Electronics
Equivalent circuit model
Vm = E + IR
what happens when the sodium channels are open, what is ENa? Then what happens if K opens up?
Driving Force
Ion channels; where is the selectivity filter, where is the gate?
ion channels select between different ions, they have chemical properties to select; this is the selectivity filter
gating - opening and closing of ion channels
equilibrium conditions equal concentration; if Na, K, on both inside and outside
if channels are open, inside of pipette positive, upward deflection, inside of pipette negative downward deflection
current vs voltage relationship - currents are negative when voltage is negative, currents are positive when voltage is positive, can determine a value of G
single channel conductance; siemens = 1/ohm
reversal potential - provides information on selectivity; tells about ion channel voltage at which the sign of the current changes, will equal zero
in a real cell, potassium channels hold -70 mv, no current flow + will be outward + current, - will see inward - current; conductance!
Vm = E + IR
what happens when the sodium channels are open, what is ENa? Then what happens if K opens up?
Driving Force
Ion channels; where is the selectivity filter, where is the gate?
ion channels select between different ions, they have chemical properties to select; this is the selectivity filter
gating - opening and closing of ion channels
- voltage gated - some voltage across membrane
- neurotransmitter gated; ligand gated acetylcholine; glutamate
- stretch activated ion channel; open via mechanical force; proprioception; tell what state you're in; also hearing
- intracellular voltage w/ respect to outside, ground pull in tip of membrane
- gigaohm seal - high resistance, current can't leak out
- acting as a machine without any memory of earlier states
- approximately 6 picoamps???
- can add "things" to control environment if there is a g-protein, etcetera, fluorescent dyes, etcetera
equilibrium conditions equal concentration; if Na, K, on both inside and outside
if channels are open, inside of pipette positive, upward deflection, inside of pipette negative downward deflection
current vs voltage relationship - currents are negative when voltage is negative, currents are positive when voltage is positive, can determine a value of G
single channel conductance; siemens = 1/ohm
reversal potential - provides information on selectivity; tells about ion channel voltage at which the sign of the current changes, will equal zero
in a real cell, potassium channels hold -70 mv, no current flow + will be outward + current, - will see inward - current; conductance!
*LH*
Electron - Proton + Neutron - neutral
charge is the force of attraction or repulsion between 2 particles (q1 & q2), the unit of measure is the coulomb
charge density can cause damage or burns
the density, the duration and the surface area. the greater the surface area can have larger
if we apply electrical stimulation through a needle, the needle has smaller surface area than a surface electrodes. if we apply the same charge for the same length of time, the patient is more likely to receive a burn from the needle
attraction and repulsion; unlike charges attract, like charges repel
voltage is an electromotive force calculated by coulombs law as a measure of electric force directly proportional to the number of positively and negatively charged ions indirectly proportional to the square of the distance between the neurons and recording electrodes.
the neurons produce voltage *the further we get recording electrodes away from the voltage source (neuron) the smaller the amplitude will be x amplitude reduces with the square of the distance
the thinner the skull the higher the amplitude of the response
current is measured in amperes and measures the flow or movement of electrons. mA where voltage is the force behind
how does current flow, charged particles move from atom to atom to make current flow in electrodes electrons are the charged particles that move from atom to atom in the body ions move to create current flow
ions an on is an atom that has gained or lost one or more electrons and as a result has a negative or positive charge
remember 50m/s upper 40-50-55/lower 37ms for med/rad to reach brain
resistance is measured in ohms and measures the opposition to direct current flow
impedance is measured in ohms and measures the opposition to alternating current flow
ohms law; v=ir voltage current resistance electromotive force
multiple resisters know that parallel is a current divider and know that series is a voltage divider
resistors in parallel are a current divider that divides the current flow among each resistor voltages remain the same across the resistors
resistors in series are a voltage divider that divides the voltages between each resistor the current remains unchanged across each resistor
capacitance is the ability to store charge, a capacitor consists of 2 metal plates separated by an insulator. voltage rises exponentially across a capacitor and the time constant = the time required to charge a capacitor 63% of its maximum charge 5t required to reach maximum charge while charging current flows when charged no flow
capacitor schematic
time constant t=RC capacitors with small plates charge more quickly than a capacitor with large plates the larger the resistance the slower a capacitor will charge the time constant limits how quickly the capacitor can charge
filters we can use capacitors resistors and the time constant to filter unwanted frequencies long time constants will attenuate higher frequencies and short time constants will follow faster frequencies filter cutoff frequency is inversely proportional to the time constant
