4-20ma to digital input

[cedax]

Hi everyone, On my EXD16A3TO16 I need more inputs.

It' possible to use Analogs inputs?

if I connect a 2.7K resistor between 24v and the input it can work?

[Ausman]

A single analog input can be used successfully to implement multiple switch inputs if you need to go that far.  Depending on different switch positions, a different resistance is applied resulting in different analogue readings.  You have to map this out carefully if doing this approach, so that every switch combination gives you a distinct "zone" of an input, and you then use a range reading in the plc logic.  If you use a single value you will likely run into problems.

In setting this sort of thing up, I always use a multi-turn 10K trimpot (or a number of them) to initially find optimum resistances for what I want.  Theory doesn't necessarily work out correctly due to drift, component tolerances etc.

cheers, Aus

[Joe Tauser]

Or you could just buy an IO-DI16 and tack it on.  

Joe T.

[Flex727]

Or even a IO-DI8-RO4, which might be just a smidgen cheaper.

[Don2015]

One time I needed more Inputs but did not have room in the enclosure for 2 more modules, so I took 5 inputs and treated them as binary, depending on which inputs were on I knew which switch was pushed,  so I got 25 inputs from just 5 inputs, I also used 5 small relay cards at 4 relays per card . Then the rest was just in programming!

 

Don2015

[Isakovic]

13 hours ago, Don2015 said:

One time I needed more Inputs but did not have room in the enclosure for 2 more modules, so I took 5 inputs and treated them as binary, depending on which inputs were on I knew which switch was pushed,  so I got 25 inputs from just 5 inputs, I also used 5 small relay cards at 4 relays per card . Then the rest was just in programming!

I had a similar situation but with outputs. Each output controlled two valves, but one valve was getting negative from supply from NC contact of reley, and other one was getting it from NO contact, so that relay altered which group will be activated. So I got 14 valves from 8 outputs.

Crude and patchy solution, but it was some pneumatic cleaner so nothing critical.

[kratmel]

To solve a problem similar to yours, I used 1 input and alternatively connected various sources to it for analysis.

In my case, there were a few free relay outputs and I used them to connect various alarm signals.

This option is good for slow processes. Therefore, having analyzed the problem I have created a program

in which the high priority inputs are being surveyed more often than others.