Electro-Sensors FB420 User Manual

2.75

Ø0.32

FB420 Shaft Speed Sensor

Description:

Electro-Sensor’s FB420 is a shaft speed sensor that provides a
4-20 mA signal that is directly proportional to the rotational
speed of a monitored shaft.
Since both the 4 mA and 20 mA calibration points are
programmable the user can also if desired operate the FB420 with
the 4 mA offset from 0 RPM.
The FB420 has a 4 digit LCD display that is used for calibration
and for trouble-shooting. The LCD is capable of displaying from
‘0.000’ to ‘9999.’ RPM, or from ‘04.00’ to ‘20.00’ mA.
The FB420 has one relay that can be programmed for either
failsafe over/underspeed alarm.

FB420 Installation:

The FB420 needs a rotating target installed on the application’s
drive-shaft, etc. A typical rotating target is a 255 Pulser Disc (with
or without an optional EZ-Mount bracket), or an optional custom­made Pulser Wrap. (See Figure’s 4a, 4b, and 4c).

Figure 2: FB420 Front-View

Electrical connections

The FB420’s electrical connections are as follows:

FB420

0.25 4.40

1.25

0.26

1.63

0.56

4.00

1.38

2.38

1.84

1“ NPT

Figure 1: FB420 Dimensions w/Bracket and U-Clamp

3.90

Ammeter

(optional)

-

TB1-2

+

4-20mA

PLC, Etc.

250 to 500

ohm load

4.81

+24Vdc

Power Supply

(+)

(-)

TB1-1

Shield

TB1-3

Figure 3:

• Connect any shield wire to the earth ground (if used).

• Connect TB1-1 to the power-supply (+24 Vdc) terminal.

• ConnectTB1-2toaresistiveloadof250Ωto500Ω,(usually

this load is internal to a PLC, etc.).

• Connect TB1-3 to the power-supply (-) terminal.

Note: TB1-2 is the 4-20 mA DC output line.

 Theothersideofthe250Ωto500Ωloadmustbe 

connected to the power-supply (-) terminal.

6111 Blue Circle Drive
Minnetonka, MN 55343
Phone: [phone]

Fax: [phone]

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Free Catalog and Application Assistance

1.800.328.6170

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990-003400 Revision C

Pulser Disc:

The end of the shaft to be monitored must be center drilled to a
depth of 1/2–inch with a #21 drill and tapped for a 10-32 UNF.
After applying Loctite™ or a similar adhesive on the threads
to keep the pulser disc tight, the pulser disc should be attached,
decal side out with the supplied 10-32UNF machine screw and
lock washer. Dimension (A )is 1/16 inch to 1/4 inch.
The center-line of the magnets (B) must align with the center of
the sensing head as the Pulser Disc rotates.

Pulser Wrap (optional):

Pulserwrapsarecustommanufacturedtottheshafttheywill

be mounted on. When the wrap is shipped, four Allen-head cap
screws hold the two halves of the wrap together. These screws
must be removed so the wrap is in two halves. Place the halves
around the shaft, reinsert the screws and torque them to 8 foot­pounds. Dimension (A) is 1/16 inch to 1/4 inch.
The center-line of the magnets (B) must align with the center of
the sensing head as the Pulser Wrap rotates.

B

A

Figure 4a: FB420 with 255 Pulser Disc

EZ-Mount Bracket with Pulser Disc (Optional)

Pulser Disc (Included)

EZ-Bracket

Assembly

Spacer

(Included)

FB420

Shaft Center Drilled
and Tapped for
1/2-13 UNC 2A

Retaining

Washer

(Included)

B

A

Figure 4c: FB420 with Pulser Wrap

SW1: Increment Button

SW2: Enter Button

TB1-1: +24Vdc Pwr
TB1-2: 4-20mA Out
TB1-3: DC Ground

SW1

SW2

TB1

A

321

321

TB2

D5

TB2-1: N.O.
TB2-2: Common
TB2-3: N.C.

Relay LED

Figure 4b: FB420 with EZ-Mount Bracket

List of Variables

VA R Mnemonic Description Range Decimal Place Default User’s Value

01 Pulses Per Rev Pulses per revolution of target 0001. to 9999. Fixed at XXXX. 0008

02 Min. RPM RPM value corresponding to 4 mA 0000 to “97.5% of Var03” dec pt tied to Var03 0000

03 Max. RPM RPM value corresponding to 20mA 0.000 to 9999. User selectable 200

04 Relay Function Select Unused, Over-speed, Under-speed 0000. to 0002. Fixed at XXXX. 0000

05 Relay Set-point RPM Relay alarm trip point in RPM 0000 to 9999 dec pt tied to Var03 0000

06 Relay Set-point Delay Alarm event ‘wait’ time in seconds 0000. to 0030. Fixed at XXXX. 0000

Figure 5: FB420 Rear-View (Cover Removed). Showing the

power/signal terminal TB1, the relay terminal TB2, the push-

buttons SW1 and SW2, and the relay LED

Free Catalog and Application Assistance

1.800.328.6170

Website: www.electro-sensors.com

2-4

990-003400 Revision C