The INA126 is partially pin compatible with the 741:
the pins that they have in common are in the same place.
So if you try to wire it like a 741, it won't blow up,
but it won't work very well either.
Here's the pinout:
Fig. 8.2: INA162
The differences with respect to the 741 are:
(a) pin 5 must be connected to ground,
and (b) gain is set by a single resistor rather than
a feedback network.
If a gain greater than 5 is desired,
a gain programming resistor (
) must be
connected between pins 1 and 8.
The formula for gain is
Choose the resistor from your parts kit which gives
a value for
as close as possible to 100.
Set the function generator to produce a 100 Hz sine wave.
and connect the function generator output to
Adjust the function generator amplitude and offset
is an unclipped 10 V p-p
|Measure the input and output amplitudes and determine the actual gain of the amplifier. Is is reasonably close to 100? Increase the frequency until the output drops to 7 V p-p. This is the 3 dB bandwidth.|
If a thin diaphragm experiences a difference in pressure between its two sides it will be deformed: concave (compressive strain) on the high pressure side and convex (tensile strain) on the low side. If strain gages are placed at appropriate locations on a such a diaphragm, the strains resulting from the pressure differential will be translated to changes in resistance which can be measured with a bridge circuit.
The MPX Pressure Sensor contains just such an arrangement. The four pin package provides a connection to each corner of the bridge:
Ports for tubing are provided for each side of the diaphragm. The port directly above pin 4 is the positive pressure port ( ) while the one above pin 1 is the vacuum port ( ).
Plug the MPX2010 into the breadboard
and connect it
to the INA126
as shown below.
Also connect to A/D input channel 6.
Since the bridge circuit is less sensitive to changes
in the excitation voltage,
we won't explicitly monitor it like we did in Lab 4.
However, for maximum accuracy you should use your DMM
to set the power supply voltage to
exactly 15 V.
with the oscilloscope set to 20mv/div, DC.
Press the tip of your finger against the pressure port of
the MPX2010. You should observe a positive signal on the scope.
Similarly, pressing your finger against the vacuum port
should produce a negative signal.
one end of
a 3' piece of 1/8" i.d. vinyl tubing to the
pressure port of the MPX2010.
Speak, whistle, or otherwise make noise at the other end.
You should observe an appropriate signal on the oscilloscope.
Load the Lab 8 VI from the ELEC 243 Start menu.
The left-hand half of
this VI reads the amplified output of the pressure
sensor, converts the voltage into the equivalent
pressure, and displays the result.
We'll look at the right-hand half in the next Experiment.
Start the VI. The value of the Vin indicator should correspond to the value measured by the oscilloscope. Since both ports are connected to the same pressure (ambient atmospheric) this should be zero. However, the amplifier input offset voltage and any imbalance in the sensor bridge elements will likely result in a non-zero value. Wait a minute or two for things to warm up, then enter the value of Vin into the offset control. The displayed value of pressure should now be zero.
Draw the plunger of a
3 ml Syringe
to the 2 ml mark.
Insert the tip of the syringe into the free end of
the tubing connected to the pressure sensor.
Adjust the plunger until the pressure reads zero
and note its position.
Slowly press the plunger in until the pressure reading
is 10 kPa
and again note the position.
Is the observed change in pressure consistent with the
change in volume? Explain.
|When finished with this Experiment, be sure to stop the VI.|