CA1138932A

CA1138932A - Device for measuring and indicating changes in resistance of a living body

Info

Publication number: CA1138932A
Application number: CA000335278A
Authority: CA
Inventors: John D. Mccormick; Ron W. Conners
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-03-08
Filing date: 1979-09-07
Publication date: 1983-01-04
Also published as: FR2451037B3; GB2113853A; GB2113853B; DK163385B; AU5067079A; DK163385C; ZA794716B; AU529659B2; FR2451037A3; JPS55119065A; DK375879A; DE2935528C2; JPH0297675U; GB2043918A; GB2043918B; DE2935528A1; JPH0353179Y2; MX150268A

Abstract

ABSTRACT OF THE DISCLOSURE
In accordance with the invention there is provided an electrical resistance measuring indicating device including a bridge network having on one side thereof a first resistance arm connected to a second resistance arm and on the other side thereof, first voltage arm connected to a second voltage arm, there being between the junction of the first and second resistance arms and the junction of the first and second arms are transisterized amplifier circuit and indicating means responsive to changes in the balance of the bridge networks so as to indicate or measure the resistance or variation in resistance of a subject such as a body are part connected to the network across one of the resistance arms. The indicating means includes a moving coil meter which includes a split metal frame having a meter coil wound thereon and an indicating needle coupled to the frame.

Description

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1 This invention relates to the responsiveness of devices for indicating variations in the electrical resistance of the human body.
Prior to Lafayette R. Hubbard's Device for measuring and indicating changes in a living body, resistance measuring devices were not designed to indicate small changes in resis-tance of a living body. Mr. Hubbard's invention was specific-ally to be used for measuring these small changes.
Mr. Hu~bard's invention while being designed to indicate small changes in resistance of a living body was hampered in that while the circuitry could detect the small changes in resistance, the meter could not accurately track and indicate the changes. To improve the tracking, prior art meters were utilized. Such prior art meters improved their tracking by increasing the torque to moment ratio of the movement by decreasing the mass of the needle and by decreasing the mechanical resistance of the movement suspension. Such improved meters while being better still do not sufficiently and accurately track and indicate the changes. In addition, such meters are undesirable since the meter is critically damped so that the needle does not overshoot the level and the descrease in mass of the needle results in a very fine needle ~hich is difficult to see.
Accordingly, it is a general object of the present invention to provide a highly sensitive device for measuring changes in electrical resistance of a living body with an extremely sensitive meter movement.
It is another object of the present invention to pro-vide a meter for a device for measuring changes in electrical resistance of a living body with substantially improved tracking.

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1 It is yet another object of the present invention to provide a meter for a device Eor measuring changes in electri-cal resistance of a living body in which the needle accurately follows the variations in the input signal to the meter.
It is still another object of the present invention to provide a meter for a device for measuring changes in electrical resistance of a living body which is not critically damped.
It is still another object of the present invention to provide an uncritically damped meter for a device for measuring changes in electrical resistance of a living body which includes a frame or the meter movement with zero conductivity.
The inventive improvements, that are the subject of this patent have greatly enhanced the sensitivity of the indicating means of the device for measuring the resistance of a living body,: thereby making a more effective device overall, and this has directly affected the state of the art by creating more sensitive and responsive metering than has ever been accomplished previously.
In accordance with the invention there is provided an electrical resistance measuring or indicating device com-prising a bridge network having on one side thereof a first resistance connected to a second resistance arm and on the ~ 2 -~, 1~3~3~

1 other side thereof, a first voltage arm connected to a second voltage arm, there being between the junction of the first and second resistance arms and the junction of the first and second arms, a transistorized amplifier circuit and indicat-ing means responsive to changes in balance of the bridge net-work so as to indicate or measure the resistance, or variations in resistance, of a subject such as a body or part connected to the network across one of said resistance arms.
In a preferred form of the device, a first variable potentiometer means is associated with one of the voltage arms for controlling the range over which the device can operate in the indication of variations in resistance and a second variable potentiometer means is arranged between the junction of the first and second resistance arms and the amplifier circuit, the arrangement being such that when the bridge network becomes unbalanced by the application of a subject thereto, balance can be restored by the adjustment of the first potentiometer means so that the indicating means will res~
pond to very small changes in resistance of said subjec-t. The indication of the changes of resistance must be immediately re.sponsive. A special movement using a frame with no conducti-vity is used to do this.
For a better understanding of the device and the method by which it is to be performed, an embodiment thereof is shown in the accomp~nying drawi.ngs, wherein, Figure 1 is a schematic diagram illustrating the circuit of the device.

