991 Thrust Transmitter
Datasheet

Bently Nevada Machinery Condition Monitoring141618 Rev. M

Description
The 991 Thrust Transmitter is intended primarily for theoriginal equipment manufacturers (OEMs) of centrifugal air
compressors or small pumps, motors, or fans who prefer toprovide a simple 4 to 20 mA proportional axial displacement(thrust) signal as the input to their machinery control system.
The transmitter is a 2-wire, loop-powered device that
accepts input from our 3300 NSv proximity probe and its
matching extension cable (available in 5 m and 7 m system
length options). The transmitter conditions the signal into
appropriate engineering units proportional to the shaft’s axial
position1, and provides it as a 4 to 20 mA industry-standard
signal for input to the control system where machinery
protection alarming and logic occurs2.
The 991 transmitter provides the following notable features:
l
l

l

l

l

l

l

l

l

Integrated Proximitor Sensor requires no external unit
Non-isolated "PROX OUT " and "COM" terminals plus a
coaxial connector provide a dynamic vibration andgap voltage signal output for diagnostics3.
Non-interacting zero and span potentiometers under
the Transmitter label supports loop adjustment.
Test Input pin allows quick verification of loop signal
output, using a variable DC voltage source as the input.
A Power-up Inhibit circuit eliminates signal errors due
to line voltage transients.
A Not OK/Signal Defeat circuit prevents high outputs or
false alarms due to a faulty proximity probe or loose
connection.
Choice of DIN-rail clips or bulkhead mounting screws
as standard options simplifies mounting.
Potted construction for high humidity (up to 100%condensing) environments.
Compatibility with 3300 NSv proximity probe allows
transducer installation in small areas with minimal

991 Thrust Transmitter
Datasheet

141618 Rev. M

equipment such as oscilloscopes andanalyzers, and preserving industrystandard conventions for signal polarity.
We strongly recommend that you use
this test adapter for all applications tomaintain isolation between test
equipment and the loop signal, and tomaintain machinery protection integrity.

clearance, typical of centrifugal air
compressors.

Notes:
1. Probe adjustment and range are criticalin thrust position measurements.
Incorrect probe gap settings may
prevent the transmitter from reachingfull-scale in either the normal or counter
directions (no machinery monitoring). For
proper adjustment, follow the instructionsin the manual.
2. Thrust transmitters have many
limitations when compared to acontinuous monitoring system. They area practical solution in some applications
for measuring rotor axial position and area valuable tool for trending thrust
readings. While the transmitter is capableof alarming on thrust position and nonOK checking, monitor functions such as
Timed OK channel defeat, Danger
Bypass, and Trip Multiply cannot be used.
In addition, PLCs attached to the thrusttransmitter are not suitable for plantwide diagnostic systems such as System
1 or Rule Paks.
3. The 991 Vibration Transmitter's "Prox Out"coaxial connector provides a nonisolated dynamic transducer signal formachinery diagnostics. You can connect
this signal directly to battery-powered or
isolated test equipment to diagnose
machinery problems. However, since the"PROX OUT" signal is not isolated from the
4 to 20 mA loop signal, an interface isavailable (and strongly recommended)for signal isolation. The 990/991 Test
Adapter conditions the 990 Transmitter's"PROX OUT" signal for use with acpowered test equipment. The adapter
also inverts and isolates the 990's
transducer signal, making it suitable for2/19

991 Thrust Transmitter
Datasheet

141618 Rev. M

Specifications
Unless otherwise noted, the following
specifications apply at +22°C (+72°F) using a
3300 NSv Probe and Extension Cable, and an
AISI 4140 steel target.

OutputImpedance

Prox Out has a 10 kΩ output
impedance calibrated for a
10 MΩ load.

Linear Range

0.25 to 1.65 mm (10 to 65 mils)for Prox Out. Suitable for 0.60-0.6 mm or 25-0-25 mils
current loop linear ranges.

