Motor-driven switcher-recorder periodically registers the zero drift and gain drift signals of a dc amplifier subjected to changes in environment. A time coding method is used since several measurements are shared on a single recorder trace

Cree, D.

Wenzel, G. E.

English

NASA Technical Reports Server

47-5- 
April 1966
	
Brief 66-10148 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Tester Periodically Registers DC Amplifier Characteristics 
The problem: 
To provide a device for measuring automatically 
and periodically the gain and zero drift characteristics 
of a dc amplifier subjected to changes in environment. 
Standard industry tests measure the difference be-
tween the initial voltage and the voltage that is pro-
duced after a period of environmental change. Such 
methods erroneously assume that an amplifier that 
performs satisfactorily at the end of an environ-
mental test period has also operated properly while 
being subjected to changing conditions. 
The solution: 
A motor-driven switcher-recorder to periodically 
register zero drift and gain drift error signals.
How it's done: 
The motor drives the switches at a chosen rate, for 
example, one rpm. In the number 1 position, the re-
corder input terminals are shorted. This position will 
verify that the recorder zero has not chánged. In the 
number 2 position, the amplifier has no input signal. 
The recorder will then register the amplifier zero 
drift. In the number 3 position, a 5-volt signal is ap-
plied to the voltage divider. The select resistor is cal-
culated to divide the 5 volts by the same value as the 
amplifier gain. Therefore, the amplifier output voltage 
will be 5 volts. The recorder will register zero drift 
plus gain drift. In the number 4 position, one half of 
the 10-volt transducer excitation power supply is con-
nected to one input terminal of the recorder while the 
Alls	 (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
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.
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other input terminal is connected to the reference 
5 volts. The recorder will record one half of the power 
supply drift. 
Notes: 
1. Since several measurements are time-shared on a 
single recorder trace, a time coding method is 
needed. One method of coding is to have unequal 
percentages of time for one or more of the meas-
urements. A second coding method is to slightly 
adjust the different measurement outputs so that 
the recorder will not read zero, but a known value 
near zero.
2. Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
Manned Spacecraft Center 
Houston, Texas, 77001 
Reference: B66-10148 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C., 20546. 
Source: Guss E. Wenzel and David Cree 
(MSC-l90) 
Brief 66-10148	 Category 01


Tester periodically registers dc amplifier characteristics

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