Figure 2 is a front view of the device Fic~ure 3 is a perspective view of the frame coil.

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I Figure 4 is a perspective view of the meter movement showing the frame coil in use.
Referring now to the circuit diagram of Figure 1, the D.C. amplifier comprises three transistors QI, Q2 and Q3 which derive their operating power from the battery BI, the transistors each consisting in the present embodiment, of a 2NI303 transistor.
It will be noted that in Figure 1 the input to the D.C. amplifier is applied between the base and emitter of the first transistor QI, the emitter of QI being returned through a 4.7 K resistor R5. This potential difference is equal to the battery voltage so that the circuit behaves exactly as though it were indeed ; connected as a simple bridge.
Transistor QI of the input stage, is an emitter follower ,;
having a fairly high input resistance, it being necessary to keep the input resistance of the amplifier high relatively to - the resistance of the bridge in order to prevent loading, since loading is particularly important when the bridge is operated ,~ in an unbalanced condition.

For the connection of the sub~ect electrodes to the instrument, there is provided a telephone jack JI having spring contacts adapted to be connected. Upon insertion of an appropriately wired plug tnot shown) to the electrodes, contact

2 is connected to the slider of the range control potentiometer VR 2 and is also operatively associated with a single pole switch S3 in such a manner that when the plug is withdrawn, switch S3 closes to connect across the jack contacts I and 2, a 5K ohm resistor RI in place of the subject's body. In the present embodiment, the resistance arms R3 and R2 and R3, of the bridge comprise resistors of 22K ohms, and 3.9K and 2.5K ohms res-pectively. The range control potentiometer VR2 is connected i~ ~

113E~932 1 at one end to the negative side of the battery BI through switch SIA and at the other end to the Tap of battery BI through a SK ohm resistor VR4 and a switch SIO. The base of the transistor QI
is also connected through resistor RI2~or RI3 or RI4, depending on desired range of sensitivity:as seIected by S2A~to the negative side of meter MI and the collector of transistor QI is connected ~ through switch SIA to the negative side of battery BI. The ~- emitter of QI is connected through a 470 ohm resistor R6 to the ~`. base of the second stage transistor Q2, the latter being arranged as a conventional common-e~itter stage which provides most of the current gain. The emitter of Q2 is connected through SK ohms ; preset variable resistor VR6 to the positive side.of battery BI
~;~ and this emitter is also connected through a sensitivity control ,~
VR5 comprising a IOK ohm reverse-log variable resistor, and through the switch SID to the Tap of battery~BI. The collector p of Q2 is connected:directly:to the emitter of Q3, and is also ~ connected through a 5.6K ohm resistor R8 and:switch SIA to~the .~;. negative side of battery BI. The base of Q3 is connected to the junction of resistors RIO and RII,~each of~22K ohms, RIO
~--. 20 bæing connected through switch SIA to the negative side of ; battery BI and RII being connected to the slider of resistor VR5. The collector of Q3 is connected to a switch SIC so that by operation of that switch:the collector can be connected to . the positive.side of the meter. The meter is shuntqd by a : 5.6K ohm resistor RI6, and a 5K variable resistor VR7, in series, .~ and the negative side thereof is connected through 22K ohm resistor RI and switches SIB and SIA to the negative side of the ~- ~ battery BI.
. The switch SIC and SIA and SIB, when SI is in the 3rd . 30 position, respectively connects the positive side of the meter to _ 5 1~ ' ,,~ , . ..

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I the positive side of BI, and connects the negative side of the meter to the negative side of BI via a 90K ohm re,sistor RI9.
'jWith SI in the 3rd position the meter is shunted by a SK ohms variable resistor VR8.
, ~ -~', The transistor Q3 of the output stafe is connected in `' the common-base configuration and constltutes an lmpedance matching device feedlng the indicating meter.

