the “b” book guide to vibration measurements

the “b” book guide to vibration measurements
THE “B” BOOK GUIDE
TO VIBRATION MEASUREMENTS
HOW TO MEASURE MACHINE VIBRATION
WITH A VIBRATION METER
Page 2
“B” Book Guide To Vibration Measurement
The “B” Book Guide
To Vibration Measurements
Practical Uses for Vibration Measurements
Why Use Vibration Measurements?
Vibration measurement is an effective method for
looking at the condition, or “health”, of rotating
machinery in commercial and industrial applications.
Periodically checking machine conditions (known as
“trending”) is easy to do with vibration meters.
Pinpoint Vibration Problems
Identify Mechanical Looseness
Detect Bearing Wear
Spot Bent Shafts
Condition Monitoring
Predictive and Preventive Maintenance
Troubleshoot Machinery
Quality Control
Vibration meters help operators spot deteriorating
machine conditions before they become critical. By
identifying and quantifying a vibration problem,
corrective action can be taken before the problem
becomes significant and expensive.
Trending with vibration meters allows maintenance
technicians to plan repairs during normal work hours
rather than scheduling costly overtime or even shutting
down production or an entire HVAC system.
Fig 2 - Balmac hand-held pocket size
vibration meter
Applications for Vibration Measurements
Fig 1 - Balmac Digital Vibration
Meter with 100 mV/g Accelerometer
Bearings
Blowers
Centrifuges
Compressors
Conveyors
Cooling Towers
Fans
Grinders
HVAC Systems
Mixers
Motors
Pumps
Spindles
Page 3
“B” Book Guide To Vibration Measurement
WARNING
Exercise extreme caution when performing any task
around rotating machines. Failure to do so may result
in equipment damage and personal injury. Operators
are encouraged to become familiar with the equipment
and operating procedures before attempting vibration
analysis.
Select either the Magnetic Clamp Base or Probe Tip.
The advantages of each are discussed below. Both
accessories have a 1/4- 20 or 1/4-28 studs and attach
to the mounting holes in the base of the transducer or
accelerometer.
How To Use a Vibration Meter
Magnetic Clamp (Recommended) or Probe Tip
Step 1: Attach the Standard Accessories
Typical Vibration Meters have standard accessories
that are included with the Meter. They include: a
vibration Transducer or Accelerometer (often called the
Sensor), a connecting cable (Pickup Cable) , a
Magnetic Clamp (for securely attaching the transducer
or accelerometer to the surface of the application being
measured) and a Vibration Probe Tip (sometimes
called a “Stinger.”)
The Magnetic Clamp Base is recommended to provide
a secure, stable mounting for the transducer. The
magnet has a 12 lb pull, but allows an operator to
detach it without difficulty. Vibration readings are
affected by the stability of the transducer mounting.
The 7" Probe Tip is typically used in hard-to-reach
areas. It is convenient for operators to use on vibration
points on machines because it is not as bulky as a
magnet. However, some practice is required to
achieve consistent, repeatable readings.
Fig 4 - Magnetic Clamp and Probe Tip.
Fig 3 - Attach cable to meter and
transducer then attach magnet or probe
tip.
Attach one end of the Pickup Cable to the Meter and
the other end to the transducer (or accelerometer).
One connector matches the transducer and one
matches the connector on the meter.
Page 4
“B” Book Guide To Vibration Measurement
Step 2 - Select a Mode
Step 3 - Select a Range
The Mode is a vibration
parameter you want to
measure. Balmac Vibration
Meters have three modes:
Displacement = DISP,
Velocity = VEL and
Acceleration = ACC.
Ranges on Balmac meters are:
200
2
Very Low Range
200 (very rough vibration)
Fig 3 - Modes are DISP,
VEL and ACC.
Velocity
Velocity is read in inches per
second (Peak). Velocity
measures the rate of change
of displacement. Velocity is
more proportional to the
destructive forces generated
in a machine than either
displacement or acceleration.
Velocity readings reveal more
about vibration at all
machinery speeds (RPMs).
20
Most applications will never
be this rough. Used with
extremely large primary
movers (Class 4) type of
equipment.
Max
199.9
Min
19.0
20 (moderate vibration)
Fig 4 - VEL selected.
Recommended starting range
for most measurements. Go
to 2 for smaller vibration
levels.
Max
19.99
Min
1.9
Displacement
Displacement measures the
distance the part moves read in
Mils (one Mil = .001 inch)
(Peak to Peak). It is necessary
to know the RPM of the
equipment to establish a
vibration limit in Displacement
(Mils).
2 (smooth to moderate
vibration)
Use for small vibration levels
and for QC levels for motors
and fans.
Fig 5 - DISP selected.
Max
1.999
Min
0.01
Acceleration
Very Low Range
Acceleration is the rate of
change of velocity read in g’s
(Peak). G’s are useful when
measuring very high frequency
vibrations such as signals
generated in rolling element
bearings or gear trains.
Multiply reading on display by number on label that
corresponds to Mode used.
Example: Mode is Velocity Model = Vel. Display
reading = 197.6. Answer: 197.6 x .001 = .19 in/sec.
Fig 6 - ACC selected.
Page 5
“B” Book Guide To Vibration Measurement
Step 4 - EXAMPLE: Taking a Measurement in
Velocity
Step 6 - Where To Measure Vibration?
1. Complete Step 1. Attach Magnetic Clamp (or Probe
Tip) to Transducer. Connect Transducer to proper
cable end and then connect the other cable end to the
Meter.
