Vibrating-membrane transducer in a circuit can measure current below 10 to-the-minus 17 ampere. This electrometer has a high conversion gain and a minimum internal power consumption

Coon, G. W.

Dimeff, J.

English

NASA Technical Reports Server

rn 
Forcing 
Electrome 
.	
Input 
Coupli nç 
Capacitc 
AC ml
ting Plate 
Output 
tor 
April 1965
	 QP) 791-^ Brief 65-10056 
NASA TECH 10 ffN A^J_^ 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
Vibrating-Membrane Electrometer Has High Conversion Gain 
Housing	 Hard Vacuum 
-.
 
Insulator	 Membrane 
The problem: Devising a technique that would 
allow measurement of currents below 10-17 ampere 
in a small, rugged transducer with high conversion 
gain and minimum internal power consumption. 
The solution: An instrument employing a vibrat-
ing-membrane transducer in a circuit that utilizes its 
characteristics to provide a conversion gain three 
orders of magnitude greater than that of present elec-
trometer transducers. 
How it's done: The electrometer embodies a com-
bination of mechanical and dynamic capacitance 
principles. Basically, the membrane is driven at its 
resonant frequency by an electrostatic force which is
derived from voltages applied between the membrane 
and a stationary forcing plate in close proximity to 
one side of the membrane. The electrometer input 
current controls the displacement amplitude and 
affects the capacitance which is developed through the 
mechanical resonant properties of the membrane to 
provide a high conversion gain. This is accomplished 
with a drive voltage of two components: the first, 
a large sinusoidal voltage at resonant frequency, 90° 
out of phase to the membrane motion; and the second, 
a steady voltage derived from the small input current 
to be measured. A high conversion gain is obtained by 
using the voltage from a small input current as a dc 
voltage to control the membrane displacement ampli-
tude when driven at its resonant frequency. Since the 
(continued 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights; or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19650000056 2020-03-11T17:18:09+00:00Z
transducer has an excellent arrangement for shielding, 
high voltage may be applied to its detecting side to 
provide a large ac output signal. The result is an 
amplified sinusoidal voltage which is proportional to 
the high mechanical Q of the membrane. The ejec 
trometer is capable j conversion gains of 2 x 10 
voltage and 2 x 10 in current, giving a 4 x 10 
power conversion gain. 
Notes: 
1. A model using this technique was constructed; it 
has an input impedance of better than 10 ohms 
and is sensitive to less than one millivolt impressed 
on the forcing plate from the low-impedance 
source. The results of initial tests indicate that a 
compact, rugged instrument can be developed ca-
pable of measuring currents smaller than 10-17 
ampere with low internal power consumption.
2. Inquiries concerning this invention may be directed 
to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California, 94035 
Reference: B65-10056 
Patent status: NASA encourages the immediate 
commercial use of this invention. Inquiries about 
obtaining rights for its commercial use may be made 
to NASA, Code AGP, Washington, D.C., 20546. 
Source: John Dimeff and Grant W. Coon, 
(ARC-38) 
Brief 65-10056	 Category No. 01


Vibrating-membrane electrometer has high conversion gain

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server