Proper grounding is an essential component for safely and reliably operating electrical systems. Improper grounding methodology has the potential to bring disastrous results from both an operational as well as a safety standpoint. There are many different categories and types of grounding principles.
Proper Grounding of Instrument and Control Systems in Hazardous Locations paper’s primary focus is to demonstrate proper grounding techniques for low voltage Instrument and Control Systems (IACS) that have been proven safe and reliable when employed in process control facilities. The grounding practices discussed are intended instrument and control systems that operate at 50 VDC or less.
It is commonly accepted that grounds in the process industry can be broadly classified as either dirty or clean. Dirty grounds inside the facility are typically those 120VAC, 220VAC, 480VAC power grounds that are associated with high current level switching. Examples of clean grounds are the DC grounds, usually 24VDC, that reference the PLC, DCS or metering/control system in the plant.
Structural grounds physically and electrically tie the facility together. In the typical plant or house, the 0V ground reference is most often a heavy gauge copper wire embedded around the base of the building and tied into ground rods at the corners as well as into the AC ground feeds at critical junctures. In a ship, it is the hull of the ship; on an offshore oil/gas platform, it is the structural steel of the platform.
It is necessary to adopt a consistent approach throughout your systems, employing star point grounding and proper grounding bed techniques. Recommended codes of practice are drafted after considerable study for the safety (both you and your plant).
10 Comments
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Grounding issues and minimizing EMI « Tomi Engdahl’s ePanorama blog says:
[...] start with grounding. Proper grounding is an essential component for safely and reliably operating electrical systems. Improper grounding methodology has the potential to bring disastrous results from both an [...]
kamran says:
other ppt grounding send piz
encoder product company says:
Can you give an example of an operational amplifier in an industrial control application and also can you explain why the op amp is so well suited for many industrial control applications?
tomi says:
Check out this application note
http://www.analog.com/static/imported-files/application_notes/28080533AN106.pdf
Tomi Engdahl says:
How Isolation and IoT Play a Role in Industrial Automation
https://www.arrow.com/en/research-and-events/articles/how-isolation-and-internet-of-things-play-a-role-in-industrial-automation
Industrial automation arguably dates back to Henry Ford’s installation of a moving assembly line for the Model T in 1913; it is the use of various control systems to operate industrial equipment such as machinery, manufacturing processes and material handling equipment, with little or no human intervention.
Automating industrial processes has a number of benefits: it saves energy and materials; it improves the quality, accuracy and precision of industrial processes; it allows operation in hazardous environments (in nuclear plants, for example); and it vastly saves on labor.
The results are impressive
The Connected Factory and the Internet Of Things
The next stage after automating individual industrial processes is to make sure that they all work together smoothly – and provide data to their human masters, of course! The modern automated factory therefore relies on an industrial network using one of the numerous automation protocols such as Ethernet, Fieldbus, or HART Protocol to provide connectivity at the factory level.
Galvanic Isolation and Industrial Automation
Adding electronic control and connecting multiple systems together via a network has many benefits, but there are issues and challenges, too. One of these is the challenge of combining high-voltage, high-current machines such as industrial robots and CNC machines with low-voltage, low-current data acquisition systems and networked communications. We’re going to talk about an important technique used to battle this problem –galvanic isolation.
Galvanic isolation is the technique of isolating functional sections of electrical systems to prevent current flow between them; no direct (i.e., resistive) conduction path is permitted. Although there’s no resistive path between sections, power or information is still transferred by capacitive, inductive, optical, or other techniques.
Why is galvanic isolation needed in industrial automation?
Safety – Protecting users of electrical equipment from potentially lethal voltages and currents is a key requirement in any electrical design
Ground Differences & Ground Loops- Unlike the simple schematics we drew in school, as practicing engineers we soon learn that ground is most certainly not the same at different points in a system, especially when those systems are widely separated – between different parts of an industrial plant, say. This can lead to errors or even failure in a digital network because any difference in the ground reference
Common-Mode Voltages – in many cases we need to extract a small signal riding on top of a larger common-mode voltage: an in-phase signal or voltage that appears simultaneously on both input terminals. In some cases, this can offset the signal being measured
A number of regulatory standards govern isolation for industrial applications, including IEC 60204; UL508; UL60947, and CSA 14-10. In addition, IEC 61010-1 and VDE 410/411 cover industrial control.