RMS is root mean squared where Vrms is the effective voltage of an alternating voltage. RMS is the value that would produce the same power loss is a continuous voltage were applied to a resistor
electricity being delivered via 120v lines this is an average of the voltage that is being delivered through electrical lines
major freqs 30hz-300 or 500hz
apply filters to remove extraneous noise; shorter the shifts to left longer the shifts to the right
excessive low frequency filter-increased low freq too much
500 hz filter w/ noise can bring down to 250 which will increase the latency
instrumentation and other technical stuff
we have very small voltages superimposed on very large voltage variation so we remove the large undulations from the waveform
the standard EP system the lo-pass high cut low freqs pass through and hi-pass = lo-cut lets the high freqs pass through
technical concepts electrodes, stimulation, differential amplification, analog to digital conversion, signal averaging, filtering, artifact rejection, repetition rate, display parameters
electrodes impedance is the opposition to alternating current flow; ohm's law Voltage = Current x Resistance
resistance is the opposition to direct current flow think battery circuit
impedance is the opposition to alternating current flow, think electricity coming from the power company
electrode impedance must be less than 5000 ohms skin and bone is generally considered to be a good insulator because it has a relatively high impedance internal body tissue is generally a good conductor as it has a relatively low impedance having a low electrode tissue impedance is essential to recording good quality signals it is also essential to have matched electrode impedances for good quality signals
electrode types are surface, needle, corkscrew, hookwire, endotracheal tube, epidural, subdural grid, cueva direct nerve, cottonwich and silver ball
surface electrodes attach to the surface of the patients skin prepping of the skin is necessary prior to electrode placement to reduce skin impedance types gold cup, EKG pad, surface disk
subdermal needle electrodes are placed in the skin and does not require prepping to reduce impedance but alcohol prep is required for sterile placement easy to place rapidly carries risk of infection minor bleeding and burns made of stainless steel or platinum alloy
subdermal needle electrodes and bipolar subdermal needle electrodes
needle impedance versus surface pad impedance needle surface area is approximately 20mm2 and pad surface area is approximately 78mm2
with adequate prep, surface scalp electrodes will have slightly lower impedance than needles in an individual with a normal scalp
corkscrew electrodes are spiral shape of needle which allows for greater surface area hence lower impedance than straight needles self securing must be screwed into and out of the skin used for transcranial electric stimulation by some neuromonitoring groups
hair grew back differently, sensitivity is possible post surgery example; woman with a hair dryer
hook wire electrodes
spinal epidural electrode - spinal cord tumor
subdural cortical grid
silverball and cotton wich
xomed endotracheal tube electrodes; blue left red right same for abr's for thyroidectomies, ACDF, vagus nerve, inter-cranial procedures, motors, different sizes could possibly elicit emg
stimulation anode positive cathode negative
current flow versus electron flow current flow by convention is flow of positive charge
electron flow is movement of negative charge opposite that of conventional current flow
stimulating electrodes optimal inter-electrode spacing approximately 3 centimeters too far apart and current spreads causing excessive stimulation artifact too close and current may not penetrate deep enough to adequately stimulate the nerve
differential amplification differential amplifiers amplify the difference between two input signals remember their name and you know what they do
the differential amplifier has a non inverting positive reference and a inverting negative active inputs, gain, voltage difference in the inputs x the gain is the output and gain =output voltage/input voltage
amplifiers amplification, unity gain, attenuation
signals at the non-inverting input do not get inverted
signals at the inverting input get inverted
summary of basic scenarios not that opposite input voltages in different inputs yield the same output
in order to know whether the output is positive or negative you must know which input it came from
cueva nerve electrode
common mode rejection the common mode signals cancellation of common mode signals
partial common mode rejection can occur, partial cancellation of similar signals this is what is happening when the impedance values are different
noise reduction with differential amplification
using electrode placement to optimize differential amplification; to maximize the response place the active and reference as far apart as possible to minimize noise place the active and reference as close as possible in practice you have to reach a reasonable compromise
common mode rejection ratio
CMRR=output of differential applied input output of same input applied in common mode; this ratio must be at least 10,000:1 in a perfectly balanced amplifier this denominator would be zero
common mode rejection ration CMRR indicates how well an amplifier reflects common mode signals guidelines require the CMRR must be at least 10,000:1 or expressed in decibels 80dB
Typical convention for amplifier inputs; active electrode is plugged into the negative (inverting) input
reference electrode is plugged into the positive (non-inverting) input
this convention results in negative peaks being displayed upward and positive peaks being displayed downward
beware, sometimes the active and reference are reversed!
