Guardato, S.

Iannaccone, G.

Earth-prints Repository

RS-485 interface for external use of the GPS
receiver of the Kinemetrics® dataloggers
S. Guardato, G. Iannaccone
Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Naples, Italy
SUMMARY
In this technical report, we present an electronic interface that we designed
and produced as part of a new system that allows the remote acquisition of
data provided by the GPS receiver for the Quanterra Q330 and Q330HR data-
loggers, and for the whole range of the Altus series of systems produced by
Kinemetrics, using an RS-485 bus via a serial cable that can be of kilometres
in length. This function is not normally available for any of the equipment
reported and it is needed when the installation of the GPS receiver antenna
needs to be more than some tens of metres from the datalogger. This can be
necessary, for example, for installations in tunnels, in large buildings, or for
seafloor systems with a cable connection to the surface.
This document describes the functioning and the hardware of the interface
boards, particularly considering the Quanterra Q330 datalogger. The system
designed in this way is introduced as an element that maintains all of the func-
tions of the apparatus in a fully transparent mode without the need to modify
the communication-software procedures for the exchange of data between the
datalogger and the integrated GPS receiver, therefore leaving untouched the
various functional modalities normally associated with the GPS receiver.
FUNCTIONING PRINCIPLES
The Quanterra Q330 is equipped with a GPS receiver module (M12
Motorola®) for the correct time marking of the data acquired. The operating
manuals specify that the GPS receiver inside the Q330 can be used in various
modes: continuous functioning, or for a predefined time, or only when the trac-
king of the phases is lost. In this last case, the quality of the GPS signal drops
to 60% (still a good level of GPS signal) and decreases by a further 1% about
every 10 minutes. This means that under these conditions after a time of about
8 hours the level drops to 10% (equivalent to an absence of GPS signal).
In such cases, a new time base is used, provided by a TCXO (high-stability
quartz with temperature compensation) usually coupled via the use of a
phase-locked loop (PLL) circuit, with the timing signal from the GPS receiver.
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The quartz oscillates with a clock at 15,360 MHz and has a thermal stability of
10 ppm/°C. This results in a time drift of the datalogger clock of a few sec-
onds about every 30 days of use in the absence of a GPS signal, with the data-
logger continuously functioning.
The technical specifications supplied by Kinemetrics describe the possibility
of using an external GPS receiver through the use of some lines of the con-
nector labelled as "Ext. GPS" on the front panel of the Q330. In this case, it
is possible to export the data in NMEA format directly from the GPS recei-
ver through a serial interface made available physically via this connector (sup-
ported by two serial standards: RS-232 and RS-422).
For our needs for the running of a data acquisition experiment from the sea-
floor, there was the need to use an external GPS receiver to be connected to
the Q330 datalogger via a serial cable of a length of about 400 m . Initially, we
thought to use the active GPS antenna, provided with the equipment for the
Q330 datalogger with an appropriate RF cable of the required length. This,
however, meant that there was the need for a line-amplifier for the GPS signal
due to the high loss along the cable (about 0.3 dB·m-1 for a very good quality
cable), without knowing if it would be possible to continue to use the GPS
receiver inside the Q330 on the seafloor, at about 100 m feet in depth.
Therefore, it was preferable to modify the Q330 datalogger by taking out the
integrated GPS receiver and designing two electronic modules that would at
the same time provide for further functions. Importantly, these would act as
RS-485 interfaces between the GPS receiver (once removed from the Q330)
and the datalogger, allowing the digital GPS signals to be passed over long dis-
tances (up to 3,000 metres of cable with a baud-rate of 9,600 bps, or over with
appropriate digital line amplifiers that are commercially available at low-cost).
The bidirectional interface conversion system from the serial RS-232 standard
(TTL with active low voltage levels of +3 V) to the RS-485 bus standard, here
referred to as GPS-485, comprises two electronic modules that need to be
installed as described below.
Specifically, the system allows the reception of the data by the Q330 from the
above-mentioned GPS receiver connected to the antenna, through a serial
cable provided of four differential twisted pairs. This allows the exchange of
control data and the receiving of information from the GPS, with the recei-
ving of the 1PPS signal and the turning on (and turning off) of part of the
electronics of the two interfaces, and consequently, of the GPS receiver.
