content describes the types of pressure transducers used in biomedical application

1. PRESSURE
TRANSDUCERS

2. Pressure Transducer
 Pressure transducers are converting pressure into measurable
electrical signals.
 The fundamental principle involves applying the pressure to be
measured onto a flexible diaphragm.
 The diaphragm, typically a thin, flat, circular plate, deforms in
response to the applied pressure.
 Deformation of the diaphragm is then translated into an electrical
signal for measurement.
 Common diaphragm materials include stainless steel, phosphor
bronze, and beryllium copper.

3. Diagphragm

4. Pressure transducers make use of the
diaphragm are of the following types:
 Capacitance manometer—in which the diaphragm forms one
plate of a capacitor.
 Differential transformer—where the diaphragm is attached to
the core of a differential transformer.
 Strain gauge—where the strain gauge bridge is attached to the
diaphragm.

5. LVDT
 A Linear Variable Differential Transformer (LVDT) is an electrical transducer or
sensor used for the measurement of physical quantities like displacement,
force, pressure, acceleration, etc.
 It works on the principle of mutual inductance, that generates an electrical
signal proportional to the physical quantity applied which is to be measured.
Let us see the various applications of LVDT.

6. LVDT Principle
 It works on the principle of mutual
inductance(When changing
in one coil induces an EMF in the
other),
 It generates an electrical signal
proportional to the physical
quantity applied which is to be
measured.

7. LVDT PRESSURE TRANSDUCER

8. Construction
 An LVDT consists of one primary winding to which an ac supply voltage is given and two secondary
windings.
 The two secondary windings are connected in series of opposite connections so that a differential
output voltage can be obtained.
 Between the primary and two secondary windings, a core is placed
 Depending on the position of the core, more or less output will be generated in the two secondary
windings.
 Now connect pressure sensing elements, to the core of LVDT such that the output displacement
resulting from this transducer by the applied pressure will be transmitted to the core of LVDT

10. LVDT

11. 3D View

12. Case 0:
 Let the emf induced in the two secondary windings are es1 and
es2 respectively.
 Under the normal condition, when there is no displacement is
applied to the movable core.
 An equal amount of voltages will be induced in the two
secondary windings. Since the secondaries are connected in series
opposition the net output voltage will be zero.

13. Case 1
 When the pressure to be measured is applied to the diaphragm, the
diaphragm deflects (expands upwards) and this movement is given
to the rod of the core of LVDT. With this, the core will be lifted up
and more voltage will be induced in the upper part of the secondary
winding 1. (es1 > es2).
 Therefore, a positive voltage is generated at the output (i.e., Eo =
es1 - es2).
 This positive output will indicate applied pressure.

14. Case 2
 when the pressure is decreased the diaphragm contracts (comes
downwards) and the core comes down from the null position
causing more voltage to induce in secondary winding 2 , which is
denoted by es2
 The net output voltage is negative which indicates the decrease in
pressure (es1 < es2).
 Therefore, a negative voltage is generated at the output (i.e., Eo =
es1 - es2).
 This output will indicate applied pressure.

15. LVDT

16. Advantages of LVDT Pressure Transducer
• Sensitivity is very high
• Rugged construction
• It has low hysteresis
• It has very good repeatability

17. Disadvantages of LVDT Pressure Transducer
• It has poor accuracy
• The performance of this transducer is
affected by temperature change

18. Strain Gauge Transducer
 A strain gauge pressure sensor is a device
that measures pressure by converting the
mechanical deformation experienced by a
material into an electrical signal.
 This type of sensor is widely used across
various industries and applications, including
automotive, aerospace, medical, and industrial
automation.

19. Strain Gauge
 At the core of a strain gauge pressure sensor is a
strain gauge
 It is a thin, flexible material
 The strain gauge is typically made from a metal,
such as constantan or nichrome, or a semiconductor
material, like polysilicon or amorphous metal.
 Its electrical resistance when it undergoes
mechanical deformation.
 It is bonded to a diaphragm or another structure
that deforms when subjected to pressure.

20. Contd…
 As the diaphragm experiences pressure, it deforms
and causes the strain gauge to change its shape as
well.
 This change in shape leads to a change in
electrical resistance, which can be measured using a
Wheatstone bridge circuit.
 The output voltage from the Wheatstone bridge is
proportional to the amount of strain experienced by
the gauge, and thus to the pressure applied to the
diaphragm.

21. Strain Gauge

22. Strain Gauge- Pressure Transducer

23. Pressure Transducer
 This type of pressure transducer utilizes a foil or silicon strain gauge (arranged
as a Wheatstone bridge) attached to the surface of the diaphragm, on the
opposite side of the media.
 When a change in pressure of the media occurs, this will result in deformation of
the elastic material, thereby also changing the resistance of the strain gauge.
 This resistance change is converted into an electrical signal, which is then
amplified and conditioned to provide transducer-voltage or transmitter-current
output.

24. Types of Strain Gauges
Electrical resistance strain gauges are mainly classified into
two types.
They are,
 Unbonded strain gauges
 Bonded strain gauges

25. Unbonded Strain Gauge
 In an unbounded strain gauge, the strain gauge is not directly
bonded to the surface which is subjected to stress
 It consists of resistance wire stretched between frames P and Q with
the help of insulated pins .
 These two frames are movable with respect to each other, and this
arrangement can be connected in one of the arms of Wheatstone's
bridge.

26. Unbounded Strain Gauge

27. Bonded strain gauges
 Bonded strain gauges are directly placed or bonded on the
surface of the device or component which is subjected to
stress.
 In bonded type, the strain gauge is directly pasted on the
surface of the structure under test.
 To paste the strain gauge on the structure, adhesives are used
which are responsible for transmitting the strain from the
structure to the gauge wires.

