Penning Measuring gauge configuration

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Discussion Overview

The discussion revolves around the configuration of Penning pressure gauges and their measurement accuracy in vacuum systems, particularly focusing on the effects of valve and pipe diameters on pressure readings. Participants explore theoretical and practical implications of these configurations in the context of vacuum measurements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that Penning gauges are used to measure pressures from approximately 1E-7 to 1 mbar and suggests that smaller valves may lead to higher measured pressures due to entrapped particles.
  • Another participant speculates that the increased pressure readings might be related to the free path length of molecules being greater than the dimensions of the pipe leading to the gauge.
  • A question is raised about the typical dimensions of the system components, with specific sizes provided for the Penning gauge and associated pipes and valves.
  • It is mentioned that a clear increase in measured end pressure occurs with a DN16 valve, despite the vacuum itself remaining unchanged.
  • A participant with experience in vacuum systems indicates that there is no established documentation correlating gauge size and measurement results, suggesting a lack of consensus on the issue.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the effects of valve and pipe sizes on pressure measurements, with no consensus reached on how to quantify these effects or the underlying mechanisms involved.

Contextual Notes

Participants acknowledge the complexity of the relationship between gauge configuration and pressure readings, with limitations in available documentation and empirical data noted.

Who May Find This Useful

This discussion may be of interest to individuals working with vacuum systems, particularly those involved in pressure measurement and gauge configuration in experimental or industrial settings.

Ryyder
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We use, among others, Penning pressure gauges for determining pressures (aprox. 1E-7 to 1 mbar (about the same in Torr... for the Americans here ;-) ).
The Penning is placed just outside the recipient, behind a valve to make sure its never in pressures of 1mbar or more.

When using a smaller valve, the measured end pressure is higher (entrapped particles probably?). But the question now is, how to pre-determine how much higher the measured pressure will be due to this effect, without having to measure for each application.

My feeling is that a smaller valve and therefore smaller pipes in front of the gauge, result in relatively more particles being entrapped in the volume of the gauge. But I can't find a good way of approximating the effect.

More general:
* What is the effect a decreased diameter in front of the measurement?

Any thoughts are welcome!
Ryyder
 
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No ideas at all? I was thinking it might be due to free path length being a lot more then the length and diameter of the pipe in front of the Penning.

If the inlet to this pipe is made smaller, molecules might get trapped inside the pipe?
 
Basically one is measuring the pressure of a vacuum?

Perhaps there is no one here who works with vacuum systems on a regular basis.


How small is small? Or what are typical dimensions?
 
Yes, measuring the pressure of the vacuum. And yes, maybe not many people have experience or direct knowledge, could be.

The dimensions are as follows, for two cases (in mm):
* Penning is typically DN40
* Pipe from penning to valve is DN40 or DN16, ~75 mm long
* Valve is DN40 or DN16
* Pipe from valve to recipient (the vacuum) is DN40, ~20 mm long

For the DN16 valve we see a clear increase in end pressure that is measured for the vacuum, even though we know the vacuum itself has the same end pressure (or at least will not change in the order of decades).
 
hi ryder..
the penning gauge and the size of the whole are directly linked for certain..ive worked with edwards and leybold gauges many years , no one has ever to my mid actually produced a document to corrulte any results..its the nature of the gauge I am afraid..ill put link to our gauges section if you ley me know ill could possibly geta pdf on sucha unit for you http://www.absolute-vacuum.com/product_gauges.php
 
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