Manual 82510
Magnetic Pickups and Proximity Switches
Woodward
15
Appendix.
Using the Output of a Woodward MPU to Drive a
Remote Tachometer or Other Device
Attach to Control Posts
Should a remote device be driven by a magnetic pickup, it is important that the connection be made on
the governor posts which accept the input from the MPU. Polarity must be maintained as indicated on
these posts or it is possible to short the system to ground and cause damage to the electronic circuits,
rendering the governor inoperable. Woodward electronic controls are not directly grounded, but in many
cases the negative (–) post or common is tied to ground through the battery powered supply. Should an
additional device also be grounded or powered by the same grounded battery system, a short circuit is
possible.
The MPU device provided by Woodward is not grounded, and polarity is not established until connections
are made to the governor. Almost all remote devices will have a power source in addition to two leads for
input. One of these input connections will be circuit common (–) and this should be determined prior to
connection with the governor.
EPG and 2500 Governors
Since these units are indirectly tied to ground, care must be taken that polarity of the remote device and
the governor is not reversed.
2301 Governor
The 2301 governor is isolated from ground; care should be taken that any device added to the system is
also isolated from earth ground.
Shielding
Governor circuits have been carefully shielded, and circuits to remote devices must also be shielded from
interference since this could prevent adequate governor control. Inadequate shielding could cause
unstable control.
Minimum Signal
Most Woodward controls require a minimum speed-signal strength of 1.5 V (ac) from the magnetic pickup
during cranking. The addition of remote devices to the output of the magnetic pickup could prevent the
reception of an adequate signal to allow engine start-up.
before trying to start the engine after adding an auxiliary device to
the MPU output, make sure all polarity has been established and the
system is not shorted to ground. Attempting to start the system with
reversed polarity between the auxiliary device and the control could
destroy either or both devices. Should the control be damaged due
to the reversed polarity, dangerous overspeed is possible, which
could damage equipment, causing personal injury or even death.
Woodward advises dedicating the entire output of a governor
magnetic pickup to the exclusive use of driving the control system.
This information is provided for those installations where the output
of the magnetic pickup is also used to drive other devices.
Released