Examples from Laboratory Practice

Abstract

In Chap. 14, we have dealt with topics on signal conditioning and manipulation. We have also considered the use of a digital voltmeter and the current loop. In most measurement applications, the experimental setup would use several instruments to monitor the various process variables, possibly in real time. In most cases, the experimenter would like to have a real time (or near real time) tracking of the variables as they change during the experiment. It is quite difficult or impossible to take readings individually, note them down in a record book, and later use these in obtaining the information that is to be communicated as the outcome of the experiment.

Issues involved in signal conditioning have been considered in Chapter 15. In practice, it is necessary to make sure that the measurement using a particular instrument will give readings that are authentic. Authentication of the reading is made by calibration of the measuring instrument, i.e. by validating it against measurement by a standard instrument that is traceable to an accepted standard. It is generally insisted that the standard instrument should have an accuracy of at least four times that of the instrument that is being calibrated. For example, if the measuring instrument is accurate to within 1% the standard instrument should have an accuracy of at least 0.25%.

Exercise V

 

Ex. V.1::

Ready-to-use instrumentation amplifiers are available in the form of IC chips from many manufacturers such as Analog Devices.* Study the specifications of some of them and comment on how they may be used in laboratory practice. Discuss the methods of removing or reducing noise in high gain amplifier circuits.

*(accessible at http://www.analog.com)

Ex. V.2::

An inexpensive amplifier is the 741$^\star$ series IC available from various manufacturers. This IC is available with one, two, or four amplifiers in a single package. Refer to manufacturer Application Notes and discuss how they may be used for simple laboratory applications.

$^\star$ A useful tutorial on 741 is available at

http://www.uoguelph.ca/~antoon/gadgets/741/741.html

Ex. V.3::

Charge amplifiers are used in many instrumentation applications. Prepare a note on these, using library and web resources.

Ex. V.4::

We have discussed in brief about filters in Chap. 15. More details can be found in appropriate references that deal with signal conditioning. Prepare a note on filters and how they may be used for signal conditioning in instrumentation.

Ex. V.5::

A stroboscope is useful in the measurement of angular velocity. It consists of a lamp that may be “flashed” at the desired frequency. Use library resources to learn about stroboscope and how it may be used. What are all the uses to which a stroboscope may be put to? Discuss.

Ex. V.6::

An experimental rig is to be designed to measure the variation of heat transfer coefficient with airflow normal to the axis of a cylinder. Give a schematic of a suitable rig for this purpose. What are the instruments you will need to use for conducting the experiment? Indicate all the precautions you need to take in performing an experiment using the rig. Indicate how you would tabulate the data and also how you would analyze it to arrive at a useful design relationship.

Ex. V.7::

Data Acquisitions Systems and Digital Data Loggers are used very commonly in the laboratory. These are available from many manufacturers. Prepare a detailed report on these and compare Data Acquisition Systems from at least two different manufacturers. Discuss the factors that go into the choice of a particular system.

Ex. V.8::

The mean effective pressure in an engine cylinder is to be estimated using a suitable pressure transducer. The maximum engine speed is $3000\;\text {RPM}$ while the idling speed is around $800\;\text {RPM}$. How would you choose a suitable pressure transducer for this purpose? Also, how would you analyze the data?

The following reference may be useful:

W. Doggett, Measuring Internal Combustion Engine In-Cylinder Pressure with LABVIEW, accessible at: http://www.ni.com/pdf/csma/us/361574a1.pdf.