,~ The resistors RI2, RI3 and RI4 are~negative feedback `~ resistors which determine the overall gain. Their value depends i:
upon the position of S2A.
~ Switch S2 is a double pole treble throw. In position one, ,~ a 470K ohm resistor RI2 is connected. In position 2, a mega ~' ohm resistor RI3 is connected. In position 3, two one mega ohm resistors RI3 and RI4 are connected in series.
~,' To compensate for the change in potential at the base '17~ of QI, caused by the changing resistances at S2A, a variable opposite potential is applied to the base of QI using switch ~'s~ S2B. In position 2, a mega ohm resistor RI3 is connected. In , position 3, two one ,mega ohm resistors RI3 and RI4 are connected in series.
To compensate for the change in potential at the base of ~, QI, caused by the changing resistances at S2A, a variable opposite potential is applied to the base of QI using , `~ switch S2B. In position I, a 200K ohm resistor R4 and a 75K
ohm resistor, R2I is connected between the'base of QI and the negative side of BI. In position 2 a 200K ohm resistor R4 and a 17.5K ohm resistor R20 is connected between the base of QI

and the negative side of BI. In position 3 a 200K ohm resistor R4~is connected between the base of QI and the negative side of BI.
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This is a new improvement as it allows for a boosting of the sensitivity not available in the previous device.
Switch SIA, B, C, D, E, F, is a 5 pole treble throw switch operated by knob B' (FIGURE 2).
The indicating meter Ml is a moving-coil meter capable of reading from 0 to 100 microamps at full scale deflection, the meter having an arcuate scale H' (FIGURE 2) divided into sections.
~; At about one-third scale deflection, there is provided a small sector of the arc marked "SET". At the full-scale end of the arc there is another small section marked "TEST". Between these two small sectors, the scale is marked "FALL". The 5K ohm preset variable resistor VRl is provided between the subject terminals and the amplifier detector, to permit compensation for variations in component values. The resistance value of the optimum female subject is SK ohms and the instrument is therefore standardized at this value. For the setting of VRl there is provided a control C' (FIGURE 2) marked "TRIM".
The range control potentiometer VR2 has a control knob E' and a linear scale I' marked from "1" to "6" and extending over an arc of 240 , which is divided into divisions of 48. In the initial adjustment of the instrument, VRl is adjusted in uch ~anner that when the input jack plug is ~ithdrawn, and the 5K ohm resistor ~1 is thus connected across the input, a balance is established when the range control VR2 is set to "2"
on its scale. IWhen this adjustment has been made, the balance point should be at "3" on the range control scale I' of VR2 ; With a resistance of 12, 500 ohms connected across the input.
Thus when the instrument is correctly adjusted the meter pointer G' should indicate the center of the "SET" sector of the scale when the control E~ of VR2 iS set to read "2" on its scale. In _ 7 --~' , .. ~ . .

1 order to set up the calibration it is merely necessary to se-t the control E' to "2", withdraw the plug of the jack Jl and adjust VRl by means of the control C' to bring the meter pointer to the correct deflection.
With the body of a subject connected to the electrodes, - and the range control VR2 adjusted for balance, a fall in the resistance of subject's body will cause the base current of transistor Ql to change in a negative direction. This increases the current in R5 so that the base of Q2 is also carried negative.
This, in turn, makes the emitter of Q3 more positive. The co]lector current of Q3 then increases and thereby increases the deflection of the meter pointer. l:E, on the other hand, the body resis-tance of the subject increases, the base current of Ql will change in a positive direction and there will be a consequential reduction in the deflection of the meter pointer.
When the bridye is in a balanced condition, there will be 1.5 volts applied to the base of Ql and the meter pointer G' should indicate the center of the "SET" sector of the scale.
The amplifier should be so adjusted that this becomes a virtual zero condition. That is to say, wheJ- Ih:is COIlCl:i t:ion prevails, variation o ampl.i:Eier gain should not al-ter the me-ter reading.
If however, there is unbalance voltage such that the meter indication is above or below this vir-tual zero reading, an increase i.n gain will move the pointer fur-ther above or below the zero condition as the case may be.
The gain of the ampli.fier is adjusted by means of the knob D' (FIGIJRE 2) of the sensi-tivity control VR5 which varies the negative feedback applied to transistor Q2, ~art of the emit-ter current of Q2 flowing throucJh VR5 and part through the preset variable resistor VR6. The latter is adjusted to ~ 8 --.~

