Thank you for choosing a Metra Vibration Measurement Instrument!
1. Purpose
The VM25 has been developed, particularly, for the measurement and monitoring of
vibrations on rotating machines. The purpose of such measurements is to monitor
the condition of the machine in order to avoid unscheduled shut-down. Furthermore
vibration measurement is carried out prior to the distribution of new machinery and
subsequently to repair with a view to quality control and the issuing of product guar-
antees.
The basis for successful machine condition monitoring is the measurement of the vi-
bration severity over a longer period of time. Measurements are taken at regular in -
tervals of time and recorded.
The VM25 measures and records vibration acceleration, vibration velocity or vibra-
tion displacement. The VM25 specification complies with the ISO 2954 regulations
for machines that measure vibration velocity and is therefore suitable for measuring,
among other things, machine vibrations in accordance with ISO 10816.
In addition to vibration quantities the VM25 also measures the temperature and the
rotation speed with contactless sensors.
An external piezoelectric accelerometer is used as the sensor, and is provided to -
gether with the instrument. The VM25 is fitted with an electronic measurement
point detector (VMID) which enables it to take routine measurements of a large
number of measurement points very effectively. A software package for transferring
the measurement data to a PC is also available from Metra.
In the common hierarchy of condition monitoring the VM25 is equivalent to 'Level
1'. This represents the long term monitoring of parameters with low technical and
personnel requirements.
For fault detection ('Level 2'), as a further step, spectral diagnostic measurements are
taken, which require a large degree of expertise and sophisticated measurement tech-
nology.
In the development of the VM25 value was placed on simple operation and mainte-
nance requirements, which enable trained personnel to operate the instrument with-
out the need of being specially qualified.
2. Function
2.1. The Vibration Sensor
The VM25 operates with a piezo ceramic shear accelerometer. Piezoelectric vibra-
tion transducers are characterized by high precision and resolution with great robust-
ness. The accelerometer of the VM25 has an integrated electronic circuit for imped-
ance conversion in accordance with the IEPE standard. At the base of the sensor a
magnet has been integrated for mounting to the measurement point. In the center of
the magnet there is a contact point from which the identification number can be
read. The measurement point ID is saved in the available VMID measurement
points.
The coupling surface is protected by a metal cap which attaches to the sensors mag-
netic base.
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