bipolar versus referential recording montages; a bipolar montage means the electrodes are in the same area (close together) more specific on near field signals are amplified far field signals are common mode rejected less sensitive some common mode rejection of the signal may occur
a referential montage means the electrodes are widely spaced (reference located in a distant "inactive" site) less specific both near field and far field signals will get amplified more sensitive less common rejection occurs due to distance between electrodes
far field subcortical responses
the differential amp adds these two together this is a negative response even though it has an upward deflection
input impedance
AEEGS guidelines for amplifiers A/D converter to amplify .005 to 50 mMVolts at full range
10Megaohm input impedance with common mode rejection of 80dB
Frequency range of .1 to 5000Hz and noise <2 microvolts *****These numbers have changed*********
A/D conversion noise reduction and response enhancement take advantage of computer manipulations waves must be converted to digital form in order for the computer to manipulate them
time resolution A/D converter samples analog signal at specific intervals at the time determined by the sampling frequency sampling frequency is the # of data points per second
each discrete interval is a bin bin width or dwell time is the time between samples bin width is 1/sampling frequency
guidelines bin width must be no more than 20 usec/data point or the sampling frequencey must be a minimum of 50 khz
Aliasing can be though of as naming a waveform by other than its proper name this occurs because the sampling rate is too low
nyquist frequency is the minimum acceptable sample rate 2 times the highest frequency
amplitude resolution the a to d converter must have enough vertical gradations to adequately define the amplitude of the waveform the amplifier must have enough dynamic range to pass the waveform without distortion
amplitude resolution number of available voltage values is determined by the number of bits in the A/D converter
# of voltage values
N = # of bits
Therefore the range must be appropriate
range = maximum - minimum voltages
Guidelines - minimum of 8 bits (most systems have 16 bit A/D convertors) 8 bit 2^8- 256 voltage step range, 16 bit 2^16 = 65,536 voltage step range
need to know the minimum guideline number need to know dwell time and bin width are the same width aliasing nyquist frequency
samples are random date values each sample doesn't necessarily look like the other this is how things cancel out, essentially zero after average this is foundation of SSEP/s 40 m/s to head for each trial we average out the random noise
AEEGS guidelines for averagers horizontal resolution of 20 microsec per data point vertical resolution of at least 8 bits 500 addresses of memory per channel must have artifact reject 4000 averages and accurate stimulus synchronization 4 channels minim for PREP and SSEP with 2 ch for BAER display show live and averaged CRT with hard copy output Goodies 10-12 bits A/D 8 channels digital filtering DC capability
periodicity periodic signals have a repeating pattern or cycle these ccles ore periods repeat at equal intervals frequency = the number of repeating cycles that occur per unit time
frequency and period frequency is the number of repeating cycles that occur per unit time the unit of frequency hz cycles/second 1 hertz = 1 cycle per second
period = time for one cycle
circuit model illustrating ohms law
spectral analysis
filters eliminates or reduces certain unwanted frequencies or frequency ranges from an input signal
filters may alter the phase of frequencies in a signal guidelines recommend filter roll-off slopes be limited
Locut maximum of 12dB/Octave Hi-cut - maximum 24 dB/Octave if the hi-cut is too low, peak latencies will be prolonged if the locut is too high then peak latencies will be earlier
filter types; low pass/high cut, band pass, high pass/low cut
notch filter steep roll - off slope used to eliminate a very specific frequency or frequency range should not be used with evoked potentials because it will cause ringing
low pass filter
high pass filter
AEEGS Guidelines for Filter Characteristics
High to low filter settings should be 100:1
Be aware that filtering can cause latency shifts
don't use notch filters and watch for responses or live waveforms with inter-peak intervals of 16.6 msec (1/60 Hz)
Artifact reject; samples with an acceptably high amplitude are not included in the average this only effective for intermittent noise
repetition rate is the number of samples per second measured in Hz it indicates the number of stimulation per second Beware,your repetition rate must not be faster than you can acquire your sample data; the tibial nerve requires 100 msec recording sweep per side if you record from both sides the effective sweep is 200msec therefore your repetition rate can not be above a theoretical max of 5 hz to take advantage of the averagers ability to eliminate 60 hz noise, your repetition rate should not be a multiple of 60
