Download - Centrifugal Compressor Impeller

Buffalo State College

Mechanical Engineering Technology

Senior Design Project Proposal

Spring 2015

Centrifugal Compressor Impeller

Tip-to-Shroud Measurement System

Sponsor: FS-Elliott Co. LLC

Date Presented: March 10, 2015

Design Team:

Morgan Allis _________________________

Chuck Mantell _________________________

Bradley Brooks _________________________

Jeff Villont _________________________

FS-Elliot Design Proposal Buffalo State College


ABSTRACT

This project will introduce sensor technology to measure impeller-tip-to-shroud clearance

into FS-Elliott’s Polaris+ centrifugal air compressor model P300. FS-Elliott Co., LLC, is a

leading centrifugal air compressor manufacturer with manufacturing locations around the world.

FS-Elliott is seeking solutions to maximize efficiency of their compressors by controlling and

monitoring distances between impeller blade tip and compressor shroud; the first step to this is

installing a sensor to measure impeller tip clearance. This project will explore different sensing

options to measure blade tip to shroud clearance. FS-Elliott will receive a package including

optimal sensing recommendations, product installation into their P300 compressor, and cost

analysis.



TABLE OF CONTENTS

Section Title Page Number

LIST OF FIGURES 1.0 4

LIST OF TABLES 2.0 5

INTRODUCTION 3.0 6

P300 COMPRESSOR 4.0 8

GUIDELINES 5.0 12

SENSOR TECHNOLOGY 6.0 13

CAPACITIVE 6.1 13

INDUCTIVE 6.2 15

LASER DOPPLER 6.3 16

EDDY-CURRENT 6.4 18

FIBER OPTICAL 6.5 20

VARIABLE RELUCTANCE SENSOR (VR) AND HALL EFFECT 6.6 22

Variable Reluctance 22

Hall Effect 23

PHOTOELECTRIC SENSOR 6.7 25

MICROWAVE DISTANCE SENSOR 6.8 27

RESTRICTIONS 7.0 28

CHOSEN DESIGN 8.0 28

CAUSE AND EFFECT MATRIX 8.1 29

PROJECT MANAGEMENT 9.0 30

APPENDIX 10.0 31

REFERENCES 11.0 32



LIST OF FIGURES 1.0

FIGURE 3.1. A CENTRIFUGAL COMPRESSOR IN THE MANUFACTURING PROCESS 6

FIGURE 3.2. AN INTERNAL VIEW OF A COMPRESSOR BEING ASSEMBLED AT FS-ELLIOTT’S MANUFACTURING

FACILITY 7

FIGURE 4.1. FS-ELLIOLTT’S P300 COMPRESSOR SHOWING OUTBOARD (A.) AND INBOARD (B.) VIEWS 8

FIGURE 4.2. A LOOK AT INTERNAL COMPONENTS OF FS-ELLIOTT’S P300 COMPRESSOR 9

FIGURE 4.3. TYPICAL OPERATION FLOW-DIAGRAM OF FSE’S P300 COMPRESSOR 10

FIGURE 5.1. SENSOR PROBE INSTALLATION ANGLE 12

FIGURE 6.1.1. POSSIBLE CAPACITIVE SENSOR PROBES 14

FIGURE 6.2.1. INDUCTIVE SENSOR PROBE 15

FIGURE 6.3.1. FIBER OPTIC LASER DOPPLER SYSTEM 17

FIGURE 6.4.1. TWO BODY STYLE EDDY-CURRENT PROBES 19

FIGURE 6.5.1. PHOTO OF MONARCH OPTICAL SENSOR 21

FIGURE 6.6.1. IN A VR SENSOR, THE RESULTING ANALOG SIGNAL MUST BE FILTERED AND

THRESHOLDED TO YIELD A USEFUL PULSE OUTPUT 22

FIGURE 6.6.2. IN A HALL-EFFECT SENSOR, ALL LOW-LEVEL SIGNAL PROCESSING IS PERFORMED ON

THE SILICON CHIP HOLDING THE TRANSDUCER 23

FIGURE 6.6.3. WAYS THAT SENSORS TAKE THEIR READING FROM ROTATING OBJECT 24

FIGURE 6.7.1 PHOTO OF PHOTOELECTRIC SENSOR 26

FIGURE 6.8.1 MICROWAVE SENSOR DIAGRAM 27

FIGURE 8.1. SIMPLIFIED SCHEMATIC OF HB-01 30



LIST OF TABLES 2.0

Table 8.1 Cause and Effect Matrix 29

Table 9.1. Gantt chart for project management section of our design 31



INTRODUCTION 3.0

FS-Elliott Co., LLC is a leading manufacturer of oil-free centrifugal air and gas

compressors with sales, service, and manufacturing locations around the world. They

manufacture a variety of air compressors that range from 450 HP (335 kW) to 2500 HP (1864

kW) and 2090 CFM (987 l/sec) to 11500 CFM (5430 l/sec), As shown in FS-Elliott Co., LLC

Polaris+ (2014). Markets and industries they serve include air separation,

chemical/petrochemical, electronics, general industry, medical, mining, oil and gas,

pharmaceutical, and refining.