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1 such a value that, when the me-ter pointer is at the center of the "SET" sector of the scale, the voltage drop across is just equal to the battery voltage; thus, for this reading and for this reading only, no current flows in VR5 and its setting does not affect the indication of the meter.
Because the instrument is primarLLy intended for the detection of changes in the body resistance of a human subject, precau-tions must be taken to minimize changes in the meter de-flection due to other causes. Changes due to unstable or noisy transistors are overcome by careful selection of transistors, but a change in gain with change in temperature, which is one of the fundamental characteristics of all transistors, can give rise to a steady drift which may be misleading. To correct for this type of instability, the transistor Q3 is introduced, tapped inside of BI, and across transistor Q2. The emitter of transistor Q3 is connected to the collector of -transistor Q2;
therefore a voltage drift on the collector oE transistor Q2 will produce a cornpensatin~ voltage change on the emitter of transistor Q3. Thus, transistor Ql is an emitter follower whose output is delivered to the base of transistor Q2 through resistor R6. The emitter of Q2 receives bias voLtage at the junction of resistors VR6 and VR5, adjusted by means of VR5. The base of transistor Q3 receives bias voltage at the junction of resistors R10 and Rll. The ou-tpu-t curren-t of the amplifier flows from the collector of Q3 through the indicating meter Ml with compensation for voltage drift provided by the interconnection of the collector of Q2 and the emitter of Q3, as above described.
In FIGURE 1, the first s-tage of the amplifier is an emitter follower and the second and third stages are cascaded in a manner to provide drift compensation, as above described.

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1 When the switch Sl, operated by the knob B' is turned to "TEST" (position 3) to disconnect the meter from the amplifier, it operates to place resistor Rl9 and Ml across the batteries. With the switch Sl in this position, a deflection of the meter scale to the "TEST" sector is obtained only when the batteries are delivering their correct voltage.
Switching Sl to position 3 also connects a half wave rectifier, charging unit, powered at J2 by 115 volts A.C. The rect~fier consists of Diodes Dl and D2 that allow only one direction of the A.C. current to pass. A slow blow fuse Fl is to protect the device in case of high voltage surges. Resistor R17 of 27 ohms protects the batteries from high voltage surges.
A capacitor of .68 microfarads Cl determines the speed of charging. R18 of 470K ohms drains Cl of charge when the unit is not charging. This is an improvement as nickel cadmium batteries can now be recharged when in the device, where in the original device the batteries had to often be replaced.
Also in the new device much of the static has been eliminated by using wire wound potentiometers and metal strip resistors instead of carbon, which had a tendency to get "dusty"

with its own carbon and cause internal surges not related to the living body being measured.
The meter movement used in the device for measuring and indicating changes in resistance of a living body is 1450 ohm wire coil wound on an electrically circular metal frame. The improvement is based on the inductance of the electrically circular metal frame absorbing a significant amount of any sudden change of current in the coil. In a prior art meter, the absorbed energy is lost in setting up a current in the metal frame, as the frame is an inductor of negligable resistance.

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1 Thus there is significantly less energy available to deflect the needle.
In the new movement a small section is cut out of the frame to prevent the energy of the pulse from becoming lost in the form of current in the frame as there is now infinite resistance. This makes for maximum utilization of the energy in instantaneously deflecting -the needle. Thus the needle response quicker and more fully to sudden changes of current.
~ eferring to FIGURE 3, the device comprises a metal frame A, shaped to hold a wire wound coil, with a slit at point B, to reduce the conductivity of the frame to zero, thus pre-venting energy loss in the form of current inducted magnetically into the frame.
Referring to FIGU~E ~, a 1450 ohm, wire wound, coil C, one end of which is electrically connected to wire D, which is used both as one of the electrical connections for coil C, and one of the pivots for frame A and needle G. The other end of coil C is electrically connected to wire E which is used for both the electrical connection for coil C and the other pivot for frame A and needle G.
Needle G is physically connected to frame A, and is the indicator of the device for measuring and indicating changes in resistance o~ a living body. Counter weight ~l is used to balance needle G at the point needle G is connected to frame A. An iron cylinder F is provided within and is pivotally coupled to the frame A and therefore remains motionless. The iron cylinder F further serves to concentrate the magnetism on which the device opera-tes.
A s-tationary housing is used (but not shown) to connect the movemen-t electrically, magnetically, and physically to the ~L3~3;;~

