Solved: Use LabVIEW to create a virtual instrument that

Name the elements of a computer-based instrumentation system.

Draw the equivalent circuit of a sensor in which the open-circuit sensor voltage is proportional to the measurand.What are loading effects? How do we avoid them when we need to measure the Thvenin (i.e., open-circuit) sensor voltage?

What signal-conditioner input impedance is best if the sensor produces short-circuit (Norton) current that is proportional to the measurand?

A load cell produces an open-circuit voltage of 200 V for a full-scale applied force of 104 N, and the Thvenin resistance is 1 k. The sensor terminals are connected to the input terminals of an amplifier. What is the minimum input resistance of the amplifier so the overall system sensitivity is reduced by less than 1 percent by loading?

A certain liquid-level sensor has a Thvenin (or Norton) resistance that varies randomly from 10 k to 1 M. The short-circuit current of the sensor is proportional to the measurand. What type of signal-conditioning unit is required? Suppose we allow for up to 1 percent change in overall sensitivity due to changes in the sensor resistance. Determine the specification for the input resistance of the signal conditioner.

How are bias errors different from random errors?

List four types of bias error.

An instrumentation system measures distances ranging from 0 to 1 m full scale. The system accuracy is specified as 0.5 percent of full scale. If the measured value is 70 cm, what is the potential range of the true value?

Explain how precision, accuracy, and resolution of an instrument are different.

Three instruments each make 10 repeated measurements of a flow rate known to be 1.500 m3/s with the results given in Table P9.10. a. Which instrument is most precise? Least precise? Explain. b. Which instrument has the best accuracy? Worst accuracy? Explain. c. Which instrument has the best resolution? Worst resolution? Explain. Table P9.10 Trial Instrument A Instrument B Instrument C .......................................................... 1 1.5 1.73 1.552 2 1.3 1.73 1.531 3 1.4 1.73 1.497 4 1.6 1.73 1.491 5 1.3 1.73 1.500 6 1.7 1.73 1.550 7 1.5 1.73 1.456 8 1.7 1.73 1.469 9 1.6 1.73 1.503 10 1.5 1.73 1.493

List four or more functions of signal conditioners.

How is a single-ended amplifier different from a differential amplifier?

Suppose that the input voltages to an ideal differential amplifier are equal. Determine the output voltage.

The input voltages to a differential amplifier are v1(t) = 0.002 + 5 cos(t) and v2(t) = 0.002 + 5 cos(t) Determine the differential input voltage and the common-mode input voltage. Assuming that the differential amplifier is ideal with a differential gain Ad = 1000, determine the output voltage of the amplifier.

A sensor produces a differential signal of 6 mV dc and a 2-V-rms 60-Hz ac commonmode signal. Write expressions for the voltages between the sensor output terminals and ground.

Suppose we have a sensor that has one terminal grounded. The sensor is to be connected to a DAQ board in a computer 5 meters away. What type of amplifier should we select? To mitigate noise from electric and magnetic fields, what type of cable should we use? Draw the schematic diagram of the sensor, cable, and amplifier.

What is a floating sensor? When would we want to use a floating sensor?

Suppose that the data collected from a sensor is found to contain an objectionable 60-Hz ac component. What potential causes for this interference would you look for? What are potential solutions for each cause of the interference?

In principle, analog-to-digital conversion involves two operations. What are they?

What is aliasing? Under what conditions does it occur?

What causes quantization noise?

We need to use the signal from a piezoelectric vibration sensor in a computer-aided instrumentation system. The signal is known to contain components with frequencies up to 30 kHz. What is the minimum sampling rate that should be specified? Suppose that we want the resolution of the sampled values to be 0.1 percent (or better) of the full range of the ADC. What is the fewest number of bits that should be specified for the ADC?

A 2-V-peak sinewave signal is converted to digital form by a 12-bit ADC that has been designed to accept signals ranging from 5 V to +5 V. (In other words, codewords are assigned for equal increments of amplitude for amplitudes between 5 V and +5 V.) Practice Test 465 a. Determine the width  of each quantization zone. b. Determine the rms value of the quantization noise and the power that the quantization noise would deliver to a resistance R. c. Determine the power that the 2-V sinewave signal would deliver to a resistance R. d. Divide the signal power found in part (c) by the noise power determined in part (b). This ratio is called the signalto-noise ratio (SNR). Express the SNR in decibels, using the formula SNRdB = 10 log(Psignal/Pnoise).

We need an ADC that can accept input voltages ranging from 0 to 5 V and have a resolution of 0.02 V. How many bits must the codewords have?

A 10-kHz sinewave is sampled. Determine the apparent frequency of the samples. Has aliasing occurred? The sampling frequency is a. 11 kHz; b. 8 kHz; c. 40 kHz.

A 60-Hz sinewave x(t) = A cos(120t + ) is sampled at a rate of 360 Hz. Thus, the sample values are x(n) = A cos(120nTs + ), in which n assumes integer values and Ts = 1/360 is the time interval between samples. A new signal is computed by the equation y(n) = 1 2 [x(n) + x(n 3)] a. Show that y(n) = 0 for all n. b. Now suppose that x(t) = Vsignal + A cos (120t + ), in which Vsignal is constant with time and again find an expression for y(n). c. When we use the samples of an input x(n) to compute the samples for a new signal y(n), we have a digital filter. Describe a situation in which the filter of parts (a) and (b) could be useful.

Briefly describe how virtual instruments are created

Explain the data-flow concept used by LabVIEW

Use LabVIEW to create a virtual instrument that converts a complex number of the form x + jy into polar form A . Provide frontpanel controls for the operator to input the values of x and y, each of which can range from 10 to +10. Also, provide displays for A and (in degrees) on the front panel.

Use LabVIEW to create a virtual instrument that converts a complex number in polar form A (with in degrees ranging from 360 to +360 and A ranging from 0 to 20) into the form x + jy. Provide front-panel controls for the operator to input the values for A and . Also, provide displays for x and y on the front panel.

Open the VI stored in the file named Figure 9.24.vi from the folder named Hambley Virtual Instruments. Click on the run continuously button. Set the sinewave amplitude to 10 and the frequency to 1. Then, gradually increase the frequency in unit steps several times and observe the changes in the waveform. Next, set the frequency to 355 and again gradually increase the frequency in unit steps to 365, observing the changes in the waveform after each step. Discuss and explain your observations.

Create aVI to demonstrate a concept or solve a problem from your own field. Write a short description of the concept or problem and of the vi.