Turbo machinery is widely used with countless applications. Efficient aerodynamics

makes centrifugal compression ideal for many industrial applications. Centrifugal compressors

produce pressure by transferring energy from a rotating impeller to the air. Centrifugal

compressors are efficient, low maintenance with minimum wearing parts, low vibration, and

have excellent reliability over extended periods of time. FS-Elliott Co., LLC Polaris+ (2014).

Figure 3.1. A centrifugal compressor in the manufacturing

process

at FS-Elliott’s manufacturing facility in Export,

PA

This project will specifically deal with FS-

Elliott’s Polaris+ P300 centrifugal compressor. This

compressor is a medium to small multi stage compressor with three stages of compression. P300



compressors range from 250-450 hp (186-335 kW) and flow rates of 900-2090 CFM (424-986

l/sec), and a discharge pressure of 45-150 psi (310-1034 kPa). FS-Elliott Co., LLC Polaris+

(2014).

This project involves introduction of a sensor that will measure impeller tip-to-shroud

clearance on FS-Elliott’s P300 centrifugal compressor. Numerous sensing technologies will be

analyzed based on characteristics including cost, size, resolution, temperature rating, surface

area, installation, electronics, durability, life expectancy, sensitivity to contamination, and need

for calibration. FS-Elliott will receive design recommendations based on six-sigma matrix, 3D

model of design, and project management analysis for the project. Successful introduction of

sensor technology into FS-Elliott’s centrifugal compressors could lead to further control of

impeller tip-to-shroud distances by means of actuation.

Figure 3.2. An Internal view of a compressor being assembled at FS-

Elliott’s manufacturing facility

1. Driving bull gear for centrifugal

compressor

2. Driven pinion gear in which compressor impeller will be mounted

P300 COMPRESSOR 4.0



FS-Elliott’s P300 compressor is a medium to small size, oil free, multi stage compressor,

with three stages of compression. The P300 is the smallest centrifugal compressor that FS-Elliott

manufactures and also has the highest rotational impeller speed as shown in FS-Elliott Co., LLC

P-300 (2008).

Rotational impeller speeds range from 51,310 rpm at low speed and 68,414 rpm at high

speed. The P300 compressor has 15 full and 15 splitter blades in its 1st stage of compression, and

17 blades in its 2nd and 3rd stages of compression. It operates at or below a temperature of 350°F

(177°C). FS-Elliott Co., LLC P-300 (2008).

Figure 4.1. FS-Ellioltt’s P300 compressor showing Outboard (a.) and Inboard (b.) views, as shown by Smith, D.,

Tursky, M., Wellek, R. (2013).



Figure 4.2. A look at internal components of FS-Elliott’s P300 compressor, as shown, in Smith, D., Tursky, M.,

Wellek, R. (2013).

1. Pinion (driven gear), attached to the impeller.

2. Bull gear (driving gear), connected to engine output, and drives impeller pinion.

3. Impeller, consisting of 15 or 17 blades, moves air in a rotational direction to

diffuser plates.

4. Diffuser plates, causing a decrease in velocity allowing for pressure to increase.

5. Shroud of compressor, component concerned with impeller tip clearance.



Operation of the P300 compressor consists of ambient air entering an inlet control into its

first stage of compression. A centrifugal impeller accelerates air and then velocity is slowed and

pressure in increased, by means of a diffuser. Air then enters a bundle tube heat exchanger for

cooling. The following diagram shown in (FSE P300 brochure), demonstrates the typical

operation of FS-Elliott’s P300.

Figure 4.3. Typical operation

flow-diagram of FSE’s P300 compressor,

as shown in FS-Elliott Co., LLC P-300

(2008).

1. Ambient air entering inlet control

2. Air accelerated by first impeller. Temperature and velocity rise, before a radial

diffuser plate slows velocity and creates pressure.

3. Hot air enters first stage of intercooling. Air passes over water filled tubes with fins.

4. Air makes two 90-degree turns begins to flow upward, allowing separation of

condensed moisture from cooled air.

5. Air exiting heat exchanger and flowing through second inlet control device for

second stage of compression.



6. Air discharging form second stage of compression, enters second intercooler,

identical to the first.

