Experiment #5 Pressure Transducers / Gages:
http://egweb.mines.edu/eggn250/exp5.htm
3 ways to measure pressure:
1.) Bourdon Tube Pressure Gauge
http://www.wika.com/web/ProductInformation/ProductInformation_Technical_BourdonTubeOperatingPrinciple.html
1. Pointer
2. Bourdon tube
3. End piece
4. Link
5. Quadrant
6. Movement
7. Connection (or socket)
8. Dial
Bourdon tube pressure gauges are widely used in all branches of industry. The construction is simple yet rugged, and operation does not require any additional power source. The Bourdon tube element is directly exposed to the medium being measured and is normally made of copper alloy (brass) or stainless steel as the application demands. Except for absolute pressure gauges, WIKA Bourdon tube gauges measure pressure relative to the pressure of the surrounding air.
The Bourdon tube measuring element is made of a thin-walled tube that is either bent into a semicircle (C-shape tube) or spirally wound (coiled safety tube). When pressure is applied to the measuring system through the Pressure port, the pressure causes the Bourdon tube to straighten itself, thus causing the End piece to move upward (or downward for vacuum measurements). The movement of the end piece is transmitted via the Link to the Movement. The movement converts the linear motion of the Bourdon tube end piece to a rotational movement which in turn causes the Pointer to indicate the measured pressure.
Bourdon tube pressure gauges are designed for the measurement of pressure and vacuum and are generally suitable for all clean and non-clogging liquid and gaseous media.
Various types of Bourdon tubes are used. C-shape Bourdon tubes are typically used for ranges up to 800 psi. Higher ranges use coiled Bourdon tubes for safety. All WIKA Bourdon tube pressure gauges are capable of withstanding pressures up to 30% above their full span without a shift in calibration.
Bourdon tube pressure gauges are available to measure full vacuums, compound and pressure ranges from 0-10 psi to 0-60,000 psi with an accuracy from ±0.1% to ±3/2/3% of span (ASME Grade 4A to Grade B).
2.) CSM Pressure transducer:
The CSM made transducer has a strain gage mounted on a circular flat plate of brass/copper.
· Air is confined in a chamber with a copper/brass spherical cap (E ~ 16*106 psi)
· Air pressure causes the spherical cap to bulge
· Knowing
o the modulus of elasticity of this spherical cap
o the strain associated with the bulging cap
o the geometry of the cap (spherical)
allows you to calculate the pressure inside the chamber
Use a ¼ Wheatstone bridge to measure the strain of the deflecting plate:
To find P from CSM pressure transducer:
Record Vout from CSM transducer as a function of the pressure
- Check for hysteresis: (Q7, Q11,
Get data points while both loading and unloading the gage
- Check for repeatability: (Q11)
Get two sets of data taken by two different people
The stress on a circular surface whose outer edge is supported and has a uniform load over the entire area is:
s = (39/80)(pa2/T2),
where:
p = differential pressure,
Note:
Differential pressure = inside p – outside p
Outside pressure: http://www.srh.noaa.gov/data/forecasts/COZ039.php?warncounty=COC059&city=Golden
http://www.crh.noaa.gov/den/products/webpres.html
Absolute pressure = inside pressure, or pressure measured relative to a vacuum
a = radius = 0.75 in
T = thickness = 0.03 in
For #7 Use the following excel spreadsheet:
Example graph from CSM transducer (Notice hysteresis, nonlinearity in data…)
3.) Omega manufactured transducer
http://www.omega.com//Pressure/pdf/PX178.pdf
Sensitivity:
60mv for 0-150 PSIG
With a 10V bias:
With a 5V bias
PX236 Pressure transducer:
This transducer has a full bridge built in
All you have to do is
provide excitation voltage (10 V)
ground it
measure the signal out of it
Three wires:
+ excitation voltage (red)
ground (black)
signal = Vout across bridge (Green and white wires)
Example graph from OMEGA transducer… (It is allot more linear and repeatable than CSM…)
Note:
Max Pressure at Each Lab Bench Station in CTLM 125
Spring ‘03
3 52 psig / 4 45 psig / 9 46 psig / 10 22 psig2 53 psig / 5 31 psig / 8 45 psig / 11 45 psig
1 50 psig / 6 37 psig / 7 46 psig / 12 46 psig
Avoid using benches 5, 6, & 10 for Expt. 5, so the students can obtain a larger range of data.
These pressures haven’t changed since Fall ’02.
Experiment #5 Prelab:
#1)
in short…
pressure to stress:
The stress on a circular surface whose outer edge is supported and has a uniform load over the entire area is:
s = (39/80)(pa2/T2),
where:
p = differential pressure,
Note:
Differential pressure = inside p – outside p = gage pressure = psig
Outside pressure: http://www.srh.noaa.gov/data/forecasts/COZ039.php?warncounty=COC059&city=Golden
http://www.crh.noaa.gov/den/products/webpres.html
Absolute pressure = inside pressure, or pressure measured relative to a vacuum = psia
a = radius = 0.75 in
T = thickness = 0.03 in
Stress to strain: Remember, E = stress over strain
Use Young’s modulus E = 16*106 psi (this is inbetween values for brass and copper) (see http://www.csuchico.edu/~jpgreene/itec104/m104_c12/tsld015.htm)
Strain: use calcs from previous labs…
Gage factor = 2.7
#5, #6:
go to the reference on: http://egweb.mines.edu/eggn250/
read through the error stuff…
Lab report:
#1 - #4 ) Bourdon tube pressure gauge. Put these back together when you are done for the next section to use!
