Hi,

A customer is asking for a PLC having a key switch to enable/disable all the outputs by interrupting the power supply to output circuits, so program tests can be done without risking people/equipment on the filed.

Does anyone know what PLC can do this ?

Thanks a lot.

Any PLC made can do this.

It all depends on how you wire the system.

You don't need a PLC for this, Just add a keyswitch on the front panel and label it "Test switch" or something like that and wire the contact block on that switch in line with the output hot wire. When you engage this switch you will shutoff the outputs!!!. Or you can have the switch enegize or denergize a relay that is inseries with the output loads!! either way will work. You can also add a contact block on the same switch and bring that into the PLC input and address that input asas a test input that will allow minimal funtionality. The sky's the limit!!!

Hi,
Thanks for those replies.

I know I can do that outside the PLC. The thing is I'm reading this specification our customer gave us, and it lists a lot of PLC features that the model we currently use does not meet.

The most curious feature is that the CPU should have a key switch to enable/disable the outputs.

I know these guys have a specific model in mind, I just don't know what it is.
They're also asking for a SCADA capable of generate historic trendings that can be "flageable" (data can be flagged as "manually entered", "not trusted", "erratic", etc).

If anyone here knows what brand meets this requierements, I'll really preciate the tip.

Thanks in advance.

Most A-B PLC's have a "Test" mode in which the program runs but outputs are disabled. This is an internal function and does not physically isolate power from the outputs, but rather prevents the processor from writing to them.

My memory is a bit hazy but I think this used to be a function of the processor key switch on PLC-2's and 1774 (PLC-1). With current models the test mode can only be set from the programming software (RSLogix) when the key is in 'Remote'.

I think the old Square D Symax had a disable outputs position on it's run/stop keyswitch. Otherwise, I can't think of one that has the ability to disable outputs from a built-in keyswitch.

AB SLC 5/03-05 and PLC5's have a keyswitch (run<>remote<>program), that when placed in the program mode, all outputs are disabled.