1. BASIC AUTOMATIC CONTROLS UNIT 16 ADVANCED AUTOMATIC CONTROLS
SECTION 3
BASIC AUTOMATIC CONTROLS
UNIT 16
ADVANCED AUTOMATIC CONTROLS

2. UNIT OBJECTIVES Recognize advanced control terminology
After studying this unit, the reader should be able to
Recognize advanced control terminology
Demonstrate control applications
Describe electronic control circuits
Describe pneumatic control circuits
Discuss a control loop
Discuss sensitivity or gain in controls

3. CONTROL APPLICATIONS
Older controls were manually activated and operated
Thermostats and other simple controls were added to reduce human contact with the equipment
Automatic control systems require little human attention
Large buildings can be maintained by a small staff of technicians
Technicians need to be educated
Should be able to calibrate controls
Need to be able to interpret blueprints

4. TYPES OF CONTROL SYSTEMS
First control systems started and stopped main system components
Newer controls can modulate (start, stop, or adjust) the flow or operation of system components
Control systems are divided into control loops
Three basic components of a control system
The sensor measures changes in conditions
The controller sends an output signal
The controlled device reacts to the controller

5. Controller
Air gage
Diaphragm
Main air
Branch air
Chilled water coil
Return air
Supply air
Main air
Hot water coil
T-stat

6. PNEUMATIC CONTROL SYSTEMS
Mechanical systems
Use air to transmit signals between the sensor and the controlled device
Require a clean and dry permanent air supply
Air pressure (100 to 125 psig) generated by an air compressor
Regulator reduces pressure to working pressure (20 to 30 psig)

7. Pressure reducing valve
Compressor
Air drier
Service valve
Pressure reducing valve
Intake filter
Belt
Motor
Tank
To system
Submicron filter
To drain
Normally closed test cocks
Auto separator filter
Auto trap

8. Air tank
Float
Water level
To drain

9. Air tank
Float
Water level
To drain

10. CLEANING AND DRYING CONTROL AIR
Prefilter to the compressor
Moisture is removed from the air
Chilled water coil
Desiccant
Refrigerated drier (most common)
High-density filters
Final filtering stage
Removes oil vapor and remaining liquid

11. CONTROL COMPONENTS
The pressure on control valves is equal to the air pressure multiplied by the cross sectional area of the diaphragm
Pilot positioners use a small volume of air to control a larger volume of air
Fluid flow can be modulated
Pressure gages used to measure pressure at the controls
Can be used to control electric switches or circuits
Electric devices can be used to control pneumatic controls

12. Diaphragm in actuator assembly
20 psig
Diaphragm in actuator assembly
20 psig exerted on a 4” diaphragm can result in a pressure of over 250 pounds which can be used to open valves, etc.
Area of a 4” round diaphragm = πr2= 3.14 x 22= 3.14 x 4 = in2
Total pressure = 20 x = pounds

13. 0 psig
Air cylinder
Shaft position when there is 0 psig of air

14. Shaft position when there is 7.5 psig of air
Air cylinder
Shaft position when there is 7.5 psig of air

15. Shaft position when there is 20 psig of air
Air cylinder
Shaft position when there is 20 psig of air

16. Air line from thermostat
Pilot positioner
Main line

17. Valve is positioned for full flow
20 psig
15 psig from thermostat (calling for cooling)
Valve is positioned for full flow
20 psig (main line)

18. CONTROL COMPONENTS Fluid flow can be modulated Sensitivity or gain
Pressure and temperature at fully open and fully closed positions
Sensitivity = Δ pressure ÷ Δ temperature
High sensitivity will cause the control to “hunt”
Low sensitivity will result in noticeable change in space temperature

19. Valve positioned for full flow through the cooling coil
55 degree return water from cooling coil
Bypass line
45 degree supply water to cooling coil

20. Valve positioned for partial flow through the cooling coil
55 degree return water from cooling coil
Bypass line
45 degree supply water to cooling coil

21. Valve positioned for no flow through the cooling coil
55 degree return water from cooling coil
Bypass line
45 degree supply water to cooling coil (no water actually flowing to coil)

22. DIRECT DIGITAL CONTROLS
Referred to as DDC
Operate at very low voltages
Can be used to open, close, or modulate valves, dampers, motor speeds, etc.
Can be controlled from remote locations via computers
Corrective actions can be taken from remote locations via computers
System parameters can be observed

23. RESIDENTIAL ELECTRONIC CONTROLS
Entire board is evaluated, not the individual board components
Use manufacturer’s diagnostic systems
Boards are often treated as switches
Boards often have diagnostic codes for troubleshooting
Thermistors are often used
Often equipped with DIP switches
Allows control to be configured
Allows user to customize system operation
Status lights indicate mode of operation

24. UNIT SUMMARY - 1 Older controls manually activated and operated
Automatic control systems require little attention
Newer controls modulate fluid flow
Control systems are divided into control loops
Control systems are made up of the sensor, controller and the controlled device
Pneumatic control systems use air to transmit signals between the sensor and the controlled device

25. UNIT SUMMARY - 2 Pneumatic systems require clean and dry air supply
Control air used to position controlled devices
Sensitivity = Δ pressure ÷ Δ temperature
DDC can be used to open, close, or modulate valves, dampers, motor speeds, and other devices
Corrective actions can be taken from remote locations via computers
Entire board is evaluated, not the individual board components