Unfortunately, even the existence of a corporate network at a factory does not always resolve the problem of having
remote control over the given production process. This is because in addition to the issue of compatibility of the equipment
with these networks, there is also the problem of transmitting data from the network itself. As a rule, it is necessary to
set up a separate channel in order to send data back and forth between the control object and the central office of the system
administrator. A cellular communications system can be used as such a channel.
Specialists at Gaz-Inzhiniring have built a remote control system that uses GSM networks (GPRS protocol) as the
data transmission channel. The latter are now priority networks in terms of accessibility and reliability. Two remote-control
schemes have been instituted: a system in which the data transmission channel is created when needed; a system with a permanently
operating communications channel.
In the first case (Fig. 4a), the GPRS modem is connected directly to the computer with the SCADA system, since it
would be inefficient to create a permanent communications channel in order to avoid overloads on the SCADA computer.
Such overloads might arise as a result of a distributed virus attack on the Internet, for example. A terminal that can transmit
commands is used for the communications link, and a standard cell phone can perform this function. Each command is sent
in the form of an sms message to the number associated with the GPRS modem. The command is analyzed by a special application
program installed on the computer with the SCADA system, and the results of the analysis can be used to establish
communications with the Internet through the GPRS protocol and to send data both to and from the central office.
A transmission speed of 1–5 kb/sec can be expected in GSM networks using the GPRS data transmission protocol.
Under these conditions, real-time use of remote graphics consoles is possible only if an application-level protocol is
employed. In this case, the remote applications server transmits the attributes of objects. For example, it may transmit
information on the type of object and its coordinates to a display. The local control program/client reproduces the graphics
console where the operator is working. A system of commands that can be transmitted as a sms control message was
developed to minimize traffic. These commands can provide for almost complete monitoring of the system without the use
of graphics consoles.
To enhance the stability of the SCADA system and reduce the load on the MC, we developed an improved remote-control
scheme that allows the establishment of a permanent data transmission channel. The scheme entails having the Windowsbased
computer that runs the SCADA application work next to a Linux-based computer connected to the GPRS modem.
A high-speed network link based on Ethernet technology is then constructed between these two units. As a result, the computer
with the SCADA system controls the PLC, the Linux computer controls the Windows computer, and the operator controls the
Linux computer through the GPRS communications link (Fig. 4b).
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Fig. 4. Diagram of remote control system: a) with creation of the data transmission channel as needed; b) with a permanent
communications link.
In this case, the Linux computer replaces the operator to a certain extent. The operator follows the work of the application
and reboots the Windows computer in the event of an emergency. The control computer is loaded with the necessary
semantics in the form of programs and scenarios that are activated remotely. Thus, this computer acts as a server for a client
located in the central office. The Linux-based control computer is an unvented single-board computer that consumes little
power and is equipped with a flash drive, i.e., it does not have any mechanical components.
The following indices have been obtained thanks to completion of the project described above:
• the implementation of a pulse-type heating system with direct digital control ensures the creation of a uniform temperature
field in the furnace chamber and maintains the specified temperature within the range ±5°C;
• an automated system that was developed to stabilize pressure keeps the pressure in the chamber at the specified
level with an accuracy of 1 ± 2 mm H2O;
• the rate of rejection of metal due to an unsatisfactory microstructure is now approximately 3% of total output;
• average unit fuel consumption has been 81 kg equivalent fuel per ton of finished product.
Conclusions. The use of a two-stage annealing regime and attainment of a high degree of accuracy in controlling
the temperature have reduced the average rate of product rejection fivefold (from 15 to 3%) from the rate seen with the existing
furnaces operating in the one-stage regime.
The newly adopted heat-treatment regime has also nearly halved unit fuel consumption (81 kg e.f/ton for reverberatory
heat-treatment furnace No. 14 versus 146 kg e.f/ton for the section average).