#5 ) Measure pressure with the PX236 pressure transducer while simultaneously measuring Vout from the CSM ¼ bridge…
#7) C = CSM, O = omega
- Check for hysteresis:
Get data points while both loading and unloading the gage
- Check for repeatability:
Get two sets of data taken by two different people
Use this spreadsheet:
Point / Vout / DR/R / strain / Pressure (gage) / PressureCSM / Omega / CSM / CSM / gage / CSM - calc / Omega - calc / abs
1
2
3
Show the equations that you are using in the spreadsheet!!
#10) This one is worth 20 points – do a good job!
#13) Plastic vs elastic deformation…
#16) string = letters (abc, labels on graphs, etc.)
integer = 1, 2, 3, = blue lines
Boolean = true/False, On/off, green stuff
floating point = 1.3256741… = orange stuff
array = column of numbers
Experiment 5 – Big Picture, Corrections, Guidance & PreLab Help
So far, you’ve experimented with a couple of electro-mechanical devices, Thermistors and Strain Gages. And you’ve used them to measure several useful mechanical properties: temperature, temperature sensor response, cantilever beam response to force and vibration, and coefficient of thermal expansion for 2 different materials.
Big Picture: For this experiment you will be working with a New Electromechanical Device – a Pressure Transducer. You’ll be measuring the response from 2 transducers simultaneously, commercial (OMEGA) and homemade (CSM). The Homemade one uses a brass or copper plate with a bonded metallic Strain Gage[1], whereas the Commercial one uses a semi-conductor Strain Gage[2] (more info in class).
A ¼ Bridge Circuit will be required for the CSM pressure transducer. The commercial transducer’s bridge circuit is on a silicon chip inside, but you will need to supply an excitation voltage, obtain the output voltage, and ground it, of course.
Experiment 5 – Corrections/Clarifications to Lab Manual
1) Dr. King has made some useful additions to the list of reference material & fixed some of the errors with this lab. Thanks Dr. King. Use the references listed, esp. MatWeb, and Current Atmospheric Pressure.
2) We actually have only One OMEGA pressure transducer. The PX-236. This model has been discontinued at OMEGA, so you won’t find specifics at the omega website. See “Some Useful Info” below.
3) The CSM Pressure transducer is made using either a round brass or a square copper plate, as shown in class last week. However, if you use the Copper information given in the manual it will send you to the right value for Young’s Modulus (E). Any of the states given (cold drawn, cold worked or annealed) will yield the same value for E.
4) Use the plate thickness, T = 0.035” stated on the Pressure sheet, pg. 158, versus the 0.03” in the experiment write-up.
Experiment 5 – Some Useful Info
1) For the OMEGA X-ducer -- You’ll need the Specifications and Application Notes. They are on pages B-14 and Z-14 of the OMEGA manuals in the back of the lab.
a. John Synhorst has been nice enough to make a double-sided copy for each MEL I student.
b. They are on the table right inside the door of CTLM 125.
c. You can go by sometime tonight (Tues) before 8 PM or Wed 10:30 AM – 5 PM to pick one up.
2) The spec sheet lists the pressure range, max voltage output, and model#. The model # on this transducer is 236PC150G V.
a. OMEGA transducer(s) specified excitation voltage is 10 volts. We use 5 volts excitation. Therefore our maximum output at 150 psig would be 30 mV, not 60.
PX 236 0-150 psig 60 mV @ 10 V (excitation)
PX 236 0-150 psig 30 mV @ 5 V (excitation)
The equation at the bottom of the sheet shows the sensitivity with this 5V excitation.
3) The application notes (pg Z-14) describe linearity, sensitivity, hysteresis, zero (null), and repeatability errors. They also define Absolute, Differential and Gage pressure.
4) One other important note. I would read the page on Grounding, if you haven’t already. The data taking, especially for the CSM transducer, will be next to impossible without proper grounding of your circuit.
Experiment 5 – Help on PreLab Questions
Q1) Use atmospheric pressure at Jeff Co airport from the NOAA website given, under additional reference material. Use gage pressure for p. Remember that E = s/e, or e=s/E. Use the MatWeb site to find E for copper (Cu). You may have to review your notes on strain gages and ¼ bridge calculations for Vout. The Gage factor on this strain gage is 2.07, as stated on the pressure sheet.
General
Semiconductor strain gages are devices which vary in resistance as strain is applied to them. This property makes them very useful in measuring extremely small amounts of force with accuracy and precision. Creative uses for these gages have ranged from the measurement of internal pressures inside solid rocket engines to delicate medical apparatus used in microsurgery.Gages made from semiconductor materials have advantages over more conventional types of strain gages. These include homogeneity, increased sensitivity, and decreased size. Gages made by Micron Instruments range down to 0.027" (0.69 mm) in length.
