Test & Measurement Education

It used to be with large AC power systems that “power quality” was an unheard-of concept, aside from power factor. Almost all loads were of the “linear” variety, meaning that they did not distort the shape of the voltage sine wave, or cause non-sinusoidal currents to flow in the circuit. This is not true anymore. Loads controlled by “nonlinear” electronic components are becoming more prevalent in both home and industry,

Explain how an ohmmeter is able to measure the resistance of a component (in this case, a light bulb) when there is no battery or other source of power connected to it: Also, identify the reading you would expect the ohmmeter to indicate if the light bulb were burnt out (failed “open”).

An electric circuit is formed when a conductive path is created to allow free electrons to continuously move. This continuous movement of free electrons through the conductors of a circuit is called a current, and it is often referred to in terms of “flow,” just like the flow of a liquid through a hollow pipe. The force motivating electrons to “flow” in a circuit is called voltage. Voltage is a

As was stated earlier, most meter movements are sensitive devices. Some D’Arsonval movements have full-scale deflection current ratings as little as 50 µA, with an (internal) wire resistance of less than 1000 Ω. This makes for a voltmeter with a full-scale rating of only 50 millivolts (50 µA X 1000 Ω)! In order to build voltmeters with practical (higher voltage) scales from such sensitive movements, we need to find some way to reduce the measured quantity

So far, we’ve studied both S-R and D latch circuits with enable inputs. The latch responds to the data inputs (S-R or D) only when the enable input is activated. In many digital applications, however, it is desirable to limit the responsiveness of a latch circuit to a very short period of time instead of the entire duration that the enabling input is activated. One method of enabling a

PARTS AND MATERIALS Sensitive meter movement (Radio Shack catalog # 22-410) Selector switch, single-pole, multi-throw, break-before-make (Radio Shack catalog # 275-1386 is a 2-pole, 6-position unit that works well) Multi-turn potentiometers, PCB mount (Radio Shack catalog # 271-342 and 271-343 are 15-turn, 1 kΩ and 10 kΩ “trimmer” units, respectively) Assorted resistors, preferably high-precision metal film or wire-wound types (Radio Shack catalog # 271-309 is an assortment of metal-film resistors, +/- 1% tolerance) Plastic or metal mounting

We know that the current in a series circuit may be calculated with this formula: I = Etotal Rtotal We also know that the voltage dropped across any single resistor in a series circuit may be calculated with this formula: ER = I R Combine these two formulae into one, in such a way that the I variable is eliminated, leaving only ER expressed in terms of Etotal, Rtotal, and R.

Suppose I were about to measure an unknown voltage with a manual-range voltmeter. This particular voltmeter has several different voltage measurement ranges to choose from: 500 volts 250 volts 100 volts 50 volts 25 volts 10 volts 5 volts What range would be best to begin with, when first measuring this unknown voltage with the meter? Explain your answer.

An electromechanical generator is a device capable of producing electrical power from mechanical energy, usually the turning of a shaft. When not connected to a load resistance, generators will generate voltage roughly proportional to shaft speed. With precise construction and design, generators can be built to produce very precise voltages for certain ranges of shaft speeds, thus making them well-suited as measurement devices for shaft speed in mechanical equipment. A

AC electromechanical meter movements come in two basic arrangements: those based on DC movement designs, and those engineered specifically for AC use. Permanent-magnet moving coil (PMMC) meter movements will not work correctly if directly connected to alternating current, because the direction of needle movement will change with each half-cycle of the AC. (Figure below) Permanent-magnet meter movements, like permanent-magnet motors, are devices whose motion depends on the polarity of the

To enter numbers in scientific notation into a hand calculator, there is usually a button marked “E” or “EE” used to enter the correct power of ten. For example, to enter the mass of a proton in grams (1.67 x 10-24 grams) into a hand calculator, I would enter the following keystrokes: [1] [.] [6] [7] [EE] [2] [4] [+/-] The [+/-] keystroke changes the sign of the power (24) into a -24. Some calculators allow the use

Just like voltmeters, ammeters tend to influence the amount of current in the circuits they’re connected to. However, unlike the ideal voltmeter, the ideal ammeter has zero internal resistance, so as to drop as little voltage as possible as electrons flow through it. Note that this ideal resistance value is exactly opposite as that of a voltmeter. With voltmeters, we want as little current to be drawn as possible

How is it possible to assign a fixed value of voltage or current (such as “120 volts”) to an AC electrical quantity that is constantly changing, crossing 0 volts, and reversing polarity?

In order to build the circuits described in this volume, you will need a small work area, as well as a few tools and critical supplies. This section describes the setup of a home electronics laboratory. Work area A work area should consist of a large workbench, desk, or table (preferably wooden) for performing circuit assembly, with household electrical power (120 volts AC) readily accessible to power soldering equipment, power supplies,

A chandelier has five light bulbs in it, and one of them is not working. The problem could be in the chandelier’s wiring (open wire connection, open connection in socket), or in the bulb itself (burned-out filament). Describe a procedure for determining the location of the problem (chandelier vs. bulb), without using any electrical test instruments.

PARTS AND MATERIALS Operational amplifier, model TL082 recommended (Radio Shack catalog # 276-1715) Operational amplifier, model LM1458 recommended (Radio Shack catalog # 276-038) Four 6 volt batteries One meter movement, 1 mA full-scale deflection (Radio Shack catalog #22-410) 15 kΩ precision resistor Four 1 MΩ resistors The 1 mA meter movement sold by Radio Shack is advertised as a 0-15 VDC meter, but is actually a 1 mA movement sold with a 15 kΩ +/- 1% tolerance multiplier resistor. If

Being able to determine the polarity (cathode versus anode) and basic functionality of a diode is a very important skill for the electronics hobbyist or technician to have. Since we know that a diode is essentially nothing more than a one-way valve for electricity, it makes sense we should be able to verify its one-way nature using a DC (battery-powered) ohmmeter as in Figure below. Connected one way across the

PARTS AND MATERIALS Multimeter, digital or analog Assorted batteries One light-emitting diode (Radio Shack catalog # 276-026 or equivalent) Small “hobby” motor, permanent-magnet type (Radio Shack catalog # 273-223 or equivalent) Two jumper wires with “alligator clip” ends (Radio Shack catalog # 278-1156, 278-1157, or equivalent) A multimeter is an electrical instrument capable of measuring voltage, current, and resistance. Digital multimeters have numerical displays, like digital clocks, for indicating the quantity of voltage,

A peak detector is a series connection of a diode and a capacitor outputting a DC voltage equal to the peak value of the applied AC signal. The circuit is shown in Figure below with the corresponding SPICE net list. An AC voltage source applied to the peak detector, charges the capacitor to the peak of the input. The diode conducts positive “half cycles,” charging the capacitor to the waveform

PARTS AND MATERIALS 6-volt battery Electromagnet made from experiment in previous chapter, or a large spool of wire It would be ideal in this experiment to have two meters: one voltmeter and one ammeter. For experimenters on a budget, this may not be possible. Whatever ammeter is used should be capable measuring at least a few amps of current. A 6-volt “lantern” battery essentially short-circuited by a long piece of