Voltage range selection apparatus for sensing and applying voltages to electronic instruments without loading signal sourc

Camp, E. L.

Doughty, R. A.

Mccormick, C. T., Jr.

English

NASA Technical Reports Server

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NATIONAL AERONAUTICS A N D  SPACE ADMINISTRATIO 
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https://ntrs.nasa.gov/search.jsp?R=19710016768 2020-03-17T03:06:30+00:00Z
969 JAMES E WEBB 3,464, 
DMINISTRATOR OF THE NATIONAL AERONAUTICS 
AND SPACE ADMINISTRATION 
AUTOMATIC SIGNAL RANGE SELECTOR FOR METERING DEVICES 
Filed Feb. 17, 1967 
atented Aug. 26, 1969 
Other objects and man f the attendant advantages 
of this invention will be readily appreciated by reference 
to the following detailed description when considered with 
the accompanying drawings in which like reference J2z Ed!;: ~~~~~~~~~~~~r~~~~~~ ::En: 5 numerals designate like parts throughout the figures there- 
of' and wherein: 
FIG. 1 is a schematic-block diagram of the automatic 
voltage sensing and selecting device of this invention; and 
FIG. 2 is a schematic diagram of a voltage sensing and 
Referring more particularly to the drawings, there is 
shown in FIG. 1 a voltage sensing and selection device 
10 which is a preferred embodiment of the invention. A 
range selection apparatus for automatically signal voltage which is to be sensed by the device 10 and 
sensing and applying voltages to electronic instruments 15 selectively applied to an electrical instrument such as 
without loading the signal source, signal voltages are the voltmeter M is applied to input terminals l l a  and l l b  
sensed by a plurality of voltage sensing and triggering cir- of the device 10. The terminal l l a  is connected by con- 
cuits each of a voltage sensing unit and a modi- ductors 12, 1 2 ~  and 126 to voltage sensing and trigger- 
fied Schmitt trigger which operates with low hysteresis ing circuits 101, 102. For purposes of clarity and s h -  
one percent of the trigger level for operating an 20 plicity of description, only two such voltage sensing and 
associated switching relay. When energized, the triggering circuits are shown, atthough any number might 
ciated relay the input signal voltage to one of a he provided. Each of the circuits 101, 102 is adjustable 
plurality of meter ranging resistors and selectively applies to respond to a voltage signal of a sefect amplitude level, 
to one of a plurality of range indicating lamps. and when sensing a voltage of appropriate level energises 
The invention described herein was made in the per- 25 an associated relay such as the relay 13 or 14 which se- 
formance of work under a NASA and is subject lectively applies the signal voltage to an appropriate 
the provision of section 305 of the ~ ~ ~ i ~ ~ ~ l  A ~ ~ ~ ~ -  meter ranging resistor associated with the voltmeter M. 
tics and space Act of 1958, public L~~ 85-568 (72 stat. n e  relay when energized also Connects a suitable power 
source to an associated voltage range indicating lamp. 
A typical voltage sensing and triggering circuit such 
as the circuit 101 is shown in detail in FIG. 2. The input 
side of the circuit 101 comprises a potentiometer 15 
which is connected at one terminal to the conductor 124 
and at its other terminal to ground by the conductor 36. 
device, and more particularly to an apparatus for auto- 35 The variable arm 17 of the potentiometer is connected 
matically sensing and switching signal voltages. through a one megohm attenuating resistor 16 to the 
The disadvantages inherent in manual range selection base 19 of an NPN transistor 20. The emitter 21 of the 
and application of voltages t mentS such transistor 20 is connected to ground through a variable 
spent in range selection and instrument 4O the anode of a diode 24 which is connected in shunt 
damage by excessive voltage frequently Prec1udes the across the resistance 22. The collector 25 of the transistor 
use of such manual range selection devices for many aP- 19 is coupled by a conductor 26 to the base 27 of a sec- 
Plications. Although automatic range shifting devices are ond NPN transistor 28. It is also connected by conductor 
known which mitigate these disadvantages to Some ex- 29, resistor 30, and the conductor 31 to one terminal 33a 
tent, these also present problems which limit their use- 45 of the coil of a double pole double throw relay 13. The 
fulness. Complexity of instrumentation, loading of the collector 34 of the second transistor 26 is also coupled 
signal source, and inconstancy in the switching operation to the same terminal of the relay 13 by means of the 
are typical problems. conductor 35, resistor 36, and conductors 37 and 31. The 
emitter 38 is connected to the anode of the diode 2.1. The 
SUMMARY OF THE INVENTION 50 collector 34 of the transistor 28 is also coupled to the 
The voltage sensing and selection device of this inven- second terminal 33b of the relay 13 through the resistor 
tion which has been devised to overcome attendant dis- 41, conductor 42, capacitor 43, and conductor 44. 
advantages of the prior art devices provides a means of The resistor 41 is also connected by the conductors 42 
sensing and switching D.C. input signal voltages without and 48 to one terminal of a resistance 49 which is ground- 
