MMF VM22, Инструкция по эксплуатации

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2.2. The Measuring Instrument
2 shows the block diagram. The VM22 supplies the IEPE Sensor with 2 mA con-
stant current. At the sensor output, a vibration acceleration proportional AC voltage
arises, which is amplified in the instrument to produce an optimum level. The gain
switch-over takes place automatically. The subsequent analog/digital converter is a
Sigma-Delta converter with 24 bit resolution.
Further signal processing, such as filtering, integration (for calculating velocity from
acceleration) and RMS is carried out in the micro controller. The micro controller
also controls the graphic display, the USB communication and the storing of mea-
surements.
3. The Measurement Procedure
Measuring vibration velocity is a common procedure for assessing the running smooth-
ness of rotating machines. Vibration velocity, commonly known as vibration severity, is a
measurement of the energy expenditure of occurring vibrations. Vibrations are caused by
rotational imbalances, for example as a result of loose screws, bent parts, worn or slack
bearing clearance or dirt residues on fan blades. Often several factors have a mutually re-
inforcing effect. Besides rotary machines, the measurement procedure is also suitable for
reciprocating machines.
The specifications of vibration velocity measuring instruments are described in
ISO 2954. In the ISO 2954 a band filter for the vibration velocity of 10 to 1000 Hz is de-
fined. The corresponding VM22 frequency response graph can be viewed in 3.
The displayed value of the vibration severity is the true RMS.
4
Figure 2: Block Diagram
IEPE
supply
Progr.
amplifier
A
D
Micro
controller
Display
Memory
Keys
Sensor
ID
USB
Power
supply