WÄRTSILÄ PAAE051728, Instruction Manual

Page: 342 / 394

23.3.1.2 Testing of the overspeed trip by using a signal
generator
1 Connect the signal generator (848113)
to both speed
sensors one at a time. The signal generator is connected to the pins
signal and gnd of the speed sensor. See the Fig 23-26 for connec-
tions. The overspeed stop should be detected when the overspeed
limit is exceeded.
Note! To avoid lubrication shut down when simulating engine speed
on a standstill engine the pressure transmitter PT201-1 and
pressure switch PSZ201 can be disconnected. See installation
specific electrical drawings for connections.
2 Increase the frequency
of the input signal.
3 Check at what frequency
the overspeed is detected.
The speed is detected from the camshaft gear. The rotation speed of
the camshaft gear is half of the engine rotation speed. The frequency
corresponding to the overspeed can be easily calculated when the
teeth number of the camshaft gear is known. In an engine with
planetary gear the camshaft gear has 42 teeth. In an engine without
planetary gear the camshaft gear has 48 teeth.
The following formula gives the frequency detected by the
sensor corresponding to engine speed:
Frequency
(
Hz
) =
æ
ç
è
Speed [ rpm ]
2
ö
÷
ø
æ
ç
è
Teeth Number
60
ö
÷
ø
The frequency corresponding to the engine speed is shown in
tables below with engine nominal speed of 720 rpm and 750 rpm
accordingly.
Table 23-1
Frequency corresponding to
speed
No planetary gear Planetary gear
720 rpm (nominal speed) 288 Hz 252 Hz
828 rpm (15% overspeed
limit, DCU/SMU) 331 Hz 290 Hz
850 rpm (18% overspeed
limit, RM) 340 Hz 297 Hz
23 Instrumentation and Automation 32-200115/II
23-8 WÄRTSILÄ 32