Monitoring a machine that was never designed to communicate.
The turbine’s control system, a GE Speedtronic Mark IV, regularly sent its status to a dot-matrix printer. The printer output is where we connected the BOX. We decoded the signals meant for paper and filed each value like a sensor measurement, without changing anything in the control system. Less than five months passed between the feasibility study and delivery. The same method works for many machines that were never designed to communicate: listen to what they already say, measure alongside when they stay silent, and leave their program alone.
A splitter fitted to the printer port sent the BOX a copy of everything that went to paper. The longest part was still to come. Those signals were made for a printer, not for software: they had to be decoded to get values out of them. Once they were translated, we filed and classified them like sensor measurements, with their history, on the same screens as the rest of the fleet.
The connection drew interest beyond the site: OFS, an Irish turbine operations and maintenance specialist, came to see the Mark IV installation.
Then the turbine changed control system: the Mark IV gave way to a Mark VIe. That is a retrofit, in the proper sense of the word. On our side, we changed the connector. We had read the old system’s printer output, we then read the new one’s Modbus TCP, and the turbine stayed on the same screen.
An older machine almost always talks a little, if only to its printer. You need to know where to listen.
What a machine can already tell you.
The PLC. Its Modbus registers often hold temperatures, pressures, hour meters or fault codes. At a small, remote power plant, Modbus is how we read the ComAp genset controllers.
The existing SCADA. An old OPC server on Windows, from the generation known as “Classic”, built on COM/DCOM1 technology, remains a valid source for as long as it runs. Migrating to OPC UA can wait. That is how we read Schneider Modicon PLCs: over OPC DA, through the Codra Panorama SCADA already in place.
Analogue signals. A pressure, temperature or flow sensor with a 4-20 mA2 output can be read as it stands.
Contacts and meters. A fault contact, a run indicator light, a meter: simple information, and often the most useful.
When it says nothing, measure alongside.
Some machines have neither an accessible PLC nor a usable output. There is no point then in opening the cabinet to rework the internal wiring. A current sensor on the power supply tells you whether the machine is running and at what load. A temperature probe on a bearing, a pressure sensor on an air line: the measurement is taken from the outside, without touching how the machine runs.
It is less elegant than a full integration, but quicker and reversible.
On a silent machine, we fit the missing sensors and connect them to the BOX, over 4-20 mA or on its digital inputs. The equipment stays in place.
There will still be values that no sensor will pick up, and that a technician will take by hand on the round. Those too need to join the machines’ history: that is the subject of our article on paper rounds.
The Machinery Regulation, and the line not to cross.
Modbus is used to monitor equipment, but also to program it3. So the protocol allows writing, and it is up to the monitoring tool to refrain from doing so. With us, the BOX is read-only by design: it sends no commands to the equipment.
The issue will carry more weight on 20 January 2027, when Regulation (EU) 2023/1230 on machinery replaces the 2006 directive. France’s INRS4 sums up the regulation’s definition of substantial modification: a modification, “by physical or digital means”, not foreseen by the manufacturer, that creates a new hazard or increases a risk. Whoever carries it out is regarded as a manufacturer, with the obligations that go with it.
A connection that only reads, changing neither the program nor the safety functions, seems a long way from that definition. The conclusion is nonetheless the operator’s to draw, and legal advice is worth more than a supplier’s certainty.
Sources.
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OPC Foundation, “OPC Classic” page.
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Fluke, article “Comment mesurer un signal de boucle de courant 4-20 mA”.
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Modbus Organization, frequently asked questions.
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INRS, legal briefing on the new Machinery Regulation (EU) 2023/1230, updated on 20 October 2023.
