4000 Series Air Gap Sensor System
Datasheet

Bently Nevada Machinery Condition Monitoring

167885 Rev. L

Description
Bently Nevada’s Air Gap monitoring system provides
monitoring and diagnostic capability for all new and existinghydro generators and motor/generators. Air gap monitoringis fully integrated with the 3500/System 1 platform and utilizes
the 3500/46M Hydro Monitor. The 4000 Series air gap sensor
system is available in 20 mm and 50 mm ranges for optimal
resolution across a wide range of measurement
requirements.

Criticality
Air gap is a measure of the distance between rotor and stator
in a hydroelectric generator. Monitoring of air gap is criticallyimportant because both the stator and the rotor on largehydroelectric machines can be quite flexible and their shapeand location are affected by operating centrifugal, thermal,
and magnetic forces. Off-center or out-of-round conditions
will at least reduce operating efficiency and, in more severecases, can lead to damage from magnetically induced
heating or a rotor-to-stator rub.

Measuring Air Gap
Air gap monitoring utilizes multiple specially designed
capacitive proximity probes that are mounted on the innerbore of the generator stator in one or more planes.
Measurements are made from the stator bore to each rotor
pole as the rotor turns. Minimum air gap dimension andlocation along with rotor shape are directly measured during
unit operation. Stator shape is calculated utilizing themultiple air gap probes. The air gap monitoring systemprovides operations and maintenance personnel with early
warning of impending problems with shape andconcentricity of the generator rotor and stator.

4000 Series Air Gap Sensor System
Datasheet

167885 Rev. L

Typical Benefits
Air gap dimensions along with rotor and stator
shape cannot be effectively measured with thegenerator out of service because of the
combined effects of centrifugal, thermal, andmagnetic forces. Early detection of air gap
anomalies will facilitate condition-based
maintenance by allowing the user time to plan
for repairs before scheduled outages. Long
term trending of gap and shapes can becorrelated with operating conditions and usedin operational and rehabilitation planning.
Knowing the rotor and stator shapes andminimum air gap dimensions will provide theoperator with the information needed toremove a machine from service before serious
damage like that from a rotor stator ruboccurs.

Air Gap Probe and Extension Cable
The 4000 series Air Gap probe is designed formaximum survivability in the harshest hydrogenerator environment. It can continuallyoperate and maintain its accuracy intemperatures up to +125 ºC (+257 ºF). Theprobe can also continually operate andmaintain its accuracy in the 1.5 Tesla magnetic
field often experienced between the rotor poleand the stator. ClickLoc connectors comestandard on both the probe and extension
cable to prevent loosening of the connectors.

Proximitor Sensor
The 4000 series Air Gap Proximitor Sensor isbased upon our best selling 3300 XL Proximitor
Sensor technology. The Proximitor Sensor uses
a DIN rail connection to ease installation and tominimize the number of cumbersome screws
required when working around the hydrogenerator. The grounding stud on theProximitor Sensor features a safety thread inorder to ensure the locking nut does not
inadvertently fall off during the installation of
the ground wire on the extension cable.

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4000 Series Air Gap Sensor System
Datasheet

167885 Rev. L50 mm
SystemSpecifications
Unless otherwise noted, these
specifications are for a 4000 Series Air
Gap Proximitor Sensor, extension
cable, and probe between 0 ºC and+50 ºC (+32 ºF to +122 ºF), with a +24
Vdc power supply, and a 10kΩ load.

Average Scale Factor (ASF)

Electrical
Proximitor
Sensor Input

Accepts one non-contacting
4000 Series Capacitive Probeand Extension Cable.

Power45.7 mm (1800 mils). Linear
range begins at approximately
5.1 mm (200 mils) from the faceof the probe and is from 5.1 to50.8 mm (200 to 2000 mils)(approximately +1 to +10 Vdc).

