By Benjamin Brits
There is a saying that I’m sure you are familiar with: “You can’t manage what you don’t measure”, and as every avenue of optimal operation is sought out – the technology of the future is pushing us closer each day.
When considering the cold chain – from the producer to the consumer – one particular element that you may not consider to have multiple uses, and in so many different applications, is instrumentation.
Any system no matter if it’s a single retail cabinet, a fan, a refrigerated truck or a large specialised plant room – all require some or other instrumentation to either measure, monitor, or feed data into a system controller. So, no matter if a gauge, a mechanical device, a transducer, a needle or digital display device – any system will encompass either or many elements of instrumentation.
Looking at refrigeration systems alone as a common denominator in the industry, you already have to deal with many different variants in refrigerants such as ammonia, CO2, freon, natural refrigerants (propane/isobutane), glycol and even water and ice banks, all of which require different solutions in measuring and monitoring.
All of the instrumentation involved in any process-system are ultimately necessary to have oversight of elements such as temperature, pressure, flows (liquids and air), density, levels, and so on to achieve the required outcomes within a specific area or application.
As an example, a cold storage facility may require rooms to cater to +5, 0, or -25°C, and each section will require its own instrumentation and control scenario. Similarly, ensuring a fan is providing the correct volume of air, or checking the differential pressure of a filter is all possible through instrumentation devices.
A key design criteria is that one also need to consider portions of any system being functional or critical, and the correct implementation of the instrumentation in these areas would be necessary. The last thing you would want to see is a simple measurement device on a pressure vessel that is not monitored, or doesn’t form part of a controlled system.
Instrumentation is a very broad topic with as many measuring and monitoring devices you could think of. Selection of these instruments comes down to what the particular application is and if you want to be able to extract data from the instrumentation. Data is typically fed to either of the following control means:
Supervisory control and data acquisition (SCADA) is a control system architecture comprising computers, data communications and graphical user interfaces for high-level process management.
Programmable logic controller or programmable controller (PLC) is an industrial digital device the control of particular or various processes and is also commonly part of a SCADA system.
Distributed control systems (DCS) are computerised control system for a process or plant usually with many control loops, in which autonomous controllers are distributed throughout the system, but there is no central operator supervisory control.
These control systems assist to gain efficiencies, determine a devices feed or what measurements are out of range, and further allow a view of the overall status of the plant or particular sub-system.
“There are always certain basic safety control devices that are needed to protect the equipment, for example temperature controllers, sensors, high and low pressure switches, oil pressure switches, anti-freeze protection, over temperature switches, overload protection and circuit breakers. Clients also typically want a graphic or visual display which indicates when one of the safety devices shows a fault. Secondly close monitoring of the actual product or area that needs to be cooled is essential. These devices are found throughout the complete cold chain,” says Hennie Basson. managing member of Coldfact.
Measure, monitor, control
In the instrumentation world you have devices that perform a measurement-only function and you then have devices that perform monitoring. Monitoring is becoming a crucial element in today’s setting. Monitoring ties directly into the current buzz words – IoT or 4IR or industry 4.0, which is covered in more detail later in this article. To close the process loop, monitoring is typically linked to a controller that issues signals to a control device like a valve or actuator to make changes to keep the process or sub-process in a required range.
“There is always a control philosophy one could apply to any system but we like to advise our clients first that they need to be careful when they want to apply control, because you first have to consider many elements – for example the connection method between your monitoring devices and control system. If the client chooses a wireless device or this is specified for a number of reasons, the client would have to understand that no matter what wireless technology they choose, it could have issues in connectivity, teething issues, a setup or a commissioning issue and these could all impact safety grounds in the process,” says Lloyd Townsend, HVAC&R product specialist at Wika Instruments.
Monitoring (as much as it is also a measurement protocol) involves the added ability to log data or be able to get a history of a devices measurement. Measurement instrumentation merely gives you a current value of live data at the immediate point in time. Storing of measurement instrumentation data would typically be via a manual process and sometimes this device type is used only for visual indications of a systems performance.
