US3382451A

US3382451A - Instrumentation system for providing a representative output from either an a. c. or a d. c. input

Info

Publication number: US3382451A
Application number: US504579A
Authority: US
Inventors: Garry C Gillette; James A Nelson; Norman C Walker
Original assignee: Dana Laboratories Inc
Current assignee: Dana Laboratories Inc
Priority date: 1965-10-24
Filing date: 1965-10-24
Publication date: 1968-05-07
Anticipated expiration: 1985-05-07

Description

7, 1968 G. c. GILLETTE ETAL 3,382,451 INSTRUMENTATION SYSTEM FOR PROVIDING A REPRESENTATlVE OUTPUT FROM EITHER AN A.C. OR A D.C. INPUT Filed Oct. 24, 1965 1/ 1 2a I28 Awe-Ines, /14 'neev C. GILLETTE m JAML-s IQ- Hz-Lsou United States Patent INSTRUMENTATION sYsTEM Eon rRovInINo A REPRESENTATIVE OUTPUT ERoM EITIIER AN A.C. oR A no. INPUT Garry C. Gillette and James A. Nelson, Costa Mesa, and

Norman C. Walker, Newport Beach, Calif., assignors to Dana Laboratories, Inc., Irvine, Calif., a corporation of California Filed Oct. 24, 1965, Ser. No. 504,579 9 Claims. (Cl. 330147) ABSTRACT OF THE DISCLOSURE The present invention relates to an instrumentation system and more particularly to a system with AC and DC capability for providing a representative output signal, of desired polarity, regardless of the polarity of an input signal.

In various instrumentation systems the need frequently arises for a structure that provides a representative output current consistently of one polarity, regardless of the polarity of the input signal. In addition, it is sometimes desirable that the structure be capable of operating with either a DC or an AC input signal. In general, the complexity of providing AC-DC capability in prior art systems, greatly increased the cost of a basic DC system.

Therefore, considerable need exists for an accurate, inexpensive system of this type.

Accordingly, it is an object of the present invention to provide an improved structure for use as in a digital voltmeter for example, capable of developing an output.

signal that is amplitude representative of either a DC or an AC input signal, which output signal is consistently of the same polarity regardless of the input signal,

Another object of the present invention is to provide a simple, durable and inexpensive instrumentation component with AC and DC capability, for providing representative output signals of only a selected polarity.

Still another object of the present invention is to provide a simple polarity control circuit utilizing an amplifier in cooperation with a pair of diodes for developing separate phase opposed signals, related in amplitude by a factor of one half for combination to consistently provide an output of a desired polarity.

One further object of the present invention is to provide a simple polarity control circuit having AC and DC capability which can be inexpensively embodied and associated with selected signal conditioning circuits, depending upon the desired input signal.

Additional objects and advantages of the present invention both as to its organization and method of operation will be readily understood from a reading of the following description taken in conjunction with the accompanying drawings which are presented by way of example only and are not intended as a limitation upon the scope of the present invention as defined in the appended claims and in which:

FIGURE 1 is a block diagram of an instrumentation system in accordance with the present invention;

FIGURE 2 is a diagram illustrative of the operation of the system of FIGURE 1; and

FIGURE 3 is a schematic block and circuit diagram of an embodiment of an instrumentation system in accordance with the present invention.

An instrumentation system in accordance with the present invention may include two separate signal-conditioning paths, i.e. one path for DC input signals, and one path for AC input signals. Switching structure is then provided to selectively connect one of these paths to an inverting amplifier and related signal adjusting circuits to develop a signal of opposed polarity to the received signal, and amplitude related by a factor of two. Thus two oppositely poled or phased signals are provided which are amplitude related by a factor of two. If the applied signal is AC, the signals are phase inverted and if the input is DC the signals are polarity inverted. In either case, these signals are, then in part, combined. That is, the desired polarity portion of the larger amplitude signal is additively combined with the entire smaller amplitude signal, In the case of AC, this addition provides a rectified output indicative of the input and of the desired polarity. If the input is DC, the addition also produces an indicative output signal of the desired polarity. In the system, various circuits may be differently connected depending on whether the operation is AC or DC so that considerable economy is possible as a result of dual use.

