1. Review of fundamental concepts from physics

• Charge
• What is it?
• What effects does it produce - discuss inverse square force law.
• Charge units
• Positive and negative charge

2. Voltage & Voltage Sources & Sensors

• In-class demo and questions.
• Voltage is defined as Potential Energy (joules) per Unit Charge (couloumbs).
• Voltage is measured between two points in space (usually points on an electrical element or within a circuit).
• Look at a wall plug
• Examples of voltage sources (pass around in class)
• Battery
• Thermocouple
• Measuring a voltage with a voltmeter.
• Question:  Why does the voltmeter have two leads?
• Demo with battery & thermocouple.
• In class question on polarities.

• Problem 1 (Charge)
• Problem 2 (Current)
• Problem 3 (Choose Battery)

• What are charge, voltage and current?
• How do you measure voltage and current?
• AC measurements, including waveshape and frequency.

• Be able to explain voltage and current using basic physics concepts.
• Given a need to measure a voltage or a voltage signal,
• Be able to connect a voltmeter properly.
• Be able to predict situations where the voltmeter disturbs the circuit in a minimal way, or where the voltmeter produces an undesirable change in circuit operation when attached.
• Be able to determine correct range(s) for the voltmeter as necessary.

Be able to use an oscilloscope to display a signal and calculate signal paramters - frequency and voltage.  (See also objectives for Signals.)

• Definition of current (units, etc.)
• A Battery Problem
• Current, voltage and power in a simple circuit (One element connected to a voltage source).
• An example problem

4. Voltage and current in resistors

• Why worry about resistors
• Resivitive sensors are widely used.
• What is a resistor?
• How do you use resistors?  How do you calculate what goes on in a resistor?

5. Some details about symbols for electrical elements

• Voltage Sources, Resistors, etc.
• Here is a sampling of symbols.

• We have talked about sensors as voltage sources.  Just for the record, sensors that deliver an electrical signal can usually (but maybe not always) placed into the following categories
• Sensors that produce a voltage.  These sensors will usually be represented as a voltage source controlled by the physical variable they are sensitive to, and you may have to include the internal resistance in your model.
• Sensors that produce a voltage but where the physical variable is coded into the frequency of the voltage - which may be something like a square pulse train.
• Example - a flow rate sensor that produces a voltage with a frequency dependent upon flow rate.
• Resistive sensors
• Sensors that have a resistance dependent upon the physical variable.
• Example - A thermistor where resistance changes with temperature.
• Example - A strain gage where resistance changes with strain.
• Current sensors - sensors where the value of the physical variable is coded into the amount of current the sensor delivers.  To be honest, that current is many times converted into a voltage.

• Resistance is not a quantity easily sensed - at least as easy as voltage.
• Example:  A/D cards for computers can measure voltage directly, but not resistance.
• If you have a resistive sensor you need an intermediate step where you use the change in resistance to produce a change in voltage.  That implies that you have a circuit in which the resistive sensor is embedded, and as the resistance of the sensor changes, a voltage changes in the circuit.  The simplest such circuit is a voltage divider.
• The basic voltage divider circuit

• In-class analysis - Get V_out in terms of V_in, R_a and R_b.
• In-class problem.

Readings:

• Links to material in the electronic lessons.
• Voltage Dividers
• Determining temperature using a voltage divider circuit
• Bridge Circuits
• Thermal Time Constants
• Measuring Time Constants

• What are charge, voltage and current?
• How do you measure voltage and current?
• AC measurements, including waveshape and frequency.

• Be able to explain charge, voltage and current using basic physics concepts.
• Given a need to measure a voltage or a voltage signal,
• Be able to connect a voltmeter properly.
• Be able to predict situations where the voltmeter disturbs the circuit in a minimal way, or where the voltmeter produces an undesirable change in circuit operation when attached.
• Be able to determine correct range(s) for the voltmeter as necessary.
• Be able to use an oscilloscope to display a signal and calculate signal parameters - frequency and voltage.  (See also objectives for Signals.)