Electronics Flashcards
Chassis leakage current must be…
less than 300 uA
Amplifier leakage (to the patient) must be…
Less than 10uA
Leakage into the amplifier, from the patient leads, must be…
10uA unattached, or 20uA with patient leads attached
OR grounding must be…
across 1Kohm at 60Hz, less than 20mV
Macroshock
Large deadly current such as “finger in an outlet”
Microshock
Smaller current, but still lethal due to direct application to heart
Ground loops
Occurs when more than one earth ground exists and a voltage difference exists across them
Current can potentially flow from one ground to the other (across the pt) forming a loop
What is a line isolation monitor?
Device that measures combined leakage current to ground from all devices in the OR and alarms if it detects excess current
What is an ammeter?
Measures current
What is an ohmeter?
Measures resistance
What is a voltmeter?
Measures voltage
What is a safety analyzer?
Device used by biomed to perform electrical testing
What do the colors in a power cord mean?
Green=ground
Black=hot
White=neutral
Silver-silver chloride electrodes
surface
Gold electrodes
long time constant, low drift
Platinum electrodes
non-reactive, non-toxic even when current is applied
Stainless steel electrodes
short time constant, has drift
Silver electrodes
toxic to brain tissue
Tin/lead/copper electrodes
All reactive to biochemistry with toxic by-products!
What is Coulomb’s Law?
The force exerted between two charges is inversely proportional to the square of the distance between them
F=1/(distance)^2
What is Ohm’s law?
Voltage (V) is equal to the product of the current (I) and the resistance (R)
V=IR
How do you calculate the total resistance in series?
Rtotal=R1+R2+R3+…
How do you calculate the total resistance in parallel?
Rtotal=1/R1+1/R2+…
What is the gain of a differential amplifier?
the voltage out divided by the voltage in
What is the required CMRR based on the guidelines?
10,000:1 or 80dB
What should the input impedance be based on the guidelines?
Guidelines require greater than or equal to 100 MOhms
What should the bin width be based on the guidelines?
<20uS/data point (sampling rate >50,000)
Nyquist frequency
2x the fastest frequency in a recorded signal
What is vertical resolution and what do the guidelines say?
The number of available discrete points (vertical resolution) is determined by the number of bits the system operates with, which is 2^N where N is the number of bits
guidelines require a minimum of 8 bits
What equation do you use to calculate SNR after averaging?
SNRf=SNRi(sqrtN) where N is the number of averages
