RE: R: R: Voltage Breakdown
For many topical staticides (on IC tubes and containers) to function, the RH must be < 25%. David Sterner Ademco Syosset NY __ Reply Separator _ Subject: Re: R: R: Voltage Breakdown Author: "Jim Hulbert" at ADEMCONET List-Post: emc-pstc@listserv.ieee.org Date:7/12/2000 8:40 AM I must admit I am also confused. It is a fairly common practice and has proved quite effective to install humidifiers in enclosed environments to reduce the propensity for static electricity generation. Why does this work? Jim Hulbert Senior Engineer Pitney Bowes Paolo Roncone on 07/12/2000 04:39:08 AM Please respond to Paolo Roncone To: "'Rich Nute'" cc: "'emc-p...@ieee.org'" (bcc: Jim Hulbert/MSD/US/PBI) Subject: R: R: Voltage Breakdown Hi Rich: thanks for your reply. Now I regret to say that I am a bit confused. Based on what you say I don't understand why in dry weather you have more chances of high voltage ESD than in humid weather. As I said this is a common experience that anyone can confirm. I thought the explanation is that dry air has higher dielectric strength so higher electrostatic fields need to build up before a discharge. Another point suggesting the dependence from humidity is that the ESD standard EN 61000-4-2 specifies relative humidity among ambient conditions to control during ESD tests. Regards, Paolo -Messaggio originale- Da: Rich Nute [SMTP:ri...@sdd.hp.com] Inviato: marted --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
RE: R: R: Voltage Breakdown
There are several references that talk about humidity control in handling ESD sensitive items: ESD Association - Electrostatic Discharge Control Handbook - " The effects of humidity are most noticeable in garments, plastic packaging material, process tooling, fixtures, furniture, etc., which are non-metallic and may be easily charged." "Low humidity indicates a lack of water vapor in the atmosphere. This lack of water vapor causes both volume and surface resistance to increase in most materials. Low humidity may also cause an increase in leakage resistance to the ground in the case of furniture and fixtures that are not hard grounded through a metallic path." EN100015-1 (1992) Protection of electrostatic sensitive parts - "Low humidity severely reduces the dissipation effectiveness of materials used in certain types of worksurfaces, packaging and clothing." DOD-HDBK-263 ESD control handbook for protection of electrical and electronic parts, assemblies and equipment... - "Humid air helps to dissipate electrostatic charges by keeping the surfaces moist, therefore increasing surface conductivity. Substantial electrostatic voltage levels can accumulate with a decrease in relative humidity (see table III). However, it is also evident from Table III that significant electrostatic voltages can still be generated with relative humidity as high as 90 percent. ." Table III lists various events such as walking across a carpet and corresponding ES voltage levels at 10-20% RH, and 65-90% RH. There are a number of other EOS/ESD documents that I can't lay my hands on right now. The bottom line of all of these is that the phenomenon is not so much breakdown of air as it is dissipation of electrostatic charge. That is, the increased 'conductivity' of the air with higher water content dissipates the charge quicker and therefore the discharges are less intense (and less perceptible). Bob Martin, PE, NCE Sr. Technical Manager Intertek Testing Services http://www.etlsemko.com (978)263-2662 fax(978)263-7086 r...@itsqs.com The opinions expressed are my own and not necessarily those of my employer. -Original Message- From: Jim Hulbert [mailto:hulbe...@pb.com] Sent: Wednesday, July 12, 2000 8:41 AM To: emc-p...@ieee.org Subject: Re: R: R: Voltage Breakdown I must admit I am also confused. It is a fairly common practice and has proved quite effective to install humidifiers in enclosed environments to reduce the propensity for static electricity generation. Why does this work? Jim Hulbert Senior Engineer Pitney Bowes Paolo Roncone on 07/12/2000 04:39:08 AM Please respond to Paolo Roncone To: "'Rich Nute'" cc: "'emc-p...@ieee.org'" (bcc: Jim Hulbert/MSD/US/PBI) Subject: R: R: Voltage Breakdown Hi Rich: thanks for your reply. Now I regret to say that I am a bit confused. Based on what you say I don't understand why in dry weather you have more chances of high voltage ESD than in humid weather. As I said this is a common experience that anyone can confirm. I thought the explanation is that dry air has higher dielectric strength so higher electrostatic fields need to build up before a discharge. Another point suggesting the dependence from humidity is that the ESD standard EN 61000-4-2 specifies relative humidity among ambient conditions to control during ESD tests. Regards, Paolo -Messaggio originale- Da: Rich Nute [SMTP:ri...@sdd.hp.com] Inviato: marted --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
