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Sensors And Signal Processing > Chapter 15: Measurement > Flashcards

Chapter 15: Measurement Flashcards

0
Q

How is rms voltage found mathematically?

A

Rms voltage is found by taking the square root of the average of the signal voltage squared.

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1
Q

What is root mean square voltage?

A

The rms value of an ac voltage is equal to the value of the dc voltage required to produce the same heating effect in a resistance. Also, the effective voltage.

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2
Q

What does an explicit type of rms to dc converter contain?

A

A) a squaring circuit
B) an averaging circuit
C) a square root circuit

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3
Q

What does an implicit type of rms to dc converter contain?

A

The implicit rms to dc converter contains:
A) a squarer/divider circuit.
B) an averaging circuit.

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4
Q

How does an implicit rms to dc converter work?

A

An implicit rms to dc converter uses feed back from the averaging circuit to perform the square root function.

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5
Q

What is the basic purpose of an rms to dc converter?

A

An rms to dc converter produces a dc output voltage that is equal to the rms value of the ac input voltage.

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6
Q

What is a transducer?

A

A transducer is generally a device that converts a physical parameter from one form to another.

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7
Q

What is a synchro?

A

An electromechanical transducer used for shaft angle measurement and positioning.

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8
Q

What are the basic elements of a synchro?

A

The basic synchro consists of a rotor, which can revolve within a fixed stator assembly.

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9
Q

How does a synchro work?

A

When a reference ac ( sinusoidal) voltage is applied across the the rotor winding, the voltage induced across any one of the stator windings is proportional to the sine of the angle between the rotor and stator windings.

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10
Q

How many voltages does a synchro use to function?

A

Three voltages referred to as synchro format voltages:
A) the angular difference between the stator and rotor.
B) the sum of voltages induced across two stator windings ( sine + sine)
OR
C) the difference of voltages induced across two stator windings ( sine - sine)

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11
Q

What is a resolver?

A

A particular type of synchro that uses two stator windings separated by 90 degrees instead of three windings separated by 120 degrees.

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12
Q

How many voltages does a resolver use

A

There are two resolver format voltages:
A) proportional to the sine of theta.
B) proportional to the cosine of theta.

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13
Q

What is a synchro to digital or resolver to digital converter?

A

Synchro to digital converters and resolver to digital converters are electronic circuits used to convert the format voltages from a synchro or resolver to a digital format.

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14
Q

What is a Scott-T transformer?

A

A Scott-t transformer is a special type of transformer used to change Synchro format voltages to that of a resolver.

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15
Q

Why is a Scott T transformer necessary?

A

Scott T transformers are necessary because both Synchro to digital and resolver to digital converters use resolver format voltages.

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16
Q

What is a thermocouple and how is it formed?

A

A thermocouple is a device used to measure temperature it is formed by joining two dissimilar metals.

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17
Q

How does a thermocouple work

A

A small voltage called see beck voltage is produced across the junction of the two metals when heated.

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18
Q

How does Seebeck voltage indicate temperature?

A

Seebeck voltage proportional to temperature is generated when a thermocouple is heated.

19
Q

What is a cold junction?

A

A cold junction is an unwanted thermocouple effectively created at the points where one or both of the thermocouple wires connect to circuit terminals made from dissimilar metals.

20
Q

What are the three major types of temperature transducers?

A

The three major types of temperature transducers are thermocouples ,resistance temperature detectors ,and thermistors.

21
Q

How do resistance temperature detectors work?

A

Resistance temperature detectors work by using a constant current across a resistance that is affected by temperature to produce a variation in voltage.

22
Q

What is a thermistor?

A

A thermistor is a temperature sensitive resistive device made from a semi conductive material.

23
Q

What is a negative temperature coefficient?

A

A negative temperature coefficient is a resistance that decreases as temperature increases.

24
Q

What is a positive temperature coefficient?

A

A positive temperature coefficient is a resistance that increases as temperature increases.

25
Q

Does a thermistor have a negative temperature coefficient or a positive temperature coefficient?

A

A thermistor can have either a positive temperature coefficient or a negative temperature coefficient.

26
Q

What are the relative advantages of a thermistor?

A

Thermistors have the advantage of a greater sensitivity than either thermocouples or RTD’s and are generally less expensive.

27
Q

What are the relative disadvantages of a thermistor?

A

The temperature characteristics of a thermistor are more nonlinear than RTD’s or thermocouples. also the temperature range of a thermistor is more limited than that of a thermocouple.

28
Q

How is it thermistors like an RTD.

A

Like the RTD thermistors can be used in a constant current driven configuration or in bridges.

29
Q

What is strain?

A

Strain is the deformation ,either expansion or compression, of a material due to a force acting on it.

30
Q

On what principle are strain gages based?

A

Strain gages are based on the principle that the resistance of a material increases if it’s length increases.

31
Q

What is Gage factor?

A

Gauge factor is defined as the ratio of the fractional change in resistance to the fractional change in length along the axis of the gauge.

32
Q

How does a strain gauge work?

A

In a strain gauge force produces a change in length which produces a change in resistance which in turn produces a change in voltage.

33
Q

How is a strain gauge configured?

A

A strain gauge can be configured as a constant current device in conjunction with an op amp ; in one instance as a feedback resistor for the op amp and the other instance as a bridge resistor for the input of an op amp.

34
Q

How is a pressure transducer assembled?

A

A basic pressure transducer consists of a strain gauge attached to a flexible diaphragm.

35
Q

What are the two most common assemblies of a pressure transducer.

A

Pressure transducers typically are manufactured using a foil strain gauge bonded to a stainless steel diaphragm or by integrating semi conductor strain gages ( resistors) in a silicone diaphragm.

36
Q

What are the three basic configurations of a pressure transducer in terms of relative pressure?

A

The three basic configurations of a pressure transducer in terms of relative pressure are the absolute pressure transducer, the gauge pressure transducer, and the differential pressure transducer.

37
Q

What does an absolute pressure transducer measure?

A

An absolute pressure transducer measures applied pressure relative to a vacuum?

38
Q

What does a gauge pressure transducer measure?

A

The gauge pressure transducer measures apply pressure relative to the pressure of the atmosphere or ambient pressure.

39
Q

What does the differential pressure transducer measure?

A

The differential pressure transducer measures one applied pressure relative to another applied pressure.

40
Q

How are pressure transducers usually configured?

A

Pressure transducer’s are usually in a bridge configuration.

41
Q

What is a bridge configuration?

A

A bridge configuration is a method of using a variable resistance to establish a variable voltage for the input of an op amp.

42
Q

What is the purpose of a three wire bridge?

A

The purpose of the three Wire bridge is to isolate the resistor sensing the temperature change from the resistors in the rest of the bridge.

43
Q

What type of temperature response does a thermistor possess?

A

A thermistor possesses a logarithmic temperature response.

44
Q

What is a major disadvantage of nonzero switching?

A

Major disadvantage of nonzero switching of power to a load is RF noise generation.

Sensors And Signal Processing (3 decks)

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