signal to noise ratio; signal/noise/ how large signal is compared to how large the nerve is
display parameters; vertical display resolution is measured in microvolts/division
horizontal display resolution is measured in msec/division
display resolution does not effect the waveform recording parameters only the viewing parameters
display sensitivity sometimes referred to as the display gain data acquisition is not effected acquisition gain is set independently display gain represents the number of microvolts per division that the monitoring system displays your data in display gain is available to make it easier to view your data not to effect the way in which your data is acquired
AEEG Guidelines polarity is a positive event occurring at the input yields an upward deflection
calibration is a square wave signal (0.5-100uV) should be injected into the inputs of the amplifier while the averager is running replications latency should replicate to within 1.0% of the total sweep and amplitude should b=replicate to within 15% of the peak to peak amplitude
Electron - Proton + Neutron - neutral
charge is the force of attraction or repulsion between 2 particles (q1 & q2), the unit of measure is the coulomb
charge density can cause damage or burns
the density, the duration and the surface area. the greater the surface area can have larger
if we apply electrical stimulation through a needle, the needle has smaller surface area than a surface electrodes. if we apply the same charge for the same length of time, the patient is more likely to receive a burn from the needle
attraction and repulsion; unlike charges attract, like charges repel
voltage is an electromotive force calculated by coulombs law as a measure of electric force directly proportional to the number of positively and negatively charged ions indirectly proportional to the square of the distance between the neurons and recording electrodes.
the neurons produce voltage *the further we get recording electrodes away from the voltage source (neuron) the smaller the amplitude will be x amplitude reduces with the square of the distance
the thinner the skull the higher the amplitude of the response
current is measured in amperes and measures the flow or movement of electrons. mA where voltage is the force behind
how does current flow, charged particles move from atom to atom to make current flow in electrodes electrons are the charged particles that move from atom to atom in the body ions move to create current flow
ions an on is an atom that has gained or lost one or more electrons and as a result has a negative or positive charge
remember 50m/s upper 40-50-55/lower 37ms for med/rad to reach brain
resistance is measured in ohms and measures the opposition to direct current flow
impedance is measured in ohms and measures the opposition to alternating current flow
ohms law; v=ir voltage current resistance electromotive force
multiple resisters know that parallel is a current divider and know that series is a voltage divider
resistors in parallel are a current divider that divides the current flow among each resistor voltages remain the same across the resistors
resistors in series are a voltage divider that divides the voltages between each resistor the current remains unchanged across each resistor
capacitance is the ability to store charge, a capacitor consists of 2 metal plates separated by an insulator. voltage rises exponentially across a capacitor and the time constant = the time required to charge a capacitor 63% of its maximum charge 5t required to reach maximum charge while charging current flows when charged no flow
capacitor schematic
time constant t=RC capacitors with small plates charge more quickly than a capacitor with large plates the larger the resistance the slower a capacitor will charge the time constant limits how quickly the capacitor can charge
filters we can use capacitors resistors and the time constant to filter unwanted frequencies long time constants will attenuate higher frequencies and short time constants will follow faster frequencies filter cutoff frequency is inversely proportional to the time constant
RMS is root mean squared where Vrms is the effective voltage of an alternating voltage. RMS is the value that would produce the same power loss is a continuous voltage were applied to a resistor
electricity being delivered via 120v lines this is an average of the voltage that is being delivered through electrical lines
major freqs 30hz-300 or 500hz
apply filters to remove extraneous noise; shorter the shifts to left longer the shifts to the right
excessive low frequency filter-increased low freq too much
500 hz filter w/ noise can bring down to 250 which will increase the latency
instrumentation and other technical stuff
we have very small voltages superimposed on very large voltage variation so we remove the large undulations from the waveform
