Beta 450 Uživatelský manuál stáhnout pdf (Strana 2)

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Doc# 1004730 • Rev G (October 2014) Page 2 of 10



When a decision has been made to monitor seismic vibraon

on the machine casing or support structure, velocity is oen the

best parameter to use. Acceleraon and displacement levels

are heavily inuenced by the frequency(ies) at which the vibra-

on is occurring, while velocity levels are much less inuenced.

Thus, although acceleraon, velocity, and displacement mea-

surements are inter-related mathemacally, seismic velocity

measurements tend to be more consistent over a wide range of

frequencies than either displacement or acceleraon. Conse-

quently, broadband (somemes called “overall” or “unltered”)

velocity measurements are appropriate for monitoring many

machines as a reliable indicator of damaging vibratory energy,

with the notable excepon of machines that use uid-lm

bearings, which are usually beer addressed by sha-observing

proximity probes.

Casing displacement is not a praccal measurement to make

directly, and is typically just an integrated seismic velocity

measurement. As such, the primary decision when selecng a

seismic measurement will usually be whether to measure casing

velocity or casing acceleraon. As noted above, casing velocity

will oen be more appropriate because it tends to be a more

reliable indicator of damaging vibratory energy over a broad

frequency spectrum for low- to medium-speed machinery.

NOTE: For machines with uid-lm bearings, sha-

observing proximity probes will provide more eec-

ve vibraon measurements than seismic transducers

due to the rotor dynamics of the machine and the aenua-

on of vibratory energy through a uid-lm boundary. Ac-

cordingly, Metrix recommends and provides proximity probes

and associated 4-20 mA transmiers or monitoring systems

for such applicaons.

For machines with rolling element bearings and running

speeds above 6,000 rpm, and/or where impulsive casing

vibraon occurs, acceleraon may be a beer measurement

than velocity. In such situaons, it is recommended that

you consult with your nearest Metrix sales professional who

can review your applicaon and assist with selecon of the

proper transducer type and associated transmier or moni-

toring system.

FEATURES AND BENEFITS



The use of two setpoints* (one for ALERT and one for SHUT-

DOWN) is recommended for applicaons where it is desirable

to remotely annunciate an ALERT condion to operators and/or

maintenance personnel. This allows appropriate intervenon to

occur before the machine reaches SHUTDOWN levels. Switches

with only a single setpoint are not capable of pre-shutdown

warnings unless the 4-20mA output is connected to a PLC or

other trending device, and appropriate pre-shutdown alarm

limits are programmed in the PLC.

*NOTE: The 440/450 switch provides only over-type (not over/under)

alarms.



An oponal LOCKOUT capability is available for suppress-

ing alarm acvaon during machine startup condions when

vibraon levels may be elevated compared to normal running

condions. When the LOCKOUT opon is specied, applying (or

cycling) power to the switch suppresses alarms for 20 seconds*,

allowing the machine to accelerate through its rough running

zone and reach operang speed/load without generang spuri-

ous alarms or trips, and without the need to alter setpoints or

delays that are suitable for normal running speed of the ma-

chine. The 4-20mA output is not aected while the switch is in

LOCKOUT mode, allowing actual vibraon levels to be displayed

and trended at all mes.

* NOTE: This delay is set at the factory for 20 seconds and cannot be

adjusted in the eld. Other delay mes may be available upon request

as Engineering Specials.



When ordered with the external sensor opon, the switch ac-

cepts an external accelerometer rather than using an internal

accelerometer. The external sensor opon is recommended for

most applicaons as it allows the sensor to be mounted at the

ideal measurement locaon and orientaon on the machine,

without concern for the larger mounng footprint of the vibra-

on switch compared to a sensor. It also allows the vibraon

switch to be mounted in a more convenient locaon for viewing

and servicing. Also, although the 440/450 is packaged to survive

harsh environments of dust, moisture, and corrosion, some ma-

chines may exhibit elevated temperatures at the preferred sen-

sor locaon. Use of an external sensor can allow temperatures

as high as 121°C (250°F) at the sensor locaon and 88°C (190°F)

at the vibraon switch locaon.

When an external sensor is not praccal, an internal accelerom-

eter can be specied for completely self-contained operaon.

This allows the switch to be mounted directly at the measure-

ment locaon and monitor vibraon in integrated acceleraon

(velocity) units. This conguraon is suitable when there is suf-

cient room at the measurement locaon to mount the switch,

when the measurement locaon sll allows the switch to be

conveniently viewed and serviced by plant personnel, and when

the switch’s ineral mass will not compromise the quality of the

vibraon measurement.



True RMS detecon is used to measure the amplitude of the

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