CCT Installation Procedures 2 — Questions and Answers
Question 1: When installing a pressure transmitter in a process line, which mounting orientation is typically specified to avoid measurement errors due to head pressure?
- Vertical with the diaphragm facing down
- Horizontal with the diaphragm facing sideways (Correct answer)
- Vertical with the diaphragm facing up
- Any orientation since head pressure is auto-compensated
Correct answer: Horizontal with the diaphragm facing sideways
Horizontal mounting with the diaphragm facing sideways minimizes hydrostatic head effects on the zero of a pressure transmitter.
Question 2: What is the primary purpose of performing a 'loop check' immediately after installing a calibrated instrument?
- To verify the power supply voltage is within spec
- To confirm the instrument communicates correctly with the control system end-to-end (Correct answer)
- To measure the ambient temperature at the installation site
- To document the instrument's serial number in the asset database
Correct answer: To confirm the instrument communicates correctly with the control system end-to-end
A loop check confirms that the entire signal path from instrument to control system reads correctly and alarms activate as expected.
Question 3: During thermocouple installation, what is the minimum insertion depth guideline to ensure accurate temperature measurement?
- 10 times the thermowell bore diameter
- At least 10 times the thermowell stem diameter but no less than 2 inches (Correct answer)
- Equal to the pipe inner diameter
- No minimum depth is specified; insertion is determined by pipe size only
Correct answer: At least 10 times the thermowell stem diameter but no less than 2 inches
The insertion depth of at least 10× the stem diameter (minimum 2 inches) reduces conduction error along the thermowell stem.
Question 4: A flow meter manufacturer specifies a minimum number of straight pipe diameters upstream of the sensor. What installation error occurs if this requirement is not met?
- Increased electrical noise in the output signal
- Distorted velocity profile causing flow measurement error (Correct answer)
- Accelerated corrosion of the flow element
- Incorrect power consumption by the transmitter
Correct answer: Distorted velocity profile causing flow measurement error
Insufficient straight run creates swirl and non-uniform velocity profiles that introduce systematic flow measurement errors.
Question 5: What precaution must be taken when installing a level transmitter using a wet leg configuration?
- The high-pressure tap must always be at the top of the vessel
- The reference leg fluid must be kept at a constant, known density (Correct answer)
- The impulse lines must be sloped downward toward the transmitter
- The transmitter must be mounted above the maximum process level
Correct answer: The reference leg fluid must be kept at a constant, known density
The wet leg fluid density must remain constant so the reference head pressure is predictable and the zero can be correctly set.
Question 6: When installing an RTD in a thermowell, why is it important to use thermally conductive compound between the RTD and the thermowell bore?
- To prevent the RTD leads from short-circuiting inside the thermowell
- To improve thermal contact and reduce response time lag (Correct answer)
- To protect the RTD from chemical attack by process fluid
- To mechanically secure the RTD against vibration-induced loosening
Correct answer: To improve thermal contact and reduce response time lag
Thermally conductive compound fills air gaps between the RTD and thermowell bore, significantly reducing thermal resistance and response lag.
Question 7: Which installation practice is essential when mounting an electromagnetic flow meter to ensure it operates correctly?
- Installing isolation valves on the downstream side only
- Ensuring the pipe is always full and the meter is not installed at a high point where air can accumulate (Correct answer)
- Orienting the electrodes in the vertical plane (12 and 6 o'clock positions)
- Grounding the meter body to an isolated earth separate from the system ground
Correct answer: Ensuring the pipe is always full and the meter is not installed at a high point where air can accumulate
Electromagnetic flow meters require a full pipe to complete the conductive path between electrodes; air pockets cause erratic or zero readings.
CCT Installation Procedures 2
When installing a pressure transmitter in a process line, which mounting orientation is typically specified to avoid measurement errors due to head pressure?