Monitoring devices are also available in a wide variety of models so some are able to store and supply data while others that are digitised would give you a simple open or closed contact signal. More advanced monitoring devices are able to log intervals or frequency, time spans between events, how high or low peaks, time of incidents, and so. With so much choice, understanding all the instrumentation or what the desired result should be is key to designing and maintaining an efficient system.
“As with many sectors throughout the country, company’s nowadays are always looking for the cheapest route to get the job done, there is a saying referring to ‘cheap and nasty’ and unfortunately it exists in this sector too”, says Pavlos Tsambos of Controltech – supplier of Dwyer products. “Companies will rather save a rand/dollar to make more on the bottom line, offering their client the short end of the stick. But this is not about morals and ethics, it’s how best to measure temperature and what best instruments to use.”
“Instrumentation engineering is the engineering specialisation focused on the principle and operation of measuring instruments that are used in design and configuration of automated systems in areas such as electrical and pneumatic domains, and the control of quantities being measured. They typically work for industries with automated processes, such as chemical or manufacturing plants, with the goal of improving system productivity, reliability, safety, optimisation and stability. To control the parameters in a process or in a particular system, devices such as microprocessors, microcontrollers or PLCs are used, but their ultimate aim is to control the parameters of a system,” adds Tsambos.
Instrumentation engineering is loosely defined because the required tasks are very domain-dependent. An expert in the biomedical instrumentation of laboratory rats has very different concerns than the expert in rocket instrumentation. Common concerns for both are the selection of appropriate sensors based on size, weight, cost, reliability, accuracy, longevity, environmental robustness and frequency response.
Some sensors are literally fired in artillery shells. Others sense thermonuclear explosions until destroyed. Invariably sensor data must be recorded, transmitted or displayed. Recording rates and capacities vary enormously. Transmission can be trivial or can be clandestine, encrypted and low-power in the presence of jamming. Displays can be trivially simple or can require consultation with human factors experts. Control system design varies from trivial to a separate specialty.
“Instrumentation engineers are responsible for integrating the sensors with the recorders, transmitters, displays or control systems, and producing the piping and instrumentation diagram for the process. They may design or specify installation, wiring and signal conditioning. They may be responsible for calibration, testing and maintenance of the system too,” notes Tsambos.
Considering instrumentation needs
An instrument should never be considered a consumable – no matter if it costs R1 or R100 000. Although instruments have a certain life span, if you chose the right instrument for the measurement task, these should never only last a couple of weeks or months. Instruments should last in excess of a couple of years and replacement should only be seen as an opportunity to upgrade the technology not because of instrumentation failure.
Your instrumentation and subsequent control will always come down to what you want or need to measure. Naturally, you get fit-for-purpose instruments such as a simple gauge, and very high end devices that can measure multiple factors like temperature, pressure and flow rates from one device. The higher end devices are naturally more expensive, but offer more data that may be needed by a client, or increase operational efficiency over a period. Devices can be made out of plastics, stainless steel and brass – all dependent on what is best suited for the particular application.
One key element in a refrigeration system is to establish what refrigerant is being used. You get specialist refrigerants like CO2 and ammonia that are widely used currently for their low (no) global warming potential and are much safer for the environment. So if leaks occur for whatever reason it is not detrimental to the environment. Instrumentation for these refrigerants don’t have to be made out of a special material, or undergo a gold plating process. Each different refrigerant (and there are many) all have different properties and may have a corrosive effect on components such as sensors or bodies.
Some transmitters have been optimised for the refrigerant industry and then there are some that are optimised for the cryogenic industry and similarly other industries like petrochemicals or heavy industrial where the real difference is the sensor element. The reason the material is important is to ensure that damage is prohibited as far as possible to the device but also so that the device and sensors don’t react unfavourably with the process. In some applications ceramics are used to compensate for dynamic system variations – a ceramic sensor can handle much more when it comes to over pressure situations – protecting the device and its accuracy.
