Unit 16 Advanced Automatic Controls
T7. The typical voltage that DDC controls use as their signal is
0-10 volts.
18. What is the difference between an active and passive sensor used in DDC control systems?
Active sensors send information back to the controller in terms of milliamps or volts. Passive sensors send information back to the controller in terms of resistance.
2. Pneumatic controls are operated by
Air.
T2. Pneumatic controls use what type of power to operate?
Air.
5. Pneumatic air must be
Clean and dry.
T10. Electronic controls are only used in commercial buildings.
False.
11. Another term used to describe sensitivity in electronic controls is
Gain.
10. An analog control signal
Has an infinite number of control steps.
T5. The sensitivity of a control has to do with
How it responds to a change in conditions.
T6. Electronic control components are often mounted
On a circuit board.
7. When a large volume of air is needed at a diaphragm, the thermostat may feed branch line pressure to the
Pilot positioner.
T9. A pilot positioner is used with which type of controls?
Pneumatic.
17. Describe what a sensor does in a DDC system used in today's HVAC/R industry, and list five examples of sensors.
Sensors are devices that can measure some type of environmental parameter or a controlled variable and convert this parameter to a value that the controller can understand. Sensors can measure position, moisture, velocity, enthalpy, and conductivity parameters/values.
20. List six advantages that DDC control systems have over traditional control systems.
Speed, accuracy, the ability to control many control sequences simultaneously, repeatable control of system set points, operating functions of the controller are adjustable through software, and the ability to automatically adapt to changing conditions in the controlled environment.
3. One advantage of a modern control system is
The ability to modulate.
14. One of the major components of a residential electronic control circuit that measures temperature is a
Thermistor.
T1. A control loop has ____ components.
Three.
12. One of the advantages of DDCs is
Total building control management.
13. Electronic controls have been used in the residential industry for a long time.
True ( But define a "long time")
1. Pneumatic controls are explosion proof.
True.
15. Diagnostic light-emitting diodes are often used to alert the technician to problems.
True.
9. Electronic controls operate on either low voltage or milliamperes.
True.
T3. Pneumatic controls can be used in an explosive atmosphere.
True.
T8. An analog signal has an infinite number of steps.
True.
T4. Modulating flow means
Variable.
6. The air supplied to a diaphragm is 20 psig, and the diaphragm has a diameter of 6 in. How much pressure can this diaphragm apply to a plunger?
area=3.14 x r sq. (3.14 x 3 x 3) = 28.26 sq in x 20 psig = 565.2 lbs of pressure. The formula is (3.14 x radius of diaphragm squared) x psig.
16. Describe a final control device, and give three examples of these devices used in today's HVAC/R industry.
A final control device is an on/off or open/close control. Three devices used in a DDC system in the HVAC/R industry today are supply fans speed controls, damper controls, and cooling coil valve position controls.
8. What are the typical tools the a pneumatic control technician would use?
A pressure gauge, an allen wrench, and a pocket thermometer.
19. A control system consists of what three basic components?
A sensor, a controller, and a controlled device.
4. A control loop contains
A sensor, a controller, and a controlled device.
21. Describe the difference between the analog and digital signals in a DDC control system.
Digital signals report back to the controller as one of two opposing conditions, such as yes/no, open/closed, on/off, or start/stop. Analog controls have a range of values over any given time period. Examples include temperature, pressure, humidity, flow, and light.