Forensic 5

Module 6

Polygraph Instrument

Modern polygraph services uses computerized polygraph instrument. For instance, a

Lafayette computerized polygraph instrument is common both in a desktop model for
polygraph examinations administered in the office and in a laptop model for travel as
pictured below.

Figure 1
Lafayette Computerized Polygraph

Figure 2 - (Monolog Models)

The Ambassador (Lafayette) Polygraph
And the Stoelting Polygraph

How Does the Polygraph Instrument work?

The polygraph simultaneously records various physiological phenomena by

means a horizontal Kymograph. The resulting polygram indicates tracing of external
respiration in the thoracic and abdominal cavities by means of a pneumograph
tambour assembly, systolic and diastolic contraction of the heart, as well as pulse
fluctuations with the resistance of a sphygmomanometer and psycho-galvanic skin
response by means of the electrodes to the person’s fingers. Each phenomenon is
recorded by a hallow-tube ink styles moving across horizontally and vertically ruled
being driven by a synchronous electronic motor.

Figure 3
 Attachment of the Computerized
Polygraph Instrument

The physiological changes within the examinee’s body are monitored by the
following polygraph attachments:

Respiratory Rite: Two rubber tubes filled with air, called pneumographs, are
placed around the examinee’s chest and abdomen. When the chest or
abdominal muscles expand, the air inside the tubes is displaced. The digital or
computerized polygraph employs transducers to convert the energy of the
displaced air into electronic signals.
Blood Pressure/Heart Rate: A blood pressure cuff is placed around the
examinee’s upper arm. Tubing runs from the cuff to the polygraph. Again, in
digital or computerized polygraphs, these signals are converted into electrical
signals by transducers.
Galvanic Skin Resistance: This is also called electro-dermal activity and is
basically a measure of sweat on the subject’s fingertips. The fingertips are one of
the most porous areas on the body and therefore are a good place to look for
sweat. The theory is we sweat more when we are placed under stress. Finger
electrodes, are attached to two of the examinee’s fingers. These electrodes
measure the skin’s ability to conduct electricity. When the skin is hydrated (as
with sweat), it conducts electricity much more easily that when it is dry.

Figure 4
Proper attachment of the polygraph sensors or transducers
To the body of the subject
What are the Major Components of the Polygraph Instrument?

The Pneumograph Component - This component occupies the two/upper pens

of the instrument which records the thoracic and abdominal breathing patterns of
respiration. This is accomplished through the use of a pneumograph consisting of
two hollow corrugated tubes about seven inches in length, each attached to a unit by
a rubber hose not longer than six feet and not larger than one quarter inch in
diameter. This breathing or pneumo unit is a low pressure unit. The
inhalation/exhalation of the subject causes the tubes to expand and contract, thereby
reflecting the change through billows to the pen into the chart.

Figure 5
Pneumograph Component

The device records respiration and one of the three traditional channels of the
modern polygraph used in PDD. Most contemporary polygraphs use two
Pneumograph recordings: abdominal and thoracic, the sensors are the traditional
convoluted rubber tube, the mercury strain gauge, or the newer piezoelectric.
Kraphol and Sturm Polygraph, 2002, 31(3) 205

This component records changes occurring in the respiratory or breathing system

1. The Pneumographic Tube - is a corrugated and stretchable rubberized tune

or apparatus that is to be attached to the Subject’s chest or stomach (or both)
inhalation will cause the tube to stretch and subsequently create an upward
tracing or movement of the pneumo-pen unto the polygraph chart. Exhalations
are the downward tracings, thereof.
2. The Beaded Chain - is a freewheeling string of stainless beads with a hook
which fastens the pneumographic tube unto the subject’s chest or stomach
The Cardiograph Component

The cardiographic component records the changes occurring in the human

circulatory system such as the blood pressure and pulse rates.

Cardiograph - general term for any recording of heart activity. In PDD the
use of a blood pressure cuff to monitor relative arterial blood pressure
changes and pulse wave is more precisely described as sphygmography
(recording of the arterial pulse) or occlusion plethysmography (partial
blockage of circulation to measure volume changes in a body part) while
cardiograph is not incorrect in this context, it lacks precision in denoting the
actual phenomenon being recorded in PDD. The term cardiograph in the
psychophysiological and medical literature most often refers to the
electrocardiograph. Terminology reference polygraph, 2002, 31(3)166
 Arm Cuff - shall be attached to the subjects arm
The Hand Pump Bulb - causes the arm cuff to inflate in order to produce
blood pressure and pulse rates
The Aneroid Blood Pressure Meter Gauge - measures and monitors B/P
reading while the polygraphic testing is going on

The attachment of the cuff to the subject’s arm must be centered so we

can have a normal recorded pattern of the blood. As to produce clearer
and precise pressure

Cardiographic Tracings

The Cardiograph Component - This is the fourth and the bottom pen of the
instrument. This cardio unit is a mechanically operated unit. It is a high pressure
system. This system records changes in mean blood pressure, rate and strength of
pulse beat by means of a medical blood pressure cuff containing a rubber bladder
that is wrapped around the upper arm, in a manner that places the bladder against
the brachial artery. The bladder is connected to the rubber hose, past a pressure
indicating gauge to a very sensitive billows and its connected lever system that
powers the pen.

The polygraphist inflates the bladder with a hand pump to a constant air
pressure that will provide tracing amplitude of 0.75 to 1 inch with a dichotic notch
situated about the middle of the diastolic limb of the tracing.