“A simple explanation of how an instruments works, if you can visualise a cell which is measuring the process at the bottom and at the top you have what is known as a Wheatstone bridge. This is a whole lot of resistors forming the ‘sensing element’. When the cell deflects it causes deflection in the resistor and that in turn causes a resistance change. This change is then translated into a value such as milliamps or how much pressure the device is undergoing,” says Townsend.
If you take a simple air cooling system as another example of the cold chain you have ambient air in and processed air out. You have your heat exchangers on the inside and a force in phase change. You may have filters as well. In this example you could have devices measuring ambient air, cooled air, air flow, differential pressures of the filters, temperature on the heat exchanger, refrigerant flow and so on, all with particular instrumentation, some of which is as small as a button. In refrigerated transport you may have similar devices as mentioned in this example and also monitor data from the vehicle engine power to the refrigeration system.
Now although modern refrigeration systems are designed to be efficient and leak free, improper installation, inadvertent damage or mechanical wear can result in potentially hazardous leaks which also needs strong consideration in terms of site and produce safety.
Refrigerant management is an efficient, safe and cost-effective part of operations with regards to refrigeration equipment. Today, this also means complying with evolving legislation, ensuring product quality and the safety of workers and customers, while reducing operational costs leading to improved profitability.
“Refrigerant management is not just a cost saving exercise. Effective management of a refrigeration system is critical to an organisation’s success and ability to compete. The organisation’s reliance on refrigeration means that it is a strategic asset and should be treated as such. Function around refrigerant management can be achieved by inclusion of various gas detection instruments and solutions, some of which cater to a wide range of refrigerants and offer complete leak detection solutions in chilled rooms, distribution centres, industrial cold stores and retail operations,” says Wayne Thompson, Titration and Test Systems – distributor of Bacharach products in Africa.
These instruments cater to low-temperature performance (-40° C) and have integrated audio and visual alarms. Gas detectors feature cable entry and terminal options making installation straight forward and users can also intuitively use, commission and maintain the instruments without the need for specialist training or tools.
You also get multi-gas analysers that can tell you the concentration of gas within a specific volume by analysing a sample of air revealing its composition, for example X% is hydrogen, X% is ethylene and so on. This is typically a specialised function instrument.
Common causes of failure
“Instrumentation failure could stop a system from working because, depending on the measurement task its intended to perform for example a pressure switch, there are regulations that cover pressurised vessels, pipes and mobile machinery, so if pressure is a risk, failure results that that system is shut down immediately because it could pose danger to the immediate environment or people around it and when health and safety risk is involved, this is a big deal in any industry,” notes Townsend.
Some failures are not critical risks but pose a loss to store owners. When the temperature sensor fails on a refrigeration unit the heat exchanger is affected – the fridge doesn’t switch off, so it freezes up and any environmental moisture freezes to the surfaces and builds up more and more. Without a connected device, instead of it seeing that it’s so cold or that the unit is icing up the system doesn’t know to engage a defrost cycle and in this example you lose efficiency because now you are paying more to have the fridge run continually.
There are many other aspects in instrumentation failure. If we look first at the environmental element with an industrial system, the environment plays a role in deciding what kind of electrical connection you need to use and it helps to first define if your sensor is exposed to the environment how do you ensure its protected from rain (acid rain as is common in South Africa) or direct sunlight all of the time where you may have sensors that might have a plastic digital LCD display – this will without doubt be affected by direct environmental elements when not protected including, dust, water and sunlight.
The electrical connectors also plays a critical role because on these devices you have metallic components that you can junction your wires to and if you don’t have the right electrical connectors and they are exposed to a corrosive environment, over time this will start to affect the signal output.
There are some environments that contain chlorine or a particular gas in the immediate air and one needs to think about whether the electrical connector would be resistant to these elements and their behaviour when humidity or water is added to the environment. In these environment IP65 rated units are available.
