Avoid Process Downtime With Five Device Protection Considerations

Industrial Process Instruments

Industrial process control is everywhere. Sometimes it is dangerous or complex. In other cases it may be relatively mundane. In all industrial processes, though, maintaining operation is key. Stakeholders rely on the process output and look to the designers, engineers, and operators to deliver, in many cases, uninterrupted performance. The world is a place of many uncertainties, some of which can impact your process in undesirable ways. While it's not practical to design or build to accommodate every possible adverse event, application of experience and good judgement in a few areas may significantly shorten the list of things that can negatively impact your process.

Process control is achieved through the measurement of various conditions and application of regulated adjustments to the process inputs to deliver a desired output. Process variable measurement serves as the input to the control system. In the industrial sphere, it is common to see devices used for the measurement and transmission of temperature, pressure, flow, mass, level, and electrical parameters like voltage, current, capacitance and more. Regardless of what is being measured, there are three common characteristics:

• Device - A combination of a sensor and a translator that together detect some physical condition of the process and produce an output signal that can be correlated to the process condition. 
• Location - The device will have a location that is dictated by the process construction and arrangement. Device locations have a tendency to be inflexible.
• Signal transmission path - Unless the control element is integral to, or adjacent to, the measurement device, there will be some path over which the measurement signal must travel to reach an associated control element. 

Looking at these three elements for each measurement point, consider the five risk categories below in evaluating what you can do to safeguard your process measurement instrumentation. It's advisable to open a conversation with an experienced application specialist and freely discuss your concerns. Gathering additional input from various experienced sources will help you determine how extensive your protective measures should be to deliver a balance between cost and the probability of certain adverse events.

• Local Weather: There is local weather data available for almost every place on the planet. Take the time to procure reliable data and examine the distribution of temperature, humidity, precipitation, and wind conditions throughout all seasons. Clearly, if portions of the process are located outdoors, extreme local weather conditions will need to be accommodated. Even if your process is located indoors, local weather information is important if the process is to operate continuously. Consider whether an indoor process must continue to operate, even if the building HVAC system fails and indoor conditions begin to be impacted by outdoor conditions. Also, depending upon the design of the building climate control system, changing outdoor conditions can have a noticeable and possibly significant impact on the indoor air conditions.
• Process Generated Conditions: There may be specific aspects of your process that produce occurrences of vibration, pressure spike, electrical interference, or a host of other aberrations that may affect the proper operation of measurement devices. Know your process....really know it. Protect instrument sensors from potentially damaging transients and other process conditions that can be reasonably expected to occur. Device location relative to sources of electrical interference, elevated temperature, vibration, shock, and other transient conditions should be considered.
• Security: Your design goal should be to achieve a very high level of certainty that the signals generated by the measurement devices are uninterrupted and reflect the actual process conditions. There are two cases I always consider for security. The first is cyber, which applies in the case of a process measurement device network connection. Necessary steps should be taken to thwart an attempt to breach the network and detect unusual conditions that might indicate an invader's attempt to manipulate the process. My second case is related to device access by those without proper knowledge, training, or permission. Protection from these threats will likely involve a combination of physical barriers and procedures.
• Physical Contact: Industrial settings are, well, industrial. Large, heavy, irregular, unwieldy, and sharp things can sometimes be moved through areas occupied by process measurement gear. Technicians with carts, tools, and materials frequently pass through process areas to do their work. Protecting equipment and instruments from damaging contact pays dividends for the life of the installation. Consider, in your design and layout, the proximity of instruments to areas of traffic. If applicable, also consider areas overhead. The level of protection will need to be balanced with the need for access by qualified individuals for service, maintenance, calibration, and observation, as applicable.
• Moisture: Electronics are a mainstay of modern measurement instrumentation. Clearly, liquid moisture must be kept from contact with electronic circuits. Vaporous moisture will find a path to the internals of your electronic devices. This vapor, which is present in considerable levels in almost every indoor and outdoor environment, can condense when the right conditions are present. It is imperative that enclosures, conduit, boxes, fittings must be provided with barriers to moisture entry and/or a reliable means to automatically discharge accumulated liquid moisture before damage occurs.

There is much to think about in the realm of device protection. Balancing the costs of protection, the impact of protective measures on the ability to service and operate the process, and the risk involved with process failure or shutdown requires the application of technical expertise, experience, and sound practical judgement. Draw information and opinion from multiple sources, including sales engineers. Combine their product application knowledge with your process expertise to make good decisions.

Application Advantages of Intrinsically Safe Barriers

2-Wire Transmitter in Hazardous Area With Intrinsic Safety Barrier
Courtesy Ronan Engineering Company

Industrial process measurement and control operations have few boundaries. Land, sea, air, light, dark, dry, wet, hot, cold, indoor, and outdoor environments. Did I mention potentially explosive? Well, there is that, too.

