WARNING
Make sure the whole control station is not energized before touching or starting your exercise!
Objective
Learn the use of an encapsulated relay and a contactor to keep on an AC PID controller as the first step into measuring temperture and connecting a loop.
This experiment also works as a guide to connect larger process equipment, such as electrical motors.
Material
Multimeter
AC/DC power supply. Input 120V AC and output 24V DC, 1A (at least)
Push button (green )
Push button (red)
Emergency stop button
Pilot light (green). 24V DC
Pilot light (red). 24V DC
Pilot light (yellow). 24V DC
PID controller. 210V AC
Encapsulated relay 24V DC with contacts for 8A 250V
Contactor. 24V DC coil
What to do
In this exercise you will barely use the same procedure as in Exercise LE 06. You will use the PID controller instead of the AC light bulb.
- Use the following ladder diagram:
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| Ladder diagram showing how to electrically install a PID controller using an encapsulated relay and a contactor (24V DC - coil). The power contacts of the contactors are used for the 110V AC of the controller. |
- Once the start button is pushed the green pilot light should turn off while the red pilot light turns on
- At the same time the PID controller should turn on as well. No lecture of temperature should be read since no temperature instrument is connected yet
- Check for continuity if needed
How to do it
For this exercise the same setup developed for LE 06.
Step 1. Identification of the encapsulated relay
There are several configurations of encapsulated relays of varying size, mounting, number and type of contacts, for example. The ones used for this exercise are the most common as shown,
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| Perspective view of an encapsulated review |
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| Vew of contacts in an encapsulated relay |
The encapsulated relay have a typical contact configuration as follows,
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| Detail of terminal connections in an encapsulated relay |
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| Diagrams of connections in an encapsulated relay |
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| Connection site of an encapsulated relay |
Step 2. AC PID controller
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| Two examples of PID controllers aim for temperature as its main process variable. However, these models can handle other variables provided its input signal is not as easy as for temperature. |
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| PID controller electric diagram. Example taken from the product manual. |
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| A sample PID controller electrical diagram for its terminals. In this case, terminals 9 and 10 are the ones you would use to power it on |
Then, you should connect the controller as follows. A phase wire from the block should connect to one of the terminals of the NO contact of the relay. From the other contact terminal a wire should connect to one of the terminals of the bulb. Finally, use another wire to connect the other bulb terminal to the neutral block.
Step 3. Energizing the loop
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| Thermal breaker |
Step 4. Using the buttons
If your connection was right then as the loop was powered, onlly the gren pilot light turns on. However, when you push the start button the PID controller should turn on and remain in this state. Next, when you push the stop button the controller should turn off and the green light shines again.
Step 5. Continuity and DC voltage test
Check for continuity at every contact and for 24V DC using the multimeter. Since you are using a power source for 24V DC you should get a reading not far from this value.
Continue your training with the next exercise
Any question? Write in the comments and I shall try to help.
Other stuff of interest
- LE01 - AC and DC voltage measurement and continuity test
- LE 02 - Start and stop push button installation 24V DC
- LE 03 - Turn on/off an 24V DC pilot light with a push button
- LE 04 - Latch contact with encapsulated relay for turning on/off an AC bulb light
- LE 05 - Emergency stop button installation
- LE 06 - Using a contactor to turn on an AC light bulb
- About PID controllers
- Ways to control a process
- About pilot lights
- Solving the Colebrook equation
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Ildebrando.
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