Corrosion typically leads to moisture risk and when moisture gets into any device it immediately causes some kind of failure or short circuitry, and sometimes it causes measurement fluctuation. This is where a technician would pick up ground loop errors, or the device picks up interference much easier.
Seals and gasket material on devices is also important to be made out of the correct material (polymer) because it is known that certain polymers and refrigerants don’t go well together. There are only specific polymers that can be used because the refrigerant makes the polymer brittle over time allowing liquid to seep around the cell and therefore causing electronic damage.
“Another common area of instrumentation failure or erratic measurement is electrical interference in a system. Interference could get picked up from other wires that create an energy field and this causes a type of fluctuation in instrumentation. These scenarios prove interesting as it is not always a sensor failure that causes a fault. The fault source is somewhere else in the system and this can be from an installation where all of the wiring has been bunched together in the rack. Groups of wiring, although a neat finish, sometimes can draw a lot of current creating an electromagnetic field and causing a ‘jumping effect’ to other wires in the group, just enough to cause instability in a measurement on your specific loop that you are testing. Most often controlled parts all have a bridge to ground wire and this ground wire is the same for all devices so signal interferes from other loops which are on the same ground connection could cause measurement uncertainty on the experienced sensor. This shows that a fault is not always at the instrument of measurement,” adds Townsend.
Identifying faults and system testing devices
When dealing with some of the bigger plants, they have such a big area to canvass that to find where the fault is can take a long time – even a couple of days and one needs to avoid assumption in replacing devices and then the fault doesn’t go away or is gone for a few days and then returns again.
Fault finding is always a hard topic to navigate and there are a few methods you can apply. One is process of elimination and this is known and used in the industry and technicians often prefer to have spare devices to perform a variety of tests. Especially now with new technology you are able to identify faults when combining internet of things (IoT) and 4IR, commonly known as the fourth industrial revolution of electronic connectivity.
Any logged data that you have access to, allows a view of how any particular section or device has been performing and operating in a desired range. You can compare all of your sensors on a specific system to see if all of them are within a safe or healthy band and pinpoint areas where any have exceeded the band and this way you can know which one is faulty so this assists in identifying potential faults.
“Many installations don’t have the function of connectivity so you may need to use testing methodology and equipment such as the latest thermal imaging devices which can be used at any site and is considered the perfect tool to instantly recognise the location of a temperature issue within a system. These imaging devices use scene details from the built-in visual camera and embosses them onto the full thermal image – this technology also enables technicians to test effectively in dark and difficult to reach areas,” says Nelson De Caires of Test & Measurement instruments.
“The Parasense platform, that Bacharach has recently developed, is a refrigerant tracking dashboards that empower owners or plant managers to track refrigerant across all equipment over the entire enterprise. Users can review the cause of refrigerant emissions, identify opportunities for improvement, track repairs and ultimately minimise the consumption of refrigerant in their system. This platform ties into refrigerant monitors that include products that detect levels as low as 1ppm. This is particularly important in applications using Ammonia (NH3), which is commonly used as a refrigerant in large industrial applications. Although a zero rated global warming potential refrigerant, it presents risks of toxicity and explosion if gas leaks go undetected. Ammonia leak detection systems can be installed to help mitigate these risks and ensure safety, where the Parasense platform can identify leaks in these applications when they occur for immediate remedy,” adds Thompson.
Instrumentation and IoT/4IR
IoT is a very broad spectrum of technology in applications and is commonly mistaken as wireless connectivity which it is not. IoT is the process of creating ‘smart devices’ and enabling these devices as an example to not only measure pressure but also a temperature measurement out of the same unit. IoT enables you to log and retrieve data out of a device and utilise the data in a variety of useful ways.
Everything from cars, home appliances to shoes and light switches that connect to the internet, passing and receiving data and connecting the physical world to the digital world are considered as smart objects. There are two concepts used in defining IoT. Since Industrial Internet of Things (IIoT) is developed to handle critical machines, IIoT uses more sensitive and precise sensors in the plants, including more location-aware technologies on the supply chain side with sophisticated, advanced controls and analytics. We currently have 20.4 billion IoT devices that will be online  and this is growing every second by 124 devices connecting to the internet.
