Page 318 - Introduction to Marine Engineering

292 Instrumentation and control

nm
Pick up~»>fl U
C
°" rL^ Signal Oigitai
f*s ^ modifier counter

(a) inductive

Rotating
shaft

Capacitor j M M
plate
Signal Digital
modifier counter
(b) Capacitive
Figure 15.17 Pick-up tachometers, (a) inductive; (b) capacitive

Strain gauge torsionmeter
With this device four strain gauges are mounted onto the shaft, as shown
in Figure 15.18. The twisting of the shaft as a result of an applied torque
results in a change in resistance of the strain gauge system or bridge.
Brushes and sliprings are used to take off the electrical connections and
complete the circuit, as shown. More recently use has been made of the
resistance change converted to a frequency change. A frequency
converter attached to the shaft is used for this purpose: this frequency

.Brush gear

Meter
reading
strain

Figure 15.18 Strain gauge torsionmeter