Safety gate interlock

The brief

Client

Hartwell Plastics

Site

Guarded trimming press TP-1

Work order

HP-2614

Industry

Machinery safety

Task code

PLC-14

Difficulty

Intermediate

Type of work

Programming

Run a guarded machine only while its gate is shut and the E-stop is healthy, trip it the moment the gate opens, and never let it restart by itself: it needs a fresh Reset press and then a fresh Start press.

What you do

1. Read the client brief and the tag table: 8 tags, 5 inputs and 3 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

• Guard interlock logic
• Fresh-press (one-shot) reset
• Latching and unlatching a trip
• Normally closed safety inputs
• Restart prevention

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:

• Reset, then Start and Stop run the machine
• Reset is a fresh press held for 500 ms
• Opening the gate stops the machine and it stays stopped
• Even a very short gate opening trips the machine
• The E-stop trips the machine in the same way
• A Start that is held down never starts the machine

In this lab

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