Micron semiconductor strain gages are made from Czochoralski pulled boron doped bulk silicon. They have no P/N junction. The silicon is etched to shape, eliminating the potential for molecular dislocation or cracks, thereby optimizing performance.
All gages manufactured by Micron must pass through rigorous tests before they are approved for use by our customers. The behavior of each gage at different temperatures is measured and the gages are matched to each other based upon these measurements. Customers may specify matched sets of 2, 4, or more gages, or purchase unmatched sets of bulk gages.
Bar Semiconductor Strain Gages
/ HomeDownload this data sheet
Part Number / X dim / Y dim / Z dim / Lead Attachment / Thickness / Resistance @ 78 deg F / Gage Factor / TCGF* / TCR*
SS-027-013-500P / 0.027" / 0.013" / 0.009" / Ball Bond / 0.0004" / 540 ± 50 Ohms / 155 ± 10 / -18 / 24
SS-080-050-120P / 0.080" / 0.050" / 0.008" / Welded / 0.0004" / 120 ± 20 Ohms / 120 ± 10 / -9 / 5
SS-090-060-500P / 0.090" / 0.060" / 0.008" / Welded / 0.0004" / 540 ± 50 Ohms / 140 ± 10 / -13 / 16
SS-150-125-25P / 0.150" / 0.100" / 0.009" / Welded / 0.0008" / 25 ± 3 Ohms / 100 ± 10 / -10 / 6
SS-250-225-120P / 0.250" / 0.225" / 0.009" / Welded / 0.0004" / 120 ± 20 Ohms / 100 ± 10 / -10 / 6
* per 100 degrees F
"U"-shaped Semiconductor Strain Gages
Part Number / X dim / Y dim / Z dim / Lead Attachment / Thickness / Resistance @ 78 deg F / Gage Factor / TCGF* / TCR*SS-037-022-500PU / 0.037" / 0.022" / 0.016" / Welded / 0.0004" / 540 ± 50 Ohms / 150 ± 10 / -13 / 17
SS-047-025-500PU / 0.047" / 0.025" / 0.016" / Welded / 0.0004" / 540 ± 50 Ohms / 140 ± 10 / -13 / 16
SS-060-033-300PU / 0.060" / 0.033" / 0.016" / Welded / 0.0004" / 325 ± 40 Ohms / 100 ± 10 / -10 / 6
SS-060-033-500PU / 0.060" / 0.033" / 0.016" / Welded / 0.0004" / 540 ± 50 Ohms / 140 ± 10 / -12 / 14
SS-060-033-2000PU / 0.060" / 0.033" / 0.016" / Welded / 0.0004" / 2000 ± 100 Ohms / 155 ± 10 / -18 / 24
SS-080-050-10000PU / 0.080" / 0.050" / 0.013" / Welded / 0.0004" / 10000 ± 1000 Ohms / 175 ± 10 / -23 / 42
SS-095-060-350PU / 0.095" / 0.060" / 0.016" / Welded / 0.0004" / 350 ± 50 Ohms / 120 ± 10 / -9 / 5
* per 100 degrees F
"M"-shaped Semiconductor Strain Gages
Part Number / X dim / Y dim / Z dim / Lead Attachment / Thickness / Resistance @ 78 deg F / Gage Factor / TCGF* / TCR*SS-060-040-2500-PM / 0.060" / 0.040" / 0.032" / Welded / 0.0004" / 2500 ± 150 Ohms / 140 ± 10 / -13 / 17
* per 100 degrees F
DEFINITIONS
GAGE FACTOR
The gage factor (G.F.) of strain gage is a dimensionless number defined by the formulaG.F. = (R - Rm)/RE
where
R = nominal unstrained resistance of the gage,
Rm = the measured resistance of the gage under some known strain, E,
and
E = the strain on the gage.
Thermal Coefficient of Gage Factor (TCGF)
The Thermal Coefficient of Gage Factor (TCGF) is due to thermal effects in the silicon matrix of the strain gage inhibitiing the flow of electrons. The formula for TCGF isTCGF = (100 x (GF2 - GF1))/(GF1 x (T2 - T1))
where
GF1 = Gage factor at ambient temperature T1;
GF2 = Gage factor at elevated temperature T2;
T1 = ambient temperature (78 deg F);
and
T2 = elevated temperature.
Thermal Coefficient of Resistance (TCR)
The Thermal Coefficient of Resistance (TCR) is also due to thermal effects in the silicon matrix affecting the flow of electrons. The formula for TCR is given byTCR = (100 x (R2 - R1))/(R1 x (T2 - T1))
where
R1 = Resistance at ambient temperature T1;
GF2 = Resistance at elevated temperature T2;
T1 = ambient temperature (78 deg F);
and
T2 = elevated temperature.
For further information, request a set of strain gage specifications from our technical support staff.
Strain Gage Technical Data