Micrologix 1100 using analog inputs as discrete

[blaze777]

I have a project where I'm using Micrologix 1100 1763-L16AWA controllers. I am also using two capactive type prox switches to detect water level in a tube. These sensors are Gems CAP-100 and they use 6-48vdc power. I would like to use prox sitches on the two embeded 0-10vdc analog inputs on the controller to conserve the digital inputs for other purposes.
Does anyone have any ideas of a clean way to do this? Any help would be appreciated.

 

[eeprom]

What is the output signal range for the proximity sensor?

EE

 

[blaze777]

Supply Voltage Range: 10-48 VDC
Continuous Switching Current: 300 mA
Voltage Drop: <2 VDC
Current Consumption: <10 mA
Switching Frequency: 100 Hz
Power Indicator: Green LED
Signal Indicator: Yellow LED
Overload Protection: Yes
Short Circuit Protection: Yes
Reverse Polarity Protection: Yes
Adjustable Sensitivity: Yes*

 

[eeprom]

I am assuming that this is a proximity switch which has a relay that changes state when the prox switch is some distance from its target. So the continuous switching current would be 300mA.

If that's true.... Then you can take the 24VDC supply from the 1100, wire that into the normally open relay contact on the prox switch. On the other side of the relay contact, wire a 10k ohm resistor, then wire the other end of that resistor into analog input 1. Then take a 1k ohm resistor and put one end of that also into analog input 1 and the other end of that resistor into the analog common. This will give you 0V when the relay is open, and 2.2V when the relay is closed. You can use a comparator in your ladder logic to determine the on/off state.

Of course all of this would be best done by wiring on terminal blocks.

I hope that helps.

 

[blaze777]

Yes thank you eeprom it does help.

 

[blaze777]

eeprom, Attached is wiring diagram for the prox switch I am using. Based on this and your post I would need to wire 24VDC + to IV-Com. and the black from prox to 10k-ohm resistor other end of resistor to IV-1 and 1k-ohm resistor wired between IV-Com. and IV-1. Is this correct?

Thanks

 

[itsmoked]

OK, here you go. A premium quality engineering document.

Using relays allows you to prevent polluting your analog bus.

If you're actually running the prox switches with your analog bus,(yuck),then you can just put the resistor in place of the the relay coil and read it with the AIN between the resistor and the sensor. Closed will be near zero, open will be the + rail.

If you need to conserve analog inputs this can be massaged into about 4 sensors with ease. Each one would give a different analog result. You'd need to decipher them if using a single AIN.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[eeprom]

That's a great idea to run multiple resistors of different sizes to determine which sensor has been triggered. Other than making a messy wiring job, I don't see why you couldn't run 10 or more of these sensors all with their own signature voltage divider.

That's an excellent idea. The only drawback would be if your panel was UL508A. Then you'd have to use UL rated resistors. I'm not even sure those exist.

EE

 

[blaze777]

No I'm not trying to conserve analog inputs. The Micrologix 1100 has two low-resolution 0-10volt analog inputs that I am not using for analog, but I have two of these prox switches in the project and my thoughts were to use these inputs to conserve my digital inputs. I was just looking for a simple and clean way to do that.

 

[itsmoked]

Ta da!
???

Keith Cress
kcress -

http://www.flaminsystems.com