Instrument for measuring potentials on two dimensional electric field plo

Boies, R. D.

Dameron, C. E.

Woods, G. M., Jr.

English

NASA Technical Reports Server

ct. 6, 197 +. 0. PAIN 3,532,075 
DEPUTY ADMINISTRATOR OF THE NATIONAL 
AERONAUTICS A N D  SPACE ADMINISTRATION 
INSTRUMENT FOR MEASURING POTENTIALS ON TWO-DIMENSIONAL 
ELECTRIC FIELD PLOTS 
Filed July 31, 1968 
w 7 INVENTORS GEORGE M. WOOD, JR. I CHARLIE E. DAMERON BY 
https://ntrs.nasa.gov/search.jsp?R=19710009946 2020-03-17T02:43:50+00:00Z
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3,532,975 
INSTRUMENT FOR MEASURING POTENTIALS ON 
T. 0. Paine, Deputy Administrator of the National Aero- 
nautics and Space Administration, in respect to an 5 
invention of George M. Woods, Jr., and Charlie E. 
Darneron, both of Newport News, Va., and Robert D. 
Boies. Cleveland. Ohio 
TWO-DIMENSIONAL ELECTRIC FIELD PLOTS 
’
Filed July 31, 1968, Ser. No. 749,148 
Int. C1. GQlr 17/02 
U.S. Cl. 324-72 4 Claims 
ABSTRACT OF THE DISCLOSURE 
An instrument for determining equipotential lines on a 
two-dimensional electric field plot and for measuring the 
potential at any selected point on the plot. The essential 
elements of the instrument are a dual triode for compar- 
ing the potentials applied to its two grids with a probe 
connected to one of its grids and with means for applying 
measured potentials to its other grid. 
The invention described herein was made in the per- 
formance of work under a NASA contract and is subject 
to the provisions of Section 305 of the National Aero- 
nautics and Space Act of 1958, Public Law 85-568 (72 
Stat. 435; 42 U.S.C. 2457). 
The invention relates generally to electric field plot- 
ting and more specifically concerns a simple instrument 
that provides a fast means for plotting electrostatic fields 
surrounding experimental components drawn in con- 
ductive ink on conductive paper. 
In developing certain electronic components or devices 
such as ionization sources, detectors, vacuum gages, mass 
spectrometers, etc., it is generally advantageous to resort 
to two-dimensional plotting of electric fields and force 
lines prior to moving from the drawing board to proto- 
type construction. 
The prior art procedure of two-dimensional plotting 
to develop an electronic device consists of drawing an 
outline of the device on conducting (facsimile) paper 
with low resistance paint; applying D.C. potentials, which 
have been scaled down to a few volts in the ratios that 
are to be used on the device, to painted electrodes; and 
measuring with a standard voltmeter the field strength on 
the paper relative to electronic placement. This prior art 
procedure is time-consuming, particularly when a signifi- 
cant amount of plotting is done and it requires skill on 
the part of the technician in interpolating voltmeter read- 
ings. 
It is therefore an object of this invention to provide 
an instrument for two-dimensional plotting that reduces 
the plotting time required by the prior art. 
Another object of this invention is to provide an in- 
strument for two-dimensional plotting that does not re- 
quire the skill to operate that is required by the prior art. 
A further object of this invention is to provide an in- 
strument for two-dimensional plotting that will measure 
the potential at any given point on the two-dimensional 
surface and will locate points or lines on the two-dimen- 
sional surface that have a selected potential. 
Other objects and advantages of this invention will be- 
come apparent hereinafter and in the drawing in which 
the single figure in this application is a schematic dia- 
gram of the preferred embodiment of the invention. 
Turning now to the sole figure in this application, the 
number 11 designates a standard plug for connection with 
a 110 volt A.C. power source. The 110 voltage is con- 
nected through a switch 12 to the primary winding 13 of 
a transformer 14. Switch 12 is used for the purpose of 
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disconnecting the 110 volts from winding 13 without un- 
plugging plug 11. Transformer 14 has three secondary 
windings 15, 16 and 17. The voltage in winding 15 is 
applied to a rectifier consisting of diodes 18 and 19. The 
output from this rectifier is applied through a filter 20 to 
a resistor 21. Resistor 21 is connected in series with re- 
sistors 22, 23, 24 and 25 to ground. A switch 26 having 
fixed contacts 27-30 and movable contact 31, has con- 
tact 27 connected to the junction of resistors 21 and 22, 
contact 28 connected to the junction of resistors 22 and 
