Fault-finding challenge

The brief

Client

Thornley Dairy

Site

Header tank pump P-401

Work order

TD-2619

Industry

Food and drink

Task code

PLC-19

Difficulty

Intermediate

Type of work

Programming

A colleague's program for a header tank pump is already loaded. It runs and it looks right, but it has six faults and fails the factory test. Find each one and fix it, rung by rung, or rewrite the program your own way.

What you do

1. Read the client brief and the tag table: 14 tags, 9 inputs and 5 outputs.
2. Write the logic in ladder, Structured Text or SFC.
3. Press Simulate and watch the plant answer your program.
4. Run the factory acceptance test and fix what fails.

Skills you practise

• Reading and tracing ladder logic
• Normally closed input wiring
• Seal-in and latch/unlatch faults
• Timer presets and units
• Compare instructions
• Fault-finding method

What the test checks

The factory acceptance test runs 6 numbered tests against your program. The numbers in the brief are drawn per learner. The tests are:

• Fills from the low float to the high float after a start delay
• A low sump stops the pump and lights the sump lamp
• A fill that was interrupted carries on
• High-high stops the pump and latches the alarm
• Stop and E-stop stop the pump and need a fresh Start
• The service lamp comes on at the 5th pump start

In this lab

• Ladder, Structured Text and SFC in one studio
• A plant that answers: motors, tanks, conveyors
• Numbered tests mark your program