STATE LOUISIANA UNIVERSITY MECHANICAL ENGINEERING DEPARTMENT ME3603 - Fundamentals of Instrumentation Semester II 2003-2004
LABORATORY 2
Linear Instrument Calibration Pressure Sensor
Abstract A pressure transducer with an analog voltage output requires calibration in order to become usable. The most important part of the calibration is to find the functional relationship between the input (pressure) and output (voltage) of the device. This can be achieved by using a pressure measuring standard and the appropriate calibration set-up. The objective of this laboratory is to design the calibration procedure and determine the calibration relation for a piezoresistive diaphragm pressure transducer using available instrumentation. Goals The purpose of this experiment is for students to demonstrate and gain the following skills: 1. Measure pressure using a standard pressure dial gauge. 2. Measure pressure using an electronic pressure transducer. 3. Perform a calibration of a basic measuring device. 4. Formulate a calibration curve for a measuring device. 5. Design and implement an experimental procedure. In addition, students performing this experiment should gain basic understanding of pressure measurement principles and calibration. Introduction In addition to temperature, many thermo-fluids, manufacturing, and chemical processes are also highly dependent on pressure. As a result, it is often important to measure pressure. Although many types of pressure transducers are available, two common types of gauges are used in this lab: 1. A Bourdon tube pressure gauge with dial output. 2. A piezoresistive diaphragm pressure transducer with voltage output. The latter requires calibration in order to be used, while the former has a pre-calibrated dial indicator scale. Equipment and Materials 1. Ametek Model T-740 Pneumatic Hand Pump (0-200 psi range) 2. Wika Standard Pressure Gauge (2 inch dial, 0-100 psi range, attached to pneumatic hand pump) 3. Wika Eco-Tronic Pressure Transducer (0-10 V output, 0-100 psi range, attached to pneumatic hand pump)
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4. Fluke 73 Series II Digital Multimeter (please do not drain the battery by leaving the meter on) 5. Tenma 72-4045A Triple Output DC Power Supply 6. Thermometer Procedure The objective of this laboratory is to obtain the calibration curve of a Wika Eco-Tronic Pressure Transducer. You are responsible for developing your own procedure in this lab. The procedure should accomplishing this objective. In order to facilitate the experiment design process you are required to fill out a laboratory planning form, which is available at the end of this section. This form should be presented to the lab instructor for approval within the first half hour of the lab session. If the experiment is not finished by the end of the lab session, you should make an appointment to finish the lab. You may take as much data as desired but it is recommended that you take at least 20 data points over the pressure calibration range. Information on available pressure instrumentation is provided below. Directions for Use of the Wika Standard Pressure Gauge This pressure gauge is of the Bourdon tube class. This type of pressure gauge is very widely used in practice since it is inexpensive and provides a clear direct readout on its dial. Although highly accurate pressure gauges of this type are available as calibration standards, the majority gauges of this type are not highly accurate. The gauge available in the lab has an accuracy of 1.5% FSO and a duty range limited to 75% FSO, according to the manufacturer. So, please do not exceed 75 PSI when using it as a standard of calibration. Directions for Use of the Wika Eco-Tronic Pressure Transducer This pressure-measuring device is based on a piezoresistive diaphragm sensor/transducer and produces a voltage output. Wires have already been attached to the device to allow quick electrical connections to be made. The following steps should be taken to make this device operational: 1. Connect the device to a 15 VDC power supply. The purple wire should be connected to ground, the black wire should be connected to the negative terminal of the power supply, and the red wire should be connected to the positive terminal of the power supply. Warning: there is risk of personal injury if one is careless while making the connections or manhandling the device. 2. Connect a DC voltage-measuring device (0-10 V range) between the black and yellow wires. The voltage measured is related to the pressure to which the transducer is exposed through a calibration relationship.
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ME3603: Semester II 2003-2004 Directions for Use of the Ametek Pneumatic Hand Pump [2]
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The T-740 Pneumatic Pressure Tester is designed to manually generate up to 300 psig for quick accurate checks of pressure gauges, transmitters, transducers, and other pressure measuring instruments. The following instructions are taken directly from the manufacturer's literature and do not reflect the fact that the hand pump has already been attached to two 100 psi gauges to save time in the lab. 1. Attach gauge or pressure device to be calibrated to the 1/4" NPT hose fitting. Warning: Do not attach tester to a high pressure source. Follow these instructions carefully to avoid damage to the tester and/or personal injury. 2. Turn needle valve on the left side of the tester clockwise until it is tight by hand only. 3. Pump movable handle until the desired pressure is obtained. Increase hand pressure on handle at the end of the stroke to obtain higher pressures. Warning: Do not use the hand pump's capabilities to overpressure the gauges. 4. Turn the vernier (which is part of the handle) counterclockwise to decrease pressure in the tester and clockwise to increase pressure of item being tested. Turn vernier slowly for incremental precise pressure control. References: [1] Richard S. Figliola and Donald E. Beasley, Theory and Design for Mechanical Measurements, 3rd Ed., John Wiley & Sons, New York, 2000. [2] Instruction Bulletin for Hand Held Hydraulic Pressure Tester Model T-620/T-820, Hand Held Pneumatic Pressure Tester Model T-730/T-740/T-830/T-840, Hand Held Vacuum Tester Model T-750/T-850, Form No. 84-10, Rev. 5 10/97 ER97-119, Ametek Test and Calibration Instruments Division.
Reporting Requirements
A brief-format report is required for this lab. The guidelines given in the Report Writing Guide are to be followed in the preparation of your report. Any deviation from these guidelines will result in a substantial reduction in report grade. In addition to the general requirements for the report, appropriate sections of your report should also address the following issues: 1. Provide the mathematical equation of the calibration curve of the piezoresistive diaphragm pressure transducer. 2. Determine the static sensitivity of the transducer.
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3. Present error analysis to find the range of reported accuracy for each instrument from available catalog data. Convert percent accuracy in each measurement to the appropriate physical variable. 4. Report the confidence interval for the calibration curve, and compare to the reported accuracy of each instrument. 5. The planning form filled out in the beginning of the lab session should be attached in the Appendix section of your report.
Laboratory Data Sheet
For your convenience, a laboratory data sheet is provided. This data sheet will guide you to record some of the basic information required for your technical report. Please fill out this data sheet by the end of the lab meeting. This sheet must be signed by the lab instructor and attached to your report in the Appendix section.
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LABORATORY 2
Pressure Measurement - Calibration
Data Sheet Name: Section: SSN: Lab Station: TA Signature: Pressure (psi) Voltage (Volt)
Pressure Transducer Calibration Data Manufacturer: Model: S/N Notes: Wika Eco-Tronic
# 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
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LABORATORY 2 - PLANNING FORM DATE:___________ SECTION:________________ GROUP:________________
EXPERIMENT NUMBER/TITLE:____________________________________________ GROUP MEMBERS: ___________________________________ _____________________________________ _____________________________________ _____________________________________ BRIEF STATEMENT OF OBJECTIVE:________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ TEST APPARATUS: _____________________________________________________ _________________________________________________________________ _________________________________________________________________ _________________________________________________________________ MEASURED QUANTITIES:_________________________________________________ _________________________________________________________________ _________________________________________________________________ _________________...