Why Biomedical Technologists use
Wheatstone Bridges?
By Chris Correll
result, we have a balanced bridge. However, if
R2 reading is either too low or high.
The use of Wheatstone Bridges have many
practical applications used within everyday
biomedical technological devices. Does anyone
know what the following devices have in
common: strain gauges, CT scanners,
mammography units, infusion as well as syringe
pumps, patient lifts, weighing scales, dialysis
units, and robotic surgery devices? By the end
of this paper you should be able to tell us the
answer.
First, what does a Wheatsone Bridge do? It
is an electrical circuit used in the measurement
of electrical resistances. Similiar to a
potentiometer, the circuit measures an unknown
reistance by balancing two legs of a bridge
circuit, and one leg is the unknown reistance
value. In 1833, orginally invented by Samuel
Christie, the circuit would be later redesigned
and improved after the gentleman who would be
later named after it—Sir Charles Wheatsone.
In theory, a typical bridge are two series-
For example, in a blanaced Wheatstone Bridge
configuration—where all four resistances are
known. We can analyze and calcualte this
simple circuit by substituting the values and
stepping though the formula.
R1=5Ω
R2=100Ω
R3=2Ω
R4=8Ω
Battery=12VDC
Fing Vg=?
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parallel resistors that have four resistors and in
the middle a Galvonometer, an instrument used
as an digital ammeter. Rx, an unknown
resistance, is to be measured while R 1, R2, and
R3 resistors have known reistance values even
though R2 is a potentiometer and R 1 and R3 are
fixed resistor values. If the ratio between
resistances vary then the voltage between the
two midpoints where the Galvometer (Vg)
resides will measure zero current flow. As a
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Wheatstone biomedical applications:
The original design was for electrical resistance,
but can also be used to measure capacitance,
inductance, impedance and other quantities,
such as combustible gases.