Chapter 15: Measurement

Question 0

How is rms voltage found mathematically?

Answer 0

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

Question 1

What is root mean square voltage?

Answer 1

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.

Question 2

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

Answer 2

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

Question 3

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

Answer 3

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

Question 4

How does an implicit rms to dc converter work?

Answer 4

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

Question 5

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

Answer 5

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

Question 6

What is a transducer?

Answer 6

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

Question 7

What is a synchro?

Answer 7

An electromechanical transducer used for shaft angle measurement and positioning.

Question 8

What are the basic elements of a synchro?

Answer 8

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

Question 9

How does a synchro work?

Answer 9

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.

Question 10

How many voltages does a synchro use to function?

Answer 10

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)

Question 11

What is a resolver?

Answer 11

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

Question 12

How many voltages does a resolver use

Answer 12

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

Question 13

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

Answer 13

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.

Question 14

What is a Scott-T transformer?

Answer 14

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

Question 15

Why is a Scott T transformer necessary?

Answer 15

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

Question 16

What is a thermocouple and how is it formed?

Answer 16

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

Question 17

How does a thermocouple work

Answer 17

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

Question 18

How does Seebeck voltage indicate temperature?

Answer 18

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

Question 19

What is a cold junction?

Answer 19

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.

Question 20

What are the three major types of temperature transducers?

Answer 20

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

Question 21

How do resistance temperature detectors work?

Answer 21

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

Question 22

What is a thermistor?

Answer 22

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

Question 23

What is a negative temperature coefficient?

Answer 23

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

Question 24

What is a positive temperature coefficient?

Answer 24

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

Question 25

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

Answer 25

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

Question 26

What are the relative advantages of a thermistor?

Answer 26

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

Question 27

What are the relative disadvantages of a thermistor?

Answer 27

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.

Question 28

How is it thermistors like an RTD.

Answer 28

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

Question 29

What is strain?

Answer 29

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

Question 30

On what principle are strain gages based?

Answer 30

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

Question 31

What is Gage factor?

Answer 31

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.

Question 32

How does a strain gauge work?

Answer 32

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

Question 33

How is a strain gauge configured?

Answer 33

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.

Question 34

How is a pressure transducer assembled?

Answer 34

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

Question 35

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

Answer 35

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.

Question 36

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

Answer 36

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.

Question 37

What does an absolute pressure transducer measure?

Answer 37

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

Question 38

What does a gauge pressure transducer measure?

Answer 38

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

Question 39

What does the differential pressure transducer measure?

Answer 39

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

Question 40

How are pressure transducers usually configured?

Answer 40

Pressure transducer's are usually in a bridge configuration.

Question 41

What is a bridge configuration?

Answer 41

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

Question 42

What is the purpose of a three wire bridge?

Answer 42

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.

Question 43

What type of temperature response does a thermistor possess?

Answer 43

A thermistor possesses a logarithmic temperature response.

Question 44

What is a major disadvantage of nonzero switching?

Answer 44

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