the standard EP system the lo-pass high cut low freqs pass through and hi-pass = lo-cut lets the high freqs pass through
technical concepts electrodes, stimulation, differential amplification, analog to digital conversion, signal averaging, filtering, artifact rejection, repetition rate, display parameters
electrodes impedance is the opposition to alternating current flow; ohm's law Voltage = Current x Resistance
resistance is the opposition to direct current flow think battery circuit
impedance is the opposition to alternating current flow, think electricity coming from the power company
electrode impedance must be less than 5000 ohms skin and bone is generally considered to be a good insulator because it has a relatively high impedance internal body tissue is generally a good conductor as it has a relatively low impedance having a low electrode tissue impedance is essential to recording good quality signals it is also essential to have matched electrode impedances for good quality signals
electrode types are surface, needle, corkscrew, hookwire, endotracheal tube, epidural, subdural grid, cueva direct nerve, cottonwich and silver ball
surface electrodes attach to the surface of the patients skin prepping of the skin is necessary prior to electrode placement to reduce skin impedance types gold cup, EKG pad, surface disk
subdermal needle electrodes are placed in the skin and does not require prepping to reduce impedance but alcohol prep is required for sterile placement easy to place rapidly carries risk of infection minor bleeding and burns made of stainless steel or platinum alloy
subdermal needle electrodes and bipolar subdermal needle electrodes
needle impedance versus surface pad impedance needle surface area is approximately 20mm2 and pad surface area is approximately 78mm2
with adequate prep, surface scalp electrodes will have slightly lower impedance than needles in an individual with a normal scalp
corkscrew electrodes are spiral shape of needle which allows for greater surface area hence lower impedance than straight needles self securing must be screwed into and out of the skin used for transcranial electric stimulation by some neuromonitoring groups
hair grew back differently, sensitivity is possible post surgery example; woman with a hair dryer
hook wire electrodes
spinal epidural electrode - spinal cord tumor
subdural cortical grid
silverball and cotton wich
xomed endotracheal tube electrodes; blue left red right same for abr's for thyroidectomies, ACDF, vagus nerve, inter-cranial procedures, motors, different sizes could possibly elicit emg
stimulation anode positive cathode negative
current flow versus electron flow current flow by convention is flow of positive charge
electron flow is movement of negative charge opposite that of conventional current flow
stimulating electrodes optimal inter-electrode spacing approximately 3 centimeters too far apart and current spreads causing excessive stimulation artifact too close and current may not penetrate deep enough to adequately stimulate the nerve
differential amplification differential amplifiers amplify the difference between two input signals remember their name and you know what they do
the differential amplifier has a non inverting positive reference and a inverting negative active inputs, gain, voltage difference in the inputs x the gain is the output and gain =output voltage/input voltage
amplifiers amplification, unity gain, attenuation
signals at the non-inverting input do not get inverted
signals at the inverting input get inverted
summary of basic scenarios not that opposite input voltages in different inputs yield the same output
in order to know whether the output is positive or negative you must know which input it came from
cueva nerve electrode
common mode rejection the common mode signals cancellation of common mode signals
partial common mode rejection can occur, partial cancellation of similar signals this is what is happening when the impedance values are different
noise reduction with differential amplification
using electrode placement to optimize differential amplification; to maximize the response place the active and reference as far apart as possible to minimize noise place the active and reference as close as possible in practice you have to reach a reasonable compromise
common mode rejection ratio
CMRR=output of differential applied input output of same input applied in common mode; this ratio must be at least 10,000:1 in a perfectly balanced amplifier this denominator would be zero
common mode rejection ration CMRR indicates how well an amplifier reflects common mode signals guidelines require the CMRR must be at least 10,000:1 or expressed in decibels 80dB
Typical convention for amplifier inputs; active electrode is plugged into the negative (inverting) input
reference electrode is plugged into the positive (non-inverting) input
this convention results in negative peaks being displayed upward and positive peaks being displayed downward
beware, sometimes the active and reference are reversed!
