L.2 - Transmitters

Question 1

What is a transducer?

Answer 1

> the device that performs the measurement function in a control system

> it is a device that receives information in the form of one quantity and converts it to information in the form of the same or another quantity

Question 2

What is a signal conditioner?

Answer 2

it it used to convert the transducer output into a more useable standard form

Question 2

What does a transmitter consist of (w/ details)?

Answer 2

1) Transducer (performs measurement)
2) Signal Conditioner (scales, filters, linearizes, amplifies, compensates)

Question 2

List some typical transducers:

Answer 2

1) Thermocouple (temp to mV)
2) Accelerometer (acceleration to mV)
3) Bourdon Tube (pressure to deflection/motion)
4) Photo Diode (light intensity to current)

Question 3

What is a transmitter?

Answer 3

it is a transducer that responds to a measured variable by means of a sensing element and coverts it to a standardized transmission signal which is a function only of the measured variable

Question 4

Why do we care to use standard range signals?

Answer 4

to ensure compatibility and interoperability among instruments from various manufacturers

Question 5

What are two most common signals used?

Answer 5

1) Pneumatic
2) Electronic

Question 6

What are pneumatic signals?

Answer 6

the pressure of a gas used to carry signal information

Question 7

How do pneumatic instruments work, what is the standard pneumatic signal range?

Answer 7

> they are powered by a compressed gas and use tubing to route signals between instruments

> standard range: 20-100kPag, 3-15Psig

Question 8

What are electronic signals? what is the standard electronic signal range?

Answer 8

> electrical voltage or current carries signal information

> voltage: 1-5V, Current: 4-20mA

Question 9

Define the range of an instrument:

Answer 9

> it is the region between the limits within witch a quantity is received, measured or transmitted

> expressed by stating the lower and upper range values

Question 10

What is meant by a static transfer function?

Answer 10

it describes the steady-state input-output relationship of the transmitter Eqt’n

Question 11

What is static error?

Answer 11

it is the difference between the measured value and the actual value

Question 12

What is accuracy?

Answer 12

it is the degree of conformity of an indicated value to a recognized/ideal value

Question 13

What is span accuracy?

Answer 13

[ (actual value - ideal value) / ideal span ]*100%

Question 14

What is point accuracy?

Answer 14

[ (actual value - ideal value) / ideal value ]*100%

Question 15

List some error types in a transducer system:

Answer 15

1) Bias error
2) Span error
3) Repeatability
4) Resolution
5) Linearity error

Question 16

What is a bias error?

Answer 16

it is the actual output - ideal output at the min. range value/LRV

Question 17

What is span error?

Answer 17

[ (actual input span - ideal input span) / (ideal input span) ]*100%

Question 18

What is linearity error?

Answer 18

it is the deviation from ideal after the bias and span errors are removed

Question 19

What is repeatability?

Answer 19

the ability of an instrument to produce the same measured value of a fixed given input on a number of independent trails (assuming all other variables remain constant)

Question 20

What is resolution/precision?

Answer 20

the smallest measurable change of the input or output variable

Question 21

What is the term called for a transmitter starting at 4mA instead of zero?

Answer 21

Live zero

Question 22

Why do we star the transmitter at 4mA instead of zero?

Answer 22

In case of a broken wire or any breakage, so that we have a value other than zero to record