7. Air then moves into third stage impeller, diffuser and scroll casing

8. Air finally discharges from final intercooler into the air system



GUIDELINES 5.0

Design requirements that must be met include: temperature tolerance, sensing

resolution/accuracy, target size, target frequency and probe size. The sensor must be able to

function in temperature up to 350° F. The sensor must also be small enough so that it can easily

be installed inside the compressor housing. It should be noted that because there is very little

area (0.09”) of the impeller that could be perpendicularly accessed by a sensor, the face of the

sensor would be unable to be flush with the inside of the shroud and therefore the sensor would

have to sit back inside the casing; this would lead to calibration at installation. Most importantly,

the sensor must have a relatively low target area to sensor tip ratio and be able to work with an

uninform target area, or in other words, a target area that is constantly entering and exiting the

target region with some frequency. The required operating frequency is 8500-20,000 Hz.

Because it is important that the shroud-

to-tip distance measured is from the furthest

outmost point on the impeller, the sensor probe

will be installed in a diagonal fashion to the

shroud and will be placed is such a fashion that it

will detect the furthest most impeller radius. The

arrow in figure 4.1 demonstrates the approximate

angle at which the probe will be placed. The tip

of the arrow signifies what part of the sensor will

be detected.

Figure 5.1. Sensor probe installation angle, as

shown in Smith, D., Tursky, M., Wellek, R. (2013).



SENSOR TECHNOLOGY 6.0

Sensors that have been used to measure impeller-tip-to-shroud clearance include: x-ray,

capacitive, inductive, optical, eddy-current, microwave, acoustic, and fiber optic laser Doppler.

Capacitive 6.1

Capacitive sensors are arguably the most common sensing technology used to measure

turbo machinery impeller-tip-to-shroud clearance. Noncontact capacitive sensors work by

measuring changes in capacitance As a general rule, the target should be 30-50% larger than the

capacitance sensor; the further the probe is from the target, the larger the minimum target size. A

conductive target area is necessary for a conductive sensor, but provided that the target is

conductive the specific target material does not affect capacitive sensors. Because the sensing

electric field stops at the surface of the conductor, target thickness does not affect the

measurement. Additionally, they can measure high frequency motions because no part of the

sensor needs to stay in contact with the object.

Pros: As with any sensing technology capacitive sensors have advantages and

disadvantages. A significant strength of capacitive sensors is their ability to resolve

measurements below 0.001 in., at a fraction of the cost of other high performance sensing

technologies. Their simple design allows for use in extreme environments while still

maintaining accuracy. Furthermore, they are a versatile sensor- able to be used in various

applications. They are immune to target composition and work equally well on all

conductive targets, unlike eddy current probes. Lastly, they are immune to ultrasonic

noises, lighting conditions, humidity and temperature for the most part.

Cons: A major disadvantage of capacitance sensors is that the probe must be mounted

close to the target, not a problem relevant to the application at hand. Furthermore,



capacitive sensors must be kept in a mostly sterile environment, free of dirt and debris,

and therefore frequent cleaning may be necessary. These sensors are usually not used

where fluids, or splatter of fluids is present.

Probe Cost: $100.00-$300.00

Cost of Electronics: TBD

Size: 0.125”-0.50”

Total Cost: TBD

Target Frequency: Up to 250,000 rpm

Target Area: 33% of probe head size

Temp. Range: -70°-1500° F

Figure 6.1.1. Possible Capacitive Sensor Probes, Lion Precison, (2014)

Inductive 6.2

Inductive sensors are non-contact detection devices that require a metallic target at ranges

under 2 in. The sensor emits an alternating electro-magnetic sensing field which when disrupted

by a magnetic target passing through, eddy currents are induced, which in turn reduces the signal

amplitude and triggering a change of state at the sensor output- thus measuring displacement.

Pros: Inductive sensors are not affected by water, oil, dirt, and non-metallic particles. They are

insensitive to target color or target surface finish. Also, the sensors are very short-circuit



resistant. Furthermore, inductive sensors have the ability to withstand high shock and vibration

environments.

Probe Cost: TBD

Cost of Electronics TBD

Total Cost: TBD

Size: 0.125”-0.50”

Target Frequency: Electronics Dependent

Target Area: Equal to or greater than the sensor face

Temp. Range: -40°- 446° F

Figure 6.2.1. Inductive Sensor Probe, Lion Precision (2015)

Laser Doppler 6.3

Capacitive and inductive probes are usually employed for tip clearance measurements

because they are robust and cheap, but when accuracies above 0.001” are required fiber optic

laser Doppler sensing technology can be applied. Unfortunately, fiber optic Doppler distance

sensing technology is not common practice and therefore is an in-house assembled system.

