CA1143438A - Device for measuring and indicating changes in resistance of a living body - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

This invention relates to a moving coil meter for use in a device for measuring and indicating changes in resistance of a living body. It comprises a split metal frame, a meter coil wound on the split metal frame, or stationary iron cylinder pivotally coupled to opposing sides of the frame and an indicating needle coupled to the frame. This device is a highly sensitive device and the needle accurately follows the variations in the input signal to the meter. The meter is not critically damped and includes a frame with zero conductivity, which represents a substantial improvement over the prior art.

Description

3~3 1 This is a divisional application of Canadian patent application serial number 335,278 filed on September 7, 1979.
This invention relates to the responsiveness of devices for indica~ing 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 specifi-cally to be used for measuring these small changes.
Mr. Hubbard's invention while being designed to indicate small changes in resistance of a livin~ 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 increasin~ the torque to moment ratio of the movement by decreasing the mass of the needle and by decreasing -the mechanical resistance o~ the movement suspension~ Such improved meters while being better still do not sufficiently and accuratel~
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 decrease in mass of the needle results in a very fine needle which is difficult to see~ I
~ccordingly, it is a general object o~ the present i.nvention 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 provide a meter for a device for measuring changes in electrical - ~ 1 -~ . . .

1 resistance o~ a living body with substantially improved tracking.
It i~ yet another object of the present invention to provide a meter for a device ~or measuring changes in electri-cal resis-tance o~ a living body in which the needle accurately fQllows the variations in the inpu-t signal to the meter.
It is still another object of the present invention to pr~vide a meter for a device for measuring changes in electrical resistance o~ ~ livin~ body which is not critically damped.
It is still another object of the present invention to provide an uncr~tically damped meter for a device for measuring chan~es in electrical resistance of a living bod~ which includes a frame for the meter movement with zero conductivity.
TQ this end, in one of its aspects, the invention provides a movin~ coil meter for use in a device for measuring a,nd i,ndicatin~ changes ~n resistance.o~ a living body comprising a ~plit meta,l frame, a meter coil wound on said split metal frame! a stationary iron cylinder pivotàlly coupled to opposing sides of said Erame, and an indicatin~ needle coupled to said fra~e.
The inventiVe impxovements~ that are the subiect o~
thi.s patent have. great}y enhanced the sensitiVity of the indi-ca.tin~ means of the device for measuring the resistance o~ a liYin~ body, thexeby making a more effective device overall, and this has directl~ a~ected the state of the art by creating more . sensitive and re.sponsive meteriny than has ever been accomplished prev.iousl~.
In accoxdance with the .invention there is provided an electrical resistance measuring or indicating device com-prising a ~ridge network having on one side thereo~' a first 3~ resistance connected to a second resistance arm and on the : - 2 -3~3 1 other side thereof, a first voltage a~n connected to a second voltage arm, there being between the junction of the first and second resis-tance arms and the junction of the firs 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 10 potentiometer means is associated with one of the voltage arms ~or 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 o~ 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 subiect ; thereto, balance can be xestored by the adjustment of the first potentiometer means so that the indicating means will res~

pond to very small changes in resistance of said subject. The indication of the changes of resistance must be immedia~ely responsive. A special movement using a frame with no conducti-vity i9 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 accompanying drawings, wherein, Eiyure 1 is a schematic diagram illustrating the circuit of the device.

Figure 2 is a front view of the device.

Figure 3 is a perspective view of the frame coil.

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1 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 thr~e transistors QI, Q2 and Q3 which derive their operating power from the battery BI, the transistors each consisting in the presen-t 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 1~ 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 ~eep the input resistance of the amplifier high relatively to the resistance of the briclge in order to prevent loading, since loading is particularly important when the bridge is operated in an unbalanced condition.

For the connection o:E the subject electrodes to the.
instrument, there is provided a telephone jack JI having spring ~ontacts adapted to be connected. Upon insertion of an appropriately wired plug (not shown) to the electrodes, contact

2 is connected to the slider of the range control potentiometer VR 2 and i.s also operatively assoc.iated 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 presen-t 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 .

