Principles of Operation
The LRB Series Switch is supplied with a shaft mounted magnetic disc
or wrap which generates an alternating magnetic field that is picked
up by the non-contact sensor. The sensor transmits this speed signal
as a digital pulse (frequency) to the switch via a 3-conductor shielded
cable. The LRB Switch decodes this frequency signal to determine shaft
speed, and compares this to its adjusted set point(s). This comparison in
conjunction with the choice of under speed or over speed mode, allows
the relay output to be used for alarm and/or shutdown, assuring optimum
machine protection and process integrity. A feature of the LRB-Series
Switch is the ability to mount the switch on a DIN rail. This is useful
for installation where plant electrical controls are centrally located
in a control cabinet. Consult Electro-Sensors, Inc. for information on
enclosures if needed.
The LRB-Series Switch System includes the terminal block mounted
switch, a non-contact Hall-Effect sensor and a magnetic disc or optional
pulser wrap. The Model 906 sensor is designed for standard service. An
optional explosion proof sensor Model 907 is available for hazardous
locations. The sensor is connected to the terminal block on the LRB
Series Switch (figure 3).
Start Delay
A 10-second Start Delay is built into the LRB Series Switches. In Under
Speed Mode, the Start Delay holds the relay(s) in an energized state for
10 seconds, allowing the monitored shaft to reach a speed above the set
points(s) before monitoring begins. The Start Delay begins when power
is applied to the LRB Series Switch.
Signal Loss Protection
In Under Speed Mode, a loss of the sensor signal will be detected
immediately, and the relay will de-energize. In Over Speed Mode,
the loss of signal is detected and the LRB Series Switch will wait
30-seconds for the signal to resume, preventing unwanted signal loss
shutdown when monitoring a very slow speed shaft. After the 30-second
interval has elapsed with no incoming signal, the relay is de-energized.
Special Options
Special options are available from the factory to modify the standard
functions of the LRB Series Switches. Options include:
Increased, decreased or zero start delay; increased or decreased setpoint
hysteresis; extended ranges; and signal loss protection deactivation in
over speed mode.
Pulser Disc
To mount the Pulser Disc, center drill the monitored shaft to a depth of
1/2 inch with a No. 21 drill and tap it for a 10-32 UNF screw. Apply
Loctite™ or a similar adhesive on the screw threads to keep the pulser
disc tight. Attach the disc, decal side out, with the 10-32 UNF machine
screw provided. Pulser Discs can be used with all Electro-Sensors, Inc.
sensors.
Pulser Wrap (optional)
Pulser wraps are custom manufactured to fit the specific diameter of the
shaft on which they will be mounted. To mount the wrap, remove the 4
Allen-head cap screws holding the halves of the wrap together, place the
halves around the shaft, and reinsert the screws. Tighten the screws to 5
ft. lbs. Pulser Wraps can be used with all Electro-Sensors, Inc. sensors.
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Sensor Installation
The standard sensor is supplied with a mounting bracket and two jam
nuts. The explosion proof sensor is supplied with a slotted mounting
bracket. Sensors should be installed so the center line of the magnets
pass in front of the center of the sensor as the disc or wrap rotates. When
using the pulser disc, the center of the magnetized area of the disc,
shown as Dimension B in figures 1 and 4, is 1-3/4 inches from the center
hole of the disc. The recommended gap distance between the sensor and
the disc or wrap, Dimension A in the diagrams, is 1/4-inch ± 1/8 inch. To
achieve the proper gap distance, adjust the jam nuts holding the standard
sensor in the mounting bracket, or adjust the position of the explosion
proof sensor using the slots on its mounting bracket.
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Figure 1: Standard 906 Sensor and Pulser Disc
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Figure 2: Standard 906 Sensor and Pulser Wrap
LRB1000 / LRB2000
DIN Rail Mount Speed Switch
6111 Blue Circle Drive
Minnetonka, MN 55343
Phone: 952.930.0100
Fax: 952.930.0130
ISO 9001:2000 Certified
Free Catalog and Application Assistance
1.800.328.6170
Visit Us Online
www.electro-sensors.com
990-001300 Revision E