Because the system is not a manufactured package it is a costly. The laser Doppler

measurement sensor consists of an optical head, a light-source unit, and a detection unit (see

figure 1). While this technology meets all the design requirements it is very costly in contrast

to other sensor options.

Probe Cost: TBD




Total Cost: Greater than $2000.00

Size: TBD

Target Frequency: TBD

Target Area: TBD


Figure 6.3.1. Fiber Optic Laser Doppler System, Pfister Thorsten (2008)



Eddy-Current 6.4

Eddy-current sensing technology is well established and therefore one of the cheapest

sensing technologies. Eddy-current sensors are noncontact devices capable of high-resolution

distance measurement. Tolerance to heat and dirty environments is very high. With eddy-current

sensors the spot size (the area that will be detected) must be 33% larger than the sensing element

diameter. This results in a cone shaped cylinder from the point of the end of the sensor to the

inside surface of the shroud. Compared to other noncontact sensing technologies eddy-current

sensors have some distinct advantages: high tolerance to dirty environments, higher temperature

tolerances, not sensitive to material in the gab between the probe and target, and they are less

expensive than most other sensors. A major drawback to eddy-current sensing technology is that

the target area must have infinite frequency (be solid). The only way it would be able to be used

in the specific impeller tip clearance application is for it to measure the back of the impeller and

to be calibrated based on the static shroud to sensor displacement- this is a cumbersome

approach.

Probe Cost: $100.00-$300.00


Total Cost: TBD

Size: 0.125”-0.50”

Target Frequency: Infinite

Target Area: 33% larger than probe face




Figure 6.4.1. Two Body Style Eddy-Current Probes, Lion Precision (2015)

Fiber Optical 6.5

A fiber optic sensor works by converting light rays into electronic signals. It measures the

physical quantity of light and then translates it into a form that is readable by an instrument. An

optical sensor is generally part of a larger system that integrates a source of light, a measuring

device and the optical sensor. This is often connected to an electrical trigger. The trigger reacts to

a change in the signal within the light sensor. An optical sensor can measure the changes from

one or several light beams. When a change occurs, the light sensor operates as a photoelectric

trigger and therefore either increases or decreases the electrical output. Optical switches are

optoelectronic devices which can be integrated with integrated or discrete microelectronic

circuits.

In general, the optical sensors have the best resolution using triangulation method and they

also have the highest system bandwidth. But optical sensing technology, compared with other

technologies, is relatively complex, expensive, bulky, and are sensitive to contamination. Also,

another downfall could be the lack of light that’s needed to take these measurements.

Probe Cost: $151.90 for the probe


Total Cost: TBD

Size: 0.256” D

Target Speed: 1-250,000 RPM



Target Area:

Resolution:

Temp. Range: -10 to 250 F

Figure 6.5.1 Photo of Monarch optical sensor shown in, Remote Optical Sensor (2015).



Variable Reluctance Sensor (VR) and Hall Effect 6.6

Many sensor technologies are out there on the market to measure speed of a rotating

object and can also be used to measure distance away. For many applications especially those

that operate in extreme environments the choice often comes down to either Hall-effect or

variable-reluctance (VR) speed sensors as said by Ed Ramsden (2000). Sensors based on either

of these technologies can be applied in both conditions, with both extreme heat and extreme

cold. These sensors can maintain function even in the presence of dirt and debris. For these

reasons our group has found these two sensors to be extremely important to thoroughly research

in our continuation of sensor research.

VR sensors

In its most basic form, a VR sensor consists of a coil of wire wrapped around a magnet as

shown in Fig5.7.1. As gear teeth (or other target features) pass by the face of the magnet, they

cause the amount of magnetic flux passing through the magnet and consequently the coil to vary.

Figure 6.6.1. In a VR sensor, the resulting analog signal must be filtered and thresholded to yield a

useful pulse output Ed Ramsden (2000).

When a target feature such as an impeller blade is moved close to the sensor, the flux is at

a maximum. When the target is further away, the flux drops off. The moving target results in a



time-varying flux that induces a proportional voltage in the coil. Electronics are then used to

massage this signal to get a digital waveform that can be more readily counted and timed. One

area in which VR sensors stands out, is in high-temperature applications which we are somewhat

dealing with. With appropriate construction VR sensors can be made to operate at temperatures

up to and possibly higher than 300°C. Ed Ramsden (2000).

Hall-effect sensors

In a Hall-effect speed sensor the Hall-effect transducer element detects target-induced

flux changes from where it is situated, between the magnet and the target being measured.

Unlike a VR sensor, however, a Hall sensor is sensitive to the magnitude of flux, not its rate of

change.

Figure 6.6.2. In a Hall-effect sensor, all low-level signal processing is performed on the silicon chip

holding the transducer from Ed Ramsden (2000).