Prox Out
Incremental
Scale Factor

7.87 mV/µm (200 mV/mil)±6.5% typical includinginterchangeability errors
when measured inincrements of 0.25 mm (10mils) over the linear range
using a flat 30 mm (1.2 inch)target.

Temperature
Stability

Incremental scale factor
remains within ±10% of 7.87
mV/µm (200 mV/mil) from
0°C to +70°C (+32°F to+158°F).

Minimumtarget size

9.5 mm (0.375 in) diameter.

Leadwire
LengthProximitor Sensor Output(BNC connector), maximum
cable distance is 3 meters (10feet).

NonHazardous,
Zone 2 or Div 2
Hazardous
area locations

13 km (8 miles) maximum
between transmitter andreceiving device for signal
output.

Electrical
Input

Accepts 1 non-contacting
3300 NSv Proximity Probe andextension cable.

Power

Requires +12 to +35 Vdc input
at the transmitter terminal.

4 to 20 mA
Signal Output

4 to 20 mAdc over specified
full-scale range in 2-wireconfiguration.

4 to 20 mA
Loop
Accuracy

Within ±1.5% over specified
full scale range(typical). Accuracy is rated
from the TEST signal input tothe voltage measured acrossa 250 Ω loop resistance.

Maximum
Loop
Resistance

1,000 Ω including cable at 35
Vdc.

Current
Limiting

23 mA typical.

Zero and Span

Non-interacting external
adjustments.

Not OK/Signal
DefeatSignal output will go to lessthan 3.6 mA within 100 µs
after a Not OK condition
occurs. Signal output isrestored within 0.1 seconds
after the Not OK condition isremoved.

Proximitor
Sensor Output

Compatible with
ungrounded, portable test
equipment. When using
grounded, ac-powered test
equipment, use the 122115-01
Test Adapter for signal
isolation.

Environmental Limits
Transmitter Temperature
OperatingTemperature-35°C to +85°C(-31°F to +185°F)

Storage
Temperature-51°C to +100°C(-60°F to +212°F).

Probe Temperature
OperatingTemperature

3/19-52°C to +177°C(-62°F to +351°F)

991 Thrust Transmitter
Datasheet

141618 Rev. M

Storage
Temperature-52°C to +177°C(-62°F to +351°F)

Relative
Humidity

100% condensing, nonsubmerged, with protectionof coaxial connectors.

with thread engagement lengths
exceeding the values in the table
above may exhibit binding during
installation. Contact your Bently
Nevada representative if you require
probe thread engagement lengths
exceeding the values above. Bently
Nevada does not replace proximity
probes under warranty due toexcessive thread engagement
lengths.

MechanicalTransducer
Tip Material

Polyphenylene sulfide (PPS).

Transducer
Case
Material

AISI 303 or 304 Stainless Steel(SST).

Probe Cable75Ω coaxial, fluoroethylene
propylene (FEP) insulated.

When drilling and tapping amounting hole for a 1/4-28 probe, a#3 or larger tap drill isrecommended.

Cable Armor Flexible AISI 302 SST with
(optional)
optional FEP outer jacket.
TensileStrength222 N (50 lbf) probe case toprobe lead, maximum.

Transmitter
Weight0.43 kg (0.9 lbm).

Total System
0.82 kg (1.8 lbm) typical.
WeightThread Engagement Limits
Probe
Case
ThreadMaximum Length of Thread
Engagement

1/4-280.375 in

3/8-240.563 in

M8x1

12 mm

M10x1

15 mm

Maximum thread engagement
lengths are per the industry standardof 1.5 times the nominal thread
diameter. A fit class matching that of
the external probe thread is assumed
for all internal threads. Applications

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991 Thrust Transmitter
Datasheet

141618 Rev. M

Compliance and Certifications
FCC
This device complies with part 15 of the
FCC Rules. Operation is subject to thefollowing two conditions:llThis device may not cause harmfulinterference.
This device must accept any
interference received, includinginterference that may cause
undesired operation.