The system comprises:
– Antenna for receiving the GPS signal;
– Interface board (referred to as the GPS-485 receiver side) with which, as
indicated below, the GPS receiver module from the Q330 will be connec-
ted. It also contains the RS-232/RS-485 interface with the line-
driver/receiver circuits, the power supply circuits, and all the electronics
necessary for the monitoring of the charge condition of a specific back-up
battery for the GPS module;
S. Guardato, G. Iannaccone
388
– Serial connection cable (1:1) for the two boards;
– Interface board (referred to as the GPS-485 datalogger side) containing, as
will be shown later, the RS-485/RS-232 interface with the line-driver/recei-
ver circuits, and the power supply circuits.
Figure 1 illustrates the complete connection scheme of the two interface
boards with the GPS antenna and the Q330 datalogger.
RS-485 interface for external use of the GPS receiver of the Kinemetrics® dataloggers
389
Fig. 1. The final connection scheme.
INTERFACE DESCRIPTION
The system includes two interface boards. One of these (on the GPS receiver
side) contains all of the electronics necessary for the power supply to the GPS
receiver, the active antenna, and the interface circuits necessary for the control
of the GPS data to be transmitted through the RS-485 bus with a serial cable
over long distances. This board can also receive configuration commands
from the GPS receiver that are sent from the datalogger; in particular, this
board is used to interface this information from electrical levels that conform
to the RS-485 standard, to TLL at +3 V logic levels.
The other board (on the datalogger side) will carry out the same functions as
the board above but in an opposite sense, except regarding the GPS receiver
and the antenna, which, obviously, are not a part of this side.
The exchange of information between these two interface boards is through
the above-mentioned cable containing four twisted pairs (with a characteristic
impedence of 120 Ω). The cable can be up to 3 km in length.
The interface boards are completely active only when the GPS is turned on via
the Willard© management software of the datalogger. Once this is done, the
controlling digital differential line reaches the high-logic state and activates all
the rest of the electronics that had remained in standby mode. The introduc-
tion of the two interface boards allows the use of the GPS receiver for the
datalogger in an fully transparent mode.
No software modifications are needed for the system, which will therefore
continue to function as before. The two boards can be installed inside their
own containers to protect them from external atmospheric agents, or they can
be mounted in the same box that normally contains the instrumentation.
THE DATALOGGER-SIDE BOARD
The Figure 2 shows the interface circuit that manages the data acquired by
the GPS receiver and that is directly connected to the datalogger (modified).
Table 1 provides a summary of the technical specifications of this circuit
board.
S. Guardato, G. Iannaccone
390
Fig. 2. GPS-485 (datalogger side).
The power supply to the board is external and can be provided by a normal
12 V battery. The power supply input circuit is protected by a self-resetting
fuse to protect against possible short circuits or other anomalies; moreover,
there is also diode protection against possible accidental inversions of the
polarity of the power supply.
There are also two switching-type voltage regulators. One of these provides
the power supply at +5 V for the line-driver/receiver circuits for the RS-485
bus. The other voltage regulator, at +3 V output, provides the power supply
for the step-down DC/DC converter from +5 V to +3 V for the signals recei-
ved from the GPS receiver module1.
The line driver/receiver interface circuits on the RS-485 bus in this board are
used to be able to correctly carry out dialogue with the remote GPS receiver.
In particular, this involves adapting the differential signals received (RX+,
RX-, 1PPS+ and 1PPS-) to a TLL logic level standard and then to adapt them
to a TLL logic level at +3 V, as described below. As a similar concept, but in
the opposite sense, this is done to adapt the differential signals to be trans-
mitted to the GPS receiver (TX+, TX-, ON+ and ON-) and to the activation
circuit of the power supply, from a TLL logic level at +3 V to differential
levels compatible with the characteristics of the RS-485 bus.
An equivalent circuit was planned for the differential input signal pair (1PPS+
and 1PPS-) coming from the GPS receiver, and for the differential output
signal pair (ON+ and ON-) needed for the remote turning on of the GPS
receiver (which under normal running conditions the current absorption is
about 100 mA).
Downstream of the 1PPS signal received, there is a LED that flashes at a fre-
quency of 1 Hz to indicate the correct functioning of the external GPS receiver.