~ ~3~;38 at one end to the neyative side of the bat-tery BI through switch SI~ and at the other end to the Tap of battery BI through a 5K 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 selected 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 throuyh a 470 ohm resistor R6 to the base of the second stage transistor Q2, the latter being arranged as a conventional common-emitter stage which provides most of the- current gain. The emitter of Q2 is connected through 5K ohms preset variable resistor VR6 to the positive side of battery BI
and this emitter is also connected throuyh a sensitivi.ty control VR5 comprising a IOK ohm reverse-log variable resistor, and through the switch SID to the Tap of battery BI. The collector of Q2 is connected directly to the emitter of Q3, and is also ~onnected 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
being 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 SQ that by operation o~ that switch.the collector can be ~onnected to the positive.side of the meter. The meter is shunted by a S.6K ohm resi~tor RI6~ and a 5K variable resistor VR7, in series, and the neya-tive side thereof is connected throuyh 22K ohm resistor RI and switches SIB and SIA to the neyative side of the battery BI.
The switch SIC and SIA and SIB, when SI is in the 3rd position, respectivel, connect tbe positive side of the meter to

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1 the positive side of BI, and connects the negative side of the meter to the negative side of BI via a 90~ ohm resistor RI9.
~ith SI in the 3rd position the meter is shunted by a 5K ohms variable resistor VR80 The transistor Q3 of the output staEe is connected in the common-base configuration and constitutes an impedance matching device feeding the indicating metex.
The resistors RI2, RI3 and RI4 are negative feedback resistors which determine the overall gain. Their value depends upon the position of S2A.
Switch S2 is a double pole treble throw. In position one-, a 470K ohm resistor R12 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 of QI, caused by the changing resistances at 52A, a variable opposite potential is applied to the base of QI using switch-S2B. In position 2, a mega ohm resistor RI3 is connected. In position 3, two one mega ohm resistors RI3 and RI~ 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 i5 connected between the base o~ QI and the negative side of BI. In position 2 a 200K ohm resis-tor R4 and a 17.5~ 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 connec-ted between the base o~ QI and the negative side Of BI.

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1 This is a new improvement as it allows for a boos-ting of the sensitivity not available in the previous device.
Switch ~IA, B, C, D, E, E~ is a S pole treble throw switch operated ~y 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 havin~ 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 ull-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 ampliEier detector, to permit compensation ~or variations i,n component values. The resistance value of the optimum female sub~ect is 5K ohms and the instrument is there~ore standardized at this ~alue. For the setting of VRl there is provided a contxol C' ~FIGURE 2) marked l'TRIM".
The range control potentiometer VR2 has a control knob E' a,nd ~ linear scale I' marked fr~m "1" to "6" and extending over an arc of 240, which is divided into divisions of 48o In the ~nitial a,djustment of the instrument, VRl is adjusted in such ~anner that when the input jack plug is ~ithdrawn, and the 5K ohm xeslstor Rl is thus connected across the input, a balance is established when the range control VR2 is set to "2"
on its scale.l When this adjustment has been made, the balance point should ~e a~ "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" sec-tor of the scale when the control El of VR2 is set to read "2" on its scale. In .