Cardiograph Component

The Galvanograph Component

Galvanograph Component

The Galvanograph Component - This is the longest and the third pen of the
instrument. The electrodes are attached to the index finger and the ring finger of the
left hand, or to the palmar and dorsal surfaces of the left hand. The electrodes used
for obtaining the recording of the GSR or electro-dermal responses, are fastened to
the hand or finger by means of the passage of an imperceptible amount of electrical
current through the hand or finger bearing the attached electrodes, a galvanometer
unit provides recording of the variation in the flow of the electrical current.
The galvanographic component, sometimes called the galvanic-skin-reflex (GSR)
component, records the changes occurring in the nervous-excretory systems. It has
been studied that brain’s activities and electrical charges have been recorded thru
the epidermal skin reflexes passed through different nerves of the human body

Finger electrodes - are special types of sensitive metal plates to be

attached to the subject’s end-joints of both the index and ring fingers for the
recording of the electrical charges (ohms) from the brain to the skin

Figure 11

Figure 12

Figure 11 and figure 12 shows the proper attachment procedure using

both the index and ring fingers for the recording of the galvanic skin reflex
responses

Kymograph Component
 The Kymograph Component - This is the chart-drive recording unit of the
instrument. It has a synchronized motor that drives the charts at the rate of six (6) to
twelve (12) inches per minute and its speed constant is vital because the vertical
lines, which are spaced either at one-half of an inch interval, represents five or ten
seconds interval on the chart. This provides the polygraphist with a means of
determining pulse rate and the questioning space.

What are the detachable parts of the Polygraph?

Finger Electrodes and Blood Pressure Cuff

Pneumo Tube 1 and Pneumo Tube 2

What are the Built-in Accessories of the Polygraph Instrument?

1. KYMOGRAPH or chart driving mechanism

- Chart roll arbor, Idler roller, Pen table Paper guides, Sprocket roller,
Cutter bar, Off and on power switch, Synchronous motor

2. Pen and Inking System

- Capillary pen, Ink well plates, Ink dropper, Cuct bill

3. Pneumograph section
- Rubber jellows, Beaded chain, Rubber flexible tubing, Pneumograph
connecting tube, Pneumograph tube connection, Pneumograph
distributing ink, Pneumograph pipe line, Vent value and vent bottom,
Tambour assembly, Sphygmomanometer, Resonance control
4. Cardio section
- Pump bulb assembly, Blood pressure pump connection, Blood pressure
cuff assembly, Connector block, Sphygmomanometer pipe line

5. Galvanograph section
- Finger electrode, Electrode jellow, Galvanometer

PARTS AND FUNCTIONS OF THE INSTRUMENTS

1. Pen lifter – raises or lowers pen to three positions
2. Chart Drive Module – propels chart paper at the rate of 6-12 inches per
minute. Also known as Kymograph.
3. Paper tear bar – provides cutting edges for removal of charts
4. Mechanical Pneumo Module – recording part of Mechanical Pneumo Channel
5. Galvanic Skin Reflex Module – recording of GSR Channel
6. Mechanical Cardio Module – recording part of Mechanical Cardio Channel
7. Chart Drive Roller Lever – lifts chart drive roller for paper changes and chart
removal.
8. Sphygmomanometer Dial – reads operating pressure of Cardio Channel
9. Pneumo 1 – pneumatic connection for upper (thoracic) pneumograph
10. Pneumo 2 – Pneumatic connection for lower (abdominal) pneumography
11. Cuff – connection for Cardio Channel subject cuff tubing
12. Pump – Connection for hand pump used to inflate subject cuff
13. Centering control – positions pen on chart. Rotating clockwise raises the pen,
while counterclockwise rotation lowers it. Operates similarly on all channels.
14. Sensitivity control. Determines the tracing size (amplitude). Rotating clockwise
increases size while counterclockwise rotation decreases size.
15. GSR mode switch – selects the operating mode for GSR Channel Manual or
Automatic
16. GSR input connector – accepts plug from GSR subject attachment cord
17. Cardio Lock lever – immobilizes mechanical cardio mechanism when not in
use.
18. Vent – performs venting function on pneumatic systems.

CONTROL MECHANISMS
1. Resonance Control – it allows you to clear up or make a better pattern when
you have too much pulse pressure of the subject
2. Hand Electrode – this is fastened to the hand by a stretched band. Function is
to make electrical contact with the subject
3. Panel control – to allow the operator to control or adjust the operation of the
galvanograph

FIVE IMPORTANT CONTROLS

1. Off and on power switch – on switch energizes the galvanograph section
2. Subject’s resistance control – balances the galvo section to the skin
resistance of the subject
3. Reactivity control – adjusts sensitivity of the galvo section
4. Self-centered normal switch – selects either mode of operation
5. Self-centering mode – the circuit electronically centers the pen itself after
every excursion
CONTROL OF CARDIO-SPHYGMOGRAPH section
1. Manual centering knob – used to place cardio in its proper place on the chart
2. Vent valve – is used to left atmospheric pressure into the system and used to
release pressure all or parts of the pressure
3. Resonance control – is used to decrease the amplitude of the cardio tracing
and used to sharpen the diacrotic notch

CONTROL OF THE PNEUMOGRAPH section

1. Manual centering knob – used to position base line of the pneumo tracing on
the upper heavy horizontal line.
2. Vent – with the vent down, the system is closed and non-operative. With the
vent up the system is open and ready to use.

Uses of Vent:
a. To stop the pen between the tests and to prevent possible tambour
assembly
b. To prevent pen from possible jam by moving up or down in one place of
the chart
c. To stop pen during the tube adjustment
d. To assist in gaining amplitude
e. To let atmospheric enter into the system.