As indicated above, the interface line-receiver circuits on the RS-485 bus
installed on this board have output signals at the TLL logic level standard.
RS-485 interface for external use of the GPS receiver of the Kinemetrics® dataloggers
391
1 In this case, for the power supply to the interface board on the side of the K2 datalogger, no
power supply circuits are needed at present. Indeed, here the need is only for a voltage of +5 V
for the power supply to the line driver/receiver circuits on the RS-485 bus that is taken from the
connector of the datalogger itself that is normally used as the power supply of the internal GPS
receiver. Moreover, the +3 V voltage is not needed because the GPS receiver (ACEIII, Trimble®)
has a serial communication interface with the TTL standard of +5 V.
Power supply 8 ÷ 14 V DC
Current 30 mA @ 12 V DC
Data Rate Up to 100 kbps for a cable length less than 1200 m 
Connectors DB9 male (RS-485 cable side)
DB9 female (datalogger side)
Monitor LEDs GPS power, 1PPS
Container Plastic box 
Weight 40 g
Dimensions 100 x 50 x 20 mm
Tab. 1. Technical specifications of the board on the datalogger side.
Since it is planned that the interface to the GPS receiver of the Q330 will carry
out dialogue with the Q330 via a serial port with a TLL of +3 V, instead of
the standard, the signals received (RX and 1PPS) need to be adapted to this
voltage logic level.
An equivalent circuit was planned for the RX input signal coming from the
GPS receiver2.
THE GPS RECEIVER-SIDE BOARD
The Figure 3 shows the interface circuit that manages the data acquired by the
GPS receiver removed from the Q330 (and the commands directed to it) to
be transmitted to (received by) the Q330 datalogger (modified) via the serial
connection cable on the RS-485 bus, and Table 2 provides a summary of the
technical specifications of this board.
S. Guardato, G. Iannaccone
392
2 In this case, there are no DC/DC step-down converter circuits. Indeed, here the need is only for
a single pair of line-driver/receiver circuits on the RS-485 bus, because the GPS receiver (ACEIII)
has a serial communication interface with the TTL standard of +5 V.
Fig. 3. GPS-485 (GPS receiver side).
The power supply is also external for this board and can be provided by a nor-
mal 12 V battery. The power supply input circuit is protected by a self-reset-
ting fuse to protect against possible short circuits or other anomalies; moreo-
ver, it is also protected by a diode against possible accidental inversions of the
polarity of the power supply. There are also three switching-type voltage regu-
lators that are the same as those for the interface board on the datalogger side.
One of these provides the power supply at +5 V for the line-driver/receiver
circuits for the RS-485 bus. The other two voltage regulators at +3 V provide
the power supplies for the step-down DC/DC converter from +5 V to +3 V
for the signals transmitted by the GPS module towards the datalogger, and for
the power supply to the GPS antenna.
The electronics scheme adopted for the power supply section is the same as
that for the interface board on the datalogger side, with the particular consi-
derations already discussed.
In addition, there is a monitoring circuit for the recharging of the 3 V lithium
back-up battery for the retain of the data received by the GPS module in the
case of loss of external power.
In the same way, the line-driver/receiver interface circuits on the RS-485 bus
on this board are also used to allow dialogue between the GPS receiver and
the remote datalogger. In particular, this involves the adapting of the diffe-
rential signals transmitted to the datalogger (TX+, TX-, 1PPS+ and 1PPS-) to
a TTL logic level standard and then their adapting to a TLL logic level of +3
V. The same procedure, but from the opposite side, is followed to adapt the
differential command signals transmitted from the datalogger to the GPS
receiver (RX+, RX-, ON+ and ON-) and to the power supply activation cir-
cuit, from TLL logic levels at +3 V to differential levels on the RS-485 bus.
The pair of integrated devices used is the same as that for the interface board
on the RS-485 bus for the datalogger side with the relevant changes in the
input/output signals.
Also in this case, the signals needed for the dialogue with the GPS receiver
must be converted to +3 V. Therefore, a pair of voltage step-down DC/DC
converters are used, identical to those designed for the interface board on the
RS-485 interface for external use of the GPS receiver of the Kinemetrics® dataloggers
393
Power supply 8 ÷ 14 V DC
Current 40 mA @12 V DC (GPS receiver off)
Data Rate Up to 100 kbps for a cable length less than 1200 m
Connectors DB9 male (cable side)
MMCX plug (GPS antenna)
Monitor LEDs GPS Power, 1PPS 
Container Plasic box 
Weight 80 g (GPS receiver not included)
Dimensions 150 x 80 x 20 mm
Tab. 2. Technical specifications of the board on the GPS receiver side.
datalogger side, with the exception that the signals to be treated are RX and
POWER_ENABLE (ON)3.
