sentry system
TECHNICAL
INFORMATION
PREDICTIVE
MAINTENANCE
SYSTEMS
SENTRY SYSTEM
MO8612 – MARK SPACE RATIO,
DIFFERENTIAL EXPANSION MODULE
* EDDY CURRENT PROBE INPUT.
* MODULAR, RACK MOUNTED.
* INDEPENDENT MICROPROCESSOR.
* PROGRAMMABLE SET UP VIA RS232
* INDEPENDENT POWER SUPPLY.
* HIGH VISIBILITY LED DISPLAY.
* 4 ALARM RELAYS PER MODULE.
* 6 RECORDER/SERIAL OUTPUTS.
* DESIGNED TO MEET API 670.
The Sensonics MO8612 Module is one of the SENTRY series microprocessor based signal conditioning units
that is used to measure shaft differential expansion by means of an eddy current probe and mark space plates
fitted to a turbine shaft. The modules in the SENTRY series are designed to be housed in the Sensonics
RA8600 series 19 inch 3U extended eurocard rack system.
The signal conditioning unit is fitted with an LED digital display and alarm indications. The former will normally
indicate displacement in the selected engineering units (selectable from the front panel). The full scale range
and other parameters can be set up in the windows based software on a laptop PC, stored then downloaded to
the module via an RS 232 connection to the monitor module. Front panel buttons permit selected operational
software settings to be viewed on the indicator/display without the need for a PC. A "time out" function ensures
that the display will revert to the normal reading after a preset time.
The signal input to the module is a series of pulses per revolution derived from a specially-shaped target
high/low pattern on the shaft of the machine being monitored. These pulses will normally be voltage pulses
produced from a Sensonics eddy current probe mounted on the machine at right angles to the shaft axis and
in proximity to the shaft target pattern. An associated EC driver unit provides the signal output to the markspace module, the latter supplying -24V dc power to the driver unit.
The module has an adjustable or self-tracking threshold level through which the input signal pulses must pass
to produce a trigger.
The module calculates the pulse width ratio of successive input pulses and uses the result to establish the
axial relationship between the shaft target and the fixed structure on which the EC probe is mounted.
During normal operation the HB LED (Heart Beat) on the front panel will flash rhythmically, which shows that
the microprocessor is working.
Dual positive and negative going level alarms (A1 ± and A2 ± ) and relays are fitted and red LED indicators on
the module front panel will illuminate when the signal exceeds the level set by the software programming; after
a delay of selectable time the A1 or A2 alarm relay will change state.
The module also has a transducer and system integrity alarm and relay fitted, with an internal microprocessor
watchdog. Depressing the ‘RATIO’ button will cause the display to jump from the current engineering units of
displacement display (µm, mm, thou, or inches) to ratio in percentage.
The ‘MON’ BNC connector mounted on the front panel is to provide information on the input signal. The signal
level is the ‘raw’ input voltage direct from the module signal input from the transducer. The output is buffered
and therefore an accidental overload or a short circuit will not affect the integrity of the module. Signal
accuracy is nominally 1%.
The 'TACH' BNC connector at the front panel provides the conditioned tacho signal as seen by the
microprocessor.
DS1145
SENTRY SYSTEM
MO8612 – M.S.R. DIFFERENTIAL EXPANSION MODULE
Front Panel Facilities and Functions
SPECIFICATION
Input
Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transducer Type . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Programmable to suit measurement range
Eddy current probe system
110V or 240V AC 50-60 Hz or DC
Output
Displays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Meter accuracy . . . . . . . . . . . . . . . . . . . . . . . . . .
Recorder outputs . . . . . . . . . . . . . . . . . . . . . . . .
Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 1/2 digit indicator.& 20 LED indicators
+/- 5% of true value
Up to 6 voltage or current outputs per module plus serial RS485
4 alarm relays per module as standard
(6 optionally available)
A1 and A2 - level alarms
A3 - Channel integrity alarm
A4 - Reading invalid alarm
Buffered transducer output . . . . . . . . . . . . . . . . . . . . BNC connector on front of panel, and rear of rack.
Tach signal (TTL)
BNC connector on front of panel
Dimensions
Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
128.8mm (3U)
70.7mm (14HP)
DS1145
Sensonics Ltd
Northbridge Road
Berkhamsted
Herts, HP4 1EF
United Kingdom
Tel: +44 (0)1442 876833
Fax: +44 (0)1442 876477
www.sensonics.co.uk
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