instrumentation Flashcards
What are the four most common measurements we make in order to control the process (select 4)
level
pressure
flow
weight
temperature
A,B,C,E
Because we use two different reference states, we have two systems for measuring pressure. They are:
Metric and standard pressure
high and low pressure
Guage and absolute pressure
answer c
what would for 4 psig be in absolute units
remember count up from 14.7
10.7 psia
3 psia
18.7 psia
answer C
3 psiv in absolute units remember count down from 14.7
3 psia
11.7 psia
20.7psia
answer B
To measure the pressure in a vessel, a piece of tubing would be connected from the vessel to which side of the differential pressure transmitter?
high side
low side
answer A
Why is the low side of the DP cell often connected to the vapor space of a tank that we are measuring level inside?
To compensate for changes in pressure inside the tank
o provide a second level reading as a backup
answer A
If a level transmitter reads 38% and the valve that connects it to the bottom of the tank is closed, what will the level reading do?
reads 100%
38% stays the same
reads 0%
answer B
If a level transmitter were calibrated with a “dry leg” and some liquid accidentally got into the dry leg, how would it affect the level reading?
The level reading would read lower than the actual level in the tank
The level reading would read accurately
The level reading would read higher than the actual level in the tank
answer answer A
If a differential pressure level transmitter were calibrated for water, but the tank was filled with oil (specific gravity = 0.8), how would it affect the level reading?
The level reading would be higher than the tank
the level would be lower than the actual tank
it would read the same
answer B
If a level transmitter were calibrated with a “wet leg” and some liquid from the wet leg leaked out to the ground, how would it affect the level reading?
The level reading would read lower than the actual level in the tank
the level reading would read higher than the actual level in the tank
The level reading would read accurately
answer: B
how does a bubbler read a level
It measures the volume of gas added to the tank through the bubbler
it measures the pressure needed to blow bubbles inside the liquid
It measures how long it takes for a bubble to rise to the surface
answer: B
If a bubbler level transmitter is reading 38% and the air or nitrogen supply to the bubbler is shut off, what will the bubbler read?
100%
0%
38%
answer: B
When using a DP cell with an orifice to measure flow, higher flow produces what measurement in the pressure under normal conditions?
high pressure
low pressure
answer A
When using a DP cell with an orifice to measure flow, if a plug occurred IN the orifice hole, restricting the flow through the orifice, what would the pressure transmitter read?
actual flow
lower flow than actual
higher flow than actual
answer C
When using a DP cell with an orifice to measure flow, if a restriction occurred DOWNSTREAM (~3 ft) of the orifice, what would the flow transmitter read?
flow meter would read higher than actual flow
flow would be same
flow would read lower than actual flow
answer B
What are the two devices most often used to electronically read temperature in the process? (Pick two)
thermocouple
RTD Resistance Temperature Detector
thermowell
answer A,B
Which units does a thermocouple sense?
mA
mV
kW
answer B
If a thermocouple breaks at the junction, what value will the temperature transmitter indicate?
ambient temp
zero
full high scale
answer: Full High scale
If a thermocouple shorts out, what value will the temperature transmitter indicate?
ambient temp
zero
full high scale
answer A
Which units does an RTD sense?
kW
mA
mV
ohms
answer: D
RTD’s have how many wires running to them?
0
1
3 or 4
2
answer C
If a thermocouple or RTD falls out of the thermowell, what value will the temperature transmitter indicate?
ambient temp
zero
full high scale
answer answer A
What is the most common use of a transducer in a control loop?
4-20mA to 0-120%
3-15 psig to 0-100%
4-20mA to 3-15 psig
answer C
What is an equivalent way of saying “fail closed”
air to close
air to open
fail open
answer B
When using a DP cell to measure level, which side of the transmitter is connected to the BOTTOM part of the tank?
Low
High
Answer B
