Delta OHM HD9408.3B User manual



Operating manual
Barometric transmitter
HD9408.3B
www.deltaohm.com
Companies / Brands of
GHM
English
Keep for future reference.

HD9408.3B - 2 - V1.2
TABLE OF CONTENTS
1INTRODUCTION.................................................................................................... 3
2DESCRIPTION....................................................................................................... 4
3INSTALLATION ..................................................................................................... 5
3.1ELECTRICAL CONNECTIONS OF THE MODELS HD9408.3B.1 AND HD9408.3B.2 ..................... 5
3.1.1RS485 CONNECTION ................................................................................ 5
3.1.2RS422 CONNECTION ................................................................................ 6
3.1.3RS232 CONNECTION ................................................................................ 7
3.1.4CONNECTION OF THE ANALOG OUTPUT ............................................................ 7
3.2ELECTRICAL CONNECTIONS OF THE MODEL HD9408.3B.3 ................................................ 8
3.2.1SDI-12 CONNECTION ............................................................................... 8
4CONFIGURATION.................................................................................................. 9
4.1CHOOSING THE DIGITAL OUTPUT TYPE IN HD9408.3B.1 AND HD9408.3B.2 MODELS .................. 9
4.2CHOOSING THE PROTOCOL IN HD9408.3B.1 AND HD9408.3B.2 MODELS ........................... 9
4.3SELECTING THE UNIT OF MEASUREMENT .................................................................... 10
4.4CONFIGURING THE ANALOG OUTPUT ......................................................................... 10
4.5SERIAL COMMANDS OF DELTA OHM PROTOCOL FOR HD9408.3B.1 AND HD9408.3B.2 ............. 11
4.6SERIAL COMMANDS OF DELTA OHM PROTOCOL FOR HD9408.3B.3................................... 14
5MODBUS-RTU PROTOCOL.................................................................................... 17
5.1MEASUREMENTS READING ..................................................................................... 17
5.2SETTING THE MODBUS PARAMETERS ....................................................................... 17
5.3CONFIGURATION REGISTER.................................................................................... 19
5.4ERROR REGISTER ............................................................................................... 19
6NMEA PROTOCOL ................................................................................................ 20
7SDI-12 PROTOCOL .............................................................................................. 21
8TECHNICAL SPECIFICATIONS ............................................................................. 26
9INSTRUMENT STORAGE ...................................................................................... 28
10SAFETY INSTRUCTIONS...................................................................................... 28
11ORDERING CODES .............................................................................................. 29

HD9408.3B - 3 - V1.2
1INTRODUCTION
HD9408.3B is a barometric transmitter that uses a piezoresistive high accuracy and
temperature-compensated sensor. It allows measuring the atmospheric pressure in
the range 0…1350 hPa (digital outputs) or 500...1200 hPa (analog outputs), providing
extreme accuracy and time stability, with excellent repeatability, low hysteresis, and
excellent temperature behavior.
The superior performances are obtained thanks to the employment of a piezoresistive Sil-
icon sensor that integrates both a pressure sensitive as well as a temperature sensitive
element. The measurement of pressure and temperature are processed by a microproc-
essor to obtain an output signal that is compensated over the transmitter’s whole, wide
temperature operating range: -40…+85°C.
The sensor is factory calibrated at several points at different temperatures in the
range of use.
The transmitter is available in three versions which differ in the output type:
•HD9408.3B.1: configurable 0…5 V or 1…5 V analogue voltage output and digi-
tal RS232, RS422 or RS485 output. Standard MODBUS-RTU and NMEA 0183
protocols.
•HD9408.3B.2: active configurable 0…20 mA or 4…20 mA current output and
digital RS232, RS422 or RS485 output. Standard MODBUS-RTU and NMEA 0183
protocols.
•HD9408.3B.3: digital SDI-12 output, compatible with version 1.3 of the proto-
col.
The digital output enables the transmission of the measurements over long distances
and connects the transmitter to sensor networks.
The pressure measured and transmitted with MODBUS RTU and SDI-12 protocols can
be expressed in different user-selectable measuring units.
The watertight housing with IP 67 protection degree allows the use of the instrument
even in harsh environments.
The instrument is particularly suitable for meteorological applications (AWOS - Auto-
mated Weather Observing Systems), environmental monitoring systems, meteorologi-
cal and environmental data logging, measurement laboratories, atmospheric pressure
compensation in the performance of internal combustion engines, barometric pressure
compensation in clean rooms, vehicle emission test.
Its low power consumption makes it ideal for remote acquisition systems such as au-
tomatic weather stations powered by solar cells.
DC power supply 10…30 Vdc.