ATEX
ATEX Directive 2014/34/EU

RoHS
RoHS Directive 2011/65/EU

Maritime
ABS 2009 Steel Vessels Rules
1-1-4/7.7,4-8-3/1.11.1,4-9-7/13

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991 Thrust Transmitter
Datasheet

141618 Rev. M

Hazardous Area Approvals
For the detailed listing of country andproduct-specific approvals, refer tothe Approvals Quick Reference Guide(108M1756).
For additional technicaldocumentation, please log in to
bntechsupport.com and access the
Bently Nevada Media Library.

cNRTLusClass I, Div 2Groups A, B, C, D
T5@ Ta [+85°C, Type 4]
Installed per Drawing 128838

ATEX/IECEx

II 1 GEx ia IIC T4 Ga
T4 @ Ta = -35°C to +85°C

II 3 GEx nA IIC T4 Gc
T4 @ Ta= -35 ˚C to + 85˚C

Entity Parameters
Zone 2
Power Supply: 28 V

Zone 0/1
Terminal
Terminal
blocks E3-E4
blocks E1-E2
and“Power supply
connector J2
4-20 mA”"Proximitor"

Connector J3"Probe"Ui [28 V]

Uo [28 V]

Uo [28 V]

Ii [120 mA]

Io [6 mA]

Io [100 mA]

6/19

Pi [0.84 W]

Po [0.17 W]

Po [0.8 W]

Ci [20 nF]

Co [80 nF]

Co [27.3 nF]

Li [10 μH]

Lo [1 H]Lo [5.3 mH]

991 Thrust Transmitter
Datasheet

141618 Rev. M

3309023300 NSv Probe, 1/4-28 UNF
thread, with armor.

For the detailed listing of country andproduct-specific approvals, refer tothe Approvals Quick Reference Guide(108M1756).

3309083300 NSv Probe, 3/8-24 UNF
thread, without armor.

3309093300 NSv Probe, 3/8-24 UNF
thread, with armor.

For additional technicaldocumentation, please log in to
bntechsupport.com and access the
Bently Nevada Media Library.

A: Unthreaded Length Option

Ordering Information

Unthreaded length must be at least
0.7 in less than the case length.
Order in increments of 0.1 in

991-AA-BB-CC-DD

Length configurations:

A: Full-scale Option

Minimum length: 0 in06

0.6-0-0.6 mm

Maximum length: 9.2 in

25

25-0-25 mils

Example: 04 0.4 in

B: System Length Option

B: Case Length Option

50

5.0 meters (16.4 feet)

Order in increments of 0.1 in

70

7.0 meters (23.0 feet)

Threaded length configurations:

C: Mounting Option

Minimum length: 0.8 in

01

35 mm DIN-rail clips

Maximum length: 9.9 in

02

Bulkhead screws

Example: 35 3.5 in

03

DIN clips and screws

C: Total Length Option

D: Agency Approval Option

05

0.5 meter (1.67 feet)00

Not required10

1.0 meter (3.25 feet)01

CSA Division 250

5.0 meters (16.4 feet)

05

CSA Division 2, ATEX Zone 0, ATEX
Zone 2 and includes ABS
maritime approval70

7.0 meters (23 feet)

D: Connector Option

3300 NSv Proximity Probes

01

Miniature coaxial ClickLoc
connector with connector
protector, standard cable

02

Miniature coaxial ClickLoc
connector, standard cable

Part Number-AA-BB-CC-DD-EE
3309013300 NSv Probe, 1/4-28 UNF
thread, without armor.

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991 Thrust Transmitter
Datasheet

141618 Rev. M

11

Miniature coaxial ClickLoc
connector with connector
protector, FluidLoc cable

Maximum length: 250 mm

Miniature coaxial ClickLoc
connector attached, FluidLoc
cable

C: Total Length Option

12

Example: 25 250 mm

E: Agency Approval Option00

Not required

05

Multiple Approvals (CSA NRTL/C
and BASEEFA/CENELEC, which
includes CSA Division 2)

Part Number-AA-BB-CC-DD-EE
3300 NSv Probe, M8 x 1 thread,
without armor.