23, contact 29 connected to the junction of resistors 23 
and 24, and contact 30 connected to the junction of re- 
sistors 24 and 25. The movable contact 31 of switch 26 is 
connected to a potentiometer 32 which is connected in 
series with a resistor 32a to ground. 
A switch 33, having fixed contacts 34-37 and movable 
contact 38, has contact 34 connected through a resistor 39 
to ground, contact 35 connected through a resistor 40 to 
ground, contact 36 connected through a resistor 41 to 
ground and contact 37 connected through a resistor 42 
to ground. The resistances of resistors 39-42 decrease as 
their numbers increase. That is, resistor 40 is less than 
39, 41 is less than 40, etc. The slider of potentiometer 
32 is connected to the plates of a dual triode 43 and 
through an ammeter 44 to movable contact 38. Movable 
contacts 31 and 38 are mechanically connected together 
so that they change in unison. 
The plate voltage switching circuit controlled by 
switches 26 and 33 acts as a ranging circuit by altering 
the totd amount of plate current passed. With fhe plate 
voltage high (when movable contact 31 is on contact 
27 and movable contact 38 is on contact 34), a given 
small change in grid voltage will have a greater effect 
on plate current than will the same change with the 
plate voltage low (when switches 26 and 33 are in the 
positions shown), and will cause a larger deflection of 
ammeter 44. It therefore amplifies or attenuates the range 
by changing the amount of input required for full scale 
deflection of the meter. Because it is not possible to meas- 
ure below zero (ground) potential, a judicious choice of 
the reference point must be made to avoid tube cutoff. 
This causes no real problem since the fields produced are 
a function of potential differences between electrodes on 
the paper rather than of their absolute values. Thus, a 
zero-2 volt 4 volt plot using the 2-volt electrode as refer- 
ence will be identical to a plot of minus 2 volts-zero-2 
volts using zero as reference. 
.The voltage induced across secondary winding 16 of 
transformer 14 is applied to a rectifier 45. The output 
from rectifier 45 passes through a filter 46 to a potentiom- 
eter 47. The slider of potentiometer 47 is connected tO 
contacts 49 and 50 of a switch 48 having stationary con- 
tacts 49, 50 and 51, and having a movable contact 52. 
Contact 51 is connected to ground and movable contact 
52 is connected to grid 53 of dual triode 43. A voltmeter 
54 is connected between the slider of potentiometer 54 
and ground. The voltage induced across secondary wind- 
ing 17 of transformer 14 is applied to the filaments of 
dual triode 43. 
A cathode 55 of triode 43 is connected to a null meter 
56 and resistors 57 and 58. The other cathode 59 of triode 
43 is connected to null meter 56, and resistor 57 and 60. A 
potentiometer 61 with its slider grounded is connected 
between resistors 58 and 60. 
The other grid 62 of triode 43 is connected to the mov- 
able contact 63 of a switch 64 having stationary contacts 
65, 66 and 67. Switch 64 operates in unison with switch 
48. Contact 65 is connected to a probe 68 and contacts 66 
and 67 are connected to ground. A capacitor 69 that will 
pass high frequency signals is connected between contact 
65 and ground. Probe 68 is shown in contact with a two- 
3,532,975 
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dimensional plot 70 laid on a supporting means 71. Only a 
partial side view of plot 70 and supporting means 71 is 
shown. 
There are two possible modes of operation of the instru- 
ment that constitutes this invention. The first, or standard, 
mode of operation is for tracing a particular line on the 
two-dimensional plot. The second, or fixed point, mode of 
operation is for measuring a potential at any given point 
on the two-dimensional plot with minimum difficulty. Be- 
fore operating in either mode the desired sensitivity is ob- 
tained by adjusting potentiometer 32 and switches 26 and 
33. Then with movable contact 52 of switch A8 on contact 
51 and with movable contact 63 of switch 64 on contact 
67 a null between cathodes 55 and 59 of triode 43 must be 
observed on meter 56. Null in this position is accom- 
plished by adjusting potentiometer 61. 
For the standard mode of operation movable contact 52 
of switch 48 i s  put on contact 50 and movable contact 63 of 
switch 64 is put on contact 66. Then the potential to be 
found on the plotting paper is placed on grid 53 of triode 
43 by adjusting potentiometer 47 and observing meter 54. 
For ease of operation, values chosen are usually integers 
