Chapter 11
INSTRUMENTS
OBJECTIVES
▪ Describe the basic instruments used in the process industry.
▪ Identify and draw standard instrument symbols.
▪ Describe temperature, pressure, flow, and level measurement techniques.
CHAPTER 11 REVIEW QUESTIONS
1. List seven basic types of instruments found in the processing industry. Answer: Examples
2. Describe the operation of a DP cell. Answer: A differential pressure cell measures the
3. What is a rotameter used for? Answer: Measure the flowrate of a fluid.
4. List the basic elements of a control loop. Answer: Primary element or sensors,
5. Draw a pressure control loop. Answer: See figure.
6. Draw a level control loop. Answer: See figure.
7. Draw a flow control loop. Answer: See figure.
8. Draw a temperature control loop. Answer: See figure.
9. How do the basic elements of a control loop work together. Answer: A primary element
10. Describe controllers and control modes. Answer: The primary purpose of a controller is
11. List the primary elements and sensors used with temperature and pressure. Answer:
12. List the primary elements and sensors used with level and flow. Answer: Level- float or
13. Define the term DCS. Distributed control system. Answer: A computer based system
14. Draw a cascaded control loop. Answer: See Figure 11.27 Cascaded Control Loop.
15. Describe manual and automatic control. Answer: Manual and Automatic Control
During a unit startup, console operators will use manual control to initially establish a
16. Draw an analytical control loop. Answer: See Figure 11.28 Analytical Control Loop.
17. Explain how a process technician uses a valve’s operating percentage in manual
operation. Answer: Typically, when a new process is being brought on line, a control
18. List the primary elements or sensors for temperature. Answer: Thermocouple, RTD’s.
19. Describe a thermocouple and explain how it is used. Answer: Thermocouples are
composed of two different types of metal (see Figure 11.2). A thermocouple is designed
Explain how a bourdon tube works. Answer: C-type bourdon tubes are named for their C-shaped,
hollow pressure element (Figure 11.7). C-type bourdons are composed of a C-shaped hollow
tube, a pressure inlet attached to one end of the tube, a mechanical linkage attached to the top of
the bourdon tube, and a pointer. During operation, the tube expands and contracts in response to