1 order to se-t up the calibration it is merely necessary to set the control E' to "2", withdraw the plug of the jack Jl and adjus-t VRl by means of the control Cl to bring the meter pointer to the correct deflection D
With the bod~ 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 collector current of Q3 then increases and thereby increases the deflection of the meter pointer. If, on the other hand, the body re.sistance 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 bridge is in a balanced condition, there will be 1.5 volts applied to the base of Ql ànd the meter pointer G' should indicate the center of the "SET" sector o~ the scale.
The amplifier should be so adjusted that this becomes a virtual zero condition. That is to say, when this condition prevails, variation o~ amplifier gain should not alter the meter reading.
If however, there is unbalance voltage such that the meter indication is above or below this virtual zero reading, an increase in gain will move the pointer further above or below the zero condition as the case may be~
The gain of the amplifier is adjusted by means of the knob D' (FIGURE 2) oE t~e sensi-tivity control VR5 which varies the negative feedback applied to transistor Q2, part of the emitter current of Q2 flowing through VR5 and part through the preset variable resistor VR6. The latter is adjusted to ~;343~3 1 such a value that, when the meter 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 set~ing does not affect the indication of the meter.
Because the instrument is primarly intended for the detection of changes in the body resiskance of a human subject, precautions must be taken to minimize changes in the meter de-flection due to other causes. Changes due to unstable or noisy 1~ 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 t.ransistor Q2. The emitter of transistor Q3 is connected to the collector of transistor Q2;
therefore a voltage driEt on the collector of transistor Q2 -will produce a compensating voltage change on the emitter of transistor Q3~: Thus, transistor Ql is an emitter follower whose output is deli~ered 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 output current of the amplifier flows from the coll~ctor of Q3 throug~ the indicating meter M1 with compensation for voltage drift provided by the interconnection of the collector of Q2 and the emitter of Q3~ as above describe~.
In FIGURE 1, the first stage 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 ~hen 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 b~tteries. ~ith the switch Sl in this position, a deflec-tion of the meter scale to the "TEST" sector is obtained only when the batteries are delivering their correct voltage.
Switching S1 to posi-tion 3 also connects a half wave rectifier! charging unit, powered at ~2 by 115 volts A.C. The rect~fier con~ists 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 ~oltage surges.
capacitor of .68 microfarads Cl determines the speed of charging. R18 of 470K ohms drains Cl of chargè when the unit is not char~ing. This is an improvement as nickel cadmium batteries can now be recharged when in the device, where in the ~riginal device the ~atteries had to often be replaced.
Also in the ne~ device much of the static has been eliminated by using wire wound potentiometers and metal strip xesi~tors instead o~ carbon, which had a tendency to get "dusty"
with its own carbon and cause internal surges not related to the livin~ body being measured.
The meter movement used in the device for measuring and indicating c~anges in resistance o~ a living body is 1450 ohm wire coil wound on an electrically circular metal frame. The impr~vement ls based on the inductance of the electrically cixcular metal frame a~sorbing ~ significant amount oF any sudden change of current in the coil. In a prior art metert the absorbed energy ~s 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 currentD
Referring 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-~enting energy loss in the form of current inducted magnetically into the frame.
Re~erring to FIGURE 4, 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 th~ electrical connection for coil C and the other pivot for ~rame A and needle G.
Needle G is physically connected to frame A, and is the indicator o~ the device for measuring and indicating changes in resistance o~ a living body. Counter weight H is used to balance needle G at the point needle G is connected to frame A. An iron jcy~inder F is provlded 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 operates.
A stationary housing is used ~but not shown) to connect the movement electrically, magnetically, and physically to the .

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I device for measuring and indicating changes in resistance of a living body.
It should be apparent that with -the above described constructionl 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 significan-tly 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 prod~lct is very similar, i.e., a coil without the extra inductance and therefore current flow, in the frame, and it has demonstrated similar results.
I'ABLE:
Input Original ~evice With split frame .01 to .001 second, not visible or Very visible high energy pulse barely visible //
~O .2 to .01 second, Visible after a .2 to Visible after a .02 high energy pulse .5 second la~. Amount .05 second la~.~mount of de~lection noticeably of deflection not reduced by inductance measurable reduced by absorption of pulse absorption of pulse //
.02 to .01 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 bs modified as required, according to the nature of the transistors and the particular form of circuit described, as previously indicated, the device hereinbeEore 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~

Claims

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

1. A moving coil meter for use in a device for measuring and indicating changes in resistance of a living body comprising:
a split metal frame;
a meter coil wound on said split metal frame;
a stationary iron cylinder pivotally coupled to opposing sides of said frame; and an indicating needle coupled to said frame.