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IN
THIS ISSUE
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- New
Product Additions to the On-Line Catalog (Now over 250
products!)
- Reliability
Direct now provides Secure
On-Line Credit Card Transactions! As before, we are also
happy to accept purchase orders, as well as telephone
and fax orders.
- Ask
the Expert "How
do I know if my accelerometers are working
properly?"
- Application Note: Grounding
- Hot
Product: New
Transmitter
- Trivia
Contest: See Bottom of Page
To
unsubscribe follow the instructions at the bottom of the
page.
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RDI
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| New
Product Additions |
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V-Trainer, is
a comprehensive, multimedia training library for vibration
analysis and related predictive technologies.
V-Trainer is a past winner of the prestigious
Plant Engineering Product of the Year.
Due to customer demand, RDI
has added alignment shims. STILT
LEG®
and Straight
Leg®
Slotted
Shims are manufactured from the highest quality,
corrosive -resistant stainless steel. The shims are
dimensionally uniform and electro-etched for permanent
easy to read identification. The shims come in a variety
of standard assortments and each kit is offered in a
sturdy metal carrying case with a removal tool. Shims are
also available in any custom assortment to fit your needs.
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V-Trainer
Shims
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| Ask
The Expert |
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Question:
How do I know if my accelerometers are working correctly?
Answer:
Two methods come to mind: observe (and trend) the
sensor’s BIAS VOLTAGE or dynamically test the sensor.
Observing
the BIAS VOLTAGE is relatively easy and quick. Most
industrial accelerometers available today are powered by +18
to 30 volts DC (typically +24 volts DC). This power is
supplied on one of the two wires connected to the sensor.
The accelerometer amplifier circuit inside the sensor pulls
this power voltage down to a preset level. The preset level
is called the BIAS VOLTAGE and is designed at a level by the
sensor manufacturer. Many accelerometers have a nominal BIAS
VOLTAGE of +12 volts DC. The sensor operates around this
voltage level and the level should be relatively stable as
long as the power level is stable. BIAS VOLTAGE may be
measured via a volt meter or collected as part of a route
using a data collector.
Dynamically
testing an accelerometer is more involved. The sensor is
installed onto a shaker table that is capable of producing a
range of amplitudes and frequencies. The sensor’s output
is recorded and compared to a known working (preferably a
calibration standard) accelerometer. Another “quick and
dirty” method is to use a small motor or rotor kit with
some unbalance that does not change as a known vibration
source. Attach the sensor to the motor periodically and
observe the output for comparison to past observations.
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Wolf Campbell, P.E.
Sr. Reliability Engineer
SKF Service
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| HOT
PRODUCT |
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CMCP420VT is
a solid state, loop powered vibration transmitter. It
provides a 4-20 mA output that is
proportional to overall vibration in terms of velocity.
The CMCP420VT continuously monitors
machinery health and transmits directly into a PLC or DCS
for trending, alarm and machine shutdown.
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| APPLICATION
NOTE: Grounding |
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A "Single Point Grounding" scheme should be
utilized when installing a Vibration Monitoring System.
This scheme of grounding means that all grounds are
connected or tied down at one location. It is highly
recommended that for a Vibration Monitoring System
installation the Single Point Ground should be at the
Monitor not at the Machine. On a large machine or where
multiple machines are being monitored, substantial ground
differentials (potentials) can be found between transducer
locations.
All Instrument Wire shields must be grounded at one end
of the cable, and the other end left floating or not
connected. The Instrument Wire should be grounded at the
Vibration Monitoring System. If the shield is not
grounded, the shield will become an antenna increasing
induced noise on the signal path. If the shield is
grounded at both ends, it will allow ground differential
(potential) current (ground loop) to flow through the
shield seriously increasing induced noise and voltage
transients.
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| CASE
HISTORY |
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A skid packager has a need for 30 each four channel,
explosion proof Class I, Div. I, continuous monitoring
systems for offshore installation. Requirements included IS
Barriers, Slave Relays, Independent Displays, XP Housing and
4-20mA output to interface with a DCS system. A traditional
rack mounted system is not price competitive and Bently
Nevada is the competition. The winning solution to this
application is pictured at right via the CMCP500 Series
System.
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SPECIAL
PROMOTION: Accelerometer Accessories
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| This month's
special highlights Accelerometer accessories. Call our toll
free number and use offer code 2000
to receive an additional 5% off our Low, Low Prices on
mounting pads, motor fin mounts, adhesive, extension
cables, etc. |
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| TRIVIA
SWEEPSTAKES |
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At the end of every
month we give away three prizes to the first three
individuals who send in correct answers.
Question
#3
What common device found in everyone's
home evolved into the first Velocity Sensor?
(Hint: Operate opposite of its
intended use)
Send your answer to dgallagher@ghg.net and
put "Question #3" in the subject line.
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Trivia answers must be received
before midnight
Oct. 6, 2000!
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