Role of Anti-Static Wrist Straps in Industrial Automation

Engineers and technicians frequently work with extremely sensitive electronic equipment and components in industrial automation.

Electrostatic discharge (ESD) protection for these systems is essential to maintaining their performance and preventing expensive damage. Using an anti-static wrist strap is one of the easiest and most efficient ways to reduce the risks associated with ESD.

This article will explain the purpose, correct use, and best practices for employing anti-static wrist straps in industrial automation.

What is an Anti-Static Wrist Strap?

An anti-static wrist strap, also known as an ESD (Electrostatic Discharge) wrist strap, is a device that is worn around the wrist to prevent the accumulation and discharge of static electricity. 

It is constructed of conductive elements that safely ground the wearer, allowing any static charge to dissipate before causing damage to sensitive electronic components.

What Is the Purpose of an Anti-Static Wrist Strap?

• An anti-static wrist strap, also known as an ESD wrist strap, is a wearable device that is intended to prevent the accumulation of static electricity on a person’s body. 
• In industrial settings, static electricity can build up on an individual due to movement, posing a major risk to sensitive electronics such as programmable logic controllers (PLCs), Distributed Control Systems (DCS), sensors, and control modules. 
• When someone touches a component without sufficient protection, static electricity can discharge, causing permanent damage or equipment failure.
• The primary function of an anti-static wrist strap is to protect sensitive electronic components from electrostatic discharge (ESD). 
• Static electricity may be extremely harmful in industrial automation environments, where engineers and technicians work with delicate equipment like PLCs, sensors, HMIs, and control modules. 
• Even minor electrostatic discharges may harm electronic components or cause failures in systems such as control circuits, causing costly repairs or replacement.
• The wrist strap ensures that any static charge produced by the user’s body is regularly released in a controlled manner, rather than building up and unexpectedly discharging on sensitive equipment.

Main Purposes of an Anti-Static Wrist Strap

Preventing ESD Damage:

Static electricity can destroy delicate electronic components like microprocessors or integrated circuits. The wrist strap provides a safe grounding mechanism that dissipates the static charge, preventing equipment damage.

Ensuring Safety:

By grounding the individual, the wrist strap reduces the risk of accidental discharges that could harm sensitive electronic devices.

Maintaining a Controlled Environment:

In environments such as electronics manufacturing or industrial automation, it’s crucial to maintain an ESD-safe environment. Anti-static wrist straps are part of the standard best practices for ESD control.

Convenience:

Anti-static wrist straps are comfortable, adjustable, and easy to wear. They allow free movement while maintaining continuous grounding, enabling efficient work on complex tasks.

What is Electrostatic Discharge (ESD)?

The unexpected flow of electricity between two electrically charged objects brought on by contact, an electrical short, or a dielectric breakdown is known as an electrostatic discharge (ESD). ESD is often generated through a process called tribocharging, where certain materials become electrically charged when separated after being in contact with another material.

For example, ESD is similar to the static electricity you experience when rubbing a plastic scale on your hair and then using it to pick up small pieces of paper. On a larger scale, lightning strikes are another example of triboelectric charging, where friction between different materials generates massive electrical discharges.

How Does Electrostatic Discharge (ESD) Affect Electronics?

Electrostatic discharge can cause significant damage to sensitive electronic components. Even low-voltage discharges that are too small to be felt by humans can permanently damage circuits in electronics, particularly in low-power and electrostatic-sensitive devices (ESSDs). The potential impact of ESD depends on several factors:

1. Build-up of Static Charge: Static is the accumulation of electrical charge between two surfaces, usually when they rub together. This charge creates a voltage potential that behaves like a capacitor, storing energy until it can discharge.
2. Capacitive Effect: The surface where the charge accumulates acts like a capacitor. When no conduction path exists, the charge remains on the surface for extended periods, leading to static electricity. If a conductive path is created, the charge discharges, sometimes causing a spark or electric shock.
3. Discharge Characteristics: The speed and intensity of the discharge depend on the resistance of the conduction path:
   • High resistance: Discharge occurs slowly with lower current.
   • Low resistance: Discharge happens rapidly with a higher current, which can more easily damage electronics.
4. Impact on Circuits: ESD can lead to permanent damage by destroying delicate electronic components, such as microchips and transistors, through short circuits, burns, or degradation.

