Modified Mc Leod gage records pressure measurements automatically. The measurements can be programmed in advance by means of an automatic timer

Faeth, P. A.

English

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ource 
ottling Valves 
Solenoid 
OpE 
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July 1966	 Brief 66-10290 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Modified McLeod Gage Records Automatically 
To Measured Gas
vacuum zource 
The problem: 
When measuring pressures with a conventional 
McLeod gage, an operator must be constantly in at-
tendance and must record the measurements by hand. 
The solution: 
A modified McLeod gage that records measure-
ments automatically. Measurements can be pro-
grammed in advance by means of an automatic timer.
How it's done: 
The system consists of the gage, an air/vacuum 
pumping device, and appropriate circuitry to cycle 
the pumping device. The gage is a modification of 
standard McLeod type and indicates the pressure of a 
gas by the change in resistance of two platinum wires, 
contacted by a column of mercury as it is acted on by 
the measured gas.
(continued overleaf) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19660000289 2020-03-11T17:39:41+00:00Z
In operation, with the mercury level as shown in 
contact with valve leads A and B, the solenoid valve 
in the vacuum source line is closed. This permits air 
from the air source to enter the gage and force the 
mercury upward through the center tube into the 
tube loop and bulb. This breaks the contact between 
leads A and B but a latching relay in the control cir-
cuitry retains the solenoid valve in the closed position. 
When the mercury reaches the upper portion of the 
open capillary and contacts lead C, a circuit is closed 
between leads C and B that deenergizes the latching 
relay in the control circuit to energize the solenoid and 
connect the reservoir with the vacuum source. The 
vacuum source has sufficient capacity to override the 
air source and causes the mercury to recede into the 
reservoir. The solenoid valve remains open until the 
mercury surface in the reservoir again contacts lead A, 
at which time the solenoid valve closes and the cycle 
repeats. Cyclic period is controlled by adjustment of 
the two throttling valves. 
As the mercury rises during the test cycle, it enters 
the capillary that is closed at the top and forms a 
bridge network with the two platinum wires that are 
connected to a constant voltage source and the record-
ing circuitry. Mercury entering the closed capillary is
limited by the density of the measured gas it is com-
pressing. The change in resistance of the platinum 
wires is recorded as a voltage output change that di-
rectly relates to the pressure of the measured gas. 
Notes: 
1. This method of using a standard McLeod gage 
lends itself to a wide variety of applications. Some 
systems operating the vacuum solenoid could be 
controlled by pressure, temperature, and time 
sensing devices. 
2. Inquiries concerning this invention may be made 
to:
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B66-10290 
Patent status: 
This invention is owned by NASA and a patent ap-

plication has been filed. Royalty-free, non-exclusive

licenses for its commercial use will be granted by

NASA. Inquiries concerning license rights should be

made to NASA, Code GP, Washington, D.C. 20546.

Source: Paul A. Faeth

(Lewis-290) 
Brief 66-10290	 Category 02


Modified McLeod gage records automatically

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