Transcript 'AND' Away we go!

Wheatstone bridge as Strain Gauge interface
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AInc.
Pre-presentation Self Assessment Activity
Your comfort level with your responses to
the following single design challenge should
suggest if the presentation that follows will
increase you knowledge base on the topic
embedded within these questions.
Pre-presentation Self Assessment Activity
1)
Design a Wheatstone bridge load cell sensor interface
circuit that will provided a voltage output that indicates
the sensor’s reaction to a change in load (weight on the
sensing element).
Review Wheatstone bridge circuit
If all of the resistance values are equal the voltage
between point (a) and (b) is equal to zero.
(a)
R4 = R3 = R2 = R1
This voltage value is the
voltage difference
between point (a) and
point (b).
R3
R1
V
+
V
V=0
R
(b)
4
R2
Review Wheatstone bridge circuit
If one of the resistance values is different the voltage
between point (a) and (b) is not equal to zero.
(a)
R4 = R3 = R2 = R1
This voltage value is the
voltage difference
between point (a) and
point (b).
R3
R1
V
+
V
V=0
R
(b)
4
R2
Review Wheatstone bridge circuit
If the 4th resistor is a load cell, its resistance value changes
with the weight of the load on the strain gauge in the load cell.
(a)
R4 = R3 = R2 = R1
This voltage value is the
voltage difference
between point (a) and
point (b).
R1
R3
V
+
V
V=0
Load cell
R
(b)
4
R2
Review Wheatstone bridge circuit
its resistance
value changes
If the 4th resistor is a thermistor,
load, its resistance
value changes
with
with temperature.
weight.
This Wheatstone bridge circuit detects this resistance
change.
(a)
This voltage value is the
voltage difference
between point (a) and
point (b).
R1
R3
V
+
V
V=0
R4 changes in resistance value
as the weight changes and
the voltage between points
(a) and (b) in the
Wheatstone bridge circuit
also changes proportionally.
(b)
Load cell
R
4
R2
Post Presentation Self Assessment Activity
1)
Design a Wheatstone bridge load cell sensor interface
circuit that will provided a voltage output that indicates
the sensor’s reaction to a change in load (weight on the
sensing element).
R
Voltage across these
terminals indicates if
the weight of the
object on the load
cell has changed.
V
3
R
1
+
V
R
4
R
2
Load cell
Note:
This comparator configuration for the operational amplifier will
drive the output signal to one of the two possible saturation
values when the weight on load cell leaves its steady state
value.
End of Presentation
AInc.