Electronic ampere-hour integrator is based on current-to-frequency conversion. It operates on low power and is accurate to one percent. This device can measure the ampere-hour capacity of batteries and can be adapted for other functions

Paulkovich, J.

English

NASA Technical Reports Server

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October 1965	 Brief 65-10308 
NASA TECH BRIEF i& 
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. 
Electronic Ampere-Hour integrator is Accurate to One Percent 
0.1 amp, to 20 amp.	 +	 Ii -b.	 Current Sensors 
The problem: Normally, ampere-hour integrators 
are mechanical devices, such as a ball and disc, which 
operate on information from a recorder. They have 
the inherent disadvantages of large physical size, de-
pendence on the accuracy of the recorder, and me-
chanical wear which results in drift requiring frequent 
calibration. 
The solution: A solid state, dual-range electronic 
ampere-hour integrator based on current-to-frequency 
conversion. The integrator operates on low power, 
and is accurate to within 1 percent from a 10 milli-
ampere rate to a 20 ampere rate. 
How it's done: The circuit shown is based on the 
reflected impedance of transformer T2. A square wave
oscillator circuit, using transistors QI and Q2, alter-
nately drives transistors Q3 and Qj. Each time tran-
sistor Q3 is turned "on", saturable transformer T2 is 
reset to its negative saturation state. When transistor 
Qi is turned "on", the reflected current from the sens-
ing circuit causes a proportional current to, flow 
through transistor Q5 to charge pulse rate capacitor 
C2: The reflected current 12 is directly proportional 
to the input current II and is given by 12= Ii (Ni/N2) 
where:
Ii = current to be sensed 
12 = reflected current 
N2 = primary turns of T2 
= secondary turns of T2 
When C2 has accumulated sufficient charge to cause 
(continued overleal) 
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.
https://ntrs.nasa.gov/search.jsp?R=19650000306 2020-03-11T17:20:15+00:00Z
unijunction transistor Q6 to conduct, an output pulse 
is applied to the accumulator and, simultaneously, C2 
is discharged. Thus the circuit converts the current 
rate to pulse rate. The accumulator indicates the total 
ampere-hours and consists of a simple counter. The 
magnetizing current required by T2 during conduc-
tion of Q4 causes an undesirable error at low current 
levels; however, its effects can be minimized by utiliz-
ing the stored energy of the square-loop core. Energy 
is stored during conduction of Q3 and its level is de-
termined by Ri. When the driving source to Q3 is re-
moved the energy is transferred to the capacitor Ci 
via diode Di and the power source Et. Thus capaci-
tor Ci is capable of supplying the required magnetiz-
ing current during conduction of Qi. Resistor R2 is 
adjusted to drain off the excess stored charge on C1.
Notes: 
1. This device can be used to measure the ampere-
hour capacity of batteries. 
2. By adding series resistors to the current-sensing 
coil the output pulse rate will be directly propor-
tional to the voltage being sensed, thus making 
the circuit a voltage-to-frequency converter. 
3. Addition of an accumulator to the voltage-to-fre-
quency converter makes the circuit a volt-time in-
tegrator. 
4. Inquiries concerning this invention may be directed 
to:
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland, 20771 
Reference: B65-10308 
Patent statUs: NASA encourages the immediate 
commercial use of this invention. Inquiries about ob-
taining rights for its commercial use may be made to 
NASA, Code AGP, Washington, D.C., 20546. 
Source: John Paulkovich 
(GSFC-203) 
Brief 65-10308	 Category 01


Electronic ampere-hour integrator is accurate to one percent

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