Torque, Thrust and Power
Torque and thrust transducers are installed on the propeller shaft. Both transducers are based on the use of strain gauges. For the torque measurement a simple strain gauge bridge is glued on the shaft. The resulting signal is proportional to the torque, with intrinsic compensation of thrust and bending forces.
For the thrust measurement a simple bridge is not enough, due to the high interference from the torque deformation, so the measuring strain gauge bridge is made with two strain gauges for each of the four arms. Two pairs of 90° strain gauges are glued on the shaft, one in opposite position to the other one, with respect to the shaft axis, and two other pairs are installed on a structure not subjected to deformation. Because of the very weak signal, a special microcomputer driven amplification system is used in order to have no offset and high gain.
To calculate the power it is necessary to measure also the shaft speed (rpm). Rpm are measured detecting the passage of 3 bars installed on the shaft in an asymmetrical position. The particular configuration give the possibility to calculate not only the shaft speed but also the sense of rotation, by using only one proximity detector.The on board microprocessor calculate the transducer deformation, both torque and thrust, calculates the average values and send the results in digital form, modulating with pulses a very low frequency carrier. A fixed pick up in front of the shaft receive the pulses and send them to the main acquisition board.
All measured values can be read on a simple led display panel or sent to a monitoring system, like PEM++ (Propulsion Efficiency Monitor) and Fleet Survey. A key feature of our torquemeter solution is the reliability and accuracy of calculation, as demonstrated by dozens of installations through some naval services companies such as Pizzorno & Lini, Ship System, Abacus Marine etc.