Rugged HMI, what does it really mean?

The variety of human machine interfaces (HMIs) or operator panels in the market that claim “rugged” makes it hard to see what rugged really means. A myriad of ratings, standards and laws are referenced, but what do they entail?
Rugged implies something tough and durable; strongly built and designed to operate in harsh conditions. Truly rugged HMIs tested and certified to operate in wet, dusty, hot, cold, high vibration, and/or hazardous environments.
The purpose of rugged ratings, standards and laws is to ensure that the equipment will:
Operate properly for extended periods of time in the environments they are deployed into
Not be the source of any safety related incident
In industry, what might be considered rugged to some, may not be to others. The national and international ratings, standards and laws that define rugged vary and include different aspects, depending on particular operating conditions and country.

Equipment that may work fine in a clean, climate-controlled environment may fail quickly in a dirty, outdoor environment. Engineers must specify the components, equipment and computer based on the environments they need to operate into. HMIs are included in this specification process.
An HMI is a touch panel display that is integrated into a machine or computer system that communicates the operator’s desire to manage and control the machine.
All HMIs are designed and manufactured based on the environments they will be deployed into. Consider the following classes of HMIs in order of ruggedness:

The selection process is streamlined by understanding where a product will be used. The more harsh the deployment environment, the more rugged the components and technology must be. The HMI must not only be designed for the extremes, but also tested and certified.

The following addresses the important design and testing areas of rugged HMIs.

The most common issue and qualifier are extended operating and storage temperature ranges. Over half the applications that call for a rugged HMI demand a solution capable of performing while exposed to extreme heat and/or extreme cold temperatures. In the oil fields of the Middle East and the mines of South America, the temperatures regularly reach 50° C and higher. In Canada and Russia, operations have extended periods of -30° C.

Moisture, rain and snow

As with all electronics, moisture is a critical factor for HMIs. The slightest amount of moisture, rain or snow can ruin electrical components, shortening the life of the device or making it fail entirely. Rugged HMIs are therefore tested and certified to withstand the ingress of water.

Dust and particles
Dust causes harm and reliability issues for electronics and impacts performance, reliability and longevity of the HMI. Certain food processing plants (candy, spice, sugar), coal plants, and paper plants can produce dust in the concentrations that under certain conditions can become explosive. The HMI must not be the source of a spark that could ignite the pulverized material.

For HMIs, the mechanical vibration of the machinery and equipment it is installed on can cause fatigue life, resonant frequencies, and problems with seals. Standard HMIs undergo none or minimal vibration testing. Rugged HMI panels are tested with various methods which may include swept-sine and random testing (acceleration or power spectral density testing).

Shock occurs when an HMI is mechanically dropped, hit or struck. Depending on the scope of the shock, an HMI’s display can be broken; the touch panel partially or completely rendered inoperable; electronics broken or loosened; or the integrity of the sealing compromised. Rugged HMIs are designed to withstand reasonable shock given the targeted operating environments.

In outdoor applications, the read-ability or view-ability of a standard HMI displays will be difficult if not impossible in direct sun. Rugged HMI backlights are sufficiently bright to enable the HMI to be read in direct sunlight. A standard HMI has a screen brightness of 300-500 cd/m²; a rugged HMI display that will be deployed in direct sun environments requires a backlight of 1,000 cd/m² or greater. Direct sun on an HMI introduces additional heat and damaging effects of ultraviolet (UV) rays. This is an important reason rugged HMIs are designed to operate in the 60°-70° C range and include a special UV coating.

Power source issues
Outdoor environments often have volatile power sources which are dangerous to electronic devices. Load dumps , reverse polarity and spikes can cause electrical havoc for standard HMIs. Rugged HMIs are designed to operate with unreliable or inconsistent power conditions.

Electromagnetic compatibility
HMIs must be immune from a certain level of electromagnetic interference (EMI) in order to operate properly. They also must not emit electromagnetic disturbance that will impact the operation of nearby electrical equipment. Rugged HMIs will withstand a higher electrostatic discharge (ESD) and tolerate higher radiation emissions.

Some industries require much of its electronics and computing equipment to meet certain rugged characteristics. Rugged HMIs are often deployed outdoors, in direct sun, into hazardous and explosive situations, as well as dusty, wet, and/or corrosive settings. Also in extremely harsh applications, for example onboard icebreakers, a rugged HMI can be used on deck and reliably solve visualization tasks in snow and arctic cold. The most common industries that require rugged HMIs include:

Oil and gas (drilling, refining, processing, distribution)
Water and wastewater
Paper and pulp
Maritime and off-shore
Agriculture (storage, processing, refining)
Power generation and distribution (coal, biomass, hydro, wind, solar)
rugged industries

Manufacturers that produce rugged HMIs are aware of the special requirements demanded by these industries. They will ensure that the collective product meet the rugged testing and certification requirements. Rugged HMIs will take the abuse that standard HMIs cannot, while still functioning reliably and efficiently. While there are some indoor environments that demand rugged HMIs (dusty, high vibration, wet), it is the outdoor environment that dictate the need for unique features not found in off-the-shelf standard HMIs.

Certifications are extremely important on most rugged-type applications. In the industrial manufacturing segment, certifications specify and dictate electrical, mechanical, emissions, environmental, safety requirements and conditions for acceptable installation and usage. Typically, certifications are specific to industries, individual countries and/or established global standards where the products will be installed and operated.

Rugged is more than tough or durable. A rugged HMI must be rugged to the core – designed, tested and certified to operate in wet, dusty, extreme temperatures, direct sun, high vibration, unreliable power, and hazardous environments.
Oil and gas, mining, water and wastewater, and marine industries demand HMIs that have been proven to the extremes. The HMIs must be tested and certified against some of the world’s most rigid standards.

The process of designing, engineering, testing and certifying rugged HMIs is a core competency. Those companies that build rugged HMIs understand the industries and environments the HMIs will be deployed into. They want their products to be ruggedly reliable and operational for years. “Test early, test often” is not just an adage, it is fundamental to the culture of those manufacturers.