This feature of Hall-effect technology allows you to make speed sensors that can detect

targets moving at arbitrarily slow speeds, or even the presence or absence of nonmoving targets

as noted by Ed Ramsden (2000). This can be useful if we test the sensor when the machine is at

rest, or cold. An important feature of Hall-effect speed sensors is that the signal-processing

electronics are typically included into the same package as the transducer, providing several

tangible benefits. The most important is that little or no additional signal-processing circuitry is



required--most Hall-effect speed sensors directly provide a digital output signal that is directly

compatible with digital logic, microcontrollers, and PLC.

Figure 6.6.3.

Ways that

sensors take their reading from rotating object as shown from www.daytona-

twintec.com/tech_sensors (2015).

Hall Effect Sensor Cost: $150-$250

Electronics Cost: TBD

Total Cost: TBD

Size: 0.472” D

Target Speed: TBD

Area: TBD

Temp. Range: -40-150oF

Variable Reluctance

Probe Cost: $100-$200 range

Electronics Cost: TBD

Total Cost: TBD

Size: 0.375” D

Target Speed: TBD



Target Area: TBD

Resolution TBD

Temp. Range: Can handle in excess of 300oC

Photoelectric Sensor 6.7

Proximity photoelectric sensors use the target as the reflector to measure displacement

which can be useful in our application due to wanting to find how far away the impeller is.

Presence is detected when any portion of the reflected signal bounces back from the detected

object. Reflective properties of the target must be evaluated for correct placement, as these

sensors can be affected by target material and surface properties as noted in the article by IHS

Engineering 360 (2015). Convergent proximity photoelectric sensors are used to focus the

emitter beam at a fixed distance from the sensor which we can measure when it is broken and

how far back its path is broken. This allows for good sensitivity but limited depth of detection

which is okay for the system at hand. This sensor is small in size and does not require much

technology to obtain readouts.

A major downfall to the photoelectric sensor is that it more likely than not can be used

while the compressor is operational; which is an option FS-Elliot would like to have if possible.

The speed that the impellor will rotate at is much too great for what the sensors is rated for

reading at.

Cost: Unit in Figure 5.8.1 is $7.50

Size: 60 x 20.5mm/ 2.4" x 0.8"

Target Speed:

Target Area:

Temp. Range:



Figure 6.7.1 Photo of photoelectric sensor from

Amazon (2015), seller is Lantee Limited Sales.

Microwave Distance Sensor 6.8

A microwave measure system can be defined as systems that are coupled together with a

transmission line having a uniform cross section. The concept of traveling electromagnetic

waves on that transmission line is fundamental to the understanding of microwave

measurements. The particular sensor being considered for this project is the 300 kHz Ultrasonic

microwave distance sensor, model TA030013. Some of the technical aspects of this device are

that it has a sensibility factor of -70db, a bandwidth of 25 kHz, and has an operating temperature



between -40 to +80 degrees Celsius.

Figure 6.8.1 Microwave sensor diagram as shown from 300Khz Ultrasonic Microwave Distance Sensor(2015).

Strengths A. Small size and light weight

B. Low power consumption

C. High Reliability

Weakness

A. Bad temperature range

B. Not really a probe may be hard to correctly assemble inside the compressor



CHOSEN DESIGN 8.0

Table 8.1 Cause and Effect Matrix

Rating of Importance to

Customer

7 7 7 8 8 10 10

Sensor Type Pro

be

Co

st

Elec

tro

nic

s C

ost

Tota

l Co

st

Res

olu

tio

n

Targ

et A

rea

Max

imu

m

Tem

per

atu

re

Req

uir

ed

Targ

et

Freq

uen

cy

Weighted Totals

1 Capacitive 5 5 5 3 5 5 5 269

2 Inductive 5 5 5 3 5 5 1 229

3 Optical 3 3 3 5 4 5 5 235

4 Eddy-

Current 5 5 5 3 2 5 5

245

5 Microwave 3 3 3 3 4 5 5 219

6

Fiber Optic Laser

Doppler 1 1 1 5 4 5 5

193

7 VRS 4 4 4 3 5 5 5 248

Using the cause and affect matrix it is determined that capacitance sensor technology will

be used (See the appendix for the weighted scales used in the matrix). Two suppliers will be used

in conjunction with each other, Aerogage Inc. and Capacitec, Inc. Aerogage will supply all

necessary electronics while Capacitec will supply the probes. Aerogage will supply the model

HB-01 hi-band amplifier, an amplifier that has been used for similar applications. The HB-

01amplifier is designed to be coupled with capacitor sensor. The HB-01 contains a low-noise,

high-efficiency switching power supply, which generates a dc voltage of approximately 100

volts for biasing the capacitive probe. The output stage of the HB-01 is capable of driving 50-

ohm cables up to 1000 feet or more in length. The bandwidth of the system is about 5 MHz,

which covers most applications between 150,000-200,000 rpm.



