Dynamic terms

Question 1

Process variable (PV)

Answer 1

The variable we are trying to control

Question 2

Set-point (SP)

Answer 2

The desired value of the process variable

Question 3

Final control element

Answer 3

The device that will enable us to manipulate the process.

Question 4

Controller

Answer 4

Person, Brain, algorithm

Question 5

Time constant

Answer 5

time at which 63% of the response has occurred (first order)

Question 6

Actuator

Answer 6

1. Top of the valve with the diaphragm and spring

2. All of the valve (final control element)

Question 7

Equal percentage valve

Answer 7

For each absolute change in valve signal, the opening changes by the same %

Question 8

Valve Hysteresis

Answer 8

Friction of the stem on the seal, slop in the linkages, which results in limited resolution in the D/A convertor or I/p. at low signals changes the stem doesn’t move = error.

Question 9

Valve positioner

Answer 9

Measures the actual stem position and compares it with the control signal. It uses an internal controller to adjust the air pressure in the valve actuator to obtain the required stem position.