HD9408.3B - 4 - V1.2
2DESCRIPTION
1. Housing mounting holes.
2. M12 connector for power supply and outputs.
3. Barometric pressure input.

HD9408.3B - 5 - V1.2
3INSTALLATION
The sensor and electronics are housed in a sturdy metal housing with IP 67 degree of
protection. The transmitter can be mounted in any position, but typically is attached
to a vertical wall with the outlet pressure facing downward. The two holes on the
housing’s sides allow you to secure the base of the transmitter directly to a panel or a
wall. See the chapter “TECHNICAL SPECIFICATIONS” for the dimensions of the mounting
holes.
3.1 ELECTRICAL CONNECTIONS OF THE MODELS HD9408.3B.1 AND HD9408.3B.2
The transmitters HD9408.3B.1 and HD9408.3B.2 have an 8-pole M12 male connector.
On request, CP18… cables with 8-pole M12 female connector and 2 or 5 m
standard length are available (other lengths on request).
Fig. 3.1.1: cable CP18…
TAB. 3.1.1: connections of HD9408.3B.1 and HD9408.3B.2
Function
Connector
numbering Symbol Description
12-pole cable
numbering
1 PWR- Power Negative / serial grounding 12
2 PWR+ Power Positive 1
3 RX- Rx- for RS422 3
4 TX- Tx for RS232/ Tx- for RS422 / DATA- for RS485 9
5 TX+ Tx+ for RS422 / DATA+ for RS485 5
6 RX+ Rx for RS232/ Rx+ for RS422 8
7 AGND Analog output Negative 10
8 AOUT Analog output Positive 11
3.1.1 RS485 CONNECTION
The RS485 connection of the transmitter is made over a screened twisted-pair cable for
the signals and a third grounding wire.
At the beginning and at the end of each segment you should apply the line terminator.
The maximum number of devices that can be connected to the (Bus) line 485 depends
on the load characteristics of the devices to be connected. The RS485 standard requires
that the total load does not exceed 32 unit loads. The load of a transmitter is equal to 1
unit load. If the total load is greater than 32 unit loads, divide the network into segments
and then put a signal repeater between a segment and the next. At the beginning and
end of each segment of the line, terminations should be applied. The RS485 output of the
transmitter is not isolated.
Male M12 connecto
r
of the transmitter
Numberin
g
on
the
cable wires
Cable CP18….

HD9408.3B - 6 - V1.2
Fig. 3.1.2: RS485 output connection
The cable maximum length depends on baud rate and cable characteristics. Typically,
the maximum length is 1200m. The data line must be kept separated from any power
lines in order to prevent interferences on the transmitted signal.
Each transmitter placed on the network is univocally identified by an address. Trans-
mitters having the same address shall not be present in the network.
NMEA, MODBUS-RTU and Delta OHM proprietary protocols can be used with RS485
connection. Before connecting the instrument to the network, configure address and
Baud Rate (see paragraph 4.5).
3.1.2 RS422 CONNECTION
The RS422 standard is used for the point-to-point connection over long distances. The
instrument is connected to the PC by means of a screened cable with two twisted-pair
cables for the signals and an additional wire for grounding. It is necessary to provide
for line terminations at the ends of the connections.
Fig. 3.1.3: RS422 connection
Shield
Power su
pp
l
y
10…30 Vdc
CP18…cable
PLC, datalo
gg
er o
r
converter RS485/USB
or RS485/RS232 for PC
Other sensors with
RS485 output
Termination
T
ermination
Termination
T
ermination
Power su
pp
l
y
10…30 Vdc
PLC, datalo
gg
er o
r
converter RS422/USB
or RS422/RS232 for PC
Shield
CP18…cable

HD9408.3B - 7 - V1.2
The cable maximum length depends on baud rate and cable characteristics. Typically,
the maximum length is 1200m. The data line must be kept separated from any power
lines in order to prevent interferences on the transmitted signal.
NMEA, MODBUS-RTU and Delta OHM proprietary protocols can be used with RS422
connection. Before connecting the instrument to the network, configure address and
Baud Rate (see paragraph 4.5).
3.1.3 RS232 CONNECTION
The length of RS232 cables should not exceed 15 m. If the PC is not fitted with RS232
serial ports, it is possible to interpose the adapter cable RS52 (optional) between in-
strument and PC, which has an integrated USB/RS232 converter.
Fig. 3.1.4: connection of RS232 output
NMEA and Delta OHM proprietary protocols can be used with RS232 connection.
3.1.4 CONNECTION OF THE ANALOG OUTPUT
Fig. 3.1.5: connection of the active 0…20/4…20 mA analog output
In case of analog current output, the maximum shunt resistance Rs of the receiver
depends on the power supply: Rs ≤100 Ω@ 12V, Rs ≤700 Ω@ 24V.
Fig. 3.1.6: connection of analog 0…5/1…5 V voltage output
Power su
pp
l
y
10…30 Vdc
RS232 serial
p
ort
CP18…cable
Shield
Instrument with current in
p
ut
CP18…cable
Shield
10…30 Vdc
p
ower su
pp
l
y
Instrument with volta
g
e in
p
ut
CP18…cable
Shield
10…30 Vdc
p
ower su
pp
l
y

