Copyright © 2005 Heathkit Company, Inc. All Rights Reserved Automating and Integrating Residential Systems Presentation 7 – Closed Loop Control

2 Objectives At the end of this exercise, you will be able to:

3 Explain the difference between open loop control and closed loop control and site examples of each. Demonstrate how PLC technology can be used for closed loop control of motors. Demonstrate how PLC technology can be used to control drapes.

4 Open Loop Control vs Closed Loop Control We want to find out what closed loop control is all about, but first, we need to know what open loop control is.

5 Open Loop Control This simply means that once started, an operation continues with no consideration for what is happening as a result of the operation.

6 Example: You turn a hallway light switch on, and want it to stay on for five minutes. First, the light switch will stay in the on position whether the light actually turns on or not.

7 The light probably will turn on.

8 The light switch does not care about the outcome. The switch will stay on forever. The switch has no way of knowing if the light actually turned on or not.

9 What if we add a timer to the switch to turn the switch off in five minutes? Is this now a closed loop control?

10 No. It is not a closed loop control? The switches still don’t know if light is coming from the bulb.

11 The light will turn off in five minutes. So, it is not a closed loop control yet.

12 Closed Loop Control So, how do we make our original circuit a closed loop control circuit?

13 We could add a light sensor.

14 This also means, that if the light bulb fails to light, the light switch will stay in the on position.

15 So, an open loop control does not sense the output. But a closed loop control senses the output and feeds a control signal back to control the input.

16 A Practical Closed Loop Control A practical closed loop control device. It is the fill valve.

17 You turn the valve on, it turns itself off.

18 Other Examples: Is the lavatory faucet an open loop control device or a closed loop device?

19 It is an open loop device.

20 Heating or cooling thermostat. Is this part of an open loop or closed loop control system? Explain your answer.

21 Heating or cooling thermostat. This is closed loop.

22 TV remote control. Is it open loop or closed loop control?

23 It is open loop.

24 Summary Open loop control devices allow you to turn things on and off. Closed loop control devices also allow you to turn things on and off, but they monitor the output of the controlled device to make sure it happened or happened correctly.

Copyright © 2005 Heathkit Company, Inc. All Rights Reserved Automating and Integrating Residential Systems End