micrologix 1100 analog input

Micrologix L16BWA

It has two built in analog input ports. How do I change the input type and range? current/voltage, 0-5v, 0-10v, 4-20ma, etc.

I see on the add on modules there is dipswitches but I see nothing in the manual regarding built in ports.

I don't think you can. The user's guide shows them as 0 - 10VDC only.

The MicroLogix 1100 built-in analog channels are not as full-featured as the expansion I/O modules.

The range and type are fixed at 0-10.0 Volts, with 10-bit resolution (0-1023).

If you want to use a 4-20 mA current loop, you can just provide a precision 250 ohm resistor across the input and measure the voltage drop. That's how most current-loop analog input modules work internally.

A note about some low-end A-B analog inputs because I've been doing some comparison:

MicroLogix 1100 built-in analog inputs are 10-bit resolution (0-1023).
MicroLogix 1400 built-in analog inputs are 12-bit resolution (0-4095).
Micro 820 built-in analog inputs are 12-bit resolution (0-4095).
POINT I/O 1734-IE2V analog inputs are 15-bit resolution (0-32767).

Ken Roach said:

If you want to use a 4-20 mA current loop, you can just provide a precision 250 ohm resistor across the input and measure the voltage drop.

Click to expand...

I keep seeing this "250 ohm resistor" thing, and I can't for the life of me work out where it came from.


Ohms law: V=I*R
*or*
R=V/I
R=10V/20mA
R=10/0.02
R=500 ohms

A 500 ohm resistor will convert 4-20mA into 2-10V.
A 250 ohm resistor will convert 4-20mA into 1-5V.

Sure, you can use a 250 ohm resistor and just scale your input accordingly, but why halve your resolution for the sake of a correctly sized resistor?

Not picking on you specifically Ken - I've just never been able to work out where the whole 250 ohm resistor thing came from!

Forgive me, I pulled a defective bit of math out of my foggy recollection. I had most recently been using a stepper controller whose analog inputs are 0-5 V and I'm short on coffee.

You are of course correct that a 500 ohm resistor is correct and appropriate for converting a 4-20 mA current loop signal to a 2-10 V voltage input.

Oh! Oh! Teacher! Teacher!...

..."The resistor must be a 500 Ohm low-drift precision resistor valued at 0.05% or 10 ppm. The power rating for the resistor should be 1/4 Watt."...

16415 - Converting MicroLogix/PICO Analog Input to 4-20mA Current Inputs
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