The factors influencing the strength of the discharge include:

• Size of the person generating the charge.
• Level of movement or friction involved.
• Material that the person or object is in contact with.
• Humidity levels: Dry air promotes static buildup, while higher humidity reduces static accumulation.

Click here for What is Personal Protective Equipment (PPE) and its types?

Triboelectric Series of Materials

The triboelectric series ranks materials based on their ability to gain or lose electrons through friction. Materials higher on the list tend to acquire a positive charge when rubbed against those lower on the list, which acquire a negative charge.

Positive Charge (Loses Electrons Easily)

• Skin
• Hair
• Wool
• Silk
• Paper
• Cotton
• Wood

Negative Charge (Gains Electrons Easily)

• Rubber
• Rayon
• Polyester
• Polythene
• PVC
• Teflon

What are Static Straps used for?

Static straps play a vital role in environments where sensitive electronic components are assembled, maintained, or handled. In industrial automation, these straps protect various critical systems:

PLCs and HMIs (Human-Machine Interfaces):

These systems are essential for process control and human interaction with machinery. An ESD event could lead to system failures or incorrect commands.

Sensors and Transmitters:

Automation systems rely on accurate sensor inputs. A static discharge can interfere with the calibration and functionality of these devices.

Printed Circuit Boards (PCBs):

Static electricity can damage the components on PCBs used in control systems, potentially leading to system downtime.

Communication Modules:

Devices responsible for networking and communication in industrial automation are susceptible to ESD damage, which could disrupt control signals and data flow.

Why use an Electrostatic Wrist Strap?

There are several reasons why electrostatic wrist straps are critical in industrial automation:

Prevention of ESD Damage:

Even low levels of static electricity can cause severe damage to expensive and critical equipment. A wrist strap ensures that static is safely discharged before it can do harm.

Increased Safety for Equipment:

Sensitive control systems, microprocessors, and electronic components are shielded from disruptions caused by ESD.

Cost Efficiency:

Preventing damage due to ESD avoids the high costs associated with replacing components and system downtime.

Compliance with ESD Standards:

Many industries have ESD protection guidelines that professionals must adhere to in order to ensure equipment safety and longevity.

How to Use an Anti-Static Strap?

Anti-static wrist straps are essential for preventing electrostatic discharge (ESD) when handling sensitive electronic components. 

are three methods of using and maintaining an ESD-safe environment, with detailed explanations for each method.

Method 1: Using an ESD Strap to Ground Yourself

Choose a Wired Strap for Better Protection

• Wired straps connect you directly to the ground and are ideal for sensitive electronic work.
• While there are wireless straps available, studies (such as those by NASA) have shown they are less effective at preventing discharges compared to wired straps. 

Secure the Strap around your Wrist

• Before handling ESD-sensitive components, wrap the strap around your wrist, ensuring it is snug and in contact with your skin. 
• This ensures a constant path for static discharge.

Attach the Strap to a Common Ground

• The other end of the strap is usually an alligator clip, which should be connected to a designated common ground point. 
• In ESD-safe workstations, these points are typically marked with a symbol or label.

Alternative Grounding Option

• If a common ground is not available (for example, in a home), secure the strap’s alligator end to an unpainted metal surface such as a computer chassis or power supply. Ensure that the metal is clean and grounded to avoid inefficient grounding.

Keep the Strap on when Handling ESD-Sensitive Items

• Wear the strap at all times when working with components such as motherboards or video cards. Electrostatic shocks, even minor ones, can gradually degrade component performance.

Test the Resistance of Your ESD Strap Periodically

• To provide adequate protection, the wrist strap resistance should range from 1 to 10 MΩ. 
• This may be checked with a multimeter. In occupational settings, straps are tested on a daily or continuous basis.

Click here for Electrical safety in power distribution

Method 2: Maintaining a Static-Free Work Environment

Use ESD-Protective Mats

• Cover work surfaces and floors with protective mats to prevent the accumulation of static. 
• These mats dissipate charges and protect sensitive components from accidental discharges caused by static buildup on surfaces or shoes.

Connect Work Surfaces and Tools to a Common Ground

• In an ESD-protected workstation, all surfaces and equipment should be connected to the same common ground point, which is usually a central metal pole or bar.

Use Grounded Electrical Tools

• Only use electrical tools that have 3-prong grounded plugs in a static-free environment to ensure proper grounding and safety when handling ESD-sensitive components.

