Lab 12: Multi-Function Timer Modes

Application Scenario

A maintenance technician at a large plant is called because a machine stopped working: its timer has failed. The storeroom does not stock every type of timer. Instead, it stocks one multi-function timer as a universal spare. The same device can work as an on-delay, off-delay, or interval timer, depending on how its mode is set.

The technician must be able to:

1. look at what the old timer was doing and decide which mode is needed,
2. set the mode and time correctly, and
3. wire the replacement so that it behaves exactly like the old one.

Setting the wrong mode is one of the most common mistakes in the field. In this lab you will build one circuit with TR4, run it in all three modes, and compare the results. At the end, your instructor will set TR4 to a secret mode, and you will find out which one it is by testing.

Learning Outcomes

After this lab you will be able to:

• Set a multi-function timer (TR4) to on-delay, off-delay, and interval modes.
• Explain why off-delay mode needs the coil always powered and uses the trigger input.
• Record observations and draw a timing diagram for each mode.
• Identify an unknown timer mode by testing its behavior.
• Choose the correct timer mode for a written requirement.

Required Components

Background

TR4 terminals. TR4 is wired like TR2, not like TR1:

What the input is in each mode.

This is why the circuit in this lab has one wire that you move: TR4:2 (the coil feed) goes to the command node N3 for on-delay and interval, and to L1 for off-delay. The trigger wiring stays in place for the whole lab; in the other modes, TR4 simply ignores it.

Ladder Diagram — Step-by-Step Drawing Guide

Draw on the Ladder Diagram Worksheet. Use pencil. This design uses 6 grid lines.

Step 1 — Rungs 1–2: command relay

1. Grid line 1: PB2 (N.C.), PB1 (N.O.), CR1 coil (2–7). Mark N2 and N3.
2. Grid line 2: CR1A N.O. seal-in (1–3) from N2 to N3.

Step 2 — Rung 3: COMMAND lamp

1. From N3, draw a line down to grid line 3. Draw R1 and connect it to L2. R1 shows the timer's input.

Step 3 — Rung 4: TR4 coil

1. From N3, continue the line down to grid line 4. Draw the TR4 coil (pin 2 on the left, pin 10 on the right). Connect pin 10 to L2.
2. Draw a dashed line from L1 to TR4:2 and label it "Part B (off-delay) only: move TR4:2 from N3 to L1."

Step 4 — Rung 5: trigger loop

1. Draw a box labeled TR4 trigger with terminals 5 and 6.
2. Draw a CR1B N.O. contact and connect CR1:8 to TR4:5 and CR1:6 to TR4:6, as in Lab 10. Mark the two wires N6 and N4. This loop does not touch L1 or L2.

Step 5 — Rung 6: TIMER OUTPUT lamp

1. Starting from L1, draw a TR4A N.O. contact (1–3), then G1. Connect G1 to L2. Mark the node between them as N5.

Step 6 — Fill in the contact allocation table

From Ladder Diagram to Wiring Table

Build the node table for the Part A wiring (TR4:2 on N3). The N4 row is done for you.

Chain the terminals of each node (k − 1 wires per node, no more than two wires per terminal), then fill in the wiring table on the worksheet. Mark the TR4:2 coil-feed wire clearly in the Purpose column: "MOVE for Part B."

Get instructor approval before wiring.

Key Wiring Points

1. TR4 uses TR2-style pins: coil 2–10, contacts 1-3-4 and 11-9-8, trigger 5–6.
2. The trigger is a dry-contact input. Wire CR1B directly across 5 and 6. Never connect 5 or 6 to L1 or L2.
3. The mode decides what the input is. On-delay and interval: the coil is the input. Off-delay: the coil is always powered, and the trigger is the input.
4. Power OFF before changing the mode or moving the coil-feed wire.

Procedure

Wiring and meter check

1. Power OFF. Wire the circuit for Part A (TR4:2 on N3).
2. Meter check, power still OFF:

   Reading the meter: once the circuit is wired, the meter can find a path through coils and lamps. A reading of tens to thousands of ohms is normal and counts as high. Only a reading near 0 Ω means a direct connection.

   • L1 to CR1:1 should read near 0 Ω, and high while PB2 is pressed.
   • CR1:1 to CR1:2 should read high, and near 0 Ω while PB1 is pressed.
   • CR1:2 to TR4:2 should read near 0 Ω (Part A wiring).
   • CR1:8 to TR4:5 and CR1:6 to TR4:6 should read near 0 Ω.
   • TR4:10 to L2 should read near 0 Ω.
3. Ask your lab partner to do a buddy check, then show the instructor.

Part A — On-delay mode (coil fed from N3)

Set TR4 to on-delay, 5 s. Power ON. For each step, write ON or OFF for R1 and G1.

Part B — Off-delay mode (coil fed from L1)

Power OFF. Move the coil-feed wire from N3 to L1 (TR4:2 to L1). Set TR4 to off-delay, 5 s. Power ON.

Part C — Interval mode (coil fed from N3)

Power OFF. Move the coil-feed wire back to N3. Set TR4 to interval, 5 s. Power ON.

Part D — Mystery mode

Power OFF. Leave the coil-feed wire on N3. Your instructor will set TR4 to a secret mode and time (and may cover the dial). Power ON and test the circuit with PB1 and PB2 and a stopwatch until you can answer:

Troubleshooting

Review Questions

1. Using your observation tables, draw a timing diagram of R1 and G1 for each mode. Use this sequence: PB1 at t = 0 s, PB2 at t = 8 s, until t = 15 s.
2. Why must the coil be always powered in off-delay mode? What did you observe (or what would you observe) if the coil were fed from N3 in off-delay mode?
3. In Part D, which single test is the quickest way to tell on-delay from interval? Explain.
4. Choose the timer mode for each requirement, and explain your choice:
   1. A stairwell light stays ON for 2 minutes after the last person leaves.
   2. An alarm sounds only if a cooler door has been open for more than 30 seconds.
   3. A horn sounds for 3 seconds whenever a crane starts moving.
   4. After a power outage, a compressor must wait 3 minutes before it is allowed to restart.
   5. A heat-shrink tunnel fan must keep running for 5 minutes after the heaters are turned off.
5. A replacement TR4 is installed and set to the right mode, but the old timer was wired with its coil fed from L1. What must the technician check before powering it up in on-delay mode?

Applying This Circuit Pattern

The same three timing functions appear in every PLC. When you learn PLC programming, you will recognize them immediately:

A multi-function timer is the relay-panel version of a PLC's timer library: one device, several behaviors, chosen by a setting. A well-stocked maintenance storeroom keeps a few multi-function timers instead of many single-function ones.

Extension

Power OFF. Move G1 from TR4:3 (N.O.) to TR4:4 (N.C.). Before powering on, predict what G1 will do in each of the three modes. Then test one mode of your choice and check your prediction.