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 Copyright © 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 Positive + Negative - Many of the materials used in clean 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 Charged Object Isolated Conductor When an isolated conductive object is placed in an electric field, a charge separation occurs 7Copyright © 2014 NRD LLC and Electronics Workshop

Electrostatic Forces Affect Weighing Particle Attraction Static Charge Electrostatic Force Electrostatic Field Attraction and Repulsion 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 results Wafer 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 Common Point Ground Service Equipment 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 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 Workshop16

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 BarIonizing 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