3309043300 NSv Probe, M8 x 1 thread,with armor.

3309053300 NSv Probe, M10 x 1 thread,
without armor.

3309103300 NSv Probe, M10 x 1 thread,with armor.

0.5 meter (1.67 feet)10

1.0 meter (3.25 feet)50

5.0 meters (16.4 feet)70

7.0 meters (23 feet)

D: Connector Option

3300 NSv Probes, Metric33090305

01

Miniature coaxial ClickLoc
connector with connector
protector, standard cable

02

Miniature coaxial ClickLoc
connector, standard cable

11

Miniature coaxial ClickLoc
connector with connector
protector, FluidLoc cable

12

Miniature coaxial ClickLoc
connector attached, FluidLoc
cable

E: Agency Approval Option00

Not required

05

Multiple Approvals (CSA NRTL/C
and BASEEFA/CENELEC, which
includes CSA Division 2)

A: Unthreaded Length Option
Unthreaded length must be at least
20 mm less than the case length.

3300 NSv Reverse Mount Probe

Order in increments of 10 mm

330906-02-12-CC-DD-EE, 3/8-24 UNF
threads

Untreaded length configurations:
Minimum length: 0 mm

330907-05-30-CC-DD-EE, M10 x 1 UNF
threads

Maximum length: 230 mm
Example: 06 60 mm
B: Case Length Option

C: Total Length Option

Order in increments of 10 mm

05

0.5 meter (1.67 feet)

Minimum length: 20 mm

10

1.0 meter (3.25 feet)

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991 Thrust Transmitter
Datasheet

141618 Rev. M

50

5.0 meters (16.4 feet)

C: Agency Approval Option

70

7.0 meters (23 feet)00

Not required

05

Multiple Approvals (CSA NRTL/C
and BASEEFA/CENELEC (which
includes CSA Division 2)

D: Connector Option
02

Miniature coaxial ClickLoc
connector, standard cable

12

Miniature coaxial ClickLoc
connector attached, FluidLoc
cable

E: Agency Approval Option00

Not required

05

Multiple Approvals (CSA NRTL/C
and BASEEFA/CENELEC, which
includes CSA Division 2)

Extension Cable
330930-AAA-BB-CC
A: Cable Length Option
040

4.0 meters (13.1 feet)045

4.5 meters (14.8 feet)

060

6.0 meters (19.7 feet)065

6.5 meters (21.3 feet)

B: Armor Option
00

Without stainless steel armor

01

With FEP covered stainless steel
armor

02

With stainless steel armor

03

Without stainless steel armor,
with connector protector

04

With FEP covered stainless steelarmor and connector protector

05

With stainless steel armor andconnector protector

9/19

991 Thrust Transmitter
Datasheet

141618 Rev. M

Accessories

l990/991 Test Adapter. Package
includes: 990/991 Test Adapter,
9V battery, Universal ac Adapter,
Power Cord (North American),User Guide and Soft Carrying
Case.

990/991 Test Adapter Accessories

The 990/991 Test Adapter inverts
and isolates the PROX OUT
signal from the 991 Transmitterso you can connect 991
Transmitters to ac-powered
diagnostic equipment. The
Adapter modifies the PROX OUT
signal so that it matches our
Proximitor Sensor signals byperforming these functions:ll122115-01l

2 channels, so that you can display anorbit for XY probe configurations.

123266-01

Coaxial Cable Kit. Includes 4
cables with length of 1.5 meters(5 feet) each.

02211505

Single coaxial cable with lengthof 1.5 meters (5 feet).

990/991 Test Adapter Spare Parts

Shifts the phase of the
PROX OUT signal by 180ºby changing the voltage
from positive to negative
Isolates the transmitterfrom diagnostic
equipment so that
equipment with different
grounds does not affectthe transmitter's 4-20 mA
loop signal
Reduces noise in thesurrounding area from
affecting the PROX OUT
signal01810700

Battery (9 V alkaline).

02270056

AC adapter. Has universal ac
input to 9 volts dc output. Input
is 108 to 132 Vac with 120 Vac
nominal, or 207 to 253 Vac with
240 Vac nominal.

