省榕城司法强戒所领导深入所属医院开展工作调研
 | A Wikibookian suggests that this book or chapter be merged with Electronics/Diagnostic Equipment. Please discuss whether or not this merger should happen on the discussion page. |
Measuring Instruments
[edit | edit source]Ammeters
[edit | edit source]Ammeters are devices that measure current. Current in electronics is usually measured in mA which are called milliamperes, which are 1/1000s of an ampere.
..... Basically an ammeter consists of a coil that can rotate inside a magnet, but a spring is trying to push the coil back to zero. The larger the current that flows through the coil, the larger the angle of rotation, the torque (= a rotary force) created by the current being counteracted by the return torque of the spring.
..... Usually ammeters are connected in parallel with various switched resistors that can extend the range of currents that can be measured. Assume, for example, that the basic ammeter is "1000 ohms per volt", which means that to get the full-scale deflection of the pointer a current of 1 mA is needed (1 volt divided by 1000 ohms is 1 mA - see "Ohm's Law").
..... To use that ammeter to read 10 mA full-scale it is shunted with another resistance, so that when 10 mA flows, 9 mA will flow through the shunt, and only 1 mA will flow through the meter. Similarly, to extend the range of the ammeter to 100 mA the shunt will carry 99 mA, and the meter only 1 mA.
Ohmmeters
[edit | edit source]Ohmmeters are basically ammeters that are connected to an internal battery, with a suitable resistance in series. Assume that the basic ammeter is "1000 ohms per volt", meaning that 1 mA is needed for full-scale deflection. When the external resistance that is connected to its terminals is zero (the leads are connected together at first for calibration), then the internal, variable, resistor in series with the ammeter is adjusted so that 1 mA will flow; that will depend on the voltage of the battery, and as the battery runs down that setting will change. The full scale point is marked as zero resistance. If an external resistance is then connected to the terminals that causes only half of the current to flow (0.5 mA in this example), then the external resistance will equal the internal resistance, and the scale is marked accordingly. When no current flows, the scale will read infinity resistance. The scale of an ohmmeter is NOT linear.Ohmmeters are usually useful in checking the short circuit and open circuit in boards.
Multimeters
[edit | edit source]
Multimeters contain Ohmeters, Voltmeters, Ammeters and a variety of capabilities to measure other quantities. AC and DC voltages are most often measurable. Frequency of AC voltages. Multimeters also feature a continuity detector, basically an Ohmmeter with a beeper if the multimeter sees less than 100 Ω then it beeps otherwise it is silent. This is very useful for finding whether components are connected when debugging or testing circuits. Multimeters are also often able to measure capacitance and inductance. This may be achieved using a Wien bridge. A diode tester is also generally onboard, this allows one to determine the anode and cathode of an unknown diode. A LCD display is also provided for easily reading of results.
Electronics Laboratory Instruments
[edit | edit source]Oscilloscope
[edit | edit source]The oscilloscope is an instrument used to view waveforms, typically with voltage on the vertical axis vs time on the horizontal axis. Trigger logic ensures the view starts at the same point in the waveform each time, so that the waveform shape can be viewed clearly.
Spectrum Analyzer
[edit | edit source]The spectrum analyzer is a device that graphs signal power (typically in decibels) vs frequency. Using a spectrum analyzer, one can determine how much distortion is caused by an amplifier, or how much attenuation a filter provides at a given frequency. The input of a spectrum analyzer is particularly sensitive; ignoring the warnings on the device is likely to result in irreparable damage.
Signal Generator
[edit | edit source]This instrument is used to generate low voltage AC signals. Most common signal generators can create sinusoidal(sine), triangular and square waves of various frequencies. They are used in conjunction with the oscilloscope to test analog circuits. Another name for this device is waveform generator.
Vector Network Analyzer
[edit | edit source]The Vector Network Analyzer, or VNA, is a tool used in the radio-frequency realm. It analyzes the impedance of RF devices (coaxial cables, antennas, filters, and so on), determining their resistive, inductive, and capacitive components.
Logic Probe
[edit | edit source]This instrument generates high and low logic states to test digital circuits. If a logic probe is not available a square wave through a signal generator can be used. Square waves can also be used to test the response time of a digital circuits.
Other instruments
[edit | edit source]There are many other instruments, including the vector voltmeter, lock-in amplifier, selective voltmeter, sourcemeter, and electrometer.