0
\$\begingroup\$

enter image description here

I have read the manual, but I am not sure how the omron safety PLC works.

I guess this safety PLC use Output Power Supply Output (21,22) to drive the output circuit, but why does it need (1,2) the power supply for input device and test output.

Also what is test output? Why is it useful?

\$\endgroup\$
  • 1
    \$\begingroup\$ There are only few subject matter experts on industrial control on this website, so you'll have to provide a lot more detail if you want this question answered. Start by linking to the manual and the product sheet. What makes a PLC a safety PLC? \$\endgroup\$ – jippie Mar 12 '13 at 7:36
  • \$\begingroup\$ That is probably because terminal numbers 1-10 are isolated from 21-30. However, that is just a guess, I know nothing about PLCs. \$\endgroup\$ – abdullah kahraman Mar 12 '13 at 12:04
1
\$\begingroup\$

Most likely the outputs are galvanically isolated from the inputs, necessitating multiple power supplies.

Below that image you posted is a reference to the DeviceNet Safety DST1-series Safety I/O Terminals Operation Manual. An explanation for the test outputs is provided there:

enter image description here

The test outputs are most likely not galvanically isolated from the inputs since they share a common power supply. This could limit their usefulness.

\$\endgroup\$
0
\$\begingroup\$

Best to review IEC61508 & IEC61511 (SIL) and understand the requirements for a certified safe hot redundant PLC. Big part of the redundancy (separate power supplies, redundant processors, code, etc.) is to leave machine in a safe state on failure, not necessarily shut it down. So while in a particular safety system, you may remove power from all outputs, you may still need input signal for redundant processor.

You need the test output pulse to constantly check for short/opens.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.