Because the blade and probe will be at an angle from each other the calibration will be

affected, but not the ability to measure the tip clearance. Because capacitance versus the gap

relationship is affected by the size of the blade and the size of the active sensing area of the

probe, a calibration process is required to determine the exact relationship; the angle of the probe

will be automatically included in this process. The resolution of the system is 1% of the target

area distance.

Figure 8.1. Simplified Schematic of HB-01

A capacitive sensor, shown as Cs in Figure 7.1, consists of a electrode plus the grounded

target, the compressor blade. The HB-01 manual states, “this structure can be modeled as a

grounded capacitor, whose capacitance changes (increases) when a blade passes in front of the

sensor. A coaxial cable connects the sensor capacitor, Cs, to the HB- 01 Hi-Band Preamp. The

center conductor of the coaxial cable is attached to the sensor electrode, and the shield of the

cable is attached to the engine casing, which is at ground potential. At the HB-01 end of the

cable, the center conductor is connected the input of the first stage amplifier and the shield of the

cable is connected to the analog ground of the circuit.”



PROOF OF CONCEPT BENCH TEST 9.0

It is necessary to have a proof of concept bench test system before the final system is

implemented. As the name implies, the proof of concept system will prove that theoretically the

final system is sound and will work as expected once implemented in the actual compressor. The

system will be made of two main parts: (1) the mechanical system that will mimic the

compressor and impeller blades, and (2) the electronics that will allow the sensor measurement

to be read. Refer to table 9.1 for the complete bill of materials.

Table 9.1 Capacitive Sensor Bench Test Bill of Materials

Item Supplier Part # Item Price Quanity Total Price

Electric Motor McMaster 5990K47 $240.92 1 $240.92

Bearings McMaster 2722T34 $111.22 2 $222.44

3" Dia. Pulley (4L, A) McMaster 6245K67 $9.91 1 $9.91

5.25" Dia. Pulley (4L, A) McMaster 6245K93 $15.86 1 $15.86

V-belt (4L, A) McMaster 6191K16 $6.15 1 $6.15

Feeler Gauge McMaster 2334A2 $5.84 1 $5.84

Capacitive Sensor Capacitec, Inc. HPT-150I-A-L2-2-B $475.00 1 $475.00

Impeller FS-Elliott $0.00 1 $0.00

Oscilliscope Buffalo State College $0.00 1 $0.00

Electronics Buffalo State College $0.00 1 $0.00

Total: $976.12



APPARATUS

Impeller Assembly

As seen in figure 9.1 the impeller assembly is made up of an impeller, an electric motor, a

motor speed controller (not pictured), a set of bearings, two pulleys, a v-belt, a sensor stand, and

a base that everything is mounted to.

Figure 9.1 Proof of Concept Impeller Assembly

The impeller was supplied by FS-Elliott. Their team balanced it by removing material

from the bolt and washer that fastens the impeller to the pinion shaft.



The electric motor was purchased from Mc-Master. The motor is an AC motor and has a

maximum operating speed of 3450 rpm. An AC motor speed controller is used to ramp up the

system and to have variable operating speeds.

Two bearings purchased from Mc-Master are used to hold the pinion shaft. The bearings

are rated for a maximum of 9000 rpm. The test system operating speed will be approximately

6000 rpm, leaving a safety factor of 1.5.

Two pulleys with a velocity ratio of 1.75 will be used. This means that when the motor is

running at 3450 rpm the impeller will be rotating at 6038 rpm. A standard v-belt will be used to

transfer power from the motor to the pinion shaft.

A sensor stand will be used to hold the sensor in place and allow ample adjustment of

impeller tip to sensor tip distance as desired.

Electronics

A highly simplified circuit, as seen in figure 9.2, will be used in the bench test

system. Simply put, the circuit will take the change in capacitance from the probe and convert it

into an output voltage; this signal will be directly proportional to the distance from the impeller

tip to the sensor; the system will need calibration.