20 mm
System0.50 V/mm (12.5 mV/mil),nominal50 mm
System0.20 V/mm (5.0 mV/mil),nominal

Deviation from a Straight Line
20 mm
SystemRequires +23.25 Vdc to +24.75
Vdc at 85 mA maximum
consumption.

Less than ±1.02 mm (±40 mils)
with system between 0 ºC and+50 ºC (+32 ºF and +122 ºF).

50 mm
SystemSupplySensitivity

Less than 2 mV change inoutput voltage per volt change
in input voltage.

Less than ±2.54 mm (±100 mils)
with system between 0 ºC and+50 ºC (+32 ºF and +122 ºF).

Frequency
Response

OutputResistance

0 to 2.0 kHz: +0, -3 dB typical withup to 305 metres (1000 feet) offield wiring.

50 Ω ± 5%.

Mechanical

Extension
Cable
75.5 pF/m (23.0 pF/ft) typical.
Capacitance
0.2 to 1.5 mm2 (16 to 24 AWG).

Field Wiring

Recommend using twoconductor shielded cable.
Recommended maximum
length of 305 metres (1000 feet)between the 4000 Series
Proximitor Sensor and themonitor.

Linear Range

20 mmSystem

18.3 mm (720 mils). Linear range
begins at approximately 2 mm(80 mils) from the face of theprobe and is from 2 to 20.3 mm(80 to 800 mils) (approximately+1 to +10 Vdc).

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Probe
Material

FR4 type material

Probe andExtension
Cable
Material

75 Ω triaxial, fluoroethylene
propylene (FEP) cable

Proximitor
SensorMaterial

AluminumTensileStrength(maximumrated)

312 N (70 pounds) probe lead toprobe. 89 N (20 pounds) at
probe lead to extension cableconnectors

Connector
Material

Gold-plated brass and goldplated beryllium copper4000 Series Air Gap Sensor System
Datasheet

167885 Rev. L

Environmental Limits

Connector-to-connector Torque
Recommended
Finger tight.
TorqueMaximum
Torque0.565 N•m (5 lbf•in).

Minimum Bend
Radius25.4 mm (1.0 in).

Probe Temperature Range
Operating
0 to +125 ºC (+32°F to +257 ºF).
Temperature
Storage-35°C to +125 ºC (-31°F to +257
Temperature ºF).

System Mass (typical)
Probe

Approximately 140 g (0.3 lbs).

Extension Cable Temperature Range

Extension
Cable

Approximately 320 g (0.7lbs).

Operating
0°C to +125ºC (+32°F to +257ºF).
Temperature

Proximitor
SensorApproximately 380 g (0.8lbs).

Storage-35°C to +125 ºC (-31°F
Temperature to+257ºF).
Proximitor Sensor Temperature Range
Operating
0°C to +70ºC (+32°F to +158ºF).
TemperatureStorage-35°C to +85ºC (-31°F toTemperature +185ºF).

Relative
Humidity

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Less than a 5% change inaverage scale factor whentested in 93% humidity inaccordance with IEC standard
60068-2-78 for up to 56 days.

4000 Series Air Gap Sensor System
Datasheet

167885 Rev. L

Compliance andCertifications
FCC
This device complies with part 15 of theFCC Rules. Operation is subject to thefollowing two conditions:ll

This device may not cause harmfulinterference.
This device must accept any
interference received, includinginterference that may cause
undesired operation.

RoHS
RoHS Directive 2011/65/EU

EMC
EMC Directive 2014/30/EU

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4000 Series Air Gap Sensor System
Datasheet

167885 Rev. L

B: Linear Range Option

Ordering Information

02

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

20 mm (0.8 inches)4000 Series Extension Cable
400130 Air Gap 50 mm Extension Cable

4000 Series Air Gap Probes

400230 Air Gap 20 mm Extension Cable

400102 Air Gap 50 mm Probe

Product Number-AAA
A: Cable Length Option

400202 Air Gap 20 mm Probe100

Product Number–AAAccessories

A: Cable Length Option
01

Standard, 18 inches

167684

Includes:llllll

Air Gap Transducer System
Operation User Guide+24 Vdc Power Supply. Typically 2sensor systems will be powered by
1 power supply in each Proximitor
02200627
Housing. The power supply iscapable of running 4 sensor
systems.

