As a general rule the company profiles that have become a regular feature in SA Instrumentation & Control have focused on companies that supply products for direct use in the industry. The optimum control of any plant in order to ensure maximum efficiency and consistent high quality product is based on a large number of measurements, be they of temperature, flow, electrical or other parameters.
Correct measurement is not a trivial matter and for this reason we have seen the strong growth over the last few decades of the profession of the metrologist. Metrologists are specialists in measurement and, together with laboratory accreditation to ISO/IEC 17025 (the replacement for the better known ISO/IEC Guide 25), they provide confidence that measurements made on the factory floor are traceable to the national standards maintained by the CSIR's NML and ultimately to the international standards of measurement held by the BIPM in Paris.
This company profile is that of Spescom MeasureGraph (SMG) and more specifically is based on discussions with that company's Managing Director, John Wilson. John is a metrologist and has been associated with the world's leader in measurement, Fluke, for nearly 30 years. He has been intimately involved in the development of metrology and accreditation in South Africa since the creation of the NCS in 1980. Today he is the Chairman of SANAS, this country's sole recognised accreditation body, as well as holding the position of Chairman for the Metrology Instrumentation Group (MIG) and is a committee member of the National Laboratory Association. Fluke, which is represented by SMG, continues to expand its product portfolio most recently through the acquisition of Hart Scientific Inc.
Spescom together with the Fluke organisation identified a long time ago that the process industry was one where they would become increasingly involved, and indeed many of the sophisticated measurement tools available from Fluke today were specifically designed for troubleshooting in this industry. In the early 1980s all the instrumentation engineer needed was probably a good multimeter, screwdrivers and a pair of pliers. Although dataloggers and PLCs were around at that time the actual measurement capability and repeatability were often relatively poor. All this has changed over the last decade as external competition and increased costs have forced the declining number of manufacturers who have managed to stay in business to get more out of their existing plant, reduce waste, and often through the application of ISO 9000, methodologies try and 'get it right first time'. Implementation of the ISO Quality Management System also forces companies to look at both preventative action (if critical control parameters are changing, correct them before the quality of the output becomes unacceptable) and corrective action (take measures to get the product back within specifications). Such actions are of course based on accurate measurements of what can be many hundreds of process parameters.
Data collection
The ability today to collect data at high repetition rates has created its own problem through creating overflow in networks and masses of never used data. One example quoted by John Wilson was a company that was measuring temperature in a pressure vessel to ensure it did not reach critical levels. Without giving much thought to the problem the plant engineer was measuring the temperature at a resolution of 0,1°C at 100 times per second, whereas a simple calculation showed that the thermal mass of the system was such that the temperature at most could only rise by one degree in 30 s. This excess data was thus totally wasted. On the other hand, there are situations where such large amounts of data are useful, particularly if the measurement being made is close to basic noise levels. Here, the geometric mean of a large number of measurements can result in an estimation that is more meaningful. This is particularly true of many measurements using thermocouples especially at resolutions of a tenth of a degree.
The calibration process
In today's modern process plant there could be literally hundreds of measuring points at which regular calibration is required. Logistically, this could be a nightmare and could require the calibration technician to carry with him a manual covering the details of the measurements to be made at each point, which would then have to be logged manually and later compared with previous records to see if there are any obvious trends or drift with time. All this is today solved with the modern process calibrator which is pre-loaded with details of the required calibration points providing on-the-spot information as to what wires should be connected and what measurement to take. The current calibrated value is recorded and can be immediately compared to historical values with immediate warning if out of tolerance deviations are observed. With these process calculators it becomes very difficult for even the most inexperienced technician to make a mistake.
Thermocouples
One of the most commonly found measuring devices in any process plant is the thermocouple and here the age-old problems are still with us today. The major one is to match the correct thermocouple with the correct compensation cable. All too often today the wrong cable is used and the result of course is incorrect measurements.