Sometimes a device is only intended for pressure measurement, but if that device could understand or have a digital imprint loaded into it to know what the ideal or optimum efficiency of the pressure should be in a system – this is what is referred to as ‘making it smart’. These devices (having to already include a smart sensor) would then take a live measurement and compare it to the required ‘perfect measurement’. This information would then be feed to the overall control system or platform to calculate what kind of adjustment is needed to achieve optimum efficiency, or offer suggestions to achieve this.
“In high-spec systems, devices do not do calculations on their own but collectively with other devices. In an example using a heat exchanger, you have temperature, pressure and flow monitoring and through an interface with other devices, the system could look at the perfect heat exchange parameters and compare the current live data to that of the ideal pressure or temperature, and what can be adjusted to get to the most efficient scenario. In the IoT realm there are experts that define and create platforms and various algorithms to do this comparative analysis and this then tells the user who is monitoring the system what needs to change – maybe the system would suggest to open a flap a little more to have more air feed in and as a result it increases pressure therefore the temperature is reduced and efficiency increases because the system doesn’t need to cool down as far,” adds Townsend.
IoT is really a smart way of collectively collecting data and then feeding results of machine learning for system optimisation, or preventative maintenance to a user to implement – sometimes systems are set up to automatically make the changes and there are essentially unlimited capabilities to compensate and correct for variances.
IoT in a system can also predict and manage system failures or breakdowns. What could happen is the compressor is close to break down – the IoT-enabled system would be able to advise you that your compressor is starting to strain and is not going to last much longer based on its performance, and further can predict that either service is required or a break down is on its way. This is particularly useful if you are running a critical system and can’t go into a shutdown state, however you have a lot of activity over the current period and you need to make a decision as to what to do. What is possible then is to feed the system the information to determine what is possible to extend the shutdown or maintenance, whereafter the system could indicate a number of scenarios you could consider which could include less efficiency through cooling less by 1 degree and the system remain stable for X amount of time to allow you to prolong the required maintenance to a more convenient time.
The same principle applies for the determination of maintenance schedules with the intention being that technically a breakdown can be managed for minimal disruption. Breakdowns are for the most part unavoidable because something may go wrong that was unforeseen, but the systems will progress to notify you in advance to know and plan ahead what you need to replace. It will also be able to establish what components failed, why they failed and what to do in future so that it doesn’t re-occur – this process is what is referred to today as ‘machine learning’ and already exists as a solution.
“IoT is opening a new avenue of doing business and a new avenue of control – a lot of people just think you are implementing artificial intelligence and it’s taking away jobs, but it also creates an opportunity for higher skilled jobs. Not everyone knows what IoT is and what it does, so if you go and learn about it you will discover the skill set is in high demand. Implementing IoT in current technology today is already inexpensive because it has been around for many years but companies have only now started to extract data and use it to create more efficient systems. The era of IoT and 4IR that we are in is creating a phenomenal imprint on everyday industries. The more efficient you can be the more profit you make. Efficiency is what will save business in South Africa under the current economic climate and the pandemic, although devastating, has forced people to fast forward their thinking to find or develop ways to retain profitability and that ultimately means optimal efficiency in every aspect. Instrumentation and control will play the most major role in efficiency of the future,” Townsend says.
“Instrumentation goes hand-in-hand with IIoT to shape our future of a better connected world, better supply chain, better accountability and monitoring progress at your fingertips. This being said, this opens up another can of worms on how much data one generates and what intelligence can be extracted from the data, and further what better decisions can be made in this ever-changing world. The secret to success with IIoT is preventative and corrective maintenance saving companies time, headaches and loads of money if they could predict a potential breakdown on a chiller and losing the entire load because of lack of foresight and predictions that could have been avoided by the help of IIoT,” adds Tsambos.