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11.9.2 Installation
Specific settings for GPRS communication in the CU 36X:
To find the parameter in the CU 36X, go to Settings >
Communication settings > GPRS settings >
• APN
• Username
• Password.
There are some advanced GPRS settings which have default
values that usually work, but in special cases, it might be
necessary to change some of them. This can only be done with
the Grundfos PC Tool WW Controls:
• Authentication: Normal/Secure. Only used by some service
providers. Default: Normal.
• Roaming: Enabled/Disabled. Default: Disabled.
• Modbus TCP port number. Default: 502.
• GENIpro port number. Default: 49152.
Other relevant settings in the CU 36X:
To find the parameter in the CU 36X, go to Settings >
Communication settings > SCADA settings >
• SCADA PIN code enabled
• SCADA PIN code.
11.9.3 Status
In the CU 36X display Status > System > GSM/GPRS, you will
see the following information:
• GPRS connection state
– Detached: No connection to any GPRS service.
– Attached: Connection to GPRS service established.
– Context active: IP address has been assigned, ready for a
client to establish a socket connection.
– Connected: A client has established a socket connection.
The system is ready for TCP/IP data exchange (or already
exchanging data).
• Total GPRS data sent (in kb).
• Total GPRS data received (in kb).
• IP address (e.g. 218.214.34.201).
The same display also supplies statistical information about SMS
messages, call-up connections and GSM signal strength.
Fig. 20
Modbus TCP telegram
11.9.4 Operation
When powering on a CU 36X with the correct GSM/GPRS setting,
the following GPRS connection sequence will take place:
1. The CIM 250 locates the GSM/GPRS service. The connection
state changes from "Detached" to "Attached".
2. The CIM 250 attempts to connect to the APN it has been
given and requests an IP address. The base station looks
through its record of legal SIM cards and finds the IP address
(the address associated with this SIM card) to assign to the
CIM 250. After the CIM 250 has got the IP address, the
connection state changes to "Context active".
3. The CIM 250 is now ready for a client (e.g. SCADA system) to
establish a socket connection and begin TCP/IP data
exchange. When a client connects the CU 36X, the
connection state will change to "Connected", and the GSM
status LED1 will indicate when data transfer takes place. See
section
.
A client, e.g. SCADA, establishes connection to a CU 36X by
specifying the IP address and the TCP port 502. Data transfer is
always initiated from the client in the form of a Modbus TCP
telegram embedded in a TCP/IP frame and directed to TCP port
502. To the client software, the connection to the CU 36X is
completely transparent.
The protection against unauthorised data access is high. The
access to the GSM network from the internet can only take place
via the VPN tunnel. See fig.
. Moreover, data transfer requires
a Modbus master client, knowledge of the Modbus functional
profile and the use of a SCADA PIN code, if enabled.
The CIM 250 supervises the GPRS/GSM system to ensure that it
is still working. An automatic procedure ensures restarting of the
CIM 250 and repetition of the GPRS connection sequence in case
a deadlock situation has occurred. It also closes down socket
connections that are left open by the client and unused for more
than 24 hours.
It is possible to use SMS communication while GPRS
communication is active. However, in the "Connected" state the
delay time between reception and reply will increase.
If the connection state is different from "Connected", it is possible
to establish a call-up connection. When the call-up connection is
established, GPRS data exchange will be blocked until the call-up
is terminated by the caller.
A total of three Modbus clients can be connected to the Modbus
TCP port of the CU 36X and communicate simultaneously. Each
connection, called a socket connection, is handled independently.
If all three sockets are used simultaneously, a "Silence timeout" of
only 5 minutes is used to prevent a complete occupation for a
long time.
If an alarm appears in the Dedicated Controls wastewater system
and the SCADA call-back function in the CU 36X has been
enabled in general and also enabled for this particular alarm, the
CIM 250 will attempt to establish a GPRS connection to the
SCADA system.
If the GPRS connection state is "Connected" (one or more socket
connections are established), the call-back function in the CU
36X will use the GPRS connection and perform a GPRS call-back
to all clients connected to port 502. Otherwise it will use a
standard GSM call-back. See section
TM
04
49
07
22
09
Modbus RTU telegram
Modbus TCP/IP data
Modbus application program header
Modbus TCP/IP application data unit
Slave ID
Func
code ID
Data
CRC
Data
Func
code ID
Unit ID
Length
Protocol ID
Transaction ID
Note
When no GPRS data is being transferred, the
connection states "Attached", "Context active" and
"Connected". All show the same LED1 status (short
pulse).
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