Download Biology Gas Pressure Sensor

Biology Gas Pressure Sensor
(Order Code BGP-DIN)
Many biology activities involve the production or consumption of a gas, resulting in
a change in pressure. The Biology Gas Pressure Sensor can be used to monitor these
pressure changes. It can be connected to any of the Vernier interfaces (ULI, Serial
Box Interface, MPLI, or Voltage Input Unit), as well as the Texas Instruments
Calculator-Based Laboratory™ (CBL™) System. The following is a partial list of
activities and experiments that can be performed using this probe:
• Monitor the production of O2 during photosynthesis of an aquatic plant in a closed
system.
• Determine the rate of transpiration for a plant under different conditions.
• Determine the rate of respiration in germinating pea or bean seeds.
• Monitor the pressure of a confined air pocket as water moves in and out of a semipermeable membrane by osmosis.
• Study the effect of temperature and concentration on the rate of decomposition of
H2O2.
• Determine the effect of temperature on cold-blooded organisms by monitoring
their respiration.
• Monitor the pressure exerted as yeast ferment sugars and produce carbon dioxide.
• Study human respiratory patterns using the Respiration Monitor Belt.
• Investigate the relationship between pressure and volume, Boyle’s law.
• Study the effect of temperature on gas pressure, Gay-Lussac’s law.
• Monitor barometric pressure associated with weather phenomena.
• Measure vapor pressure of liquids.
Inventory of Items Included with the Biology Gas Pressure
Sensor
Included with your Biology Gas Pressure Sensor are accessories to allow you to
connect it to a reaction container, such as an Erlenmeyer flask. Check to be sure that
each of these items is included:
• two ribbed, tapered valve connectors inserted into a rubber stopper.
• one two-way valve
• two Luer-lock connectors (white) connected to either end of a piece of plastic tubing.
• one 20-mL syringe
How the Biology Gas Pressure Sensor Works
The heart of this circuit is the SenSym SCX30ANC. It has a membrane which flexes
as pressure changes. This sensor is arranged to measure absolute pressure. One side
of the membrane is a vacuum, while the other side is open to the atmosphere. The
sensor produces an output voltage which varies in a linear way with absolute
pressure. It includes special circuitry to minimize errors caused by changes in
temperature.
Pressure Units
Pressure can be measured in many different units. We quote values here in
several of the units shown below. Some equivalent values for 1 atmosphere
are:
1 atmosphere = 760 mm of Hg
= 101.325 kPa
= 29.92 in. of Hg (at 0°C)
= 1.013 bar
= 14.696 psi
We provide an amplifier circuit that conditions the signal from the SCX30ANC
sensor. With this circuit, the output voltage from the Biology Gas Pressure Sensor
will be linear with respect to pressure, with 0.00 volts corresponding to 0.75 atm and
3.0 volts corresponding to 1.54 atm. The output voltage increases 1 volt for each
0.271 atm. This allows the sensor to be used over the range of 0.75 to 1.54 atm.
There is a plastic tube on the Biology Gas Pressure Sensor running from a port inside
the box to a three-way valve on the outside of the box. The two openings (or stems)
on the three-way valve have a small threaded end called a luer lock. You may attach
plastic or rubber tubing to one of the ports using the supplied adapter (already
mounted on extra tubing). The adapter accepts tubing with an inside diameter of
0.125 inches (3.2 mm), and commonly available 3/16-inch plastic tubing can be
connected to it. You can also attach the 20-mL plastic syringe included with the
Biology Gas Pressure Sensor directly to this stem. The other port (pointing upward in
the figure below) of the three-way valve opens to the atmosphere and can serve as a
pressure release. As you set up your experiments, you can always return the pressure
to atmospheric pressure by opening this side stem. When the blue control (or “off”)
handle is aligned with one of the stems, it closes off this stem. Note: Since the side
stem also has a luer lock, it is possible to connect the syringe or the adapter with
tubing in this side position.
Biology Gas
Pressure Sensor
Biology Gas
Pressure Sensor
System closed to the outside atmosphere
Gas pressure sensor open to outside atmosphere
Calibration
We feel that you should almost never have to perform a new calibration for this
sensor. You can simply load the appropriate calibration file that was included in your
data-collection program from Vernier. In older versions of the data-collection
program, there is no calibration file for this probe. If this is the case, and you feel
uncomfortable performing a new calibration, call us and we will send you a free disk
which contains the appropriate calibrations and experiment files. If you would like to
perform your own calibrations, then follow the steps described here.