2. Complete Step 2. Select Velocity Mode.
3. Complete Step 3. Select 20 Range.
4. Secure Magnetic Clamp/Transducer assembly to
first measurement point. (See Vibration Directions and
Measurement Points later in this brochure)
Vibration signals are
strongest at or near
bearings. They tend to
weaken as you move
farther away from
bearings. Example:
the vibration signal is
strongest on a direct
drive motor/fan
assembly on the
bearing closest to the
fan.
Fig 13 - Typical measurement
points on a blower.
5. Depress OFF/ON button until it latches. (Power ON Display comes on)
CAUTION: Extreme
care must be taken when working around rotating
machinery belts, pulleys, sheaves and shafts.
6. Depress VEL button until it latches. (Mode =
Velocity)
Step 7 - What Does the Reading Mean?
7. Depress 20 button until it latches. (Range = 20)
Refer to the Vibration Severity Chart .
8. Allow readings to stabilize. (Do not be concerned if
the digits to the far right of the display vary up or down,
this is normal operation.)
9. Record reading.
Step 5 - What Direction to Measure?
Vibration is measured in
Vertical, Horizontal and
Axial directions. Test all
three to find the direction of
the strongest signal.
Typically, the Horizontal
(Radial) direction provides
the strongest signal.
Fig 14 - Typical Vibration Severity Chart
Machine mountings can
influence readings. Spring
isolator mounted machines
may have strong vertical
readings.
Example: an operator has set the Vibration Meter to
Velocity (VEL) on the 20 Range and has measured the
vibration level on a bearing in the Horizontal direction.
Strong axial readings often
indicate a bent shaft or
loose bearings. Take
measurements in all three
directions whenever
possible.
The operator would record the reading and then
compare the recorded reading with the Severity Chart to
determine the vibration severity.
The reading is: 00.15 (Inches Per Second, Peak):
Fig 12 - Vertical, Axial
and Horizontal
directions.
Page 6
“B” Book Guide To Vibration Measurement
Looking at the left side of the Severity Chart (see Fig
16), the operator would see these numbers
representing Velocity in inches per second.
The operator’s reading of 00.15 would fall exactly half
way between .1 and .2 and the operator could conclude
the vibration level was in the GOOD zone on the chart.
00.15 ips = GOOD
Measuring vibration in Velocity is the easiest method to
learn machine condition. Velocity readings do not
require knowing the RPM of the machine. A reading of
.1 is SMOOTH whether the machine is running at 100
RPMs, or 100,000 RPMs.
Other Examples of readings in Velocity:
0.08 ips = SMOOTH
Fig 16 - Displacement readings run across the top and
down the right side of the Severity Chart. Acceleration
is shown in lines running diagonally left to right.
0.4 ips = ROUGH.
Acceleration Measurements (g’s, Peak):
Displacement Measurements (Mils Peak-to-Peak)
Displacement (Mils) readings run across the top and
down the right side of the chart. (See Fig 16) Match
your reading with the same number at the top or right
hand column on the chart.
Acceleration readings are represented by diagonal lines
running from the top left to the bottom right of the chart.
Acceleration numbers are found in the middle of these
lines. Like Displacement readings, Acceleration
readings require knowing the machine RPM.
Example: .1 g at 1000 RPM = ROUGH.
Next to that number is a diagonal line running right to
left down to the bottom of the chart.
0.1 g at 10,000 RPM = SMOOTH.
Follow the diagonal line down until it crosses a vertical
line coming up from the bottom that corresponds to
machine RPM. (RPM is at the bottom of the chart.)
Over Range
Determine if this reading falls in the SMOOTH, GOOD,
FAIR or ROUGH range.
Vibration signal strength to strong for setting. If display
shows a 1. (see photo), select next higher range.
Example: a reading of .5 mils (top right corner of chart)
intersecting at 2000 RPM (middle bottom of chart) is in
the SMOOTH range. A reading of 3 mils (top middle of
chart) at 2000 RPM is ROUGH.
Displacement readings require knowing the machine
running speed (RPM).
Fig 18 - Over Range
Page 7
“B” Book Guide To Vibration Measurement
Vibration Maintenance Records
Vice Grip Pliers
Recorded vibration levels:
The Model 158 Pickups may
be attached to Vice Grip
Pliers for non-magnetic
surfaces.
provide machine history
trend machine conditions
help schedule maintenance
Recording intervals vary from machine to machine.
Age and machine condition are important factors, but a
general rule of thumb is readings should be made more
frequently as soon as machinery deterioration is
noticed.
Vibration Maintenance Records Samples may be
downloaded from the Balmac Inc. website.
Fig 21 - Vice Grips
Fish Tail Shaft Sticks
The Fishtail Shaft is used to
measure vibration on
rotating shafts.
Fig 22 - Shaft Stick
Headphones
Headphones are useful for listening top machinery
vibrations. With experience, an operator can learn to
identify vibration sources by listening to the pitch and
intensity of the vibration noise. This can be useful when
analyzing defective bearings. Headphones may be
used with Model 200, 205 and 211 Vibration Meters.
Fig 20 - Sample Vibration
Record
Directions:
1.
Sketch basic machine configuration in upper
left grid.
2.
Record operator identification, dates, times,
etc.
3.
Include critical machine information such as
type of equipment, RPM and special notes.
4.
Record vibration readings in HORIZONTAL,
VERTICAL and AXIAL directions in appropriate
columns. Record both VELOCITY and
DISPLACEMENT readings.
WARNING
Rotating machinery have potentially dangerous moving
parts. Potential hazards to the operator or the
surrounding area may exist. Operators should use
extreme caution when working around moving parts.
DISCLAIMER
Balmac Inc. assumes no responsibility for errors or
omissions nor assumes any liability for any damages
that may result from use of its products or the
information provided by Balmac Inc.
013014
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