Referring now to the drawings and more particularly to FIGURE 1 thereof, there is illustrated a diagram in block form representative of one embodiment of the invention. Specifically, separate input circuits 10 and 12 are provided for AC and DC signals. The DC input circuit is connected through a single-pole double-throw switch 14 to an amplifier 16. The movable contact 14a of the switch is shown in the lower position, illustrating DC operation in accordance with a connection for all switches shown in the drawings.

The output from the amplifier 16 is applied to a polarity control circuit 18 through two single-pole double-

throw switches

20 and 22. The movable contacts 26a and 22a of these switches are both shown in the lowered position engaging fixcd contacts 2% and 22b which are interconnected. The output from the polarity control circuTt I8 is applied through a single-pole doublethrow switch 24 to an output terminal 26 from which it may be variously used, as in a digital voltmeter.

In the operation of the system of FIGURE 1 in the DC mode, the input circuits condition the input signal and adjust it to a proper scale. The amplifier 16 may also scale the input signal and may additionally serve as a buffer in relation to the polarity control circuit, In considering the operation of the polarity control circuit, reference will be made to the diagram of FIGURE 2 which illustrates both the AC and the DC modes of operation.

Assuming some predetermined DC input to the polarity control circuit 18, two signals can be represented that are indicative of the operation of the circuit. For example, as shown in FIGURE 2, a positive polarity signal indicated by point 30 exists along with a negative polarity signal indicated by a point 32. The amplitude or level of these signals is referenced to a reference line 34, so that as shown, the signal represented by the point 32 is substantially twice the amplitude of the signal represented by the point 30. Both signals are representative of the input signal, though they are oppositely sensed or poled and amplitude related by a factor of two; however, the higher amplitude signal represented by the point 32 is of the desired output polarity. Therefore upon additive combination of these signals in the polarity control circuit '18, an output signal is produced which is substantially one half tially twice the amplitude of the signal represented by the point 32. That signal is passed through the switch 24 to the output terminal 26 for use as in a digital voltmeter for example, as well known in the prior art.

in the operation of the system of FIGURE 1 to accommodate AC input signals, each of the switches 1 1, 2G, 22 and 24 is altered to a raised position so that the movable contacts 14a, a, 22a and 24a engage the upper fixed

contacts

14c, 26c, 22c and 24c respectively. An AC input signal is then applied through the input circuits 12 (serving to condition and scale such signal) directly to the polarity control circuit 13. Again two signals may be represented as occurring within the circuit 1%. In this instance the AC signals are indicated in FIGURE 2 by a waveform 4t) and a phase-opposed double-amplitude waveform 12. These waveforms representing signals, are then combined somewhat selectively, to provide a DC output of the desired negative polarity, which is representative of the input signal. Specifically the negative half cycle of the signal of waveform 42 is additively combined with the entire signal of waveform 46. The result is the desired DC signal appearing as a full-wave rectified form of the signal of waveform 49. This is readily apparent upon considering the addition of the waveforms and 42, excluding the shaded portion 44 of waveform 42.

The DC signal developed during the AC mode of operation is applied back to the amplifier 16 through the switches 24 and 14 for conditioning. The output from the amplifier 16 is then passed through the switch contact 28c to the output terminal 26 for use as desired, for example, as indicated, in a digital voltmeter. Thus, the system will accommodate either AC or DC input signals and provide a representative DC output which is consistently of the desired polarity.

Considering the structure of the illustrative embodiment in greater detail, reference will now be made to FIGURE 3 showing a DC input terminal and an AC input terinal 52. The DC input terminal is connected to a variable attenuator circuit 54 as well known in the prior instrumentation art, and which may comprise a series of resistors with switching means to scale a wide range of input signals into a specific operating range.

The output from the attentuator circuit 54 is carried by a conductor 56 to a single-pole double-throw switch 58 and a filter 60 which is in turn connected to a source of reference potential. The conductor 56 is connected to a stationary contact 58b of the switch 58, which contact is engaged by a movable contact 58a during DC operation. The movable contact 58a is connected to the input of an amplifier 62 having a feedback path through a resistor 64, the input to the amplifier 62 is connected to a source of reference potential through a resistor 66.

