instrumentation

exam 2

Voltage

electrical potential difference

Current

Flow of charge

Resistance

opposition to current

ohm’s law

V = I x R

Formula for power

P= V x I

Kirchhoff’s Voltage Law

The sum of all voltage drops in a closed loop = the supply voltage.

Kirchhoff’s Current Law

• The sum of currents in all branches = the total current in the entire circuit 

Voltage divider formula

Vout = Vin × (R2 / (R1 + R2))

Current divider formula

 I1 = Itotal × (R2 / (R1 + R2))
I2 = Itotal × (R1 / (R1 + R2))

Household power

120 V 60 Hz

Voltage ratio for transformers

Voltage out/voltage in = Turns on secondary coil/ turns on primary coil

Capacitance

ability to store charge in an electric field

Inductance

ability to store energy in a magnetic field

impedance formula

 |Z| = √(R² + X²)

Capacitive Reactance formula

 Xc = 1 / (2 π f * C)

Phase angle formula

θ = arctan(-X / R)

gain in db formula

20 log (Vout / Vin)

phase shift formula

ϕ = 360 × (Δt / T)

Magnitude transfer formula, low pass

Cut off frequency formula

  fc = 1 / (2πRC)

How is Voltage measured?

Across (Parallel)

How is current measured?

through, (in series)

Parallel circuit total resistance formula

1 / Rtotal = 1 / R1 + 1 / R2 + 1 / R3 + …

Phase relation In purely resistive circuits

V and I in phase

Phase relation in purely capacitive circuits

I leads V by 90°

Total reactance formula

X = Xl − Xc

Middle ear resonance

800-1200 hz

Middle ear gain

+34 dB

Main difference in infant ears vs Adult ears

Infant ears are mass dominated

Acoustic reflex

stapedius contraction increases stiffness, decreases admittance

Best voltage transfer:

Z in is greater than Z out

Best Power transfer

Z in = Z out

Stiffness dominant Pathology

Otosclerosis, Fluid in middle ear

Mass dominated pathology

Ossicular discontinuity