MONTANA STATE UNIVERSITY   
DEPARTMENT OF MECHANICAL ENGINEERING                                   

ME 360 Spring 2014 Measurements and Instrumentation Laboratory

EXERCISE 9: VARIABLE CAPACITANCE TRANSDUCER APPLICATIONS: 
ACCELEROMETERS      

R. Larson

Goals:
1. Investigate the characteristics of a MEMS Capacitive Accelerometer, in a self-guided laboratory experience. 
2. Generate a laboratory test plan and execute the plan.
3. Utilize a portable tablet PC-supported Data Acquisition System to obtain data from the field.

References: 
A. Wheeler & A Ganji, Introduction to Engineering Experimentation
ME360 Lecture & laboratory instruction
PCB Piezotronics Capacitive Accelerometer Installation and Operating Manual  (Caution: 20MB file size.)

Equipment: 
PCB Piezotronics Model 3801D1FB20G/M001 Capacitive Accelerometer
        - Sensitivity varies with unit, approximately 99.6 mV/g (= 10.16 mV/m/s2)
      
  - Offset Voltage varies with unit, approximately = -12.0 mV @ 0 g.

MIE Department Laptop Computer with LabVIEW Software
Wire or cable sufficient to provide accelerometer excitation voltage and signal acquisition


Discussion:
PCB Piezotronics corporation states that the "series 3800 Variable Capacitance Accelerometers achieve true DC response for measuring uniform or constant Acceleration and low frequency vibration."  In this lab, each self-defined group is responsible for choosing a project of interest that involves acquisition and interpretation of acceleration data.

The accelerometers are approximately 1" cubes, and are sensitive in a single axis only. They require a minimum of 5 volts DC excitation, which can be provided from the USB-6008 DAQ system. Output signal is a function of the acceleration of the unit, per Sensitivity specifications. The accelerometers can be temporarily affixed to test articles using tape, hot glue, etc. Do not cut accelerometer wires short!

Sampling rate of the LabVIEW code should be selected with consideration of the test being performed: Impact events require very high sampling rates and produce large volumes of data in a short time.

Procedure:

A. PRE-LAB

    1. Choose your group members: Four sets of equipment are available, so for each lab please self-select a groups of 4 or fewer individuals.
    2. As a Group, define your measurement subject: Choices are endless, for instance one could monitor the acceleration of the head of a golf club or hockey stick, the acceleration of a bicycle jumping a curb, the deceleration of a dropped object. And since F=M*A, if the accelerometer is attached to an object of known mass the Forces involved in certain phenomenon can be calculated. Transient events such as impacts can be recorded. For example, How much difference in force is noted between impacts on a hard surface versus a padded one? Literally the sky is the limit, within reason.
    3. Submit your group's membership and project selection prior to the start of the lab. This document should define the specific phenomenon you plan to investigate, the data you will gather, and the location of testing. Use a format similar to typical ETME360 Lab Handouts.

Rules: All equipment must be returned intact and undamaged. All MSU, Local, State, and Federal rules/laws/procedures apply. (No guns on campus, no speeding, etc.) You MUST write and use LabVIEW code to control a DAQ system to obtain acceleration data. You MUST complete your experiment during the scheduled 2 hour lab time slot. Results must be suitable for publication/dissemination in all public forums.

B. LAB

        Once your proposal is approved, carry out your plan. You may wish to write your LabVIEW code prior to the lab period to give more time for project execution. Once completed, be sure to check data integrity immediately after each test to ensure you recorded data!

Results: 
1. 
 You wrote the requirements, and you must conform to them. Your Pre-lab document will be used to evaluate your results. For instance, if you specified comparison with some standard or have a project involving complex calculations, you must include these items in your report.

2. Prepare and include correctly formatted graphs of the results of each test, as defined in your test plan runs. INCLUDE PHOTOS of your test.

3. Compile other elements of your report in the usual manner: The Sample Calculations section should be complete and accurate.  Clearly discuss any data or sampling issues that might affect accuracy of your derived results. 

Note: Do not submit raw voltage data downloaded from the PC with your report: Your Acceleration graphs will provide sufficient information for the purpose of determining performance. Include all other pertinent data sheet items, copies of the LabVIEW code, etc.