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The standard calibration procedure we use with all of our sensors is a 2-point
calibration. All of the Vernier data-collection programs allow you to do a
2-point calibration. For the first calibration point perform the following operation:
• Open the three-way valve on the sensor to the atmosphere so it equilibrates to
atmospheric pressure. When the voltage reading displayed on the computer or CBL
screen stabilizes, enter the atmospheric pressure, as recorded with a barometer.
For the second calibration point, do one of the following:
• Connect the syringe to the Biology Gas Pressure Sensor and open the unused stem
of the three-way valve by aligning the blue valve control with the stem that leads
into the Biology Gas Pressure Sensor box. Move the plunger on the syringe so that
the syringe volume is set at 10 mL. Close the unused stem leading to the
atmosphere by aligning the blue valve control with it. Move the syringe plunger so
that the voltage reading displayed is 3.0 volts. Enter 1.54 atmospheres as the value.
If you wish to calibrate in another unit, convert the 1.54 atmospheres using the
value chart at the front of the booklet (e.g., for mm Hg, 1.54 atm X 760 mm Hg/atm
= 1170.4 mm Hg.)
• Connect the extra piece of tubing that came with the sensor to the three-way valve
of the Biology Gas Pressure Sensor. Place the end of the tube under water (see
figure below). The pressure reading will increase 9.679 X 10-4 atm for every
centimeter below the surface of the water. Note how far the air column in the tube
extends below the surface (in centimeters). Calculate the pressure you will need to
enter, using the formula below:
Pressure = atmospheric pressure in atm + depth in cm X (9.679 X 10-4 atm/cm)
If you choose to use different pressure units, make the appropriate conversion.
Enter your calculated value for the pressure to complete the calibration.
Ruler
Flexible Tubing
Water
Sensor
Specifications
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•
•
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Pressure range: 0.75 to 1.54 atm
Maximum pressure that the sensor can tolerate without permanent damage: 4 atm
Sensitivity: 0.271 atm/volt
Resolution using a 12-bit, 5-volt interface (ULI II, Serial Box): 0.000331 atm
Resolution using a 10-bit, 5-volt interface (CBL, original ULI): 0.001323 atm
Sensing element: SenSym SCX30ANC
Combined linearity and hysteresis: typical ±0.2% full scale
Response time: 100 microseconds
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NOTE: This product is to be used for educational purposes only. It is not appropriate
for industrial, medical, research, or commercial applications.
Suggested Experiments
Rate of Plant Transpiration
This experiment allows students to see how environmental factors such as heat, wind,
temperature, and light affect the process of transpiration in plants. This is done by
recording the change in pressure inside a tube filled with water (see figure). As the
plant takes in water, the pressure of an air pocket inside the tube drops. The rate of
pressure change is proportional to the rate of transpiration. To perform this activity,
cut a leafy plant stem at its base and insert the stem into a 20-cm piece of plastic
tubing. Seal the stem in the tubing with petroleum jelly. Fill the tubing with water
and connect the open end to the Biology Gas Pressure Sensor. Secure the plant and
tubing with a ring stand in an upright position with the Biology Gas Pressure Sensor
elevated above the plant base. Connect the sensor to your interface box or CBL. Run
the data-collection program and load the appropriate calibration. Collect data for
10 minutes with the plant under room conditions. Refill the water in the tube and
repeat the experiment with the plant exposed to a different condition. The resulting
graph shows a near linear drop in pressure as time progresses. When different factors
such as wind are added, the graph of pressure change shows a larger negative slope.
Biology Gas Pressure
Sensor
with fan blowing
Confined
Air
control
Base of
Plant
Water Filled
Tube
Rate of Photosynthesis
You can use the Biology Gas Pressure Sensor to graph the pressure that occurs when
oxygen gas is produce by photosynthesis. To do this, place an aquatic plant, such as
elodea, in a container filled mostly with water. Bubble your breath into the water to
saturate it with carbon dioxide. Seal the container with a single-hole stopper that will
accommodate a small section of glass tube. Connect the plastic tubing that comes
with the Biology Gas Pressure Sensor to the glass tube from the stopper. Connect the
other end of the tubing to the sensor. When the container is sealed, it should be nearly
full, with a small air space trapped at the water’s surface. Monitor the pressure in the
container for a 12 to 24 hour period of time. You can see in the graph below that the
pressure rises as the plant photosynthesizes. When there is no light, the plant enters
photorespiration and the pressure drops as the oxygen is consumed by the plant.
