Special purpose electrometer amplifier is capable of operation over a dynamic range of five orders of magnitude. This is achieved by using a zener controlled attenuator in the feedback path for the amplifier

Katz, N.

English

NASA Technical Reports Server

June 1967	 Brief 67-10199 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Electrometer Amplifier Operates Over Dynamic Range of Five Orders of Magnitude 
1 r  2	
1. 
 
l	
IN 
Ri	 Rl4j^F;[ R12
-	 T 2 R20	
• E Out 
•8 CRR21 ____
I 
1.	
CR7-.	 4OVf I 
R26 R24 
:1R6 
iLL
+ 
R. 
uA
uj
R22	 R24 ZZI 0>
Og 
gR23 CD a 
w
CR5 
I R5
Ril 
I	
.625v 
FEEDBACK AND STABILIZATION SECTION 
I	 t	 '+2OV 
Close for , '' 
	
+20V	 R3	 u11 6 jR32j Stabilize
R33	 Q12 
R34
-40V
I	 I 
	
+20V	 15ma I
Input 
-4- - 
	
.625V_	 lOma Power 
	
-40V-	
J 
The problem: 
To design an electrometer amplifier which would 
be capable of operation over a dynamic range of five 
orders of magnitude. An amplifier with these charac-
teristics was required to detect currents in the Pioneer 
plasma probe experiment, with low power consump- 
tion, small offset error, and good frequency response. 
The solution: 
A special purpose electrometer amplifier which 
covers five orders of magnitude dynamic range, which 
converts positive (ion) currents in the range of 10-14 
to 10- 9 ampere to a corresponding voltage in the
range of +.006 volt dc to —30.0 volts
'
 dc, and nega- 
tive (electron) currents in the range 10 1
 to 10-10 
ampere to a corresponding voltage in the range of 
+.006 volt dc to +10 volts dc. 
How it's done: 
The five-order magnitude of dynamic range of the 
device is achieved by incorporating a zener controlled 
attenuator in the feedback path for the amplifier. 
When the breakpoint voltage of the diode is reached, 
part of the attenuator circuit is shorted out, thus 
modifying the overall gain of the amplifier to extend 
the range.
-	 (continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States 
 
—. 2OV VOLTAGE GAIN SECTION 
20V 
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=19670000199 2020-03-11T20:49:55+00:00Z
The frequency response of the amplifier is enhanced E. Long term stability: ± 2% (max) 
by packaging the system in a driven shield which is F. Temperature stability: ± 5%	 (max) 
at the	 same	 potential	 as	 the	 pickup	 target.	 This G. Frequency Response: 30 Hz 
technique effectively reduces the input capacity to the H. Transresistance (R): 
electrometer.	 Similarly,	 the	 high	 valued	 (2X1010 (1)	 for i 1 <1.2X1O	 amp ±5% 
ohms) resistor used in the feedback path is shielded R__ - 6x 10_ l i	 h'	 -4-50/ ° 
by a wound solenoid operated at a potential to cancel 11 
the distributed capacities of the feedback resistor. (2)	 for i 1>1.2X10	 amp ±5% 
Long term drift is minimized by periodic stabiliza- R==2X1010+ 6.96 ohms ±5% 
tion of the amplifier from external commands. The ij	 11 
stabilization network included in the feedback loop 2.	 Additional technical details are available from: 
employs a capacitive network for accumulating and Technology Utilization Officer 
storing the error caused by drift between periods of Ames Research Center 
stabilization. On command, this error signal is referred Moffett Field, California 94035 
back to the input to effectively cancel out the drift Reference: B67-10199 
error signal of the amplifier. 
Notes: 
1.	 Listed below are the final specifications for the
Patent status: 
nonlinear dc periodically stabilized electrometer Inquiries about obtaining rights for the commercial 
amplifier as developed: use of this invention may be made to NASA, Code 
A. Current Range: 10- 14 to 10 9 amp (ion); GP, Washington, D.C. 20546. 
10- 14 to 10_ 1	 amp (electron) V	 Source: Norman Katz 
B. Noise:	 10_14 amp rms (max)	 •V V	 of Marshall Laboratories 
C. D-C Offset: 10-14 amp (max) V	 V	 under contract to 
D. Drift between	 stabilization	 cycles for input Ames Research Center 
currents below 10_ 11 amp: 3X10	 amp/ •V 
sec (max) V	 V	
V	
(ARC-75)
Brief 67j0,199	 V, V	 V V	 V •V	 V V
	
V V
	
V	
V V
	
V	 Category 01 


Electrometer amplifier operates over dynamic range of five orders of magnitude

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server