or decimal fractions of two significant figures. The null 
meter 56 will now be deflected due to the unbalance of 
dual triode 43. Switches 48 and 64 are then placed in the 
position shown. With the switches in this position, probe 
68 is placed on the plotting paper and moved along until 
meter 56 returns to null, indicating that the voltages 
applied to grids 53 and 62 are equal. Meter 56 is so con- 
nected that deflections to the left of null position indicate 
voltages lower than the reference. Observing the direction 
of the meter deflection while probing eliminates the need 
for interpreting a meter reading at each position, thereby 
providing a simplified method of locating the potential 
line. The value of the next potential line to be located 
is placed on grid 53 and the above procedure repeated 
until the plot is completed. 
For the fixed point mode of operation switches 48 and 
44 are placed in the position shown. Probe 68 is then placed 
on the plotting paper at the point where the potential is to 
be measured. Potentiometer 47 is adjusted until meter 56 
is again at null. The voltage corresponding to the volt- 
age at probe 68 is then read on meter 54. 
Identical plots made with the instrument that constitutes 
this invention and by the previously used voltmeter 
method have clearly established that a significant reduc- 
tion in plotting time can be realized. Use of the instru- 
ment results in an estimated 50 percent reduction of the 
technician time required for any given plot. Also, examina- 
tion of the plots made by different operators when the 
same fields were traced shows that the plots are more 
nearly the same. 
It is to be understood that the form of the invention 
herewith shovetn and described is to be taken as a pre- 
ferred embodiment. Various changes may be made in the 
shape, size and arrangement of parts. For example, 
equivalent elements may be substituted for those illus- 
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trated and described herein, parts may be reversed, and 
certain features of the invention may be utilized inde- 
pendently of the use of other features, all without de- 
parting from the spirit or scope of the invention as de- 
fined in the following claims. 
What is claimed is: 
1. An instrument for determining a line on a two- 
dimensional electric field plot that has a given potential 
at every point along the line and for measuring the poten- 
tial at any selected point on the two-dimensional plot 
comprising: 
comparing means with first and second terminals for 
indicating when the potentials applied to the two 
terminals are equal; 
means for measuring and applying any selected poten- 
tial within a range to a third terminal wherein said 
range includes all potentials on said two-dimensional 
a probe; and 
a three position switching means for connecting both 
said first and second terminals to ground when the 
switching means is in its first position, for connect- 
ing said first terminal to said third terminal and said 
second terminal to ground when the switching means 
is in its second position, and for connecting said first 
terminal to said third terminal and said second ter- 
minal to said probe when the switching means is in 
its third position. 
2. An instrument according to claim 1 wherein said 
30 comparing means includes a null meter connected be- 
tween said first and second terminals for indicating when 
the potentials applied to the two terminals are equal. 
3. An instrument according to claim 2 wherein said 
comparing means includes a balancing network connected 
35 between said first and second terminals for adjusting said 
null meter to null when said first and second terminals 
are each connected to ground. 
4. An instrument according to claim 1 wherein said 
means for measuring and applying includes a potentiome- 
40 ter with its slider connected to said third terminal; a volt- 
age source, having a magnitude at least as great as the 
greatest potential on said two-dimensional plot, connected 
across said potentiometer; and a voltmeter for measuring 
the voltage at said slider. 
References Cited 
UNITED STATES PATENTS 
6 
15 
plot; 
20 
23 
4 3 
2,542,478 2/1951 Clark. 
5o 3,005,156 10/1961 Hoberman _ _ _ _ _ _  324-123 XR 
3,222,599 12/1965 Gewirtz _ _ _ _ _ _ _ _ _ _ _ _  324-123 
RUDOLPH V. ROLINEC, Primary Examiner 
E. L. STOLARUN, Assistant Examiner 
324-98 
65 
U.S. Cl. X.R. 


Instrument for measuring potentials on two dimensional electric field plots Patent

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