Vacuum tube bridge operates in two modes, tracing and fixed potential. It reduces plotting time by fifty percent and improves measurement precision

Dameron, C. E.

Wood, G. M., Jr.

English

NASA Technical Reports Server

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April 1970	 Brief 70-10192 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Null Type Instrument for Simplifying Two Dimensional Field Plotting 
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The problem: 
In developing ionization sources for vacuum gages 
and other applications it is advantageous to make 
plots of the electric fields and force lines so that the 
design may be optimized before a prototype of the 
device is built. Two dimensional plots are usually 
sufficient for this work. These are made by-drawing 
the outline of the device on conducting. paper (fac- 
simile) with low resistant paint: The dc potentials
which have been scaled down to a few volts in the 
ratios that are to be used on the device are placed on 
the painted electrodes. 
An efficient and accurate method for determining 
the field line is needed. 
The solution: 
A null type instrument that simplifies two dimen- 
sional field plotting.
(continued overleaf) S. 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the Unitea States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19700000185 2020-03-17T00:29:14+00:00Z
How it's done: 
The instrument is essentially a vacuum tube bridge 
designed to operate in two modes, tracing and fixed 
potential. Sensitivity of the instrument in either mode 
is better than 0.01 volts. 
Tracing Mode 
This mode is used to plot equipotential lines. Initial 
balance is established with function switch SW-i in 
position I and adjusting R-6 for null reading of M-2. 
In operation, SW-i is placedin position 2 and the 
desired reference potential is applied on grid A of VT-i 
by adjusting R-16 as observed on meter M-3. 
Switch position 3 connects the tracing probe to grid 
B. When the probe is placed at a selected point on 
the conducting paper, a voltage is registered on grid B. 
If the probe is moved to a point where M-2 indicates 
zero, the voltages applied to the two grids are equal. 
Subsequent movement of the probe on the paper in a 
direction to.. maintain zero deflection of M-2 results in 
a plot of equipotential lines without the necessity of 
reading absolute values-of voltage. 
Fixed Potential Mode 
This mode' is used to find the potential at any given 
point on the field plot. With SW-1 in position 3 the
probe is placed on the desired point and R-16 adjusted 
until meter M-2 is nulled. The voltage corresponding 
to the voltage impressed on the probe is read on 
meter M-3. 
Notes: 
1. This design has reduced plotting time by some 
50% and has also improved measurement precision. 
2. Requests for further information may be directed 
to:
Technology Utilization Officer 
Langley Research Center 
Langley Station 
Hampton, Virginia 23365 
Reference: TSP70-10192 
Patent status: 
This invention is owned by NASA, and a patent

application has been filed. Royalty-free, nonexclusive

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: George M. Wood, Jr. and C. E. Dameron

Langley Research Center

(XLA-08493)
C 
Brief 70-10192	 Category 01


Null type instrument for simplifying two dimensional field plotting

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