Design factors are given for a high-input impedance differential millivolt meter designed, built, and tested as an inexpensive solid-state electronic system for use in measuring the electromotive force from solid ceramic oxygen electrolyte cells. A schematic diagram is included

Mullins, O.

Quin, E.

Williams, R. J.

English

NASA Technical Reports Server

JSC-09305
NASA TECHNICAL MEMORANDUM NASA TM X-58150
January 1975
A HIGH-INPUT IMPEDANCE DIFFERENTIAL
MILLIVOLT METER FOR USE WITH SOLID
CERAMIC OXYGEN ELECTROLYTE CELLS
C I.
(NASA-TM-X-58150) A HIGH-INPUT IMPEDANCE N75-15939
DIFFERENTIAL MILLIVOLT METER FOR USE WITH
SOLID CERAMIC OXYGEN ELECTROLYTE CELLS
(NASA) 7 p HC $3.25 CSCL 14B Unclas
G3/35 08919
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
LYNDON B. JOHNSON SPACE CENTER
HOUSTON, TEXAS 77058
https://ntrs.nasa.gov/search.jsp?R=19750007867 2020-03-23T01:05:29+00:00Z
1. Report No. 2. Government Accession No. 3, Recipient's Catalog No.
TM X-58150
4. Title and Subtitle 5. Report Date
A HIGH-INPUT IMPEDANCE DIFFERENTIAL January 1975
MILLIVOLT METER FOR USE WITH SOLID 6. Performing Organization Code
CERAMIC OXYGEN ELECTROLYTE CELLS
7. Author(s) 8. Performing Organization Report No.
Richard J. Williams, JSC, and O. Mullins and E. Quin, JSC-09305
Lockheed Electronics Company, Inc.
10. Work Unit No.
9. Performing Organization Name and Address 383-35-00-00-72
Lyndon B. Johnson Space Center 11. Contract or Grant No.
Houston, Texas 77058
13. Type of Report and Period Covered
12. Sponsoring Agency Name and Address Technical Memorandum
National Aeronautics and Space Administration p rin Agency CodeWashngto, DC. 254614. sponsoring Agency CodeWashington, D.C. 20546
15. Supplementary Notes
16. Abstract
Design factors are given for a high-input impedance differential millivolt meter designed, built,
and tested as an inexpensive solid-state electronic system for use in measuring the electro-
motive force from solid ceramic oxygen electrolyte cells. A schematic diagram is included.
17. Key Words (Suggested by Author(s)) 18. Distribution Statement
* Solid-State Devices * Electrometers
'Gas Mixtures "pH Meters STAR Subject Category: 33 (Electronics and
' Measuring Instruments * Mufflers Electrical Engr.).
* Electronic Equipment Furnaces
19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price*
Unclassified Unclassified 7 $3.25
*For sale by the National Technical Information Service, Springfield, Virginia 22151
NASA - JSC
NASA TM X-58150
A HIGH-INPUT IMPEDANCE DIFFERENTIAL
MILLIVOLT METER FOR USE WITH SOLID
CERAMIC OXYGEN ELECTROLYTE CELLS
Richard J. Williams
Lyndon B. Johnson Space Center
Houston, Texas 77058
and
O. Mullins and E. Quin
Lockheed Electronics Company, Inc.
Houston, Texas 77058
A HIGH-INPUT IMPEDANCE DIFFERENTIAL
MILLIVOLT METER FOR USE WITH SOLID
CERAMIC OXYGEN ELECTROLYTE CELLS
By Richard J. Williams, 0. Mullins,* and E. Quin*
Lyndon B. Johnson Space Center
SUMMARY
Electromotive force output from solid ceramic oxygen electrolyte cells
is usually measured with expensive special electronic devices. An inexpensive
solid-state electronic system that accurately measures cell output has been
designed, built, and tested at the NASA Lyndon B. Johnson Space Center. The
device has functioned successfully for investigators at the Lyndon B. Johnson
Space Center.
INTRODUCTION
The solid ceramic oxygen electrolyte cells used for measuring oxygen fu-
gacities in the NASA Lyndon B. Johnson Space Center (JSC) gas-mixing furnaces
require a high-input impedance device for accurate measurement of the cells
output over their full temperature-response range. The ideal device must re-
spond over the range of 0 to 2000 millivolts and should resolve ±1 millivolt.
