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GENERAL INFORMATION AND MOUNTING DIRECTIONS
OS77R-OS.PM5
EFFECTIVE: 12/93
®
Model OS-77R
Model OS-77R-I
Overspeed Speed Switch With Relay Output
WARNING
BEFORE BEGINNING INSTALLATION OF THIS MURPHY PRODUCT
Disconnect all electrical power to the machine.
Make sure the machine cannot operate during installation.
Follow all safety warnings of the machine manufacturer.
Read and follow all installation instructions.
Installation Accessories
Hardware, tools, and optional equipment needed to in-
stall the model OS77R.
■ Tools as needed for the system mounting, such as
drill and screw driver.
■ 18 ga. wire for extension and hook up.
■ Set of wire terminating tools.
■ Wire termination; such as ring or spade terminals.
DESCRIPTION
The OS77R is an Overspeed Shutdown Switch used
for protecting the engine from excessive operating speeds.
The unit monitors a frequency generated from a magnetic
pickup. The OS77R-I functions identically to the OS77R
but monitors engine speed from a distributor ignition.
If the unit senses an engine speed higher than the ad-
justable set point, the unit will cause the engine to shut
down.
SETTING THE MODEL OS77R SERIES
IMPORTANT: The the following instructions as-
sume terminal number 5 is grounded. Please refer to
wiring and mounting information before attempting to ad-
just the unit. These steps must be done before the fine
tuning can be accomplished. The following steps should
be followed for first time setup of unit.
A. Turn “OVERSPEED ADJ.” fully clockwise.
B. Remove the wire from terminal # 2 of the OS77R.
C. Start engine and run at the highest RPM desired.
This is the RPM at which the engine should be
shut down if exceeded.
D. Connect a Voltmeter (or test light) between Termi-
nal #1 (positive +) and Terminal # 2 (negative -) of
the OS77R. You should read “no voltage” (test
lamp will be OFF.)
E. Slowly turn “OVERSPEED ADJ.” counter-clockwise
and STOP the INSTANT battery voltage is indi-
cated on the voltmeter (or the test light comes ON.)
F. Slowly turn “OVERSPEED ADJ.” clockwise about
1/8 of an inch. Now, tighten the locknut on the
“OVERSPEED ADJ.” without disturbing the setting.
G. Re-connect the wire to Terminal #2 on the OS77R.
This reconnects the OVERSPEED shutdown cir-
cuitry.
NOTE: If further adjustment is needed;
Turning the “OVERSPEED ADJ.” clockwise,
RAISES the shutdown point. This allows the en-
gine to run at a HIGHER RPM.
Turning the “OVERSPEED ADJ.” counter-clock-
wise LOWERS the shutdown point. This will shut
down the engine at a LOWER RPM.
NOTE: Relay contacts are between terminals 2 and 5.
WARNING: Perform the mounting operation with
power source off. The OS77R module is de-
signed to be mounted in a flat panel. First, drill
the mounting holes as shown on the template
included with the packing. Insert the module from
the back side of the panel and install mounting
hardware.