The output of the amplifier 62 is connected to the movable contact 68a of a single-pole double-throw switch 63. The lower stationary contact 68b in the switch 68 is connected to a similar contact 70b in a similar switch 70, the movable contact 7ila of which is connected through a resistor 72 to the input 74 of a ground referenced amplifier '76. The output 73 of the amplifier 76 is returned to the input through parallel similar feedback circuits, as shown, the upper feedback circuit includes a serially-connected diode 8t and a resistor 32. The lower circuit includes a similar diode 84 and resistor 85. The junction point 88 between the diode 8i) and the resistor 82 is connected to the movable contact 90a of a switch 90. The lower stationmy contact 2% of the switch 90 is connected through a resistor 92 to a source of reference potential while the upper stationary contact 90:: is connected through a resistor 94 and a capacitor 96 to a source of reference potential. The junction point between the resistor 94 and the capacitor 96 is connected through a resistor 98 to the upper stationary contact 700 of the switch 70.

In a somewhat related configuration, the junction point 100 between the diode 84 and the resistor 86 is connected to the movable contact 102a of a switch 102. The upper stationary contact 1020 of a switch 102. The upper stationary contact 1020 of the switch is connected through a resistor 1114, back to the upper contact 58c of the switch 58 through a conductor 106 that is connected through a filter 108 to a source of reference potential. The lower stationary terminal 1112b of the switch is connected through a resistor 110 to the output terminal 112 of the system, which is also connected to the stationary contact 68c of the switch 68.

The AC input to the system is from the input terminal 52 through a parallel RC circuit including a capacitor 114 and a resistor 116 to an amplifier 118, having a feedback circuit including a resistor 120 shunted by a capacitor 122. The output of the amplifier 118 is applied through 9. capacitor 124 to the stationary contact 70c in the switch 70.

An understanding of the detailed operation of the system may new best be accomplished by assuming various input signals and explaining the function of the individual elements in the system to cooperatively provide the desired output signal. Therefore, assume initially that a positive signal (related to reference potential) is applied to the DC input terminal 50 and further that all switches are set in the raised position as shown, to provide the DC mode of operation.

The DC input signal is amplitude adjusted to the desired operating range of the system by the variable attenuator circuit 54 and is then smoothed by the filter 60. The non-inverting amplifier 62 further refines the signal to provide a representative signal through the switches 68 and '70 and the resistor 72 to the input 74 of the amplifier 76. Assume, for example that the signal at the input 74 is of positive polarity, so that the signal at the switch contacts 68b and 70b is also positive. That signal is applied through a resistor 126 directly to the output terminal 112 for additive combination with another signal, the development of which will now be considered.

The positive-polarity input signal applied to the amplifier 75 is inverted therein to provide a negative-polarity signal at the output 78. That signal is effectively combined with the positive signal at the output terminal 112 through the diode 84, the switch 102 and the resistor 110. These signals (positive and negative) are of substantially equal amplitude on either side of the polarity inverting amplifier 76 (of unity gain) however, they are applied to the output terminal 112 through resistors of different resistance to accomplish a two to one ratio in favor of the negative signal which is illustratively selected as the desired output polarity. Specifically, the resistor 126 is twice the value e.g. 2K of the resistor 110, e.g. 1K. That is, the negative signal at the output 78 back biases the diode 80, but forward biases the diode 84 to pass a current through the resistor 110 which is greater than the current (opposed) through the resistor 126 so that the negative signal prevails at the output terminal 112 by a factor of two. Therefore, if the current through the resistor 126 is considered +Ifs (full scale positive) the current through the resistor 110 will be 2Ifs (twice full scale negative) because of the relative resistances of the resistors 110 and 126. As a result, the output to the terminal 112 is the additive combination, i.e. Ifs (full scale negative). Thus, the output is amplitude representative of the assumed positive input signal but is of the desired negative polarity.

