Installation and Operation Instructions for
SELECTRONIC Speed Switches
Please read the following information before installing. A visual inspection of this product for damage during shipping is rec-
ommended before mounting. It is your responsibility to have a qualified person install this unit and make sure it conforms to NEC
and local codes.
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.
The SS300 Series are single set point speed switches with SPDT relay dry contact Power Requirements:
2 VDC (9-16 VDC).
4 VDC (18-30 VDC).
output. The trip point is set by a potentiometer. An LED indicates when the signal
source is present. A second LED turns on when the trip point is reached. See Table 1
for available models and requirements. An optional time delay is on board to delay
operation of the relay for 2-6 seconds after the set point has been reached.
Frequency Signal: Voltage (all models):
Minimum Input Voltage Signal: 4.5 Vrms.
Maximum Input Voltage Signal: 50 Vrms.
The SS300 Series speed switch is intended for installation within a weatherproof
enclosure to protect it from rain, dust, etc.
The SS300 Series shuts down the engine if RPM exceeds the pre-set limit.
Speed Sensitive Pull-in/Drop-out
Engage or disengage PTO’s, 4-wheel drives, other switch points, etc. according
to speed of engine being monitored.
Frequency Range in Hz
Engine and Transmission Alarm/Shutdowns
Oil pressure in some engines and transmissions varies widely between running
and idle speeds. The SS300 Series can select between two pressure switch set
points according to speed of the engine or transmission and thus give maximum
protection to the equipment while at operating RPM and eliminate nuisance
alarms when at idle.
Reset Differential Magnetic Pickup Signal Models:
• “Standard Models: 2 Hz Differential.
Adjustable Differential Model
The (“AD”) can be adjusted to change the speed range over which the pull-in and
drop-out differential of the relay will operate. A typical application is to insure
that engine speed is above a minimum RPM before applying a load but allows a
drop in speed of several hundred RPM without disconnecting the load.
• “AD” Models (Adjustable Differential): 650-8900 Hz Adjustable
Reset Differential Alternator Models:
“LF” Models (Low Frequency): 2 Hz Differential
“AD-LF” Models (Adjustable Differential Low Frequency):
0-1900 Hz Adjustable.
Table 1: Models Available and Input Signal
Output: Relay contact, SPDT, resistive load, 6 A, 30 VDC.
Time Delay: When terminal 7 is grounded, the relay operation is delayed for
-6 seconds after rpm set point is reached.
SS300 (std. model)
Adjustment: 20–turn potentiometer(s).
Temperature Range: -4° to 185°F (-20° to 85°C).
Relative Humidity: 0 to 95% Non-condensing.
Case: Black, ABS plastic.
SS300-LF (low frequency)
SS300-AD (adjustable differential)
SS300-AD-LF (low frq. & Adjst. diff.)
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