacts to wear out or fail under vibration. 
• Variety of electrical I/Os including both analog and digital bus outputs. 
• Low power requirement well suited to subsea operation. 
• Submersible position sensors to 11,00 feet (3,300 m) seawater depth. 

Alliance Sensors Group
www.alliancesensors.com