device for measuring and indicating changes in resistance of a living body.
It should he apparent that with the above desc-ibed construction, a meter is provided which is extremely sensitive to changes in input signal, tracks the input signal accurately and is not critically damped. As a result, the sensitivity and accuracy of the device for indicating changes in resistance of a living body is significant]y improved, a result not attainable with the prior art meter construction.
Also a wire wound coil has been used with no frame at all, but making the coil stiff with varnish (a non-conductor).
The end product is very simiJar, i.e., a coil without the e~tra inductance and therefore currerlt flow, in the frame, and it has demonstrated similar results.
TABLE:
Input Original Device With split frame .01 to .001 second, not visible or Very visible high energy pulse barely visible //
.2 to .01 second, Visible after a .2 -to V;sib]e after a .02 high energy pulse .5 second lag. Amoullt .05 second lag.~m~unt of deflection noticeably of deflection not reduced by inductance measurable reduced by absorption of pulse absorption of pulse //
.02 to .0] second, Invisible, or Clearly visible low energy pulse nearly so.
//
Sudden change to new Moves sluggishly after Moves sharptly to current flow level .2 to .5 second lag to level after only .02 new level. to .05 second lag.

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1 It will be understood that the component values indicated above are given purely by way of example, and may be modified as required, according to the nature of the transistors and the particular form of circuit described, as previously indicated, the device hereinbefore described is intended more particularly for use in indicating changes in the body resistance of a human subject, but here again, the circuit and the com-ponents thereof may be modified according to the particular use of the device.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A device for indicating changes in resistance of a living body comprising a bridge network having on one side thereof a first resistance arm connected in series with a second resistance arm, and on the other side thereof a first voltage arm connected in series with a second voltage arm, there being connected in series between the junction of a first and second resistance arms and the first and second voltage arms a transistorized amplifier circuit and current indicating means showing the changes in balance of said bridge network, two electrodes means adapted to be connected to a living body, one of said electrode means being electrically connected to a terminal of one of said resistance arms, whereby said living body can be connected across said one of the resistance arms, a range control device comprising a potentiometer connected in parallel with said first voltage arm, said potentionmeter having a sliding contact electrically connected to a terminal of said first voltage arm, another of said electrodes being electrically connected to said sliding con-tact, a variable resistance electrically connected the other said electrode means and the junction of the first and second resistance arms, said variable resistance being adjustable to enable a balance to be established in an initial setting of the bridge network, said amplifier circuit comprising a transistor emitter follower and cascaded second and third transistors connected to the output of said emitter follower, the collector of said second transistor being connected to the emitter of said transistor of said emitter follower and the indicating means comprising an

Claim 1 continued uncritically damped moving coil meter electrically connected between a collector of the third transistor and the first voltage arm, said uncritically damped moving coil meter con-sisting of an iron cylinder pivotally supporting a metal frame with zero conductivity having a meter coil wound thereon and an indicator needle fixed to said frame, a sensitivity control branch connected across the second voltage arm and comprising two series-connected resistors, at least one of which is varia-ble, the junction of said series-connected being connected to the emitter of said second transistor, said electrode means being connected directly to the base of the transistor emitter follower, and a resistive negative feedback branch connecting the output of the amplifier circuit to the base of the transistor emitter follower.
2. A device as claimed in claim 1, wherein said metal frame having zero conductivity comprises a split metal coil frame.
3. A device as claimed in claim 1, wherein said resistive negative feedback branch comprises a plurality of selectable resistors of different values.
4. A device as claimed in claim 2 wherein said resistive negative feedback branch comprises a plurality of selectable resistors of different values.
5. A device as claimed in claim 3, further comprising a resistive compensating branch provided between said base of said transistor emitter follower and a negative source of electrical power.
6. A device as claimed in claim 4, further comprising a resistive compensating branch provided between said base of said transistor emitter follower and a negative source of electrical power.
7. A device as claimed in claims 5 or 6 wherein said resistive compensating branch comprises a plurality of selectable resistors which are concurrently selectable with said plurality of resistors of said feedback resistive branch whereby changes in potential at said base of said transistor emitter follower caused by selectively changing said resistors of said resistive negative feedback branch are compensated for.