HD9408.3B - 8 - V1.2
In case of analog voltage output, the input resistance Rin of the receiver should be at
least 100 kΩ.
3.2 ELECTRICAL CONNECTIONS OF THE MODEL HD9408.3B.3
The transmitter HD9408.3B.3 has a 4-pole M12 male connector. On request,
CPM12AA4… cables with flying 4-pole M12 connector with 2 or 5 m standard
length are available (other lengths on request).
Fig. 3.2.1: CPM12AA4… cable
TAB. 3.2.1: connections of HD9408.3B.3
Function
Connector
numbering Symbol Description Color
1 PWR- Power Negative / serial grounding Blue
2 PWR+ Power Positive Red
3 Screen Black
4 SDI SDI-12 data line White
3.2.1 SDI-12 CONNECTION
More SDI-12 sensors can be connected in parallel. The distance between a sensor and
the acquisition system should not exceed 60 m. Before connecting the instrument to
an SDI-12 network containing other sensors, set the address by using the proper SDI-
12 command (see chapter 7).
Fig. 3.2.2: SDI-12 connection
M12 male connecto
r
of the transmitter
Blue
(
1
)
CPM12AA4… cable
Red
(
2
)
Black
(
3
)
White
(
4
)
10…30 Vdc
p
ower su
pp
l
y
CPM12AA4… cable
Other SDI-12 senso
r
Datalo
gg
er in
p
ut
Other SDI-12 senso
r

HD9408.3B - 9 - V1.2
4CONFIGURATION
When powered, the transmitter always starts to operate with the set operating proto-
col. The models HD9408.3B.1 and HD9408.3B.2 are factory set with MODBUS-RTU
protocol, RS485 physical interface, Baud Rate 19200 and communication parameters
8E1. To change the settings of the transmitter, see the next paragraphs.
4.1 CHOOSING THE DIGITAL OUTPUT TYPE IN HD9408.3B.1 AND HD9408.3B.2 MODELS
The models HD9408.3B.1 and HD9408.3B.2 allow selecting the type of digital output
(RS232, RS422 or RS485) on hardware level, by means of dip switches on the elec-
tronic board, or at software level, by means of an appropriate serial command. By de-
fault, the RS485 output via the dip switches is set. To access the dip switches, unscrew
the screws fixing the housing cover, remove the cover and set the dip switches as
shown in figure 4.1.1.
Fig. 4.1.1: selecting the digital output by means of the dip switches
The setting via the dip switches has priority over the setting via serial command. By
selecting the option "SW set", the transmitter uses the digital output set at software
level with the serial command CPI described in paragraph 4.5.
4.2 CHOOSING THE PROTOCOL IN HD9408.3B.1 AND HD9408.3B.2 MODELS
In the models HD9408.3B.1 and HD9408.3B.2, NMEA 0183 and MODBUS-RTU stan-
dard protocols and Delta OHM proprietary protocol are available. The selection of the
protocol is done via the serial command CPI described in paragraph 4.5. If the trans-
mitter digital output is set by means of the dip switches, the choice of the protocol
must be compatible with the selected physical interface, as reported in table 4.2.1. By
default, the MODBUS-RTU protocol with RS485 physical interface is set.