RE: R: R: Voltage Breakdown
In a quick search I found this: http://www.esdsystems.com/newsletters/v1issue3.htm It looks like a higher RH affects the ability of a surface to hold a charge. -Original Message- From: Jim Hulbert [mailto:hulbe...@pb.com] Sent: Wednesday, July 12, 2000 7:41 AM To: emc-p...@ieee.org Subject: Re: R: R: Voltage Breakdown I must admit I am also confused. It is a fairly common practice and has proved quite effective to install humidifiers in enclosed environments to reduce the propensity for static electricity generation. Why does this work? Jim Hulbert Senior Engineer Pitney Bowes Paolo Roncone on 07/12/2000 04:39:08 AM Please respond to Paolo Roncone To: "'Rich Nute'" cc: "'emc-p...@ieee.org'" (bcc: Jim Hulbert/MSD/US/PBI) Subject: R: R: Voltage Breakdown Hi Rich: thanks for your reply. Now I regret to say that I am a bit confused. Based on what you say I don't understand why in dry weather you have more chances of high voltage ESD than in humid weather. As I said this is a common experience that anyone can confirm. I thought the explanation is that dry air has higher dielectric strength so higher electrostatic fields need to build up before a discharge. Another point suggesting the dependence from humidity is that the ESD standard EN 61000-4-2 specifies relative humidity among ambient conditions to control during ESD tests. Regards, Paolo -Messaggio originale- Da: Rich Nute [SMTP:ri...@sdd.hp.com] Inviato: marted --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: R: R: Voltage Breakdown
I must admit I am also confused. It is a fairly common practice and has proved quite effective to install humidifiers in enclosed environments to reduce the propensity for static electricity generation. Why does this work? Jim Hulbert Senior Engineer Pitney Bowes Paolo Roncone on 07/12/2000 04:39:08 AM Please respond to Paolo Roncone To: "'Rich Nute'" cc: "'emc-p...@ieee.org'" (bcc: Jim Hulbert/MSD/US/PBI) Subject: R: R: Voltage Breakdown Hi Rich: thanks for your reply. Now I regret to say that I am a bit confused. Based on what you say I don't understand why in dry weather you have more chances of high voltage ESD than in humid weather. As I said this is a common experience that anyone can confirm. I thought the explanation is that dry air has higher dielectric strength so higher electrostatic fields need to build up before a discharge. Another point suggesting the dependence from humidity is that the ESD standard EN 61000-4-2 specifies relative humidity among ambient conditions to control during ESD tests. Regards, Paolo -Messaggio originale- Da: Rich Nute [SMTP:ri...@sdd.hp.com] Inviato: marted ì 11 luglio 2000 19.39 A: paolo.ronc...@compuprint.it Cc: Product Safety Technical Committee Oggetto: Re: R: Voltage Breakdown Hi Paolo: > what about relative humidity of air ? > I believe breakdown voltage depends also on humidity content of air. Contrary to "conventional wisdom," the water content of air, humidity, actually increases the dielectric strength of air by a slight amount. (Sorry, but I cannot cite where I read this.) As I recall, the increase is so small as to be negligible compared to all of the other factors affecting dielectric strength of air. Note that liquid water and gaseous water (water vapor) have entirely different physical properties. It is not unreasonable for water vapor to have a greater electric strength than air. For gases, according to the Standard Handbook for Electrical Engineers: The relative dielectric strength, with few exceptions, tends upward with increasing molecular weight. The noble atomic gases (helium, argon, neon, etc.) are poorest... and have the lowest dielectric strengths. If we applied this generality (contrary to my initial assertion), then the electric strength of water vapor, H2O, should be less than that of either oxygen, O2, or nitrogen, N2. However, note that the actual number of molecules of water vapor in air at any temperature is very small compared to the number of molecules of oxygen and nitrogen. So, the reduction of dielectric strength by the presence of water vapor, if any, will be very small. Regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
