LE 06 - Turning ON a PID controller

 WARNING

Make sure the whole control station is not energized before touching or starting your exercise!

Objective

Learn the use of an encapsulated relay 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)

• Pilot light (green). 24V DC

• PID controller. AC

• Encapsulated relay 24V DC with contacts for 8A 250V

What to do

For this exercise, one of the contacts of the encapsulated relay shall be used for latching and turning on a pilot light, with 24V DC, and the other one for turning on the PID controller.

• Connect a green pilot light (safety indicator) in series with one of the NC contacts of the relay
• Connect the encapsulated relay coil terminals (A1 and A2) after the start button
• Connect a red pilot light (danger indicator) in parallel with the relay coil
• For latching, connect the NO encapsulated relay contact in parallel with the start button. Be aware of using the same NO/NC contacts set as before
• In rung 0 for AC. Connect the other normally open encapsulated relay contacts in series with the power source contacts of the PID controller (namely C)
• Set on the power supply
• Use the following ladder diagram:

Ladder diagram showing how to turn on a PID controller using a secondary 24 V DC circuit. Notice that the PID controller requires 110 V AC.

• The green pilot light should turn on immediately when the thermal braker is allow the electricity to flow
• 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 02 and LE03 are to be used. Details shall be omitted and refer to LE 02 and LE03 for more information.

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,

Perspective view of an encapsulated review

Vew of contacts in an encapsulated relay

The encapsulated relay have a typical contact configuration as follows,

Detail of terminal connections in an encapsulated relay

Diagrams of connections in an encapsulated relay

Connection site of an encapsulated relay

Step 2. AC PID controller

As you should may suppose an AC PID controller requires AC to be powered (other models may be different). You should locate in the PID controller diagram the terminals where it is to be connected so that it can be turned on.

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

One of its terminals goes to the phase (live) wire while the other one to the neutral wire. The one thing you should care about is that this is not connected to the 24V DC blocks but to the AC blocks.

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

In order to power the loop you should activate the circuit breaker to the ON position with the lever upl and the green indicator being shown.

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

LE 05 - Emergency stop button installation

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
• About PID controllers
• Ways to control a process
• About pilot lights
• Solving the Colebrook equation

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Ildebrando.