HD9408.3B - 10 - V1.2
TAB. 4.2.1: compatibility of physical interface/protocols in models HD9408.3B.1
and HD9408.3B.2
Physical Interface
RS232 RS422 RS485
Delta OHM Proprietary 999
MODBUS-RTU 99
Protocol
NMEA 0183 999
4.3 SELECTING THE UNIT OF MEASUREMENT
The pressure measured and transmitted via the digital output with MODBUS-RTU and
SDI-12 standard protocols can be expressed in a user selectable unit of measurement
among: Pa, hPa, kPa, mbar, bar, atm, psi, mmHg, inHg, mmH2O, ftH2O, kg/cm2, Torr.
The default unit is hPa. The unit setting is done with the serial command CPU described
in paragraph 4.5. Table 4.3.1 shows the resolution of the measurement as a function of
the selected unit.
TAB. 4.3.1: measuring unit and resolution with Modbus and SDI-12 protocols
Unit of measurement Resolution
Pa 1 Pa
hPa 0.01 hPa
kPa 0.001 kPa
mbar 0.01 mbar
bar 0.00001 bar
atm 0.00001 atm
psi 0.0001 psi
mmHg 0.001 mmHg
inHg 0.0001 inHg
mmH2O 0.1 mmH2O
ftH2O 0.0001 ftH2O
kg/cm20.00001 kg/cm2
Torr 0.001 Torr
With the NMEA 0183 standard protocol, the pressure value is transmitted in two fixed
units: Pa and bar. With the Delta OHM proprietary protocol, the pressure is transmit-
ted in the fixed units mbar, psi and hPa.
4.4 CONFIGURING THE ANALOG OUTPUT
The analog output in the models HD9408.3B.1 and HD9408.3B.2 is factory preset to
have the output signal corresponding to the 500…1200 hPa measuring range. The
analog output can be configured so as to have the output signal corresponding to a
different measuring range by using the serial commands CAI (sets the initial value of
the measuring interval) and CAF (sets the final value of the measuring interval).
To reverse the operation of the analog output, so that the output signal decreases as
the measured pressure increases, use the serial command CAiE. To cancel the inver-
sion and restore the output normal operation, use the serial command CAiD.

HD9408.3B - 11 - V1.2
To add or remove an offset to the minimum value of the output signal, so that to pass
from the range 0…5 V or 0…20 mA to the range 1…5 V or 4…20 mA and vice versa,
use the serial commands CAOE (adds the offset) and CAOD (remove the offset). The
default mode is without offset.
The details on the use of the serial commands are described in paragraph 4.5.
4.5 SERIAL COMMANDS OF DELTA OHM PROTOCOL FOR HD9408.3B.1 AND HD9408.3B.2
All the operating parameters can be set by connecting the transmitter to the PC and
sending, via a standard serial communication program, the serial commands of the
Delta OHM proprietary protocol.
The Delta OHM proprietary protocol can be used with RS232, RS485 and RS422 digital
outputs. If the RS232 output is used and the PC has only USB ports, place between
the PC and the instrument a RS232/USB converter. If the RS422 or RS485 digital out-
put is used, place between the PC and the instrument a converter from RS422 or
RS485 to RS232 or USB. For the wiring diagrams, see chapter “INSTALLATION”.
If a USB converter is used, it is necessary to install the relevant USB drivers
in the PC.
NOTES ON THE INSTALLATION OF UNSIGNED USB DRIVER:before installing unsigned USB driver into
operating systems starting from Windows 7, it is necessary to restart the PC by disabling the
driver signing request. If the operating system is 64-bit, even after installation the request of
driver signing have to be disabled each time the PC is restarted.
PROCEDURE FOR SETTING THE PARAMETERS:
1. Connect the transmitter to the PC according to the selected digital output (the fac-
tory-set digital output is RS485) and power the transmitter. The transmitter always
starts to operate with the set operating protocol.
2. Start a serial communication program, as Hyperterminal for instance. In the pro-
gram, set the COM port number to which the transmitter is connecting and set the
communication parameters the same as those of the protocol currently operating in
the instrument: “57600 8N2” for proprietary protocol, “19200 8E1” for MODBUS -
RTU (default settings, the MODBUS -RTU parameters are configurable), “4800 8N1”
for NMEA.
3. If the set operating protocol is different from the Delta OHM proprietary protocol
(the factory-set protocol is MODBUS-RTU), send the command ||| (sequence of
three 124 decimal code ASCII characters followed by the Enter key). The trans-
mitter replies with the sequence &|.
4. Within 10 seconds from the previous command, send the command @(64 decimal
code ASCII character followed by the Enter key) to confirm the switch to the Delta
OHM proprietary protocol. The transmitter replies with the sequence &|. Switching
to the Delta OHM proprietary protocol, the previous communication parameters
(baud rate, data bits, parity and stop bits) are maintained.
Note: if the transmitter does not receive the command @within 10 seconds from
the command |||, the previous protocol is automatically restored.
5. Send the command CAL USER ON.
Note: the command CAL USER ON is disabled after 5 minutes of inactivity. The
command is necessary only for the configuration writing commands, it is not nec-
essary for the configuration reading commands.