Power quality
The power quality in plants is seriously deteriorating and this is not the fault of Eskom but the manufacturer itself where electrical distribution systems originally designed with straight resistive loads in mind are now being used with such add-ons as variable speed drives, PLCs and so forth that introduce harmonics. Very often these harmonics are such that circuit breakers can be tripped and transformers blown up even though the apparent current levels are within specification. Harmonics have traditionally not been looked at in the measurement process, but this has changed dramatically as not taking badly distorted sine waves into account can result in engineers looking for faults in the wrong location or causing intermittent operation of a PLC or other plant device. Harmonics can also be a serious safety issue, as their presence has also been known to burn out cables and cause fires.
Control versus measurement
Although proper control is totally dependent on the accuracy of measurement there still is a tendency to over focus and spend on the control side of the equation. This is not always the fault of the plant engineer but is due in part to ignorance of the measurement process exacerbated by the fact that we need to see more metrologists getting out of the comfort of their laboratories. It is the metrologist who should be out on the plant floor ensuring that the correct 'fit for purpose' measurement capability is put into the process. From management's side the need is probably to allocate more funds for the acquisition of the right measurement tools for the job, and of course the best type of calibration equipment. Moreover, there must be more training for technicians in the field of measurement and in fact better career paths for metrologists themselves, the latter having been a point of discussion for more than two decades.
The use of LAN and WAN networks
More and more organisations are centralising the operation of plants that are located at various centres throughout the country, making use of networks. As an example, a trend is for a production manager sitting in the head office in Johannesburg to schedule the workload remotely around the country and the maintenance manager could also see how all the plant was operating - even more important to have correct measurement data. To ensure that these LAN and WAN systems are operating effectively and that data is not being lost, the company needs access to modern test equipment.
Solutions from SMG
SMG offers a wide range of test tools from Fluke, Hart Scientific and Ideal that can address the complex measurement problems in today's process industry.
The handheld Fluke 43, for example, can be used by the instrument technician to measure power quality and to look for harmonics in both voltage and current. It is basically a troubleshooting tool and with training can be used to allow the user to track down the presence and source of poor power quality in the measurement process. While the Fluke 43 is a point-of-use tool, the Fluke VR101 can be installed on a permanent basis to monitor the continuity of supply and it can be pre-programmed with variable fault condition limits to record. The VR101 is particularly useful in picking up long term trends, measurement of power sags and so forth, that can often be used to determine why quality problems arose and if they have had an influence on the reliability of the plant.
The modern day Fluke Scope meters allow for troubleshooting of analog and digital (RS455, Profibus etc) signals to see if levels are right and whether data is actually present on the line. These sophisticated scope meters also provide the technician with all the functionality of the traditional multimeter and oscilloscope in one tool.
When it comes to LANs and WANs these can be tested using a wide range of network and telecomm analysers available from SMG such as the Nettest, Ideal and Digital Lightwave range of products.
SMG offers a full range of instruments to calibrate almost all the plant control loops. A fully documenting device (Fluke 744) is at the top of the range that will store before and after readings plus the procedure to be used at each calibration point. This device also allows the work schedule to be programmed in, thus ensuring that the operator goes to each of the relevant points to collect data and this can then be uploaded into the management database.
Of course, process calibrators and all other test equipment also needs periodic calibration and in terms of ISO 9000 the user must ensure traceability of these calibrations to national/international standards of measurement. The easiest way to achieve this is to make use of a calibration laboratory accredited by SANAS (or one of its peer bodies internationally) and SMG provides such a facility that covers most of the electrical, temperature and RF fields.
In conclusion, John Wilson believes that the technology is available today to make the job easier for the process community and to maximise output from any plant. What has to be done by industry is to invest more money into the measurement side of their business and to provide proper training so that their staff fully understand the measurement procedure, the origin of uncertainties in measurement and the importance of calibration at all levels and ultimately traceability. The global market demands that a measurement carried out in Pofadder be the same as that done in Paris and that is what measurement traceability guarantees.
Spescom MeasureGraph
(011) 266 1572
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