Usually, special-devices (electrometers or pH meters) are used in these meas-
urements; however, these devices are expensive and incorporate features not
necessary in the measurement of cell output.
A high-input impedance differential millivolt meter has been designed,
built, and tested for use with solid ceramic oxygen electrolyte cells. This
device should enable experimenters to reduce costs in building systems similar
to that designed at the JSC.
OPERATION AND ADJUSTMENT
The circuit design is rather straightforward (fig. 1). The power supply
provides stabilized direct current to the device and also provides controlled
direct current to null cell output. Resistor R15 is used to set the span of
*Lockheed Electronics Company,. Inc.
2R3 6 utp
R 1 3 IC33
R -4---
I I
Cell input i
R10 M+
P .8
Recorder
R12 output
R1R15 1
I- cI
I0
IC4
Line T1 B1
C1 C2 R
-T 13 1
C4 _
Power supply
Figure 1.- Schematic diagram of a differential millivolt meter.
2
Key
Component Description
R1, R4, R7 10-ku potentiometers
R2, R3, R6 5-ku, 1/8 W resistors
R5 1-ku, 1/8 W resistor
R8 100-k., 1/8 W resistor
R9 Resistor set during calibration
R10 1-k, potentiometer
R11 25-ku, 1/8 W resistor
R12 2-k2, 1/8 W resistor
R13 71.5-ku, 1/8 W resistor
R14 33-ku, 1/8 W resistor
R15 100-kQ potentiometer
Cl, C2 100 yF capacitors
C3, C4 0.001 yF capacitors
Dl, D2 RCA IN914 diodes*
ICi Fairchild yA 740 integrated circuit*,
IC2, IC3 Fairchild yA 741 integrated circuits*
IC4 RCA 194 integrated circuit*
Bi Motorola MDA 970-3 bridge*
Stancor P-8394
(for 110-V ac line) transformer*T11 Stancor P-8320
(for 208-V ac line) transformer*
Ml 50-0-50 microammeter
*Or equivalent.
Figure 1.- Concluded.
3
the power supply output. In the system designed at JSC, the power supply is
set for 2000 millivolts full scale. Resistor RO10 is a 10-turn potentiometer
used to read the nulling voltage. Integrated circuit IC1 is a zero-gain ampli-
fier that serves to isolate the cell from the measurement system. Resistors
R1, R4, and R7 are used to balance the amplifiers. The 50-0-50 micrometer is
a null indicator; resistor R9 is set by trial and error to adjust the span of
the meter to the desired sensitivity. Points 8 and 10 are an output to a
recorder; the signal is proportional to the offset from the null position of
the device. Transformer T1 supplies 6 V ac to the power supply from the line
voltage.
After the device has been built and prepared for span, sensitivity, and
balance, it should be allowed to operate for approximately 24 hours with the
input from the cell shunted. Then, a final check of sensitivity and balance
should be performed. Finally, a calibrated millivoltage source should be used
as an input to adjust the span-precisely. Once the device is activated,
ideally, it should never be deactivated.
In the operation of a high-input impedance device, standard precautions
must be taken: shielded lead wires, clean and dry contacts, physically stable
configuration, and good grounds. Because the meter has not been designed to
reject alternating-current signals, the sensors must be shielded.
CONCLUDING REMARKS
The high-input impedance differential millivolt meter designed and built
at the NASA Lyndon B. Johnson Space Center has proved to be less expensive
than other systems for use in measuring the output of solid ceramic oxygen
electrolyte cells. Tests indicate the device is highly stable, remains essen-
tially drift free for as long as 2 months, and provides accurate and repro-
ducible measurements.
Lyndon B. Johnson Space Center
National Aeronautics and Space Administration
Houston, Texas, January 10, 1975
383-35-00-00-72
NASA-JSC
14


A high-input impedance differential millivolt meter for use with solid ceramic oxygen electrolyte cells

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