02198937

Power cord (for North American
ac power outlet).

123133User Guide.

Probe and Transmitter Accessories

02173006

Bulk Cable (specify length infeet). 1.0 mm2 (18 AWG),
2-conductor, twisted, shieldedcable used for the 4 to 20 mA
loop. Also used for the PROX OUT
signal on the 991 Transmitter's
terminal strip.

123655990 and 991 Transmitter
Systems Installation Guide

330153-05

Cable Connector Kit. Package
Includes 1 set of 75 Ω miniature
male and female connectors,
shrink tubing and 3300 Isolator
Seal for protection of coaxial
connectors.

The 990/991 Test Adapter
provides the following benefits:
l

l

l

l

Small size and weight for
portable operation
Battery or ac adapter
power options
Automatic shutoff circuitthat powers down the unit
when the battery is low
2 channels, so that you
can display an orbit for XY
probe configurations.

10/19

991 Thrust Transmitter
Datasheet

163356

Connector Crimp Tool Kit.
Includes one set of 75 Ω ClickLoc
inserts and connector
installation instructions.
Supplied with carrying case.

330951-01

991 Mounting Screws (spares).
Contains 4 screws.

284726

DIN rail mounting kit. Installedon the 990 Transmitter to allow
mounting on 35 mm DIN rail

141618 Rev. M

11/19

991 Thrust Transmitter
Datasheet

141618 Rev. M

Graphs and Figures
Note: All dimensions shown in millimeters (inches) unless noted otherwise.

1. Mounting holes, 5.8 mm (0.23 in) diameter, 4 places
2. Bulkhead mount holes, 4 each. 6-32 x 1.326 screws
provided when mounting option specified
Figure 1: 991 Thrust Transmitter Dimensions (Top View)

1. 35mm DIN rail DIN mount clips (when DIN rail mounting is
specified)Figure 2: 991 Thrust Transmitter Dimensions (Side View)

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991 Thrust Transmitter
Datasheet

141618 Rev. M

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.

Probe tip, 5.26 mm (0.207 in) maximum diameter
Hexagonal nut
Case Thread
Wrench flats75Ω cable, 2.8 mm (0.11 in ) maximum outside diameter,
7.6 mm (0.30 in) maximum outside diameter of armor
Miniature male coaxial connector, 7.23 mm (0.285 in)maximum outside diameter “D”
Unthreaded length “A”
Case length “B”
2.92 mm (0.115 in) maximum
Total length “C”, +30%, -0%

Figure 3: 3300 NSv Proximity Probes, Standard Mount
330901, 1/4-28 UNF-2A, without armor
330902, 1/4-28 UNF-2A, with armor
330903, M8x1 thread, without armor
330904, M8x1 thread, with armor
330905, M10x1 thread, without armor
330908, 3/8-24 UNF-2A, without armor
330909, 3/8-24 UNF-2A, with armor
330910, M10x1 thread, with armor
Standard mount 1/4-28 UNF thread probes are supplied with a 7/16 inch lock nut and 7/32
inch wrench flats. Standard mount M8x1 thread probes are supplied with a 13 mm lock nut
and 7 mm wrench flats. Standard mount 3/8-28 UNF thread probes are supplied with a 9/16
inch lock nut and 5/16 inch wrench flats. Standard mount M10x1 thread probes are suppliedwith a 17 mm lock nut and 8 mm wrench flats.

13/19

991 Thrust Transmitter
Datasheet

141618 Rev. M

1.
2.
3.
4.

12 mm (0.49 in) maximum diameter
36.3 mm (1.43 in) maximum
51.1 mm (2.01 in) maximum
Connector protector (fluorosilicone material)

Figure 4: Installed Connector Protectors

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991 Thrust Transmitter
Datasheet

141618 Rev. M

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.