If your experience was anything like mine, it is likely that your first project involving a hazardous area really drove home the fact that you are working at a very serious endeavor. In addition to quality problems or downtime resulting from equipment failure, now you add "the place blows up" to the list of possible outcomes. It's sobering, and not the type of situation where you have the option of real world testing. You need to be right the first time. Every remotely possible source of ignition must be considered and rendered harmless.

One way to provide the necessary level of safety is through the use of explosion proof enclosures, conduit, fittings, and other devices. By their nature, these items are designed to contain an internal explosion and provide for the expansion and cooling of the ignited gases into the surrounding atmosphere. The expansion cools the hot gas to a temperature safe for venting from the enclosure into the hazardous area without causing an ignition.

There is a good solution for measurement and control circuits requiring only low power levels. Intrinsically safe circuit designs employ barriers that allow power limited connections between devices in a hazardous zone and those in a non-hazardous zone. Intrinsic safety relies on the limiting of available energy in the system to a level that will not ignite a hazardous atmosphere (explosive gas or dust). Without significant energy storage, and ensuring that only low voltages and currents enter the hazardous area, intrinsically safe design removes the circuit as a possible ignition source. Where it is possible to utilize an intrinsically safe circuit, there are some advantages over using an explosion proof design.

• Absence of explosion proof enclosures enhances the accessibility of system components.
• Personnel safety is increased with low voltage operation.
• Standard wiring methods and materials may be used. No explosion proof conduit, boxes, fittings.
• Calibration and maintenance can be performed with the system in operation.
• Special skill levels required by an explosion proof design are not required with intrinsically safe design.

A primary device in an intrinsically safe circuit will be the barrier. The intrinsic safety barrier forms the border between the hazardous and non-hazardous areas. There are other design considerations, all of which you should discuss with knowledgeable application specialists. I have included a document below from Ronan Engineering Company, a manufacturer of intrinsic safety barriers. It provides some additional useful information, including a listing of the many I/O applications where the barriers can be employed.

Ronan Intrinsic Safety Barriers from MSJacobs-Cali

Thermal Mass Flow Meters - Mature Technology With Modern Application

Configurations of Thermal Mass Flow Meters
Courtesy Thermal Instrument Co.

Thermal mass flow measurement technology has been used in industrial process measurement and control applications for many years. The technology measures the amount of heat required to maintain a sensor at a constant reference temperature, offsetting the cooling effect of the fluid flow over the sensor. The technology is well suited for installations requiring the measurement of low pressure gases where the fluid components are known and remain constant. Thermal mass flow measurement is also employed effectively in a number of other scenarios.


Potential advantages of thermal mass flow technology for industrial process measurement and control:

• Provides true mass flow reading using a single instrument
• Not significantly affected by fluid pressure or temperature
• Moderate comparative cost
• No moving parts
• Minimal restriction of flow introduced by sensor

Typical applications for thermal mass flow meters:

• Landfill gas outflow measurement
• Compressed air systems
• Gas distribution in semi-conductor manufacturing
• Beverage carbonation
• Tablet coating and compression in pharmaceutical industry
• Flare gas measurement in oil and gas industry
• Natural gas flow to boilers, furnaces, and other consuming equipment

Thermal mass flow sensors have attributes making them very suitable for a family of applications. Like all measurement technologies, there are also areas of caution in their application. Any measurement technology must be properly applied in order to obtain reliable results. Talk to a sales engineer about your flow measurement ideas and applications. Combining your process expertise with the knowledge of a product application specialist will produce good results.

Are You Well Grounded on Grounding? - Part 3

Electrical Drawing Symbols for Ground

Welcome to the third and final part of this series on electrical grounding for equipment and instruments. Part One and Part Two can be found as previous posts to this blog, and I hope you read them too. Those initial parts provided practical knowledge about equipment grounding and personnel protection in a format understandable to anyone. Those of us more deeply involved with electrical matters likely know someone that could benefit from these articles and I urge you to share.

The white paper that I have included below was produced by the folks at Acromag, a world class manufacturer of signal conditioners and other industrial I/O devices. They have done a fantastic job of presenting technical subject matter in a compact and very understandable form. The subjects covered in the series include:

• Ground as protection
• How a ground fault circuit interrupter (GFCI) works
• Ground as a voltage stabilizer and transient limiter
• Tips on improving safety and signal integrity
• The importance of circuit grounding
• Description of the US AC power system and its use of earth ground

This third installment includes a section entitled "Some Basic Ground Rules For Wired Equipment" which lists out an array of useful tips for connecting wired signals to devices, and more.

Product specialists are always on hand to discuss and solve your process measurement and control issues. Combine the process knowledge of the on site stakeholder with the product and application expertise of the professional sales engineer to produce the best outcomes.

Electrical Grounding Practices - Part 3 of 3 from MSJacobs-Cali

Are You Well Grounded on Grounding? - Part 2

Drawing Symbols for Ground

Electricity, like many beneficial trappings of modern society, is both beneficial and dangerous. Protecting users of equipment and appliances from the potentially harmful impact of electric shock is a socially accepted mandate that has been codified everywhere in the developed world.

