advanced static control mitigating electrostatic effects on measurement accuracy arnold steinman...

ADVANCED STATIC CONTROL

Mitigating Electrostatic Effects on Measurement Accuracy

Arnold Steinman M.S.E.E.

Electrostatics Consultant

Electronics Workshop

Dangelmayer Associates

[email protected]

Electronics Workshop

Speaker: Greg Gumkowski

National Sales Manager

NRD LLC

[email protected]

1Copyright © 2014 NRD LLC and Electronics Workshop

Outline

• Introduction• Static Charge Generation• Static Charge Control Methods

– Grounding– Material Selection– Ionization

• Measurement Issues Caused by Static• Mitigating Measurement Static Problems


Introduction


Friction

Contact and Separation

Motion

Electrostatic Force

Static Charge

Electrostatic Field

Triboelectric Charging -+

• Triboelectric charging occurs when two materials with different affinities for electrons are in contact and are then separated.

• Any material may be charged triboelectrically. Whether it stays charged depends on its being a conductor or an insulator.

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Triboelectric Series Short List

• Human Hands

• Water

• Quartz

• Nylon

• Aluminum

• Chrome

• Steel

• Polyurethane

• Polyethylene

• Polypropylene

• PVC (Vinyl)

• Silicon

• Mylar

• Teflon

Positive+

Negative-

Many of the materials used inclean measurement areas are excellent insulators that can create and hold very high levels of static charge for long periods of time.


The amount of charge generated is affected by several factors:

Factors Affecting Triboelectric Charging

• The condition of the two surfaces (rough surface = less charge)

• The size of the areas being rubbed or separated (small area = less charge)

• The pressure applied to the surfaces of the two materials before being separated (low pressure = less charge)

• The speed of the separation (slow = less charge)

• Humidity (high humidity = less charge)


Charging By Induction

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++++

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+ + + + +

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ChargedObject Isolated Conductor

When an isolated conductive object is placed in an electric field, a charge separation occurs


+ + + + +

---- -

Electrostatic Forces Affect Weighing

Particle Attraction

StaticCharge

ElectrostaticForce

Electrostatic Field

Attraction andRepulsion


Movement of Small Objects

Particle Attraction• Static charge creates forces of attraction and repulsion• Environmental particles are attracted to weighing samples,

transport carriers, and scale components• Sample particles stick to transport carriers and scale

components• Weighing inaccuracies, sample losses and contamination are

the resultsWafer at 0 V Wafer at 2000 V – 7X particles


Movement of Small Objects

• Static charge on samples and other objects in the weighing chamber interacts with the components of the precision scale

• Inaccuracies and zero drift are common results


Static Charge Control Methods

• Grounding – Work Area and Personnel

• Control of Materials– Insulators– Dissipative Materials

• Ionization


The First Step: Grounding• Anything that is conductive should be connected to

ground • A work station ground should be established and

connected to the electrical “green wire” ground

CommonPoint Ground

ServiceEquipment

Ground

Green Wire

Work Station


Control of Materials• Eliminate unnecessary insulators

• Replace insulators with static dissipative materials– Add carbon or metal particles to insulators– Hygroscopic materials – attract humidity– Use natural materials for garments

• Control the charge on process essential insulators– Topical treatments– Air ionization


An air ion is an atom of one of the gases in the air that has gained or lost an electron

Air Ions

Natural Sources:• Radioactive decay of the soil• Friction caused by wind and water• Lightning• Cosmic rays

Artificial Sources:• Ionizing radiation• Corona discharge


Neutralizing Charge with Air Ionization

Ionizers neutralize charge on surfaces by providing the opposite polarity charge from the air

+ + + + + + + + + - - - - - - - - - - -

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Insulator

Charged Air Molecules


Ionization Types• Nuclear (Alpha) Ionization

• Uses a Polonium-210 alpha source to ionize the air• Produces balanced ionization• No power source needed• Annual replacement and government regulations

• Corona Discharge• High voltage on sharp points or wires• AC – high voltage from power line (5000 VAC)• Steady DC – negative and positive high voltage supplies• Pulsed DC – alternating negative and positive high voltage supplies

• Piezoelectric• Uses mechanical forces on crystals to generate high voltage

Copyright © 2014 NRD LLC and Electronics Workshop 16

Ionizers – Zerostat Gun• Provides minimal neutralization• Charges objects negatively


Ionizers - Alpha

• Fast neutralization• Balanced Ionization• No electrical power required• Small and easily mounted


In-Balance Alpha Ionizer

Ionizers – Corona Bars and Blowers• Provide fast neutralization of objects and work areas• Use AC, Steady-State DC, and Pulsed DC technology

Corona Ionizing Bar Ionizing Blower


Conclusion

• Static charge generation is unavoidable as long as things are moving

• Static charge causes weighing equipment inaccuracies and unwanted transfers of particles during weighing operations and material transport

• There are well-established methods of controlling static charge

• Insulating materials are unavoidable in weighing operations (samples, transport materials, and scale components)

• Air ionizers effectively control static charge on insulators, improving measurement accuracy

Copyright © 2014 NRD LLC and Electronics Workshop 20

advanced static control mitigating electrostatic effects on measurement accuracy arnold steinman...

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