Figure 9.2 Bench Test Circuitry



The capacitive sensor shown in figure 9.2 as Cs, is made up of a spark-plug type

electrode plus a grounded target, in this case the impeller blades. A coaxial cable connects the

probe to the high voltage power source (usually 100 V), which enters through R1 and supplies

the voltage to the capacitive probe. The dc voltage of the sensor is blocked by capacitor C2, and

any change in voltage at the sensor is than applied to the negative terminal of op-amp U1 from

C2. Amplifier U1 has a feedback capacitor, C1, which causes the amplifier to act as a charge

amplifier. This setup will cause U1 to try and keep the voltage on Cs constant. The result is an

output voltage from U1, which will be the change in charge required to keep the capacitive probe

at a constant voltage. If the capacitance of the sensor changes due to blade passing in front of the

sensor the output charge of U1 will change as well. This relationship can be described by:

∆𝑉 =(∆𝐶𝑠)(𝑉𝑜)

𝐶1

Where: ∆𝑉 is the change in output voltage at the output of U1

∆𝐶𝑠 is the change in capacitance of the sensor

C2 is the value of the feedback capacitor

A typical value for 𝑉𝑜 is 100 volts; this value drives the amount of gain to the amplifiers

output- the higher the value the higher the output voltage. C1 is typically either 10 pF, or 47 pF;

we used 47 pF.

Concerns

There were significant concerns with regards to the proof of concept test system.

The system was highly sensitive to “electrical noise” and this had a very significant impact on

the results of the system. The noise of the system was many times greater than the output signal,

which did not allow for precise measurement.



Calibration

Every unique system must be calibrated because there are variances system to system.

The reason for this is because each system target will give a unique capacitance signal. In theory

calibration is very simple. The system is run at various clearances and the corresponding change

in voltage is observed, this represent a data point (distance vs. voltage). A significant amount of

data is then observed and then plotted. A linear trend will emerge and a function is created based

on this trend. The function should have a R-squared value no smaller than .999. A hypothetical

data set is shown in figure 9.2. The equation 𝛿 = 0.001(∆𝑉) − 0.001, would be used to

determine impeller clearance, where 𝛿 is equal to the clearance and ∆𝑉 is equal to change in

voltage.

Figure 9.2 Capacitive Sensor Calibration



Proof of Concept Conclusions

The validity of an impeller tip clearance system is supported with the proof of concept

system. With this said, the degree of accuracy that is necessary is not supported by the bench

test. The system would need significant improvements in order to support a final installation of

the system into the P300 centrifugal compressor. The general theory behind the system was

indeed proven- a change in capacitance output from a capacitance sensor can indeed be

converted into a voltage waveform, and this waveform is directly proportional to the clearance.

To eliminate noise an expanded circuit would be necessary and this circuit would need to be

encapsulated in a “Faraday cage” of sorts.

CONCLUSIONS 10.0

It is clear that measuring impeller clearance is not an easy, inexpensive thing to do. This

is mainly due to tight tolerances, high target frequencies, and most importantly, the need for very

advanced electronics. Because of the above mentioned factors it quickly becomes clear why the

leading centrifugal compressor companies have not implemented impeller sensing technology in

their products.



1/26 2/2 2/9 2/16 2/23 3/2 3/9 3/16 3/23 3/30 4/6 4/13 4/20 4/27

Initiating

Centrigugal compressor information

Different types of sensors available

Restrictions and Design Guidelines

Planning

C&E Matrix

Plant and manufacturing facility visit

Final sensor probe and electonics

Position of sensor in compressor

Design costs

Executing

implementing sensor set-up

Monitoring & Control

Sensor calibration

Accuracy of sensor measuring blade tip clearance

Closing

Design improvements

PROJECT MANAGEMENT 9.0

Project points of completion are set to have an outlook on the project, from beginning to

finish. A Gantt chart is used to keep track of all planned project dates throughout the entire

project. As unexpected problems or events occur in our project, Gantt charts can be modified

easily to keep everyone on track to finish the project by our final goal of April, 30th 2015.

Table 9.1. Gantt chart for project management section of our design



APPENDIX 10.0 Cause and Effect Matrix Key

Cost

1. Greater than $1,251.00

2. $1,001.00-$1,250.00

3. $751.00-$1000.00

4. $501.00-$750.00

5. Less than $500.00

Probe to Target Area Ratio

1. Greater than 1:4 (Greater than 25%)

2. 1:3.1-1:4 (32%-25%)

3. 1:2.1-1:3 (48%-33%)

4. 1:1.1-1:2 (100%-50%) 5. Less than 1:1 (Less than 100%)

Sensor Tolerance (in.)

1. Greater than 0.0031”

2. 0.002”-0.003”

3. 0.001”-0.0021

4. 0.00075”-.00011

5. Less than 0.00075”

Resolution (% of target distance)

1. Less than 1%

2.

3. 1%

4.

5. Greater than 1%

Maximum Temperature (°F)

1. Below 350°

2.

3.

4.

