exeededd the i/o's

komal.sukre

Member
K
Join Date
Sep 2012
Location
Pune
Posts
15
we used a plc having 256 i/o s. 224+(32 onboard).
with max of 7 modules (32 i/o each).now according to customer's
requirement we need 4 i/o's more.

we are using 80 cylinders. so for clamping declamping they used
160 read switches and connected all to the plc. one for each cylinder's
clamp and declamp action. but in actual the cylenders
are grouped and only 22 push buttons areused forclamping and 22 for declamping

my question is that how can we accomodate that extra 4 i/o's without changing the plc?
 
What else are you using on your PLC because you have used 160+22+22=204 leaving another 42 i/o's spare. You could group your reed switches into banks of four but then you will only know when a bank of cylinders are not working instead of individual cylinders.
 
If there are a set of cylinders (more than 1) used for clamping and unclamping depending on your design, then you could connect the reed switches in series for advance and retract of those cylinders in only 2 inputs. So if one cylinder fails to operate on any particilar clamp (resulting in the reed switches connected in series not to close), you could use that to generate a fault in your code for the specific clamp.
 
Sounds as if you posted the solution within your question. If the cylinders operate in groups, then wire all of the extend and retract switches for each group to a single input. If they are NO switches, then wire them in parallel. If they are NC switches, then wire them in series. You'll lose a bit of diagnostic capability, but you'll gain a great deal of free inputs for future use.

You could free up outputs in the same manner by using only 1 output for each cylinder group's extend/retract actuator and wiring the outputs to interposing relays.
 
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