Search found 288 matches

by SteveHansen
Fri May 04, 2012 11:16 pm
Forum: Vacuum Technology (& FAQs)
Topic: Baratron
Replies: 12
Views: 4586

Re: Baratron

<r><br/> You might want to check out the article "Pressure Measurement Realities" that is linked at <URL url="http://www.belljar.net/vtc_articles.htm">http://www.belljar.net/vtc_articles.htm</URL><br/> <br/> The last page of the article has a discussion of the effects of the temperature coefficients...
by SteveHansen
Thu May 03, 2012 12:01 pm
Forum: Vacuum Technology (& FAQs)
Topic: Baratron
Replies: 12
Views: 4586

Re: Baratron

<t>The microPirani is an excellent gauge and is also very repeatable if you check the zero every now and then (zero pressure is <10^-5 Torr). I have a couple of these and also Baratrons in ranges from 1 to 1000 Torr (and a couple in the 1000 psi range). <br/> <br/> The price for a new 626 Baratron (...
by SteveHansen
Wed May 02, 2012 11:33 pm
Forum: Vacuum Technology (& FAQs)
Topic: Baratron
Replies: 12
Views: 4586

Re: Baratron

<t>Baratron is a trademark of MKS Instruments so I presume you are talking about the MKS product.<br/> <br/> The standard Baratrons have a resolution of 1:10,000. Thus a 1 Torr full scale instrument will resolve to 0.1 microns. The accuracy is specified as percent of reading and is typically 1/2 per...
by SteveHansen
Tue Apr 17, 2012 9:29 pm
Forum: Fusor Construction & Operation (& FAQs)
Topic: Needle Valve
Replies: 5
Views: 2200

Re: Needle Valve

<r>I have found that laser drilled orifices are very convenient, reliable and nearly fool-proof. My gas supply consists of a 2-stage vacuum/pressure regulator that feeds to a 5 micron orifice. In choked flow the flow rate through the orifice is directly proportional to the feed pressure. <br/> <br/>...
by SteveHansen
Mon Mar 26, 2012 7:36 pm
Forum: Vacuum Technology (& FAQs)
Topic: Pirani Gauge
Replies: 5
Views: 1720

Re: Pirani Gauge

<t>Standard construction thermal conductivity gauges of all types (thermistor, Pirani, thermocouple) have a response that flattens out below a few tens of milliTorr where radiation and lead conduction loses start to dominate molecular thermal conduction. Accuracy (after correction to the gas type) i...
by SteveHansen
Sat Mar 24, 2012 12:31 pm
Forum: Vacuum Technology (& FAQs)
Topic: Foreline traps?
Replies: 4
Views: 1658

Re: Foreline traps?

<t>If you are going to be running your system at base pressure for long periods a foreline trap is a good idea to keep mechanical pump oil from backstreaming or creeping into the DP or turbo pump. However, you will probably find that you pump to base and then proceed quickly to the operating pressur...
by SteveHansen
Mon Mar 05, 2012 1:12 am
Forum: Images du Jour
Topic: Archived - Demo Fusor at Maine Engineering Expo 2012
Replies: 3
Views: 2600

Re: Demo Fusor at Maine Engineering Expo 2012

I really like the USM cathode!
by SteveHansen
Thu Mar 01, 2012 3:12 pm
Forum: Vacuum Technology (& FAQs)
Topic: How to minimize backstreaming from diffusion pump
Replies: 13
Views: 5411

Re: How to minimize backstreaming from diffusion pump

<t>Hi Jeff,<br/> <br/> You absolutely need a variable conductance between the pump and chamber for pressure control purposes. Use of the other valves depends on how you want to operate the system.<br/> <br/> If you just want to pump straight through (no roughing or foreline valves) then you will jus...
by SteveHansen
Wed Feb 29, 2012 7:36 pm
Forum: Vacuum Technology (& FAQs)
Topic: How to minimize backstreaming from diffusion pump
Replies: 13
Views: 5411

Re: How to minimize backstreaming from diffusion pump

<t>Violent agreement - all good approaches to proper practice.<br/> <br/> In the industrial world a lot of people question why throttle valves, even for large pumps, are only spec'd from just cracked to about 10% open. Max open for control purposes may be well under 10% open or less than 5% of the p...
by SteveHansen
Wed Feb 29, 2012 5:17 pm
Forum: Vacuum Technology (& FAQs)
Topic: How to minimize backstreaming from diffusion pump
Replies: 13
Views: 5411

Re: How to minimize backstreaming from diffusion pump

<t>I'll agree and disagree here. True, the vacuum requirements for a fusor are pretty trivial in terms of pressure and contamination control. Far more critical are the niceties of operation: it's very easy to really mess up a diffusion pumped system if you stall the pump. Proper throttling and contr...