Tomi Engdahl says:
When you can’t guarantee good grounding, isolation of automation bus is one option:
CAN transceiver wards off ground potentials
http://www.edn.com/electronics-products/other/4442749/CAN-transceiver-wards-off-ground-potentials?_mc=NL_EDN_EDT_EDN_analog_20160929&cid=NL_EDN_EDT_EDN_analog_20160929&elqTrackId=eb242d364d60401f98d258811a87eb16&elq=1bf46ad9b61843d6bcfb68b829f9bd24&elqaid=34083&elqat=1&elqCampaignId=29794
An ISO 11898-2-compliant CAN µModule transceiver and isolator from Linear Technology, the LTM2889 guards against large ground-to-ground differentials and common-mode transients in 3.3-V and 5-V applications. The LTM2889 separates grounds by isolating the CAN transceiver using internal inductive isolation.
The device implements multiple levels of protection to significantly improve system reliability, including 2500 VRMS of galvanic isolation, ±60 V of bus-voltage fault tolerance, greater than 30 kV/µs of common-mode transient immunity, and ±25 kV HBM ESD protection. It requires no external components, ensuring a robust solution for isolated serial data communications.
Prices start at $9.96 each in lots of 1000 units.
http://www.linear.com/product/ltm2889
Tomi Engdahl says:
Steps to ensure proper installation of monitoring and metering equipment
http://www.controleng.com/single-article/steps-to-ensure-proper-installation-of-monitoring-and-metering-equipment/150a9e34502e7eeed7da24f1f073d692.html
Following best practices for proper field device installation will help avoid performance issues and help designers realize the true return on investment (ROI). See four steps to ensure proper installation of monitoring and metering equipment and instrumentation, including proper grounding and shielding.
While investments in electronic monitoring and metering systems are made within complex industrial environments, and connections seem to be correct, problems still exist.
Some devices function perfectly, others do not function at all, while some perform erratically or occasionally send error messages. The majority of problems seem to occur within sensitive control or power transmission assemblies.
Often, a lack of attention has been given to the installation details of monitoring and metering device wiring during design and installation. Some of these important wiring issues include incorrect wire selection or installation, improper instrumentation grounding, and inadequate electromagnetic protection for wire and terminations.
1. Ensure adherence to manufacturer recommendations.
2. Understand infrastructure challenges and environmental factors.
3. Diligently review pre-approval documents and plans.
4. Test systems before and after installation.
It is vital to use testing equipment to measure capacity, harmonics, and EMI before and after installation to streamline the field wiring process; Proactive testing can help designers identify possible obstacles and implement protective measures before a bill of materials is created. These studies also should be performed following installation to ensure wiring measures have correctly addressed identified issues.
Tomi Engdahl says:
What’s your (single) point, youngster?
http://www.edn.com/electronics-blogs/tales-from-the-cube/4394491/What-s-your–single–point–youngster-
“That’s not exactly a single-point ground,” I said.
“Have you got a unit that has the problem that I can play around with?” I asked.
“I’ve got about a hundred, and I’ve got to get them fixed. I’m looking into eliminating the error in software,” he said. “You can have one, but please don’t break it.”
It was worth enduring all of his eye rolling when I found two points on the supposedly single-point analog ground that differed by 30 μV; this went away when I disconnected the battery eliminator.
The fix was simple. The ADC had differential inputs, so we tied its inverting input to the op amp’s noninverting input. We moved the detector’s ground connection to the op amp’s noninverting input. The unit behaved flawlessly, even though its ground wasn’t ground.
It turns out the youngster had inadvertently connected the return for the battery eliminator to the analog ground plane instead of the digital ground plane.
the entire load current flowed through the analog ground plane, causing a difference of approximately 1 μV