Acromag, a manufacturer of input and output devices for industrial control systems, has produced a three part series of white papers that provide readable, non-technical descriptions of various aspects of electrical grounding and its relationship to safety and operational integrity. The subjects covered in the three part series include:

• Ground as protection
• How a ground fault circuit interrupter (GFCI) works
• Ground as a voltage stabilizer and transient limiter
• Tips on improving safety and signal integrity
• The importance of circuit grounding
• Description of the US AC power system and its use of earth ground

You can find the initial installment on our previous blog post, and the third installment follows this blog post. All three parts are recommended reading for anyone, but stakeholders in process measurement and control will benefit from refreshing and enhancing their understanding of this important subject. It is a quick read and presents technical subject matter in a way that can be comprehended by anyone.

Product and application specialists are always eager to hear about your application issues and questions. Never hesitate to contact them. Your process knowledge, combined with the product and application familiarity of a professional sales engineer, will generate good outcomes.

Electrical Grounding Practices- Part 2 of 3 from MSJacobs-Cali

Are You Well Grounded on Grounding? - Part 1

Some Drawing Symbols Used For Ground

Grounding of electrical equipment and electronic instrumentation is an aspect of project design and implementation that sometimes gets taken for granted. To say that proper electrical grounding is important is an understatement because, without it, certain safety aspects that we rely upon will simply not work. Additionally, and often more confounding, is the intermittent, unexpected, or bizarre behavior of electronic measurement and control devices when proper electrical grounding is not established.

I came across a series of white papers written by some knowledgeable people at Acromag, a manufacturer of industrial input and output devices (industrial I/O). The comprehensive three part series covers best practices involved in the grounding of electrical equipment and electronic instrumentation, in language understandable to a reader of any technical level. The subject matter includes:

• Ground as protection
• How a ground fault circuit interrupter (GFCI) works
• Ground as a voltage stabilizer and transient limiter
• Tips on improving safety and signal integrity
• The importance of circuit grounding
• Description of the US AC power system and its use of earth ground

In my reading of the white papers, I gathered a few things I did not know, refreshed a few I had forgotten, and reinforced my understanding of the topic. There is something in the documents for everyone, and a small investment in time will yield some benefit. All stakeholders in industrial process measurement and control, from the factory floor to the executive office, should have the basic understanding contained in these papers.

Part One of the three part series is below. Part Two and Part Three will be published simultaneously in posts following this one. You can get any level of application assistance you need from the sales engineers that specialize in industrial process equipment, measurement, and controls. Their product knowledge and technical resources, combined with your process mastery, will yield the best solution to any issue.

Electrical Grounding Rules - Part 1 of 3 from MSJacobs-Cali

Big Signal Loop? Consider Using a Splitter.

Industrial Signal Transmitters
Courtesy Acromag

Industrial process measurement and control requires the transmission of signals from point to point with no significant distortion. Even with the growing prevalence of wireless signal transmission, over-wire transmission of signals is still a primary means of connecting one device to another.
In the cabled process measurement and control world, the 4 to 20 milliampere signal is generally considered the standard for transmitting analog control and measurement signals over any distance.
There is an immense array of instrumentation and controllers available for use with 4-20 ma signals, so expertise in routing and delivering those signals should be part of your process M&C skill set.

Like just about everything else, routing 4-20 ma signals presents its own set of challenges that require some thought and planning to overcome. Electrical interference is always a concern and must be prevented from impacting the operation of measurement and control devices. Additionally, there must be sufficient power in the signal loop to accommodate the resistance load of connected devices. There are other considerations, but I'm going to focus on these two.

One scenario that can present significant issues is multiple devices requiring connection to the same signal, but with great distance between them. A simple solution can be implemented using an isolated signal splitter.

Features of these units making them an attractive, single box, solution:

• One 4-20 ma input channel for the measuring or controlling device.
• The input signal is retransmitted as identical isolated 4-20 ma signals
• Galvanic isolation from input to output
• Isolation between channels for safety and increased noise immunity. Fault in one output channel does not impact the operation of the other channels.
• Reliable operation in industrial environments, with protection from RFI, EMI, ESD, and surges.
• Low radiated emissions in accordance with CE requirements. 
• DIN-rail mounting of the unit
• Plug-in terminal blocks

If you have a very long signal loop, connecting multiple devices, consider breaking the devices into two groups that may allow for a substantially shorter cable length for each group. Connect each group to one of the isolated outputs of the splitter, giving each group of instruments the identical signal without the risks or impractically of an excessively long cable run.

There are other devices available that may combine special characteristics that solve your signal transmission challenges. Contact a product specialist and discuss your existing or anticipated project requirements. I continually urge engineers to take their process expertise, combine it with the extensive product knowledge of a professional sales engineer, and produce the best possible outcome.

Process Signal Isolated Transmitters, 4-20 ma from MSJacobs-Cali