5. Above 350°

Required Target Frequency (Hz)

1. 17,001-Infinite Hz

2. 14,001-17,000 Hz

3. 11,001-14,000 Hz

4. 8,001-11,000 Hz

5. 5,000-8,000 Hz

Ease of Installation

1. Greater than 5 hours

2. 4-5 hours

3. 3-4 hours

4. 2-3 hours

5. Less than 2 hours



4 1 AP-04-01 Four-Channel Blade Tip-Clearance/Timing Measurement System Configured as Single-Channel System: Signal Processors: AP-04 four-channel signal processor chassis with one AP-01 Analog Processor card. Includes power supply and interconnect cable for power distribution (for upgrade to three-channel system, Item 5). Output signals for each channel include Blade Sync, Blade Tip Clearance, Minimum Tip Clearance, Maximum Tip Clearance, Average Tip Clearance.

$6,440.00 $6,440.00

5 1 AP-04-03 Upgrade

Upgrade of Single-Channel System (item 4) to Three-Channel System: Upgrade cost, including testing:

$5,376.00

$500.00

$5,376.00

$500.00

6 1 AP-04-03 Four-Channel Blade Tip-Clearance/Timing Measurement System Configured as Three-Channel System: Signal Processors: AP-04 four-channel signal processor chassis with three AP-01 Analog Processor cards. Includes power supply and interconnect cable for power distribution. Output signals for each channel include Blade Sync, Blade Tip Clearance, Minimum Tip Clearance, Maximum Tip Clearance, Average Tip Clearance. Note: Item 6 would be in lieu of items 4 and 5.

$11,816.00 $11,816.00

7 3 Probes Capacitec Probe. HPT-75 series. 0.075”

sensor tip, 400°F operation, threaded case,

0.250” diameter, Probe length: 1 inch, Cable length: 6 feet, Connector: BNC

$935.00

(estimated)

$2,805.00

(estimated)

8 1 Calibration

Probe

Capacitec Probe. HPT-75 series, 0.075”

sensor tip, 300°F operation, threaded case,

Probe length: 1 inch, Cable length: 2 inches, Connector: BNC

$890.00

(estimated)

$890.00

(estimated)

9 1 CP-01 Calibration system for probes Capacitance Preamp without probe. Includes Excel spreadsheet to facilitate calculation of probe coefficients for data acquisition system. Connector: BNC for attaching Calibration Probe (Item 8).

$1,050.00 $1,050.00

10 1 Calibration services and/or on-site technical support (optional). Billed on time and materials basis. Labor billed at $150/hour. Customer to pay for travel and lodging expenses for on-site activities.



REFERENCES 11.0

Alibaba.com. (n.d.). Retrieved March 6, 2015, from

http://astrohurricane.en.alibaba.com/product/680115363-

213150333/300Khz_Ultrasonic_microwave_distance_sensor.html

FS-Elliott Co., LLC. (2014) Polaris+ Air Compressor [brochure]. Export, PA

FS-Elliott Co., LLC. (2008) Polaris P-300 Air Compressor [brochure]. Export, PA

IHS Engineering 360. Photoelectric Sensors Information. (n.d.). Retrieved March 1, 2015, from

http://www.globalspec.com/learnmore/sensors_transducers_detectors/proximity_presence

_sensing/photoelectric_sensors

Lion Precision: High-Performance Noncontact Sensors and Experts to Help You Use Them.

N.p., n.d. Web. 26 Feb. 2015. <http://www.lionprecision.com/index.php>.

Pfister, Thorsten, Lars Büttner, and Jürgen Czarske. "Fiber Optic Laser Doppler Distance Sensor

for In-situ Tip Clearance and Vibration Monitoring of Turbo Machines." Applications of

Laser Techniques to Fluid Mechanics 14.1 (2008): n. pag. Web. 25 Feb. 2015.

P51-200-G-B-I36-5V-000-000. (n.d.). Retrieved March 1, 2015, from http://www.daytona-

twintec.com/tech_sensors.html

Ramsden, E. (n.d.). Hall vs. VR: Which speed sensor is wrong for you? Retrieved February 28,

2015, from

http://www.electronicproducts.com/Electromechanical_Components/Hall_vs_VR_Which

_speed_sensor_is_wrong_for_you.aspx

Remote Optical Sensor. (n.d.). Retrieved March 4, 2015, from

http://www.zoro.com/i/G0967486/?utm_source=google_shopping&utm_medium=cpc&u

tm_campaign=Google_Shopping_Feed&gclid=Cj0KEQjwifWnBRCB5PT57KSVw-

kBEiQASV7aRBmuW1xlS2JNCEojJ6L63S-y3i8yJTyN_RBepHlbiOcaAkaM8P8HAQ

Smith, D., Tursky, M., Wellek, R. (2013). Compressor Assembly 3 stage, 60hz. P300. [Drawing].

FS-Elliott Co., LLC. Export, PA