loading the signal source. It comprises a plurality of trig- 55 ed to the conductor 16. The resistor 41 is also coupled to 
gerhg circuits each consisting of a voltage sensing unit the base 51 of an NPN transistor 52 by the conductors 42, 
for sensing input voltages and a modified Schmitt trigger 48, and 53. The emitter 54 of transistor 52 is connected 
for controlliing application of the input signal voltage to directly to the ground conductor 16, and the collector 55 
one of a plurality of meter ranging resistors. The Schmitt of transistor 52 is coupled directly to the terminal 336 
trigger is adapted to operate with low hysteresis within 6o Of the relay 13. 
one percent of the trigger level for operating a switching For establishing collector-base bias for the several 
relay with an output voltage pulse of constant amplitude. transistors, a D.C. power source El is connected to apply 
The relay, when energized, also selectively applies power +26 volts to one side of the resistors 30, 36 and the 
from a suitable power source to an appropriate range relay coil. 
indicating lamp. A diode 57 is connected in shunt with the coil of relay 
3,464,012 
AUT0MATIC SIGNAL RANGE SELECTOR FOR 
METERING DEVICES 
tion of Charles T. McCormick, Jr., Houston, Robert A. 
Alvin and Ernest L. camp La M ~ ~ ~ ~ ,  T ~ ~ .  
&ed Fib. 17, 1967, Ser. No.'617,778 
b t .  et. GOlr 1/38,15/08 
US. C1.326115 2 Claims IO triggering circuit of the invention. 
A B S m C T  OF THE DBCLOSURE 
A 
30 435; 42 U.S.C. 2457). 
BACKGROUND OF THE INVENTION 
This invention relates to a voltage sensing and selection 
as voltmeters, and the like, The time resistance 22. It is also connected by the conductor 23 to 
65 
3,464,012 
3 4 
13 with its anode coupled to the relay terminal 336 and its to the full scale deflection current of the meter at voltage 
cathode coupled to relay terminal 33a. The diode 57 levels of 1 volt, 10 volts, and 100 volts. Furthermore., the 
protects the transistor 52 from inductive feedback caused range indicating lamps which in the device 10 are sub- 
by the relay coil. miniature 24 volt lamps, are preferably differently colored 
For operation of the device 10, the variable arm of and mounted within easy visual range of an operator. 
the potentiometer 15 may be adjusted to provide for any However, any number of ranges can be provided by addi- 
level of triggering from 0 to 100 volts D.C. For purposes tion of suitable multipliers for the voltmeter M and pro- 
of explanation it may be assumed the circuit 101 is set vision of a corresponding number of voltage sensing and 
for 1.0 volt triggering and the circuit 102 is set for trig- triggering circuits. The voltmeter M could instead be a 
gering at 10.0 volts. The potentiometer 15 has therefore 10 D.C. ammeter which would require the use of shunt re- 
been so adjusted that when a signal voltage reaches 1.0 sistors for the meter ranging resistors. 
volts the base bias of the transistor 20 allows this transistor What is claimed and desired to be secured by Letters 
to conduct current. As the transistor 20 conducts, its col- Patent is: 
lector voltage which is coupled to the base of transistor 1. An automatic electrical signal sensing and selection 
28 decreases, thereby rendering the transistor 28 non-con- 15 device, said device comprising: 
ducting. As transistor 28 is in the non-conductive state, a plurality of meter ranging resistors, each adapted to 
its collector voltage which is coupled to the base of transis- be selectively coupled to a meter for measuring said 
tor 52 rises sufficiently to cause transistor 52 to become signal; 
conducting. When the transistor 52 is rendered conducting, a plurality of signal voltage sensing circuits, each in- 
current is allowed to flow through the coil of the relay 20 cluding a trigger circuit responsive to a unidirectional 
13 to energize the relay. voltage input signal greater than a discrete 
The diode 24 is a temperature sensitive device which magnitude; 
makes compensation in the circuit for any ambient tem- said trigger circuit including a pair of cascaded tran- 
perature changes. The variable resistance 22 which is sistors having a common variable emitter resistor 
connected to the emitters of both transistors 20 and 28, 25 and a temperature compensating diode in shunt 
and in shunt across the diode 24, is a variable sens therewith, said variable resistor serving as an sen- 
control which determines the emitter current for the sitivity control means to adjustably limit the dif- 
emitters 21 and 38. The amount of emitter current al- ference betweeu the turn-on and turn-off voltage 
lowed by the control resistor 22 determines the difference levels of said trigger means, 
between the turn-on voltage and turn-off voltage levels 30 means for delivering a fraction of said signal to said 
for the transistors 20 and 28. By provision of the control voltage sensing circuits; 
resistor 22, this hysteresis effect or difference between a plurality of switching means, each operatively associ- 
the turn-on and turn-off voltage levels for the circuit is ated with a different one of said trigger circuits, each 
controlled to less than 1% of the voltage triggering level. said switching means being operable in response to 
operation of its associated trigger circuit to apply the 