ELECTRICAL INTERCONNECTIONS
The interface board for the RS-485 bus on the GPS receiver side has a DB9
male connector mounted on the printed circuit, which makes available the dif-
ferential signals for the transmission of the GPS data (TX+ and TX-), the
transmission of the 1PPS logic signal (1PPS+ and 1PPS-) and the reception
of commands directed to the GPS receiver module (RX+ and RX-) coming
from the datalogger, as well as a pair of activation signals (ON+ and ON-)
that allow the remote turning on and partial turning off of the boards through
the Willard software.
The GPS receiver side board also has a connector (SamTech®, FTSH-105-D2-
L-DH header) mounted on the printed circuit on which the logic signals (TTL
+3 V, negative logic) are available for transmission of the GPS data (TX) and
of the 1PPS logic signal from the GPS receiver module, and for the reception
of commands directed for the GPS receiver module (RX) coming from the
Q330 datalogger after the voltage conversion from the RS-485 level. This con-
nector also has an activation line that provides remote control for the turning
on and the partial turning off of the board.
The interface board for the RS-485 bus on the datalogger side has two DB9
connectors (male and female) mounted on the printed circuit. These make
available the differential signals for the transmission of commands destined
for the GPS receiver (TX+ and TX-), the reception of the 1PPS timing signals
(1PPS+ and 1PPS-), and the reception of the GPS data for the datalogger
(RX+ and RX-) coming from the GPS receiver, as well as a pair of transmis-
sion signals (ON+ and ON-) that provide remote control for the turning on
and the partial turning off of the board.
S. Guardato, G. Iannaccone
394
3 In this case, there is the need for a single switching voltage regulator at +5 V and there are no
step-down DC/DC converter circuits, in agreement with the considerations indicated above.
Automatic analysis of seismic data
by using Neural Networks:
applications to Italian volcanoes
F. Giudicepietro1, A. Esposito1, L. D’Auria1, M. Martini1, S. Scarpetta2
1 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli (Osservatorio Vesuviano), Italy
2 Dipartimento di Fisica “E.R. Caianiello”, Università di Salerno, Italy
Abstract: The availability of the new computing techniques allows to perform
advanced analysis in near real time, improving the seismological monitoring
systems, which can extract more significant information from the raw data in a
really short time. However, the correct identification of the events remains a
critical aspect for the reliability of near real time automatic analysis. We
approach this problem by using Neural Networks (NN) for discriminating
among the seismic signals recorded in the Neapolitan volcanic area (Vesuvius,
Phlegraean Fields). The proposed neural techniques have been also applied to
other sets of seismic data recorded in Stromboli volcano. The obtained results
are very encouraging, giving 100% of correct classification for some transient
signals recorded at Vesuvius and allowing the clustering of the large dataset of
VLP events recorded at Stromboli volcano.
INTRODUCTION
Active volcanoes produce a wide variety of seismic events related to different
physical processes. A systematic and efficient monitoring of the volcanic acti-
vity helps in eruption forecasting and provides the scientific data to under-
stand the structure and dynamics of the volcanoes.
A key contribute to the monitoring improvement is the automation of many
functions, which can enhance the capability to analyze several types of data in
short time and to determine the significant parameters for volcano status
description. Thus, an effective automatic strategy for the detection and discri-
mination of seismic signals integrated into an analysis system in real time
could considerably reduce the heavy and time-consuming work of the experts
without affect the monitoring system reliability.
Several methods exist in literature for the detection and discrimination of dif-
ferent typologies of seismic signals (Hartse et al., 1995; Gitterman et al., 1999;
Joswig 1990; Rowe et al., 2004). However, encouraging results have been rea-
395


RS-485 interface for external use of the GPS receiver of the Kinemetrics® dataloggers

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RS-485 interface for external use of the GPS receiver of the Kinemetrics® dataloggers

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