Learning how to use a voltmeter, an X-Y recorder and an oscilloscope

Background:

An experimental chemist is often facing the task of learning how to use a new instrument, how to fix an existing instrument or how to revive an instrument which was donated by somebody else. The purpose of this lab will be to loose some inhibition in dismantling an instrument, learning about its various parts and to study its function. A voltmeter and an oscilloscope will be used as the major tools.

Materials:

Oscilloscope

Voltmeter

Mechanical tools (screwdrivers, pliers, etc.)

A brand new boxed recorder

Old, perhaps not working recorder

Magnetomechanical universal meter (the old style, not a digital one)

Other electronic device used for dissection and learning about inside components.

Caution:

Electronic devices powered from 120 V outlet will have, when plugged in, somewhere inside high, dangerous voltage. Learn to recognize the dangerous spots inside the instrument.

1. A brand new recorder, still boxed, will be presented to you. Set it up, make it work and test whether its performance corresponds to the specifications. This is a real-life situation where usually no more information is given. Apply your skills

2. Open up an old recorder and spend some time learning about its internal workings. In particular, find the mechanism which is used to adjust the recorder range (sensitivity). Also, find the servomechanisms and from discussion with your laboratory partners, try to deduce how such a servomotor works..

3. Learn the inside workings of the universal power source used in Lab #1. Specifically:

A. Find a transformer and figure out what is (are) its secondary output(s). Caution: the primary is 120V, potentially dangerous voltage. Determine what is its rated power.

B. Find transistors, resistors, diodes and capacitors on the printed circuit boards. Document by sketches in your lab reports.

C. Find with an oscilloscope the waveform of the voltage coming from the transformer, then entering and leaving the diodes and finally passing through a series of filters.

D. Study the meaning of output 18.

4. Learn how to use a mechanomagnetic universal meter. In particular, design a series of experiments which would allow you to determine the internal resistance of the meter used as a voltmeter. Is the resistance the same at all voltage ranges? (Note that the nominal resistance is inscribed on the front panel. Report a value which you have determined from your measurement, not the one copied from the instrument.)

Results:

Report your findings commenting on problems encountered, etc.

Question: In comparison with the magnetomechanical multimeter, what are the advantage of a digital meter?