EEG calibration are some steps which was followed by technologists in conventional EEG times. they are the steps to check the machines integrity either its properly working or not before the procedure began.it is very important to calibrate machine before the initiation of the test to interpret false results.

1. PRESENTATION ON :
CALIBRATION AND ITS SEQUENTIAL
STEPS
PRESENTER :FAIZAN ABDULLAH
DESIGNATION :TRAINEE TECHNOLOGISTS NEUROPHYSIOLOGY
INSTITUTE:THE AGHA KHAN UNIVERSITY HOSPITAL
DATE: 20/08/20

2. Content
1.Introduction to calibration
2.Biocalibration
3. Sufficient ink
4. Sufficient paper
5. Paper speed
6. Pen alignment
7. Pen centering
8. Damping
9. Time constant or LFF
10. High frequency filter (HFF)
11. Sensitivity
12. Step gain
13. Amplitude linearity
14. Noise level

3. INTRODUCTION TO CALIBRATION
• Calibration are the steps of checks to make
sure the machine is properly working or not.
What are consequences is calibration not done
properly ?
• You can harm the patient
• You can make misinterpretation or false
diagnosis
we make a normal EEG abnormal.

5. BIOCALIBRATION
• Bio calibration assesses the response of the
amplifiers, filters and the recording
biological signal.
• Electrode FP1 and O2 are connected to all
amplifier inputs you can make montage of
FP2 and O1. The recordings for all channels
should be identical.
• It is a montage because a fixed pattern is set
in which throughout activity of 18 channels
is obtained.

8. THERE ARE 12 STEPS TO CHECK
DURING CALIBARTION
1. Sufficient ink
2. Sufficient paper
3. Paper speed
4. Pen alignment
5. Pen centering
6. Damping
7. Time constant or LFF
8. High frequency filter (HFF)
9. Sensitivity
10. Step gain
11. Amplitude linearity
12. Noise level

9. Sufficient ink
• Sufficient ink should be present in the tube of
writer/ printer cartridge should not be empty.
What are the if the ink is not properly checked
Consequences?
1.any paroxysmal event
2.a brief Interictal abnormality
3.onset of a seizure.
4. Loss of paper

10. Sufficient paper
• Ensure that as per plan of the recording their is
more than enough paper/Disc space.
• Before taking printout sufficient paper is
present in the printer.
What if you don’t check the quantity
of paper that you have?
1. You can miss any paroxysmal event
2. You can miss a brief Interictal abnormality
3. You can miss onset of a seizure.

11. Paper speed
• It is the speed at which the paper roles off through the
pen writer.
• Standard paper speed is 3cm/sec or
30millimeter/second
• Standard paper size is 30 cm/fold
1. Slow Paper Speed:
•  Used with time constant to make the slowing
prominent.
•  Like 15mm/sec.
1. Fast paper Speed:
•  It is used to check the onset of an event.
•  60mm/sec

12. How to check paper speed
• Paper speed could be checked in two
ways:
1. 1.Manually by;
by measuring the distance simultaneously
running the paper and monitoring the
time lapsed.
Distance/time lapsed= paper speed.
2.Automatically by;
• By using the time marker of the machine.

13. Distance=27cm, Time =30seconds P.S=27cm/30sec= 0.9cm/sec or 9mm/sec

14. Pen alignment
• All pens should start and stop
simultaneously in a perpendicular line.
•  Could be checked by drawing a
straight line perpendicular to the paper
drive by using set squares
•  If not aligned then:
1. Will cause distortion of focal activity
2. Misinterpretation of EEG

15. Misalignment of Pens

16. What if pens are not properly aligned?
•  Causes of misalignment:
1. More/ less Bent of stylus nib
2. Worn out stylus nib (Nib can be bent
inward or outward).
•  Corrections of Pen alignment:
•Simply change the stylus, all pens should
be change simultaneously.

17. Pen centering
• All pens should be in the center ( at Zero line)
of the pen writer/galvano meter.

18. Out Pen centering in conventional EEG

19. Mechanical out pen centering

20. • Types of problems:
1. Mechanical pen centering
• Apparently pens are not in the center of the
galvano meter.
2. Electrical pen centering
• While giving the electrical signal to the pens and
simultaneously on and off the switch of galvano
meter. Ideally there should no deflection.