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Biology Gas
Pressure Sensor
air space
plant
water
Measuring Respiration of Insects
In this activity the Biology Gas Pressure Sensor is used to measure the decrease in air
pressure in a test tube as crickets consume oxygen for cellular respiration. Place a
cotton ball saturated with potassium hydroxide at the bottom of a 20 X 150-mm test
tube. Insert a dry cotton ball to keep the crickets away from the caustic potassium
hydroxide. Place five adult crickets into the test tube. Seal the test tube with a onehole stopper that has a glass tube inserted in the hole. Connect a small section of
plastic tubing between the glass tube and a Biology Gas Pressure Sensor. Monitor the
pressure for a 10-minute period. Following the 10-minute period, open the air valve
on the sensor to allow the tube to return to room pressure. Place the test tube in a
water bath that is warmer or cooler than the room temperature. When the tube has
adjusted to the new temperature, close the three-way valve to the outside atmosphere.
Monitor the pressure for another 10 minutes. Compare the data of the two collection
runs. Below is a sample graph of crickets at room temperature. To serve as a control,
a second run was made without the crickets.
Gas
Pressure
Water Bath
Crickets
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Human Respiratory Patterns
The respiratory patterns of human subjects can be monitored and graphed using the
Biology Gas Pressure Sensor connected to the Respiration Monitor Belt. The
Respiration Monitor Belt is sold separately by Vernier (RMB, $58). You can study
respiratory patterns and examine how certain stimuli and conditions affect those
patterns. Study the effect of carbon dioxide concentration on respiration rate by
having students breathe into a sealed bag for a period of time. The graph below
displays the respiratory patterns of a 25-year old male using the Biology Gas Pressure
Sensor and Respiration Monitor Belt.
The graph below displays the respiratory patterns of the subject holding his breath.
Note the decreasing size of the waveforms once the subject releases his breath and
begins to take in more air.
Additional Biology Activities
Other activities that you can perform using the Biology Gas Pressure Sensor:
• Determine the rate of respiration in germinating pea or bean seeds.
• Monitor the pressure of a confined air pocket as water moves in and out of a semipermeable membrane by osmosis.
• Study the effect of temperature and concentration on the rate of decomposition of
H2 O2 .
• Determine the effect of temperature on cold-blooded organisms by monitoring
their respiration.
• Monitor the pressure exerted as yeast ferment sugars and produce carbon dioxide.
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Weather Studies
The Biology Gas Pressure Sensor can be used as an accurate barometer for weather
studies. The sensor is temperature compensated, so changes in room temperature will
not interfere with the data. It is especially interesting to watch pressure changes as a
storm moves in. Note: For more precise barometric pressure measurements in the
range of 0.80 to 1.05 atmospheres, Vernier also sells a Barometer (order code BARDIN, $56).
Boyle’s Law (Pressure vs. Volume)
Boyle’s law is a classic physics and chemistry concept that can be easily
demonstrated using the Biology Gas Pressure Sensor. One easy way to do this is to
use the plastic syringe included with the sensor. Connect the plastic syringe to one of
the valve stems with a gentle 1/2 turn. Close the stem that leads into the Biology Gas
Pressure Sensor box using the blue control handle and set the syringe to a volume of
10 mL. Then close the open stem.
Pressure Sensor
The pressure inside the syringe is now equal to atmospheric pressure at a volume of
10 mL. You are now set to collect pressure-volume data. Start your readings at 13
mL and take readings in 1-mL increments until you reach 6 mL. At reading volumes
below 6 mL or above 13 mL, you will go beyond the maximum and minimum
pressure values that can be correctly measured with the Biology Gas Pressure Sensor.
Sample data collected with this sensor and the syringe are shown here:
Sample Boyle’s Law Graph
Note: To make pressure measurements in the range of 0 to 6.8 atm, Vernier also sells
a Pressure Sensor (order code PS-DIN, $66).
Gay-Lussac’s Law (Pressure vs. Absolute Temperature)
Gay-Lussac’s law states that the pressure of a confined gas is directly proportional to
its absolute temperature if the volume remains constant. The white, threaded adapter
end of the long piece of plastic tubing can be connected to one of the valve stems
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with a full turn. The other end can be connected to the rubber stopper apparatus
(included with your Biology Gas Pressure Sensor), which is in turn inserted into a
125-mL Erlenmeyer flask. This provides a constant-volume gas sample.
