ADVANCED STATIC CONTROL Mitigating Electrostatic Effects on Measurement Accuracy Arnold Steinman...
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Transcript of 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
Electronics Workshop
Speaker: Greg Gumkowski
National Sales Manager
NRD LLC
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
2Copyright © 2014 NRD LLC and Electronics Workshop
Introduction
3Copyright © 2014 NRD LLC and Electronics Workshop
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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4Copyright © 2014 NRD LLC and Electronics Workshop
Triboelectric Series Short List
• Human Hands
• Water
• Quartz
• Nylon
• Aluminum
• Chrome
• Steel
• Polyurethane
• Polyethylene
• Polypropylene
• PVC (Vinyl)
• Silicon
• Mylar
• Teflon
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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.
4Copyright © 2014 NRD LLC and Electronics Workshop
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)
6Copyright © 2014 NRD LLC and Electronics Workshop
Charging By Induction
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ChargedObject Isolated Conductor
When an isolated conductive object is placed in an electric field, a charge separation occurs
7Copyright © 2014 NRD LLC and Electronics Workshop
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Electrostatic Forces Affect Weighing
Particle Attraction
StaticCharge
ElectrostaticForce
Electrostatic Field
Attraction andRepulsion
8Copyright © 2014 NRD LLC and Electronics Workshop
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
9Copyright © 2014 NRD LLC and Electronics Workshop
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
10Copyright © 2014 NRD LLC and Electronics Workshop
Static Charge Control Methods
• Grounding – Work Area and Personnel
• Control of Materials– Insulators– Dissipative Materials
• Ionization
11Copyright © 2014 NRD LLC and Electronics Workshop
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
12Copyright © 2014 NRD LLC and Electronics Workshop
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
13Copyright © 2014 NRD LLC and Electronics Workshop
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
14Copyright © 2014 NRD LLC and Electronics Workshop
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
15Copyright © 2014 NRD LLC and Electronics Workshop
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
17Copyright © 2014 NRD LLC and Electronics Workshop
Ionizers - Alpha
• Fast neutralization• Balanced Ionization• No electrical power required• Small and easily mounted
18Copyright © 2014 NRD LLC and Electronics Workshop
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
19Copyright © 2014 NRD LLC and Electronics Workshop
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