User Manual

ISSPRO, INC. 2515 N.E. Riverside Way, Portland OR 97211
Telephone: [phone]  Toll Free: [phone]
FAX: [phone]
Form No. IS078 (11/8/07 rev C) Page 1 of 2
Single Level Adjustable Speed Switch: P/N R4901A
The R4901A is a standard 12 VDC, nonlatched, 100-5,000 Hertz, speed switch for use with sensor applications.
Nonlatched means that once the unit is tripped, it will remain tripped only as long as the input frequency exceeds the
trip point setting. Contact ISSPRO Inc. for other options such as 24V systems, ignition sensing, latching or other
than standard frequency switch points. There is also a factory service to preset the trip and reset points if desired.
1. Calculate or estimate your set point to determine if it falls within the 100-5,000 Hertz adjustment range. If the
frequency is out of range, contact Isspro Inc. for options.
a.) For Cable Driven Applications such as Speedometers:
MPH x Cable turns per mile
x Pulses per turn/3600 = Pulses per second or Hertz
For example:
If you want to set off an alarm in a truck when the speed exceeds 55 mph and you were using an R8970
ISSPRO Sender.
55 MPH x 1,000 turns per mile (typical cable) x 30 pulses per turn (R8970) /3600 = 458 Hertz
The R4901A will work for this application.
b.) For Sensor Driven Speedometer Applications:
MPH x Tire Revs per Mile
x Rear Axle Ratio x Number of Sensor Teeth per Rev/3600 = Hertz per
mile
For example:
55 MPH x 500 Tire Revs per Mile x 3.77 Rear Axle Ratio x 16 teeth/3600 = 461 Hertz per mile
The R4901A will work for this application.
c.) For Sensor Drive Tachometers:
Flywheel Teeth x RPM trip point/60 – Set Point hertz
103 Teeth x 1800 RPM/60 = 3090 Hertz
The R4901A can be set at 1800 RPM on this application.
These are a few typical examples. Many others are possible. Contact ISSPRO if you need assistance.
2. Follow the wiring diagram to complete your installation. Adjustment directions are shown below and on the
back page:
General Information:
Output Relay contacts- normally open (N/O), normally closed (N/C), and common (COM): The common
contact switches from the normally closed to the normally open contact at and above trip point.
Output Rating (maximum): 1 amp @ 24 VDC resistive, 0.3 amp @ 24 VDC inductive (coil load)
IMPORTANT
: If amp load exceeds the above amperage, an optional relay such as the R7021 is
necessary.
Operating Voltage:
12 V units: 10-16 VDC
24 V units: 16-30 VDC