Series PC Manual V 1.0 - Rev. 3 – 03/01/01 DS Europe
16
9.7. RS-485 DIGITAL OUTPUT
RS-485 has a maximum resolution of 0,046 mm.
The transducer (slave) consents calibration and total management/configuration of its
functions by remote unit (master).
The RS-485 serial connection allows the possibility to parallel connect up to 32
transducers at the same time. The cable can have a maximum length of 1000 metres
(using 24 AWG twisted cable in accordance to EIA 485 Standard), if mounted with a good
immunity against interference. In practice the defined standard reference limits are to be
considered indicative and the results are depending on the application conditions.
Whenever particularly long signal lines are used there may be signal dampening, which
can be resolved by applying signal repeaters generally found on the commercial market.
Using this (RS 485) connection it is possible to program the outputs in the desired
modality, even during transducer working.
The transmission velocity is fixed at 57600 baud and the serial communications port must
be set in the following way:
• Data bit = 8
• Parity = None
• Stop bit stop = 1
• Flow control = None
Should transducers with RS 485 multi-drop output be connected to a computer not
equipped with suitable interface, but RS 232 serial port (like a computer notebook), it is
possible to interpose converters that pass from the RS232 to the RS485, remembering
that they must support the conversion in transparent way with full RS485 protocol
management.
On today’s market we have passive and intelligent converters. The passive ones, however
are ill-advised as they only provide relative signal level adaptation to two protocols,
whereas the intelligent converters (recommended type) also provide the data flow direction
recognition and self-adapting serial transmission velocity.
For any further details relative to RS485 connection, (specifications and requirement) not
specifically dealt with here, refer to EIA 485 standard.
9.8. CURSOR VELOCITY (for displcement measurements)
In the chart, we correlate the transducer measuring field (=FS) with maximum cursor
translation velocity in relationship to the resolution chosen for the measurement (Step)
In the figure, Y-axis refers to the maximum translation velocity while the measuring field of
transducers (=FS) is represented on the X-axis. The graph scale is logarithmic and the
reference point values reported (Y axis) on the table are expressed in metres per second
(m/sec).
The resolution values refer to a measuring step, where a Step is considered to be the
number of mm required to sample the translation velocity of the cursor having a significant
measurement in relationship with the sampling frequency used for phenomena acquisition.
For example: a transducer with FS=350 mm in the case where cursor moves at a velocity
of 1 m/sec, the significant measuring step is 1mm. If however the displacement value were
0,05 m/sec, we would have a corresponding significant measuring step of 0,05 mm.
When FS= 350 mm there is a corresponding sampling frequency = 1000 samples / sec.
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