VIBRATION MONITORING OF FANS INSTALLED IN ROAD TUNNELS
CEMB SPA
Via Risorgimento, 9
Mandello del Lario (Lc), Italy
stm@cemb.com
www.cemb.com
CEMB SPA – Mandello del Lario
INSTRUMENT FOR MONITORING VIBRATIONS OF FANS INSTALLED IN ROAD
TUNNELS
PURPOSE OF THE INSTRUMENT
The instrument measures and monitors the vibrations of each fan installed. It allows
checking for correct machine operation over a period of time thus preventing catastrophic
failures.
Hence it is possible to stop the fan when the vibrations exceed a preset value and to
schedule maintenance work in order to replace damage parts as well as to clean the
blades (uneven deposits would generate unbalances and therefore vibrations) or to check
the fan fastenings, etc.
1. TECHNICAL DESCRIPTION OF THE SYSTEM
1.1. GENERAL
A seismic vibration transducer is installed on the housing for each fan according to
any radial direction at random.
The signal generated by the transducer is sent to an electronic processing unit.
Connection is via a suitably sized shielded cable (up to 200 metres 2x1mm2 - up to
400 metres 2x1.5mm2 - up to 800 metres 2x12.5m2 ).
The processing unit is normally installed in the centre of gravity position with
respect to the tunnel section where the monitored fans are installed.
1.2. VIBRATION TRADUCERS
1.2.1. Type of transducer.
The transducer is of the electrodynamic seismic type (velocity transducer), i.e.
designed for measuring the speed of vibration parameters; there are no amplifying
or signal linearizing circuits incorporated in the transducer).
1.2.2. Frequency range.
Frequency response of the transducer is linear in the range from 10 to 1000 Hz .
1.2.3. Temperature limits.
The transducers should be able to operate correctly in the temperature range from
– 10°C to + 100°C.
CEMB SPA – Mandello del Lario
1.2.4. Resistance to environmental agents.
The transducer should be tightly sealed and insensitive to ambient humidity (max.
25%) and resistance to contamination by dusts and lubricating oils with a degree of
protection IP 65 (CEI standards)
1.2.5. Cables and connectors.
The transducers are complete with male-female connection to MIL standards, able
to withstand the mechanical and thermal stresses described in points 1.2.3 and
1.2.4.
1.2.6. Mounting.
It should be possible to install the transducer in any direction and fasten it with a
sufficiently rugged screw (e.g. M8 thread).
TEST INSTRUMENTS
1.3.1. Types of instruments.
All instruments are fully transistorized and the signal coming from a transducer is
sent to the respective conditioning and measuring circuit. The scanning system is
not permissible.
1.3.2. Measurement range.
The instrument should allow measurement and supervision of the RMS value of the
vibration speed within a range from 0 to 10 mm/s.
1.3.3. Frequency range.
The instrument response is linear in a frequency range from 10 to 1000 Hz.
1.3.4. Threshold discriminator circuit.
Each measuring channel is provided with a threshold discriminator circuit of static
type with amplitude comparator, suitable for driving an output relay (SPDT contact)
and indicator lamp (LED).
The tripping level of the alarm threshold is adjustable between 10% and 100% of
the measuring scale.
The alarm threshold is provided with a time delay device, independent from the
value and adjustable from 0 to 20 seconds.
The system output logic is as follows: under normal condition (vibration level below
the threshold) the relay is de-energized and the LED is unlit. The alarm threshold is
of the “unlatched” type, i.e. the output relay remains energized and the relative LED
is lit up only as long as the input signal is higher than the threshold value.
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