21. • Mechanical pen centering problem means that
the pen are not staying at zero line apparently
when the machine is switched on.
• Electrical pen centering problem means that the
pens are deviating from base (zero) line when
amplifier switched on or off without any
calibration signal while the machine is switched
on.
• Effect on EEG recording:
1. Decrease in the high amplitude activities.
2. Pseudo asymmetry of amplitudes

22. • Electrical out pen centering

23. • 1. Correct the mechanical pen centering by
Allen Wrench-key, pull out the pen from its
base form the galvanometer and fix it on the
zero line.
• 2. Correct the electrical pen centering by
switch on and off the amplifier and adjusting the
potentiometer. There should be no deflection off
the zero line.
• 3. Again adjusting the mechanical
pen centering

24. Galvanometer

25. Allen wrench

26. Damping
It is the pressure of the pens on the paper
• This could be
• Mechanical pressure on pens called
mechanical damping
• Electrical damping undesirable resistance
in the GVM circuit called electrical
damping.
• Standard damping is 2.5 gram.

27. Over Damping
Under Damping

28. Types of dumping
1. Over Damping (under shoot) Excessive pressure
on pens will result in over damping or Under
shoot.
• Decrease in voltages measurement b/c of
rounding of peak.
2. Under Damping (over shoot)
• low pressure on pens will result under
damping or over shoot.
• Increase in voltage measurement b/c of
• overshoot at peak.

29. What if we don’t properly check
damping?
• Undershoot result in rounding of peak
of waveform
• pseudo amplitude reduction.
• Overshoot will result in pseudo voltage
increase.
• Pens can collide with each other and can
break.
• Both will result in waveform distortion.

31. Time constant or LFF• It is the low frequency filter/High pass filter
• One of the most important component of the circuit which can make EEG
normal and abnormal.
• Defined as the time contant is the time required for the pen to fall 63%
from the peak of the deflection produced.
• T.C effects the decaying signal of the Calibration signal.
• It is measured in second but can be converted into frequency
• Formula for conversionis:
f = 1/ 2 T.C
>2x3.14=6.28
>1/6.28=0.1592
>0.1592x0.1=0.01592
>0.01592x100=1.592 f=1.592

34. • Record a known calibration signal
• Ideally at standard parameters setting of:
Sen =7 V/ mm
Input voltage =50 V
Paper speed = 30 mm / sec
TC=0.1sec
Hff=70HZ
Lff =1.6HZ

35. Effects on EEG
• Effects on EEG /usage
• It attenuates the lowfrequencies.
It can cut down slow frequencies of need

36. High frequency filter (HFF)
• Also called Low pass filter.
• It mainly effects the rise time in
calibration signal.
• In EEG we are interested in the high frequency
of 70 Hz.
• It allows low frequencies to pass and
stop higher frequencies.

39. • Effects of the HFF on EEG:
. It drops the amplitude by 30% .
. Causes rounding of peak which may the
morphology of the waveforms.
. Amplitude reduction which may lead to
asymmetry

41. Sensitivity
• This is the magnitude of input voltage requires
to produce a standard pen deflection i.e.
(known input voltage to produce known pen
deflection).
• All channels should have the same sensitivity
as standard.
• It is the ratio of;
S=V/H

43. • Effects on theEEG:
1. Misinterpretation of amplitudes.
2. Wrong sensitivity setting in individual
channels will lead to pseudo asymmetry

44. Amplitudes linearity
• A recording channel is said to be linear if
the pen deflection is proportional to the
amplitude of the input signal applied.
• If input voltage is doubled the pen
deflection should be doubled in all
channels.

45. How it can be checked
Keeping sensitivity constant e.g 7uV/mm
By inducing calibrator signals of 20,50 & 100uV.
Measuring the calibration signal.
P.D=7uv/mm/50uv
=7.1mm
H=v/s

46. Step gain
• This is the ratio of signal voltage
obtained at the output of amplifier to
signal voltage applied at the input.
• it increases with increasing amplification.
• Gain is not as important than sensitivity
because gain is not measured. It is
prebuilt in the system.
GAIN=OUTPUT/INPUT

47. Noise level
• All electrical circuit has small vibration
in the components of the circuit if
current pass through them because of
electron movements
• This give a small output even if there
is no external signal
• This is called noise level of the measuring
unit.

48. References
• Basic principles of digital and analog EEG,Fisch
and Spehlmann’s EEG Primer
• Cnp peer lecture