IONIZATION THE ESD ASSOCIATION May14, 2003
Presented by: Gary Seale - V.P. Membership - Texas ESD Association Regional Manager - Simco Ionization Scope, Purpose, & Application Definitions Safety Specific Requirements
CONTENTS Room Ionization Laminar Flow Ionization Worksurface Ionization Compressed Gas Ionizers-Guns/Nozzles Test Equipment Annex A
Scope - Standard establishes measurement techniques, to determine ion balance and charge neutralization Purpose - Standard provides test methods & procedures for evaluating air ionization equipment & systems Application - Provide performance data, qualify equipment for use
Definitions Air conductivity - Ability of air to conduct current under influence of an electric field. Air Ions - Clusters of 10 molecules bound by polarization forces to a singly charged oxygen or nitrogen molecule. Charge decay - Decrease/neutralization of net electrostatic charge
Charge plate monitor - Instrument used to measure decay times Compressed gas ionizers - Ionizer tools used to neutralize charges and remove particles with high pressure gas Corona - Production of positive & negative ions by a very localized high electric field
Discharge Time: Time necessary for a voltage to decay from an initial value to some arbitrarily chosen value. (typically 10% of beginning value) Emitter - A conducting sharp object, needle or wire, which will cause a corona discharge when kept at high potential
Neutralize - Canceling the effect of a field from a given charge, by conducting the field to ground, or introducing an equal opposite charge. Offset voltage - Observed voltage on a charge plate that has been placed in an ionized environment.
SAFETY REQUIREMENTS Electrical - Peak current limited for installation (emitter tips) Ozone - Generation not to exceed limit defined by OSHA 1910 Radioactive - License from N.R.C. Mfg. to meet all requirements of Title 10, Part 20, Code of Federal Regulations
Installation - Conform to any applicable electrical, mechanical, and safety codes. Noise exposure, PSI used, relief design Discharge test time - Plate charged to initial voltage and discharged to 10% of that value. Time required for both polarities monitored and recorded.
Offset voltage test - Ground plate to zero Monitor plate in ionized environment for deviation from zero. Locations - See Table 1 Same conditions for all tests, no equipment adjustments. Peak offset voltage - DC ionizers measured for peak voltages and reported.
Table 1- Test Setups and Test Locations Equipment Figure References Number of Test Locations Offset Voltage/Time Interval CPM Initial Voltage Room Ionization Grids, AC 3 2 1-5 Min. 1000 Bars, Pulsed & DC 3 2 1-5 Min. 1000 Single polarity emitter 4 3 1-5 Min. 1000 Dual DC line 5 3 1-5 Min. 1000 Pulsed DC emitter 6 2 1-5 Min. 1000 Laminar Flow Hood Vertical 7 & 8 7 1-5 Min. 1000 Horizontal 9 & 10 5 1-5 Min. 1000 Worksurface Ionization Bench Top 11 12 1-5 Min. 1000 Overhead 12 & 13 12 1-5 Min. 1000 Compressed Gas Ionization Guns and Nozzles 14 1 10 sec. - 1 Min. 1000
Room Ionization Testing - Monitor clear 5 horizontal area, System on for 30 minutes previously. Test person grounded - 5 feet outside area Discharge time for 1000 to 100 volts - both polarities
Laminar air flow velocity recorded Measurements taken 5 under emitters & recorded Discharge and offset voltage (1 min. test criteria) taken and recorded
ESD STM3.1-2000 Example: Room Ionization Emitters
LAMINAR FLOW HOOD IONIZATION Test area unobstructed, surface area dissipative and properly grounded Test person grounded Discharge time from 1000 to 100 volts measured for both polarities, + Offset V. Air flow recorded - test positions as per specification - See slide 17
Discharge time measured & recorded, offset voltage measured (1 minute min.) & recorded Example: Laminar flow bar
WORKSURFACE IONIZATION Test in unobstructed area, surface static dissipative and properly grounded Test person grounded, discharge for both polarities, 1000-100 volts measured Measure w/heater on & off, w/filters, at min & max airflow, air velocity measured and reported
S3.1 Test Criteria
Benchtop test results
Example: Benchtop product
Overhead Test Criteria
Overhead test - Side view
Discharge time and offset voltage (1 min.) should be measured at each test location Example - Overhead Ionizer
COMPRESSED GAS IONIZERS - GUNS AND NOZZLES Test w/out obstructions to airflow, test personnel grounded, surface dissipative and grounded Discharge 1000 to 100 volts, both polarities. 30 psi input pressure, 6 from charge plate
Discharge time and offset voltage measured and reported as per drawing #14.
Example - Compressed air ionizing gun
TEST EQUIPMENT - Charge Plate 6 x 6 conductive plate - minimum/maximum capacitance limits Construction criteria - no more than 10% discharge of plate voltage in 5 minutes
ANNEX A Air ions - Definition - Natural ions discussion - Radiation and corona induced ionization Mobility and ion current - Formula review, ion movement, current density Neutralization current - Neutralization current proportional to charge & opposite conductivity of the air
Neutralization rate - Charges decay relative to the conductivity of the air. Ion depletion - Charged fields may partially deplete the air of ions. Which may slow discharge rates. Air velocity significantly reduces this effect Charge Plate definition/capabilities
Offset voltage definition/acquisition of. Importance of ionization equipment maintenance - cleaning, emitter replacement, nuclear replacement, insure full volume of air flows