If, conversely, the input to the system at the terminal Sit is negative, resulting in a negative signal at the switch contact 68b and a similar amplitude positive signal at the amplifier output 78, the desired negative output is still provided at the terminal 112. Specifically, the negative signal at the switch contact 68b provides a current -Ifs (full scale negative) to the output terminal through the resistor 126. However, the positive signal at the output 78 is by-passcd to reference potential through the switch 90 and the resistor 92. As a result, the output is the desired signal Ifs.

In the operation of the system it is desirable to preserve balanced operation, as indicated. Therefore, the various resistors should be value related, and may have the values set forth below (only as examples).

Value, K Resistors 82 and 86 l Resistors 98 and 126 270 Resistor 72 Resistor 126 2

Resistors

110 and 92 1 Resistors 04 and 104 135 Thus, regardless of the polarity of the direct current input at the terminal 50, during the DC mode of operation, the output is a representative signal of the same desired polarity, e.g. negative as illustrated. If the system is operated in the AC mode, the same results are obtained as will now be considered in detail. Preparatory to AC operation, the switches are all placed in the raised position. That is, the

switches

58, 68, 70, 90 and 102 are all set so that their movable contacts engage the upper stationary contacts 58c, 68c, 70c, 90c and 102a respectively. Now upon application of an AC signal to the input terminal 52, the signal is coupled into the amplifier 118 for preliminary conditioning and scaling. The signal is next coupled through the capacitor 124, the switch 70 (in the raised position) and the resistor 72 to the input 74 of the amplifier 76. This signal is also supplied through a resistor 128 to the conductor 106, which during AC operation receives the signal components for combination to develop a preliminary form of the output which is finally conditioned by the amplifier 62 then applied to the output terminal 112.

Recapitulating, the conditioned AC input signal is applied to the amplifier 76 to be phase inverted, and is also applied to the conductor 106 through the resistor 128. The phase inverted output from the amplifier appearing between the diodes 80 and 84 is selectively passed to the conductor 106 to develop the desired signal. Specifically, the positive-going excursion of the signal from the amplifier 76 is passed through the diode 80 as a feedback signal through

resistors

82, 94 and 98. The negative going excursions of the amplifier output are coupled through the diode 84 and the resistor 104 to the conductor 106.

Referring to FIGURE 2, the current to the conductor 106, through the resistor 128 from the amplifier 118 may be represented by the waveform 40, while the current to the conductor 106, through the diode 84 and resistor 104 may be represented by the negative half-cycle of the waveform 42. The amplitude differences in these currents results from the fact that the resistor 128 is substantially twice the value of the resistor 104. The additive combination of these currents in the conductor 106 thus becomes a full wave rectified form (negative) of the waveform 40, the value of which is representative of the AC input signal.

The representative rectified signal developed at the conductor 106 is smoothed by the filter 108 and provided through the switch 58 to the amplifier 62 for further conditioning, then passed through the switch 68 (now in the raised position) to the output terminal as indicated, the amplifier 62 is not polarity inverting, therefore, the desired negative signal output is again provided at the output terminal 112 which is representative of the input signal.

It may therefore be seen that the system, as illustratively disclosed, functions effectively to provide a representative output of desired polarity, regardless of the polarity of a DC input signal and for AC signals as well. Although the disclosed system provides a negative polarity output, it is readily apparent that positive polarity output could be provided, depending entirely upon the desired application of the system. Of course, various other modifications to the dsclosed embodiment are readily apparent, therefore, the scope of the invention is not to be limited in accordance therewith but shall be interpreted in accordance with the claims hereof.

What is claimed is:

1. An instrumentation system comprising:

AC signal conditioning means for providing input signals;

DC signal conditioning means for providing input signals;

amplifier circuit means for inverting received signals to provide inverted signals, said amplifier circuit means including means for adjusting the amplitude of at least one of said signals therein to provide a double amplitude realtionship therebetween;

means for additively combining the desired-polarity portion of said one of said signals to provide a combined output signals representative of said input signals and of said desired polarity; and

switch means for selectively connecting one of said signal conditioning means into an operative relationship with said amplifier circuit means.

