Schematic Idiocy

Tony Stewart said:

@rjenkinsgb Do you have any idea if Siemens, Rockwell, AB, etc use gold plated contacts for PLC's.

Click to expand...

It's not the PLC itself, it's the switches and sensors on control panels and around the machinery that connect to the PLC inputs. The Siemens PLC inputs for the normal 24V DC types draw from 2.7 to 4mA, depending on the exact PLC model.

The switches are typically such things as these below, also such as the auxiliary contacts on power contactors & overload trips, pressure switches, float switches etc. which usually have 10A rated silver contacts and are equally suited for directly controlling eg. 110V switchgear.



I've had problems in the past (20+ years ago) with a certain series of thyristor drive that used 12V control circuits - they could have problems not registering contact closures. The models that replaced them used 24V control as with PLCs, and I've never had that type of problem with any of those.

I'm guessing that the American vendor is also gone, so no help from them for parts, service and advice. I remember using such a machine at a Canadian post-secondary diner.

Nope. Current vendor, good parts availability (if a little expensive) and pretty good (but a little wacky) documentation.

We're updating the control system to make the machine operate slightly differently than stock and add some unique features. As an example, an artist or crafts person selling things in the machine will be able to slide open the doors to their compartments and re-stock.