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Instrumentação e Medição
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Consider a square-waveform signal with zero mean value, as shown in the figure, where its root-mean square (RMS) value is .
Consider that, in a second phase, a half-wave (ideal) rectification is performed with as input, obtaining the signal shown in the figure.
Finally, the continuous component (dc) of is removed, obtaining the signal .
Determine , i.e. the RMS value of .
The spectral components (magnitude) of two signals is shown below.
In the circuit obtain Vx assuming that the RMS value of the current in the resistor is 2.5 mA.
Consider the following voltage reading in which the nominal closed-loop voltage gain of the (ideal) operational amplifier is and the dc output voltage is .
Both resistors are rated at , composed by metal film with thermal coefficients and thermal resistances .
The analog-to-digital converter is unipolar, rail-to-rail input, has bits, and can be assumed perfect.
Determine the minimum nominal value of the resistor for which the gain error is imperceptible.
Consider the following voltage reading in which the nominal closed-loop voltage gain of the (ideal) operational amplifier is and the dc output voltage is .
Both resistors are rated at , composed by metal film with thermal coefficients and thermal resistances .
The analog-to-digital converter is unipolar, rail-to-rail input, has bits, and can be assumed perfect.
Determine the minimum nominal value of the resistor for which the gain error is imperceptible.
Consider a digital multimeter (DMM) operating as an ohmmeter.
The manufacturer specifies the accuracy performance of the ohmmeter as follows.
| Display: 3,5 digits | Accuracy | ||||
|---|---|---|---|---|---|
| Ranges | (% of range + counts) | ||||
| 200 Ω | 2 kΩ | 20 kΩ | 200 kΩ | 2 MΩ | 1 + 4 |
Assuming the resistance reading of , determine the minimum absolute value of the reading uncertainty.
Consider the dc output voltage measurement of a device under test (DUT), which consists on a voltage regulator, as shown in figure. In order to obtain the voltage output for a given load , a 4 digital multimeter (DMM) was used as a voltmeter, always selecting the most adequate measurement range for the readings.
A large number of independent voltage readings has been performed, , leading to the average value , with standard deviation .
Obtain the absolute value for the expanded combined uncertainty (from types A and B uncertainties) at a 95 % confidence interval.
The DMM manufacturer provides the accuracy of the voltmeter in the table below.
| Range | Resolution | Accuracy |
|---|---|---|
| 60 mV | 1 μV | |
| 600 mV | 10 μV | |
| 6 V | 100 μV |
The project of an analogue temperature sensor for bakery ovens was left unfinished after the departure of the electronic engineer responsible for the circuit design (who accepted a job offer from the competition earning double). As the new employee, your mission, should you decide to accept it, is to complete the circuit design depicted below.
The circuit aims to generate a linear voltage output () proportional to the temperature in the oven (), with a sensitivity of .
For the thermocouple, type E with a Seebeck coefficient has been selected.
For cold-junction compensation, the prior approach is maintained, using an analogue temperature sensor to produce a temperature-dependent voltage () given by , where is the temperature in Kelvin and .
It is essential that is free from any offset. As such, you need to determine the value of the regulated voltage () required to meet all these specifications.
Consider the following circuit in which the thermistor NTC has at and .
Determine the output voltage when the temperature is .
The Maxwell inductance bridge shown in the figure was used to characterize the inductance under test, modeled as the self-inductance and the respective equivalent series resistance .
The bridge achieves equilibrium by adjusting the variable resistor and the variable self-inductance . The resultant values for these components are and .
The standard resistances have values and , and for inductor , its equivalent series resistance is .
Calculate the self-inductance .
The universal digital counter, with the simplified diagram representation shown below, is operating as a frequency meter. The oscilator frequency is and the decade divider provides the time-base selection of frequency signals , .
Assuming an input signal with frequency , what is the number of pulses obtained by the decade counter when the most adequate time base has been chosen?