2. A system according to claim 1 wherein said amplifier circuit means includes a phase inverting amplifier and a pair of oppositely poled diodes connected thereto for selectively passing the desired polarity portion of the output-from said phase inverting amplifier.

3. A system according to clairn 1 wherein said means for additively combining includes a first circuit for addi tively combining AC signals, a second circuit for additively combining DC signals and means for selectively connecting said first and said second circuit to said amplifier circuit means.

4. An instrumentation system for providing output signals of a desired polarity, representative of applied input signals, comprising:

an input circuit for receiving said input signals, including an AC signal conditioning means and a DC signal conditioning means; a phase inverting means for inverting the phase of said input signals to provide a phase inverted signal;

amplitude means for controlling the amplitude of said input signals and said phase inverted signals to provide first and second phase opposed signals amplitude related by a factor of two, and representative of said input signals;

means for combining the desired polarity portion of said first signals with said second signals to provide said output signals; and

means for selectively connecting one of said signal conditioning means in operative relationship with said instrumentation system. '5. A system according to claim 4 wherein said amplitude means comprises impedance means to adjust signal currents to acomplish said amplitude relationship.

6. An instrumentation system for providing output signals of a desired polarity, representative of both applied AC input signals and applied DC input signals comprising:

an input circuit for receiving said input signals; 'a phase inverting means for inverting the phase of said input signals to provide a phase inverted signal;

amplitude means for controlling the amplitude of said input signals and said phase inverted signals to provide first and second phase opposed signals amplitude related by a factor of two, and representative of said input signals and said phase inverted signals respectively; and

signal combining means for additively combining the desired polarity of the larger of said phase opposed signals with the other of said phase opposed signals to develop said output signals.

7. An instrumentation system for providing output signals of a desired polarity, representative of both applied AC input signals and applied DC input signals, comprismg:

an AC signal conditioning means for receiving said AC input signals;

a DC signal conditioning means for receiving said DC input signals;

an input circuit for receiving said input signals;

switching means for selectively connecting one of said signal conditioning means to said input circuit;

a phase inverting means for inverting the phase of said input signals to provide a phase inverted signal;

amplitude means for controlling the amplitude of said tude related by a factor of two, and representative of said input signals and said phase inverted signals respectively; and

selective means for selectively passing the desired po- 8 larity portion of said first signals; and means connected to said selective means for additively combining signals therefrom with said second signals.

9. An instrumentation system for providing output signals of a desired polarity, representative of both applied AC input signals and applied DC input signals, comprising:

an AC signal conditioning means for receiving said AC input signals;

10 a DC signal conditioning means for receiving said DC input signals and said phase inverted signals to proinput signals; vide first and second phase opposed signals amplian input circuit for receiving said input signals; tude related by a factor of two, and representative switching means for selectively connecting one of said of said input signals and said phase inverted signals signal conditioning means to said input circuit; respectively; and I a phase inverting means for inverting the phase of said means for combining the desired polarity portion of said input signals to provide a phase inverted signal;

first signals with said second signals to provide said amplitude means for controlling the amplitude of said output signals. input signals and said phase inverted signals to pro- 8. An instrumentation system for providing output sigvide first and second phase opposed signals amplitude nals of a desired polarity, representative of both applied related by a factor of two, and representative of said AC input signals and applied DC input signals, comprisinput signals and said phase inverted signals respecing: tively;

an AC signal conditioning means for receiving said selective means for selectively passing the desired po- AC input signals; larity portion of said first signals; a DC signal conditioning means for receiving said DC a first and second separate signal combining means for input signals; combining the signal from said selective means with an input circuit for receiving said input signals; said second signals; and switching means for selectively connecting one of said means for connecting said first and said second signal signal conditioning means to saidi put Cir u t; combining means into said system to accommodate a phase inverting means for inverting the phase of said 39 receipt of AC or DC signals.

input signals to provide a phase inverted signal; amplitude means for controlling the amplitude of said References Cited input signals and said phase inverted signals to pro- UNITED STATES PATENTS vide first and second phase opposed slgnals ampli 2,863,118 12/1958 Pihl ROY LAKE, Primary Examiner.

J. B. MULLINS, Assistant Examiner.