HD9408.3B - 12 - V1.2
6. Send the serial commands reported in table 4.5.1 to configure the transmitter or
read the current settings.
7. To go back to the operating protocol, send the command #(35 decimal code AS-
CII character followed by the Enter key) or power cycle the instrument.
TAB. 4.5.1: serial commands for HD9408.3B.1 and HD9408.3B.2
Command Reply Description
Instrument general information
P0 & Ping
G0 Model Instrument model
G2 SN=number Serial number
G3 Firm.Ver.=version Firmware version
G4 Firm.Date=date Firnmware date (yyyy/mm/dd)
GD F cal:date and time Date of factory calibration (yyyy/mm/dd hh:mm:ss)
Measurements request
S0 & ##.##C (or F)
####.####mbar
##.####psi /F
####.##hPa|
Last temperature (in °C or °F, accuracy ±1 °C) and pres-
sure (in mbar, psi and hPa) value measured.
The parameter “/F” that appears in the reply is reserved.
S1 & ##.##C (or F)
####.####mbar
##.####psi /F
####.##hPa|
Continuous sending, once per second, of the last tem-
perature (in °C or °F, accuracy ±1 °C) and pressure (in
mbar, psi and hPa) value measured.
The parameter “/F” that appears in the reply is reserved.
Configuration of physical interface and protocol
CPIn &| Sets the physical interface and the protocol:
n=0⇒RS485 with MODBUS-RTU protocol
n=1⇒RS422 with MODBUS-RTU protocol
n=2⇒RS232 with NMEA 0183 protocol
n=3⇒RS485 with NMEA 0183 protocol
n=4⇒RS422 with NMEA 0183 protocol
n=5⇒RS232 with Delta OHM proprietary protocol
n=6⇒RS485 with Delta OHM proprietary protocol
n=7⇒RS422 with Delta OHM proprietary protocol
Preset to 0 ⇒RS485 with MODBUS-RTU protocol.
Note 1: if the physical interface is set via hardware with
the dip switches, only the commands setting a physical
interface equal to that set via hardware are accepted.
Note 2: if the dip swtiches are set to "SW set", the
command is always accepted, even if an interface differ-
ent from the current physical connection is set (in such a
case you will need to change the connections according
to the new interface set in order to communicate again
with the instrument).
RAP & n| Reads the setting of physical interface and protocol (see
the command CPUn for the meaning of the value n).

HD9408.3B - 13 - V1.2
Command Reply Description
Configuration of units of measurement
CPTx &| Sets the temperature unit of measurement read with the
MODBUS and SDI-12 protocols: x=C⇒°C, x=F⇒°F
Preset to C ⇒°C
RAT & unit of measure-
ment|
Reads the temperature unit of measurement set for the
MODBUS and SDI-12 protocols.
CPUn &| Sets the pressure unit of measurement read with the
MODBUS and SDI-12 protocols:
n=0⇒Torr, n=1⇒Pa, n=2⇒hPa, n=3⇒kPa
n=4⇒mbar, n=5⇒psi, n=6⇒kg/cm2, n=7⇒mmH2O
n=8⇒mmHg, n=9⇒inHg, n=A⇒atm, n=B⇒bar
n=C⇒ftH2O
Preset to 2 ⇒hPa
RAU & n F| Reads the pressure unit of measurement set for MODBUS
and SDI-12 protocols. See command CPUn for the unit of
measurement corrresponding to the value n.
“F” is a reserved parameter.
Configuration of MODBUS-RTU parameters
CMAnnn &| Sets the Modbus address to nnn (1…247). Preset to 1.
RMA & nnn| Reads the Modbus address.
CMBn &| Sets the Modbus Baud Rate:
n=0⇒9600, n=1⇒19200. Preset to 1 ⇒19200
RMB & n| Reads the Modbus Baud Rate: n=0 ⇒9600, n=1 ⇒
19200
CMPn &| Sets the Modbus transmission mode:
n=0⇒8N1, n=1⇒8N2, n=2⇒8E1
n=3⇒8E2, n=4⇒8O1, n=5⇒8O2
Preset to 2 ⇒8-E-1
Note: N=no parity, E=even parity, O=odd parity
RMP & n| Reads the Modbus transmission mode (see the command
CMPn for the mode corresponding to the value n).
CMWn &| Sets the receiving mode after the Modbus transmission:
n=0⇒Violate protocol and go in Rx mode right after Tx
n=1⇒Respect protocol and wait for 3.5 characters after
Tx
Preset to 1 ⇒Respect the protocol.
RMW & n| Reads the receiving mode after the Modbus transmission
(see the command CMWn for the mode corresponding to
the value n):
Configuration of NMEA 0183 parameters
CPDnnnn &| Sets the sending interval of the string with the meas-
urements in NMEA mode to nnnn seconds.
The interval must be between 1 and 3600 seconds.
Preset to 1 second.
RN & nnnn| Reads the setting of the sending interval of the string
with the measurements in NMEA mode.