bipolar versus referential recording montages; a bipolar montage means the electrodes are in the same area (close together) more specific on near field signals are amplified far field signals are common mode rejected less sensitive some common mode rejection of the signal may occur
a referential montage means the electrodes are widely spaced (reference located in a distant "inactive" site) less specific both near field and far field signals will get amplified more sensitive less common rejection occurs due to distance between electrodes
far field subcortical responses
the differential amp adds these two together this is a negative response even though it has an upward deflection
input impedance
AEEGS guidelines for amplifiers A/D converter to amplify .005 to 50 mMVolts at full range
10Megaohm input impedance with common mode rejection of 80dB
Frequency range of .1 to 5000Hz and noise <2 microvolts *****These numbers have changed*********
A/D conversion noise reduction and response enhancement take advantage of computer manipulations waves must be converted to digital form in order for the computer to manipulate them
time resolution A/D converter samples analog signal at specific intervals at the time determined by the sampling frequency sampling frequency is the # of data points per second
each discrete interval is a bin bin width or dwell time is the time between samples bin width is 1/sampling frequency
guidelines bin width must be no more than 20 usec/data point or the sampling frequencey must be a minimum of 50 khz
Aliasing can be though of as naming a waveform by other than its proper name this occurs because the sampling rate is too low
nyquist frequency is the minimum acceptable sample rate 2 times the highest frequency
amplitude resolution the a to d converter must have enough vertical gradations to adequately define the amplitude of the waveform the amplifier must have enough dynamic range to pass the waveform without distortion
amplitude resolution number of available voltage values is determined by the number of bits in the A/D converter
# of voltage values
N = # of bits
Therefore the range must be appropriate
range = maximum - minimum voltages
Guidelines - minimum of 8 bits (most systems have 16 bit A/D convertors) 8 bit 2^8- 256 voltage step range, 16 bit 2^16 = 65,536 voltage step range
need to know the minimum guideline number need to know dwell time and bin width are the same width aliasing nyquist frequency
samples are random date values each sample doesn't necessarily look like the other this is how things cancel out, essentially zero after average this is foundation of SSEP/s 40 m/s to head for each trial we average out the random noise
AEEGS guidelines for averagers horizontal resolution of 20 microsec per data point vertical resolution of at least 8 bits 500 addresses of memory per channel must have artifact reject 4000 averages and accurate stimulus synchronization 4 channels minim for PREP and SSEP with 2 ch for BAER display show live and averaged CRT with hard copy output Goodies 10-12 bits A/D 8 channels digital filtering DC capability
periodicity periodic signals have a repeating pattern or cycle these ccles ore periods repeat at equal intervals frequency = the number of repeating cycles that occur per unit time
frequency and period frequency is the number of repeating cycles that occur per unit time the unit of frequency hz cycles/second 1 hertz = 1 cycle per second
period = time for one cycle
circuit model illustrating ohms law
spectral analysis
filters eliminates or reduces certain unwanted frequencies or frequency ranges from an input signal
filters may alter the phase of frequencies in a signal guidelines recommend filter roll-off slopes be limited
Locut maximum of 12dB/Octave Hi-cut - maximum 24 dB/Octave if the hi-cut is too low, peak latencies will be prolonged if the locut is too high then peak latencies will be earlier
filter types; low pass/high cut, band pass, high pass/low cut
notch filter steep roll - off slope used to eliminate a very specific frequency or frequency range should not be used with evoked potentials because it will cause ringing
low pass filter
high pass filter
AEEGS Guidelines for Filter Characteristics
High to low filter settings should be 100:1
Be aware that filtering can cause latency shifts
don't use notch filters and watch for responses or live waveforms with inter-peak intervals of 16.6 msec (1/60 Hz)
Artifact reject; samples with an acceptably high amplitude are not included in the average this only effective for intermittent noise
repetition rate is the number of samples per second measured in Hz it indicates the number of stimulation per second Beware,your repetition rate must not be faster than you can acquire your sample data; the tibial nerve requires 100 msec recording sweep per side if you record from both sides the effective sweep is 200msec therefore your repetition rate can not be above a theoretical max of 5 hz to take advantage of the averagers ability to eliminate 60 hz noise, your repetition rate should not be a multiple of 60
