Transcript Slide 1

Interfacing Pressure Sensor to logic device input pin
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AInc.
Pre-presentation Self Assessment Activity
Your comfort level with your responses to
the following 2 design tasks assessment
tool should indicate if the presentation that
follows will increase you knowledge base
on the topic outlined by the questions in
this tool.
Pre-presentation Self Assessment Activity
Your task is to design an interface circuit that connects a
strain gauge based pressure sensor to a TTL AND device so that
an action will occur if the pressure sensor and a temperature
sensor are active at the same time. Assume the temperature
sensor is an active low temperature sense high device
however;
(a)
Make the pressure sensor behave like an active
high PSH.
(b)
Make the pressure sensor behave like an active
low PSL.
Comparator application
“non-inverting input”
“inverting input”
+
Limit Sensor interface
output
-
Operational Amplifier’s only Rule of Operation
If the two inputs signals are equal,
then the output signal is zero volts.
Comparator application
Pressure Limit Sensor interface
V
total
Strain gauge
V
strain
A strain gauge is a thin flexible
membrane with a resistor
embedded in the film.
V
total
V
pull up
Note:
R
pull up
V
out
=
V
strain
+ V pull
up
V
= Vtotal - Vstrain
out
or
0 Volts + V pull up
V
=
out
As the pressure changes the strain gauge bends and gauge resistance changes.
Vstrain equals the voltage drop across the strain gauge.
Vpull up equals the voltage drop across the pull up resistor, R
Vtotal equals the Vstrain plus V pull up.
pull up.
Operational Amplifier’s only Rule of Operation
If the two inputs signals are equal,
then the output signal is zero volts.
Comparator application
Pressure Limit Sensor interface
V
total
Strain gauge
V
strain
V
pull up
The signal from this terminal;
Needs to be monitored to determine if
the pressure has changed from steady
state value.
R
pull up
V
out
May trigger a process change when the
pressure exceeds its allowed limit
value.
Operational Amplifier’s only Rule of Operation
If the two inputs signals are equal,
then the output signal is zero volts.
Comparator application
Pressure Limit Sensor interface
V
total
Strain gauge
+12 V
V
strain
Power terminal
for device
+
V total
V
pull up
R
pull up
If strain gauge resistance
chances from steady state
value, op amp output
voltage will continue to
increase (decrease) until;
V
out
R tune
Gauge resistance returns to
steady state value.
Power terminal
for device
-12 V
Output signal reaches
maximum possible value.
Needs to be monitored to determine if the pressure has changed from steady
state value.
May trigger a process change when the pressure exceeds its allowed limit
value.
Operational Amplifier’s only Rule of Operation
If the two inputs signals are equal,
then the output signal is zero volts.
Comparator application
Pressure Limit Sensor interface
V
total
Strain gauge
+12 V
V
strain
5 V
V
is now
out
Power terminal
for device
clamped
between 0 V
and 5 V
+
V total
V
pull up
R
pull up
an input to a
logic device
R tune
Power terminal
for device
-12 V
Needs to be monitored to determine if the pressure has changed from steady
state value.
May trigger a process change when the pressure exceeds its allowed limit
value.
Operational Amplifier’s only Rule of Operation
If the two inputs signals are equal,
then the output signal is zero volts.
Comparator application
Pressure Limit Sensor interface
V
total
Strain gauge
+12 V
V
strain
Power terminal
for device
+
V total
V
pull up
R
pull up
5 V
Vout is now an active
high high pressure
limit sensor
PSH
R tune
Power terminal
for device
-12 V
TSH
action
Temperature sensor is
from a different part
of the process.
When the pressure goes down the op amp output goes to 0 volts and action
signal remains passive.
When the pressure goes up the op amp output goes to 5 volts. If TSH is
active, action signal become active.
Operational Amplifier’s only Rule of Operation
If the two inputs signals are equal,
then the output signal is zero volts.
Comparator application
Pressure Limit Sensor interface
V
total
Strain gauge
+12 V
V
strain
Power terminal
for device
+
V total
V
pull up
R
pull up
5 V
Vout is now an active
low low pressure
limit sensor
PSL
R tune
Power terminal
for device
-12 V
TSH
action
Temperature sensor is
from a different part
of the process.
When the pressure goes down the op amp output goes to 0 volts. If TSH is
active, action signal become active.
When the pressure goes up the op amp output goes to 5 volts and action
signal remains passive.
Operational Amplifier’s only Rule of Operation
If the two inputs signals are equal,
then the output signal is zero volts.
Post Presentation Self Assessment Activity
Your task is to design an interface circuit that connects a strain
gauge based pressure sensor to a TTL AND device so that an action
will occur if the pressure sensor and a temperature sensor are
active at the same time. Assume the temperature sensor is an
active low temperature sense high device however;
(a) Make the pressure sensor behave like an active
high PSH.
V
5 V
total
+12 V
Vstrain
+
V total
V pull
up
R
pull up
PSH
R tune
-
TSH
-12 V
action
Post Presentation Self Assessment Activity
Your task is to design an interface circuit that connects a strain
gauge based pressure sensor to a TTL AND device so that an action
will occur if the pressure sensor and a temperature sensor are
active at the same time. Assume the temperature sensor is an
active low temperature sense high device however;
(b) Make the pressure sensor behave like an active
low PSL.
V
5 V
total
+12 V
Vstrain
+
V total
V pull
up
R
pull up
PSL
R tune
-
TSH
-12 V
action
End of Presentation
AInc.