Wear ESD Lab Coats

• ESD-sensitive components can be protected from your clothing by wearing ESD lab coats, which are designed to prevent static buildup. Fasten all buttons or snaps to cover all clothing underneath.

Method 3: Handling ESD-Sensitive Components

Store Components in Antistatic Bags

• When not in use, keep ESD-sensitive components (like circuit boards) in antistatic bags to avoid damage. These bags should be resealable and can be stored component-side up.

Maintain Optimal Humidity Levels

• Maintain indoor humidity between 45 and 55% to minimize static buildup while avoiding moisture damage to the components. Humidity can be monitored using a hygrometer.

Avoid Static-Generating Clothing

• Static electricity can build up in clothing, especially in cold or dry conditions. To prevent accidental discharges, avoid wearing loose clothing and never wipe components on your clothing use antistatic cloths instead.

Where to Connect Anti-Static Wrist Straps?

Proper grounding of an anti-static wrist strap is essential to ensure protection from electrostatic discharge (ESD) when working with sensitive electronics. Below are common and effective grounding options:

ESD-Safe Workstations

• These workstations are specifically designed for handling and assembling electronic components. They often come equipped with a grounding system that is ESD-safe.
• Attach the wrist strap to a grounding point provided on the workstation. These points are specifically engineered to maintain an ESD-safe environment, ensuring that any static charge is safely dissipated.

Grounding Plugs

• Many anti-static wrist straps come with a grounding plug. These plugs are designed to be inserted into an electrical socket with a verified ground connection.
• Insert the grounding plug into an electrical outlet that is known to have proper grounding. Make sure the socket is compliant with ESD-safe standards to avoid improper grounding or potential hazards.

Chassis or Grounded Metal Surfaces

• When working in environments such as control panels, cabinets, or industrial machinery, attaching the wrist strap to a grounded metal part, like the chassis, can provide effective grounding.
• Simply clip the alligator end of the wrist strap cord to a metal surface that is electrically grounded. 
• Be sure to verify that the surface is properly grounded to avoid false grounding that could lead to ineffective ESD protection.

How Does an Anti-Static Wristband Work?

• An anti-static wrist strap works by constantly transferring any static energy that accumulates on your body to a grounding point. 
• The strap incorporates conductive elements, such as carbon or silver-plated threads, which allow for the safe release of electrical energy. 
• By connecting the strap to a ground, static energy is securely transferred from the body to the earth, preventing ESD from damaging sensitive components.

What Is the use of an Anti-Static Wrist Mat?

• An anti-static wrist strap is often used alongside an anti-static wrist mat or work mat. 
• The mat provides a grounded surface for placing sensitive electronic components during assembly, repair, or testing. 
• Together, the wrist strap and mat create a fully ESD-safe environment, ensuring that neither the operator nor the components can accumulate static electricity.

Do you really need an Anti-Static Wrist Strap?

If you work with sensitive electronics in an industrial automation environment, you should wear an anti-static wrist strap. Some may argue that careful handling can prevent ESD, however even small amounts of static can cause long-term damage. Without a wrist strap, equipment may malfunction or degrade over time, requiring costly repairs or replacements.

Best Practices for Using Anti-Static Wrist Straps

1. Always test continuity: Before you begin working, use an ESD tester to confirm that your wrist strap is properly grounded and functional.
2. Replace Worn Straps: Over time, the conductive materials in wrist straps might degrade, diminishing their efficiency. Regularly inspect your straps and replace them if necessary.
3. Ensure Proper Grounding: It is vital that the connection point is properly grounded. This decreases the possibility of inadvertent discharges and ensures maximum ESD protection.

Additional Considerations for using Anti-Static Wrist Straps

Resistance and Resistors: 

Anti-static wrist straps often contain a built-in resistor (typically 1 megohm) that helps slow the discharge of static electricity. This resistor ensures that the static dissipates safely over time rather than all at once, which could still cause damage.

Grounding Methods: 

Some users may be tempted to clip the wrist strap to an anti-static mat, but this can increase the system’s resistance to ground beyond recommended levels. Always ensure the strap is grounded to an appropriate source, such as a grounded metal surface or an electrical grounding line.

Continuous Monitoring: 

In environments where the risk of ESD is particularly high, continuous monitoring systems can be used to ensure that both the anti-static wrist strap and mat are always properly grounded.