28. Bounded Strain Gauge

29. Gauge Factor
 Gauge Factor is defined as the ratio of relative
change in electrical resistance to the mechanical
 Here relative change in resistance is defined as the
change in resistance produced due to strain to its
resistance (without strained). It is also referred as
factor of a strain gauge.
 According to the definition, when applied pressure in
bar of length (L) produces change in length (ΔL)
results in gauge resistance change (ΔR) from its
resistance (R),
 Strain is defined as a change in length to actual

30. Resistance
The resistivity of a material is defined as the magnitude of electric current across it

31. Wheatstone Bridge Circuit
• In order to measure strain with a
bonded resistance strain gauge, it
is connected to wheatstone
Bridge circuit.
• The change in resistance is
proportional to applied strain
• It is measured using wheatstone
bridge circuit

32. Contd..
• A Wheatstone bridge is a divided bridge
circuit used for the measurement of
static or dynamic electrical resistance.
• The output voltage of the Wheatstone
bridge is expressed in millivolts output
per volt input.

33. Advantages
1. High accuracy: These sensors can achieve high levels of
accuracy, typically within 0.1% to 0.5% of the full-scale
pressure range. This allows for precise pressure
measurements in critical applications.
2. Wide pressure range: Strain gauge pressure sensors can
measure pressures ranging from very low to extremely high
levels, making them suitable for diverse applications.
3. Good temperature stability: With proper compensation
techniques, these sensors can maintain accuracy over a wide
temperature range, allowing for their use in environments
with significant temperature fluctuations.
4. Long-term stability: Strain gauge pressure sensors exhibit
excellent long-term stability, ensuring consistent

34. Disadvantages
1. Cost: The complexity of the sensor design and the need for precise
manufacturing techniques can lead to higher costs compared to
other pressure sensor types.
2. Vulnerability to electromagnetic interference (EMI): The
electrical signal generated by the strain gauge can be susceptible
to interference from external electromagnetic sources. This can be
mitigated through proper shielding and grounding techniques.
3. Low signal output: The output signal from a strain gauge pressure
sensor is typically in the millivolt range, requiring additional
signal conditioning and amplification to be usable.

35. Capacitive Transducer
 A capacitive transducer has a static plate and
a deflected flexible diaphragm with a dielectric
in between.
 When a pressure is exerted to the outer side
of the diaphragm the distance between the
diaphragm and the static plate changes.
 This produces a capacitance which is
measured using an capacitance bridge.
.

36. Capacitive Transducer
 A metallic diaphragm enclosed in an airtight
container
 It moves to the left when pressure is applied to
the chamber and to the right when vacuum is
applied.
 This diaphragm is used as one plate of a variable
capacitor.
 The pressure applied to the unit is determined by
Its distance from the stationary plate to its left
 The monitor indicates the pressure equivalent of
the unit’s capacitance by measuring the
capacitor’s reactance to the ac source voltage.

37. Capacitance Transducer

38. Capacitance Measurement
 From this equation, it is seen that
capacitance increases
(i) if the effective area of the plate is
increased, and
(ii) if the material has a high dielectric
constant.
 The capacitance is reduced if the
spacing between the plates is
increased.

39. Advantages and Disadvantages
Advantages
• It produces an accurate frequency response to both static and
dynamic measurements.
Disadvantages
• An increase or decrease in temperature to a high level will
change the accuracy of the device.
• As the lead is lengthy it can cause errors or distortion in signals.

40. Piezoelectric Transducer Type
 Piezoelectric pressure sensors convert
mechanical pressure into electrical
signals,
 It offering high sensitivity, wide range,
and durability for diverse applications
 The term “piezoelectric” is derived from
the Greek words “piezo,” meaning pressure,
and “electric,” referring to electricity.

41. Principle
 When piezoelectric material is placed under mechanical stress
 Material undergoes deformation
 Electric charge accumulates in a solid material in response to a
applied mechanical stress
 It causes a shifting of the positive and negative charge centers in
the material takes place, which then results in an external
electrical field.
Inverse piezoelectric effect
 When an electrical field applied to a material
 It either stretches or compresses the piezoelectric material.
 Converts electrical signal in to mechanical signal

42. Piezoelectric Pressure Sensors
• Piezoelectric materials exhibit a
specific property where they produce
an electric charge when subjected to
mechanical stress, such as pressure
or force.
• When pressure is applied to the
sensor, the piezoelectric material
deforms, causing a voltage
difference across the electrodes.
• This voltage can then be measured
and correlated to the applied

43. Piezoelectric materials
The most commonly produced piezoelectric
ceramics are
Lead Zirconate Titanate
 barium titanate
 lead titanate
Rochelle Salt
Quartz

44. Advantages of Piezoelectric Material
• High sensitivity: Piezoelectric materials can generate
significant electrical signals in response to small mechanical
forces, allowing for the detection of minute pressure changes.
• Wide dynamic range: These sensors can measure pressures over a
wide range, from a few millibars to several hundred atmospheres,
making them suitable for numerous applications.
• Fast response time: Due to their low mass and high stiffness,
piezoelectric sensors can respond to pressure changes rapidly,
making them ideal for dynamic and transient pressure
measurements.
• Excellent stability: Piezoelectric materials are inherently
stable and do not exhibit significant drift over time, ensuring
long-term measurement accuracy.
• Resistance to harsh environments: Piezoelectric sensors can
operate in extreme temperatures, pressures, and corrosive