HD9408.3B - 14 - V1.2
Command Reply Description
Configuration of analog output
CAInnnnn &| Associates the initial scale of the analog output to the
pressure value nnnnn expressed in tenth of hPa.
The parameter must be between 5000 (=500.0 hPa) and
the pressure value associated to the analog output full
scale. Preset to 5000.
RAI & nnnnn| Reads the value corresponding to the initial scale of the
analog output.
CAFnnnnn &| Associates the full scale of the analog output to the
pressure value nnnnn expressed in tenth of hPa.
The parameter must be between the pressure value asso-
ciated to the initial scale of the analog output and 12000
(=1200.0 hPa). Preset to 12000.
RAF & nnnnn| Reads the value corresponding to the full scale of the
analog output.
CAOE &| Adds the offset to the analog output (1…5 V or 4…20 mA).
CAOD &| Remove the offset from the analog output (0…5 V or
0…20 mA).
RAO & n| Reads the setting of the offset for the analog output:
n=0 ⇒senza offset, n=1 ⇒con offset
CAiE &| Reverses the direction of the analog output: 5…0 V,
5…1 V, 20…4 mA, 20…0 mA.
CAiD &| Cancel the inversion of the direction of the analog output.
RAi & n| Reads the setting of the direction of the analog output:
n=0 ⇒normal, n=1 ⇒reversed
Setting of sensor offset
CAXnnnn &| Adds the offset nnnn, expressed in hundredths of hPa,
to the measured pressure value.
The parameter must be between -1000 (=-10.00 hPa)
and +1000 (=+10.00 hPa). For positive values, always
indicate also the + sign. Preset to 0.
RAX & ##.##| Reads the offset set for the pressure measurement.
4.6 SERIAL COMMANDS OF DELTA OHM PROTOCOL FOR HD9408.3B.3
In the model HD9408.3B, the operating parameters can be set in two ways:
•directly with the SDI-12 protocol, via the extended commands described in chap-
ter 7;
•by connecting the transmitter to the PC through a converter from SDI-12 to
RS232 or USB, and by sending, via a standard serial communication program,
the serial commands of the Delta OHM proprietary protocol.
If a USB converter is used, it is necessary to install the relevant USB drivers
in the PC.
NOTES ON THE INSTALLATION OF UNSIGNED USB DRIVER:before installing unsigned USB driver into
operating systems starting from Windows 7, it is necessary to restart the PC by disabling the
driver signing request. If the operating system is 64-bit, even after installation the request of
driver signing have to be disabled each time the PC is restarted.

HD9408.3B - 15 - V1.2
PROCEDURE FOR SETTING THE PARAMETERS BY MEANS OF THE DELTA OHM PROTOCOL:
1. Connect the transmitter to the PC (connect only one transmitter at a time) and pow-
er the transmitter. The transmitter always starts to operate with the SDI-12 proto-
col.
2. Start a serial communication program, as Hyperterminal for instance. Set the follo-
wing communication parameters:
baud rate: 1200 data bits: 7, parity: Even, stop bits: 1
In the program, set the COM port number to which the transmitter is connecting.
3. Send the command aXf_int_424! where ais the address of the transmitter (de-
fault 0). The transmitter replies with fm activated!.
4. Change the settings of the serial communication program as follows:
baud rate: 57600 data bits: 8, parity: Even, stop bits: 2
5. Send the command CAL USER ON.
Note: the command CAL USER ON is disabled after 5 minutes of inactivity. The
command is necessary only for the configuration writing commands, it is not nec-
essary for the configuration reading commands.
6. Send the serial commands reported in table 4.6.1 to configure the transmitter or
read the current settings.
7. To go back to the operating protocol, power cycle the instrument.
TAB. 4.6.1: serial commands for HD9408.3B.3
Reply Description
Instrument general information
G0 a:Model Instrument model
G2 a:SN=number Serial number
G3 a:Firm.Ver.=version Firmware version
G4 a:Firm.Date=date Firnmware date (yyyy/mm/dd)
GD a:F cal:date and time Date of factory calibration (yyyy/mm/dd hh:mm:ss)
Measurements request
S0 & ##.##C (or F)
####.####mbar
##.####psi /F
####.##hPa|
Last temperature (in °C or °F, accuracy ±1 °C) and pres-
sure (in mbar, psi and hPa) value measured.
The parameter “/F” that appears in the reply is reserved.
S1 & ##.##C (or F)
####.####mbar
##.####psi /F
####.##hPa|
Continuous sending, once per second, of the last tem-
perature (in °C or °F, accuracy ±1 °C) and pressure (in
mbar, psi and hPa) value measured.
The parameter “/F” that appears in the reply is reserved.
Configuration of units of measurement
CPTx &| Sets the temperature unit of measurement read with the
MODBUS and SDI-12 protocols: x=C⇒°C, x=F⇒°F
Preset to C ⇒°C
RAT & unità di misura| Reads the temperature unit of measurement set for the
MODBUS and SDI-12 protocols.