This stopper can be inserted into an Erlenmeyer flask to provide a constant-volume
gas sample. Pressure-temperature data can be collected using a temperature probe or
thermometer along with the Biology Gas Pressure Sensor. Place the flask in water
baths of different temperatures. Take data to see how pressure changes with
temperature. Remember that all temperatures should be measured using the Kelvin
temperature scale. Using the same apparatus, pressure and temperature data may be
extrapolated to determine a Celsius temperature value for absolute zero.
Studying Chemical Reactions by Monitoring Pressure
Many chemical reactions produce gases that can cause a pressure increase in a sealed
container. The pressure change can be used as a way of monitoring the rate of
reaction. As a very simple example, the graph here was made using the Biology Gas
Pressure Sensor to monitor the reaction of Alka-Seltzer® and water. We made a hole
in the top of a plastic 35-mm film container. We then ran a tube from the Biology
Gas Pressure Sensor through the hole and sealed it with silicone sealant. We then
placed a piece of an Alka-Seltzer tablet and 10 mL of water in the container and
sealed it. The graph shows the pressure increase as the reaction takes place. Note the
sudden drop in pressure when the lid of the container pops off. You can study the
rate of reaction, change the temperature, etc.
Using the Biology Gas Pressure Sensor
to Monitor the Rate of Reaction
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Using this Sensor with the Texas Instruments CBL System
This sensor can be used with the Calculator-Based Laboratory System from Texas
Instruments. Here are some suggestions for using it with the CBL:
• Connect the CBL unit to the TI graphing calculator using the link ports located on
each unit. Be sure to push both plugs in firmly.
• Using a CBL-DIN adapter, connect the sensor to any of the analog input ports on
the top or left side of the CBL unit (CH1, CH2, or CH3). In most cases, CH1 is
used. The CBL-DIN adapter is available from Vernier for $5.
• Run a program to monitor the signal from the sensor. We strongly recommend
using programs developed specifically for use with this sensor. Vernier has
programs which support this sensor. One program we recommend for use with this
sensor is CHEMBIO from the Vernier collection of programs.
The Vernier programs for the CBL are available on the Internet or they can be
obtained in disk form. Once you have these programs, it is a simple matter to
load them into a calculator using TI-GRAPH LINK™.
• To obtain our programs through the World Wide Web, download the files
from our web site:
www.vernier.com
• These programs can also be obtained on disk. The programs are a part of our
CBL Made Easy! Package, which includes Macintosh and IBM-compatible
disks and our CBL Made Easy! user's guide (order code CMEP, $12).
Other notes for using this sensor with the CBL System
1. The resolution of this probe when used with the CBL System is 0.0013 atm or
1.005 mmHg.
2. If you write your own program for use with the Biology Gas Pressure Sensor,
keep in mind the following:
• The voltage produced by this probe is linear with respect to the pressure it
senses. The slope and intercept for calibrating this sensor are:
For pressure readings in atmospheres:
Intercept (k0): 0.729
Slope (k 1) : 0.271
For pressure readings in kilopascals:
Intercept (k0): 73.866
Slope (k 1) : 27.459
For pressure readings in mm Hg:
Intercept (k0): 554.175
Slope (k 1) : 205.825
For pressure readings in inches of Hg:
Intercept (k0): 21.875
Slope (k 1) : 8.125
If you use these values in your program, you will get reasonably accurate
pressure readings. Add or modify the command 4 line in your program so that it
reads:
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For pressure readings in atm:
{4,channel number,1,1,8.729,8.271}¸L6
For pressure readings in kilopascals:
{4,channel number,1,1,73.866,27.459}¸L6
For pressure readings in mm Hg:
{4,channel number,1,1,554.175,205.825}¸L6
For pressure readings in inches of Hg:
{4,channel number,1,1,21.875,8.125}¸L 6
• In place of "channel number", put a 1, 2, or 3 for channel the probe will be
connected to on the CBL.
• This probe should be used with the CBL set for the 0 to 5 volt range (operation
1 in command 1).
• For more information on writing programs for TI graphing calculators and the
CBL, see your calculator manual and the CBL System Guidebook.
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Vernier Software & Technology
13979 S.W. Millikan Way
Beaverton, OR 97005-2886
(503) 277-2299 • FAX (503) 277-2440
[email protected] • www.vernier.com
Rev. 3/2/00