Air gap probe with integral cable andconnector
Teflon conduit, 12.7 mm (1/2 inch)
diameter, 431 mm (17 inch) longLoop strap clamp and 1/4 - 20 boltTube of silicon adhesive (12 month shelflife)
Adhesive applicator
Two (2) fiberglass spacers (for 50 mm air
gap probes only)

4000 Series Air Gap Proximitor
Sensor

3301813300 XL Proximitor Housing.
Suggested configuration is 33018101-00-01-00-00; a housing with DIN
mount hardware, no conduit
fitting, standard 2.34 mm (0.092 in)gland plate thickness, no terminal
blocks, and no approvals. Typically
2 sensor systems and 1 power
supply will be located in eachhousing. The housing is capableof holding 1 power supply and 4
Proximitor Sensors.

02173006

Bulk Cable (specify length in feet)
1.0 mm2 (18 AWG), 2-conductor,twisted, shielded cable used for thePROX OUT signal on the Air Gap
Proximitor Sensor terminal strip.

400100 Air Gap 50 mm Proximitor Sensor
400200 Air Gap 20 mm Proximitor Sensor
Product Number-AAA-BB
A: Cable Length Option
100

10.0 metres (33 feet) system
length

10.0 metres (33 feet) system
length168448-01 Air Gap Verification Kit.

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4000 Series Air Gap Sensor SystemDatasheet

1738737-inch PEEK cable ties suitable forhydro generator environments,
bag of 50

167276

Tube of silicon adhesive (12 monthshelf life)

167885 Rev. L

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4000 Series Air Gap Sensor System
Datasheet

167885 Rev. L

Graphs and Figures
Unless otherwise specified, dimensions are in mm (inches).

Figure 1:

Typical Air Gap 20 mm Proximitor Sensor Over Temperature

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4000 Series Air Gap Sensor System
Datasheet

Figure 2:167885 Rev. L

Typical Air Gap 50 mm Proximitor Sensor Over Temperature

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4000 Series Air Gap Sensor System
Datasheet

Figure 3:167885 Rev. L

Typical Air Gap 20 mm Probe Over Temperature

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4000 Series Air Gap Sensor System
Datasheet

Figure 4:167885 Rev. L

Typical Air Gap 50 mm Probe Over Temperature

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4000 Series Air Gap Sensor System
Datasheet

167885 Rev. L

Figure 5: Typical Air Gap 20 mm Cable Over Temperature

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4000 Series Air Gap Sensor System
Datasheet

Figure 6:167885 Rev. L

Typical Air Gap 50 mm Cable Over Temperature

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4000 Series Air Gap Sensor System
Datasheet

Figure 7:167885 Rev. L

Typical Air Gap 20 mm Sensor System Over Temperature

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4000 Series Air Gap Sensor System
Datasheet

Figure 8:167885 Rev. L

Typical Air Gap 50 mm Sensor System Over Temperature

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4000 Series Air Gap Sensor System
Datasheet

167885 Rev. L

Figure 9: Air Gap Frequency Probe

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4000 Series Air Gap Sensor System
Datasheet

167885 Rev. L

Figure 10:

Air Gap 20 mm Probe

Figure 11:

Air Gap 50 mm Probe

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4000 Series Air Gap Sensor System
Datasheet

167885 Rev. L

Figure 12:

Air Gap 20 mm or 50mm Extension Cable

Figure 13:

Air Gap 20mm or 50 mm Proximitor Sensor

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4000 Series Air Gap Sensor System
Datasheet

167885 Rev. L

Figure 14:

Air Gap Verification Fixture

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4000 Series Air Gap Sensor SystemDatasheet

167885 Rev. L

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imply any affiliation with or endorsement by the respective holders.
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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
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