Probe tip, 5.26 mm (0.207 in) maximum diameter
Hexagonal nut
Case thread75Ω cable, 2.8 mm (0.11 in) outside diameter
Miniature male coaxial connector, 7.23 mm (0.285 in)maximum outside diameter “D”
5.08 mm (0.20 in)
Unthreaded case length “A”, 5.08 mm (0.20 in)Case length “B”, 30.48 mm (1.20 in)
2.92 mm (0.115 in) maximum
Total length “C”, +30%, -0%

Figure 5: 3300 NSv Proximity Probes, Reverse Mount
330906, 3/8-24 UNF-2A
330907, M10x1 thread
Reverse mount probes are not available with armor or connector protector options.

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991 Thrust Transmitter
Datasheet

141618 Rev. M

1. 7.2 mm (0.285 in) maximum diameter
2. Miniature male coaxial connector
3. FEP-coated or uncoated armor, armor length is 300 mm(11.8 in) less than cable length
4. 75Ω cable, 2.80 mm (0.11 in) maximum outside diameter,
7.6 mm (0.30 in) maximum outside diameter of armor, 7.0
mm (0.275 in) maximum outside diameter of uncoatedarmor
5. Stainless steel ferrules, 8.4 mm (0.33 in) diameter
6. FEP-insulated coaxial cable
7. Miniature female coaxial connector
8. Cable length +20%, -0%
Figure 6: 3300 NSv Extension Cable

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991 Thrust Transmitter
Datasheet

141618 Rev. M

1.
2.
3.
4.
5.
6.

To test adapter 122115-01
Receiver
Cable shield
Transmitter
Extension cable
Recommended wiring is shielded, twisted-pair, 1.0 mm (18AWG) (part number 02173006). Maximum length is 13 km(8 miles).
7. Power supply, VPS = 17 to 35 Vdc

8. Common (ground)
9. Probe
Figure 7: 991 Thrust Transmitter Loop Wiring Connections
The phase of the PROX OUT signal is inverted from the standard for Bently Nevada
products. Also, connecting grounded ac-powered equipment to PROX OUT may result in a
false alarm. Use test adapter 122115-01 to connect ac equipment to the transmitter. Note thatthe 122115-01 also inverts the PROX OUT signal.

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991 Thrust Transmitter
Datasheet

141618 Rev. M

1. Maximum loop resistance in ohms (RLOOP)
2. Power supply voltage (VPS)
3. Operating region
Figure 8: 991 Thrust Transmitter Maximum Loop ResistanceRLOOP = 43.5 x (Vps – 12) W maximum. If the maximum loop resistance is exceeded, then thefull scale current does not reach 20 mA.

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991 Thrust Transmitter
Datasheet

141618 Rev. M

Copyright 2024 Baker Hughes Company. All rights reserved.

Bently Nevada, M2, Proximitor, System 1 and Orbit Logo are registered trademarks of Bently Nevada, a Baker Hughes
business, in the United States and other countries. The Baker Hughes logo is a trademark of Baker Hughes Company.
All other product and company names are trademarks of their respective holders. Use of the trademarks does not
imply any affiliation with or endorsement by the respective holders.
Baker Hughes provides this information on an “as is” basis for general information purposes. Baker Hughes does notmake any representation as to the accuracy or completeness of the information and makes no warranties of any
kind, specific, implied or oral, to the fullest extent permissible by law, including those of merchantability and fitness
for a particular purpose or use. Baker Hughes hereby disclaims any and all liability for any direct, indirect,
consequential or special damages, claims for lost profits, or third party claims arising from the use of theinformation, whether a claim is asserted in contract, tort, or otherwise. Baker Hughes reserves the right to makechanges in specifications and features shown herein, or discontinue the product described at any time without
notice or obligation. Contact your Baker Hughes representative for the most current information.
The information contained in this document is the property of Baker Hughes and its affiliates; and is subject tochange without prior notice. It is being supplied as a service to our customers and may not be altered or its content
repackaged without the express written consent of Baker Hughes. This product or associated products may becovered by one or more patents. See Bently.com/legal.

1631 Bently Parkway South, Minden, Nevada USA 89423
Phone: 1.775.782.3611 (US) or Bently.com/support
Bently.com

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