the sensing circuit 101 is in “off conditon and the input unattenuated input signal to a select one of said meter 
signal is routed through the normally closed upper con- ranging resistors, and each said trigger circuit com- 
tacts provided by the relay arms 14a and 13a of the relays prising a bi-stable pulse generator operable to deliver 
14 and 13, respectively, to the 0 to 1 volt meter ranging a voltage pulse of constant amplitude for energizing 
resistor 61 coupled to the voltmeter M. When relay con- 40 its associated switching means. 
tact arm 130 is moved to its lower position, the input 2. An automatic electrical signal sensing and selection 
signal voltage is routed through the contact arm 13a to the 
1 to10 volt ranging resistor 62. When the voltage sensing a plurality of meter ranging resistors, each adapted to 
circuit 102 is turned “on” by an input signal voltage be selectively coupled to a meter for measuring said 
greater than 10 volts, the relay 14 is energized and the 45 signal: 
contact arm 14a is moved to its lower contact position 
to thereby route the signal to the 10 to 100 volt ranging 
resistor 63. 
The device 10 also includes a plurality of voltage range 
indicating lamps 71, 72, and 73 which are adapted to be 50 
powered by a suitable power source Ea, such as a battery 
or the like. When the device 10 is placed in operation, 
the switch 75 is closed. The relay contact arms 13b and 
146 associated with the relays 13 and 14, respectively, are 55 
normally in their upper contact positions as shown in FIG. 
1, whereby voltage is delivered to the indicating lamp 71. 
For input signal voltages less than 1 volt, the relays 13 
and 14 are de-energized and the lamp 71 is lit. When a 
signal voltage greater than 1 volt is applied to the input 
of the device 10, the relay 13 is energized by the circuit 
101 and the relay contact arm 136 is moved to its lower 
contact position to couple the power source Ez with the in- 
dicating lamp 72. It will also be seen that if the input 
signal voltage exceeds 10.0 volts, the circuit 102 responds 
to energize the relay 14 and simultaneously move the relay 65 
contact arms 14a and 14b to their lower contact positions. 
The power source Ea is thereby coupled to the range indi- 
cating lamp 13. 
It will also be apparent that when the input signal level 
is lowered, as for example from a value greater than 
10.0 volts to less than 10 volts, a reverse process occurs 
whereby the circuit 102 turns off at 10 volts. In like 
manner the circuit 101 turns “off” at 1.0volts. 
resistors 61, 62, 63 are selected to provide current equal 
When the input signal voltage is less than 1.0 volts, 35 
device, said device comprising: 
a plurality of voltage range indicating lamps; 
a power source connectable to deliver electrical power 
to a select one of said indicating lamps; 
a plurality of signal voltage sensing circuits, each in- 
cluding a trigger circuit responsive to a unidirectional 
voltage input signal greater than a discrete magnitude; 
each of said trigger circuits including a pair of cas- 
caded transistors having a common variable emitter 
resistor and a temperature compensating diode in 
shunt therewith, each of said variable resistors serv- 
ing as a sensitivity control means to adjustably limit 
the difference between the turn-on and turn-off volt- 
age levels of each of said trigger means. 
means for delivering a fraction of said signal to said 
voltage sensing circuits; 
a plurality of electromechanical relay switching means, 
each operatively associated with a different one of 
said trigger circuits and responsive to operation of 
its associated trigger circuit to switch the input sig- 
nal to a select one of said meter ranging resistors and 
for connecting said power source to a select one of 
said voltage range indicating lamps, each said trigger 
means comprising a Schmitt trigger pulse generator 
operative to deliver a voltage pulse of constant ampli- 
tude for energizing its associated relay switching 
means; and 
each of said variable resistors associated with a dif- 
ferent one of said voltage sensing circuits and trigger 
circuit means serving to adjustably limit the difference 
between the turn-on- and turn-off voltage levels of 
It is to be understood, of course, that the meter ranging 75 
3,464,012 
5 6 
its associated trigger means to withim a range of less 2,682,000 6/1954 Clayton et al. _ _ _ _  324-115 X R  
than 1% of the triggering level of said associated 2,291,181 11/1959 Leeder - _ _ _ _ _ _ _ _ _  324-115 XR 
trigger means. 3,012,195 12/1961 Slacornb et al. _ _ _ _  324-115XR 
3,016,488 1/1962 Smith et al. _ _ _ _ _ _ _ _ _  324-115 
References Cited - 3.133.278 5/1964 Millis _ _ _ _ _ _ _ _ _ _ _  324-115XR 
UNITED STATES PATENTS ' 3;187;323 6/1965 Flood et al. _ _ _ _ _ _  324-115XR 
3,383,594 5/1968 Fiorletta et al. _ _ _ _  324-11SXR 2,400,190 5/1946 Clark _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  324-115 
2,512,330 6/1950 Hendrick _ _ _ _ _ _ _ _  324-115 XR 
2,643,344 6/1953 McLarenet al. _ _ _ _  324-115 XR "' RoLINECy Primary 
2,648,015 811953 Greenfield et al. -- 324-115 XR E. F. KARLSEN, Assistant Examiner 


Automatic signal range selector for metering devices Patent

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