signal to noise ratio; signal/noise/ how large signal is compared to how large the nerve is
display parameters; vertical display resolution is measured in microvolts/division
horizontal display resolution is measured in msec/division
display resolution does not effect the waveform recording parameters only the viewing parameters
display sensitivity sometimes referred to as the display gain data acquisition is not effected acquisition gain is set independently display gain represents the number of microvolts per division that the monitoring system displays your data in display gain is available to make it easier to view your data not to effect the way in which your data is acquired
AEEG Guidelines polarity is a positive event occurring at the input yields an upward deflection
calibration is a square wave signal (0.5-100uV) should be injected into the inputs of the amplifier while the averager is running replications latency should replicate to within 1.0% of the total sweep and amplitude should b=replicate to within 15% of the peak to peak amplitude
*LH*
protect the equipment from fluid damage, cover equipment that may get wet, make sure that biomed performs annual electrical safety checks and documents the results, disconnect your equipment from the patient and stop using it immediately if you receive a shock from your equipment
Equipment safety; only use hospital grade power cords (with green dot) to power your system
chassis, outer casing of equipment; ground, non powered green wire connected to the chassis; black wire, hot wire; white wire, neutral wire; current leakage, amount of current leaking from the chassis, must be less than 300 microamps
Sources of Leakage Current, stray capacitance from power cords and power supplies, extension cords increase leakage current, stray inductance, less of a problem than stray capacitance, electromagnetic field induced current, fault current, instrument fault creating high leakage current
Current Leakage, maximum chassis leakage should not exceed 300 microamps; isolated amp input leakage must not exceed 10 microamps through patient leads with 120 V rms applied, maximum leakage current should be no greater than 50 microamps rms at the patient when the power line ground is disconnected
Grounding ground loop, when multiple non isolated grounds are placed on the patient, voltage differences between the grounds can result in current flow, no more than 1 ground per patient; a common OR grounding system that is no more than 20 mV measured across a 1Kohm resistor at 60 Hz must be shared by all electrical devices in the OR, ground and chassis resistance must be less than 0.5 Ohms
Ground Chassis to Resistance; measured between chassis and ground must be less than 0.5 ohms
macroshock - can physically feel
microshock cannot feel but if it passes across your heart it can kill you; lethal 0.4 amps
FILTERS
protect the equipment from fluid damage, cover equipment that may get wet, make sure that biomed performs annual electrical safety checks and documents the results, disconnect your equipment from the patient and stop using it immediately if you receive a shock from your equipment
Equipment safety; only use hospital grade power cords (with green dot) to power your system
chassis, outer casing of equipment; ground, non powered green wire connected to the chassis; black wire, hot wire; white wire, neutral wire; current leakage, amount of current leaking from the chassis, must be less than 300 microamps
Sources of Leakage Current, stray capacitance from power cords and power supplies, extension cords increase leakage current, stray inductance, less of a problem than stray capacitance, electromagnetic field induced current, fault current, instrument fault creating high leakage current
Current Leakage, maximum chassis leakage should not exceed 300 microamps; isolated amp input leakage must not exceed 10 microamps through patient leads with 120 V rms applied, maximum leakage current should be no greater than 50 microamps rms at the patient when the power line ground is disconnected
Grounding ground loop, when multiple non isolated grounds are placed on the patient, voltage differences between the grounds can result in current flow, no more than 1 ground per patient; a common OR grounding system that is no more than 20 mV measured across a 1Kohm resistor at 60 Hz must be shared by all electrical devices in the OR, ground and chassis resistance must be less than 0.5 Ohms
Ground Chassis to Resistance; measured between chassis and ground must be less than 0.5 ohms
macroshock - can physically feel
microshock cannot feel but if it passes across your heart it can kill you; lethal 0.4 amps
FILTERS