HD9408.3B - 16 - V1.2
Reply Description
CPUn &| Sets the pressure unit of measurement read with the
MODBUS and SDI-12 protocols:
n=0⇒Torr, n=1⇒Pa, n=2⇒hPa, n=3⇒kPa
n=4⇒mbar, n=5⇒psi, n=6⇒kg/cm2, n=7⇒mmH2O
n=8⇒mmHg, n=9⇒inHg, n=A⇒atm, n=B⇒bar
n=C⇒ftH2O
Preset to 2 ⇒hPa
RAU & n F| Reads the pressure unit of measurement set for MODBUS
and SDI-12 protocols. See command CPUn for the unit of
measurement corrresponding to the value n. “F” is a re-
served parameter.
Setting of sensor offset
CAXnnnn &| Adds the offset nnnn, expressed in hundredths of hPa,
to the measured pressure value.
The parameter must be between -1000 (=-10.00 hPa)
and +1000 (=+10.00 hPa). For positive values, always
indicate also the + sign. Preset to 0.
RAX & ##.##| Reads the offset set for the pressure measurement.

HD9408.3B - 17 - V1.2
5MODBUS-RTU PROTOCOL
In MODBUS-RTU mode (only models HD9408.3B.1 and HD9408.3B.2), the instrument
sends the acquired measurements only if specifically requested by the PC, PLC or data
logger.
The protocol is available with RS485 and RS422 serial connections.
5.1 MEASUREMENTS READING
In MODBUS mode, the function code 04h (Read Input Registers) allows reading the
values measured by the instrument. Table 5.1.1 lists the MODBUS input registers
available:
TAB. 5.1.1: MODBUS Input Registers
Register
number
Register
address Quantity Format
1,2 0,1 Temperature in the set unit of measurement [x100] 16-bit integer
3,4 2,3
Atmospheric pressure in the set unit of measurement.
See table 4.3.1 for the position of the decimal point.
16-bit integer
The measurements are signed 32-bit integer values. To read a measurement, two
consecutive 16-bit registers must be accessed. The register with lower address (for
example register number 3 for the atmospheric pressure) contains the most signifi-
cant bytes.
Note: the accuracy of the temperature measurement is ± 1 °C. The resolution is hun-
dredths.
5.2 SETTING THE MODBUS PARAMETERS
To set the Modbus address and the Modbus communication parameters, if different
from the factory default values, use the serial commands CMA (sets the address),
CMB (sets the Baud Rate), CMP (sets the parity and the stop bits) and CMW (sets
the receiving mode) of the Delta OHM proprietary protocol (see the parameters set-
ting procedure in paragraph 4.5).
Alternatively, the parameters can be set directly with Modbus commands by writing
their values in the Holding Registers (see table 5.2.1) with the function code 06h
(Write Single Register) or 10h (Write Multiple Registers).
To check if the last writing operation has been completed successfully, verify that the
Holding Register number 1 (address 0) contains the value 0, by using the 03h function
code (Read Holding Registers).
The 06h and 10h writing functions change only the value of the parameters
in the RAM memory, the change is therefore cancelled in case of power sup-
ply failure in the instrument. To make the change permanent, write the hexadeci-
mal value FF00 in the Coil Register number 3 (address 2) by using the 05h function
code (Write Single Coil). The command 05h must be sent within 10 seconds from the
last 06h or 10h command.
To check if the permanent storage has been completed successfully, verify that the
Holding Register number 2 (address 1) contains the value 0, by using the 03h function
code (Read Holding Registers).

HD9408.3B - 18 - V1.2
TAB. 5.2.1: MODBUS Holding Registers
Register
number
Register
address Datum Format
1 0
Indicator of the correct execution of the last writing
command.
If 0, the command has been executed correctly.
If 1, command execution errors occurred.
16-bit integer
2 1
Indicator of the correct permanent storage of the pa-
rameters.
If 0, the parameters have stored correctly.
If 1, storage errors occurred.
16-bit integer
3 2 Error register (see paragraph 5.4) 16-bit integer
7 6 Configuration register (see paragraph 5.3) 16-bit integer
101 100 Modbus address (from 1 to 247). Preset to 1. 16-bit integer
102 101
Modbus Baud Rate. Acceptable values: 0 and 1.
If 0, the Baud Rate is 9600. If 1, the Baud Rate is 19200.
Preset to 1 ⇒19200
16-bit integer
103 102
Modbus transmission mode. Acceptable values: from 0
to 5.
0⇒8N1, 1⇒8N2, 2⇒8E1, 3⇒8E2
4⇒8O1, n=5⇒8O2
Preset to 2 ⇒8E1
Note: N=no parity, E=even parity, O=odd parity
16-bit integer
104 103
Receiving mode after the Modbus transmission.
Acceptable values: 0 and 1.
0⇒Violates the protocol and goes immediately in re-
ception mode after the transmission
1⇒Respects the protocol and waits for 3.5 characters
after the transmission
Preset to 1 ⇒Respects the protocol.
16-bit integer
TAB. 5.2.2: MODBUS Coils
Register
number
Register
address Datum
3 2 Permanent storage of the parameters.

HD9408.3B - 19 - V1.2
5.3 CONFIGURATION REGISTER
The configuration register (Holding Register number 7) allows applying an offset to
the pressure measurement and setting the pressure and temperature units of meas-
urement. The meaning of the register bits is shown in table 5.3.1.
TAB. 5.3.1: configuration register
Bit Description
0…10 Offset, expressed in hundredths of hPa, added to the measured pressure
value.
Must be between -1000 (=-10.00 hPa) and +1000 (=+10.00 hPa).
Preset to 0.
Bit 10 indicates the sign of the value. Bits 0…9 indicate the absolute value
expressed in 2’s complement (bit 0 is the less significant):
3E8h ⇒+1000, 7FFh ⇒-1, 418h ⇒-1000
11…14 Pressure unit of measurement read with the MODBUS protocol:
0h ⇒Torr, 1h ⇒Pa, 2h ⇒hPa, 3h ⇒kPa, 4h ⇒mbar, 5h ⇒psi,
6h ⇒kg/cm2, 7h ⇒mmH2O, 8h ⇒mmHg, 9h ⇒inHg, Ah ⇒atm,
Bh ⇒bar, Ch ⇒ftH2O
Bit 11 is the less significant. Preset to 2 ⇒hPa
15 Temperature unit of measurement read with the MODBUS protocol:
0⇒°C, 1⇒°F
Preset to 0 ⇒°C
5.4 ERROR REGISTER
The function code 03h (Read Holding Registers) allows reading the 16-bit register
number 3 (address 2) containing information on the possible error status of the
transmitter.
The bits of the register indicate the error condition according to the correspondence
shown in table 5.4.1.
TAB. 5.4.1: error register
Bit Description
0 General error
1,2 Error in the values of the configuration parameters in memory
3 Error in the program memory
4 The power supply of the instrument is outside the allowed limits
5 Communication error
6 Error executing the measurement
7 Check of the instrument calibration is necessary
8 The device has executed a reset
9 Timeout of the temperature measurement
10 Error in the management of the analog output
11 Invalid data format
12…15 Not used
The register is reset after the reading. If the error condition persists, the correspond-
ing bit is restored.

HD9408.3B - 20 - V1.2
6NMEA PROTOCOL
In NMEA mode (only models HD9408.3B.1 and HD9408.3B.2), the instrument sends
automatically the acquired measurements at regular intervals. The interval is factory-
set to 1 second and can be configured within 1 and 3600 seconds. To change the in-
terval you should send the serial command CPD of the Delta OHM proprietary protocol
(see the parameters setting procedure in paragraph 4.5).
The protocol is available with RS232, RS485 and RS422 serial connections. Communi-
cation parameters should be set in the PC or data logger as follows:
•Baud rate = 4800
•Data bits = 8
•Parity = Nessuna
•Stop bits = 1
The instrument is compatible with NMEA 0183 V4.00 protocol.
The protocol establishes that data are sent in the following format:
$PXDR,<Data>*<hh><CR><LF>
with:
<Data> = values measured by the instrument, separated by commas
<hh> = checksum, consisting in two hexadecimal characters
<CR> = character ASCII Carriage Return
<LF> = character ASCII Line Feed
The checksum is calculated by performing the exclusive OR of all characters ranging
within $and * symbols. The 4 most significant bits and the 4 less significant bits of
the result are converted in hexadecimal. The hexadecimal value corresponding to the
most significant bits is transmitted as the first.
The instrument regularly sends the following string:
$PXDR,P,xxxxxx,P,x.xxxxx,B,xx.xx,C*hh<CR><LF>
EXAMPLE
Suppose that there are the following environmental conditions:
oAtmospheric pressure = 1023.64 hPa
oTemperature = 26.28 °C
The strings sent by the instrument are:
$PXDR,P,102364,P,1.02364,B,26.28,C*3D<CR><LF>
Note: the accuracy of the temperature measurement is ± 1 °C.
For additional information regarding the protocol, visit the site "www.nmea.org".
Type
of
transduce
r
: P
(pressure)
Pressure measurement in pascal
Unit of measurement: pascal
Pressure measurement in ba
r
Unit of measurement: ba
r
T
emperature measurement in °C
Unit of measurement: °C