View Full Version : Analog Input to Analog Output

March 21st, 2005, 07:37 PM
Basically I've got RSLogix 500 and an Allen Bradley Micrologix 1200 with the 1762-IF20F2 analog input/output module. I've also got two Sharp IR sensors(GP2d12). I want to take the input voltage from those sensors and scale it to use with a simple electric 10v motor. I know that I can use scaling with parameters to get the input but how does the SLC function work with outputing a voltage recieved. Does anybody have an example of a input analog signal controlling an analog output signal in RSLogix 500? How do you adress the bit inputs and outputs? thanks for your time

March 21st, 2005, 08:08 PM
I don't understand what you're trying to do.

I see the IR sensor is a distance sensor that puts out a .4-2.4 VDC (typical) signal depending on distance to the reflected object.

What is the motor supposed to do?

Are you planning on driving the 10VDC motor directly off of an analog output? Are you sure the output can supply sufficient current?
Even if it can supply the current, I'd be very hesitant about doing this.

I know that in things like RC cars they usually connect a small cap across the motor to help reduce backfeed noise that the motor is sure to generate. Even with a cap, the motor will generate sometimes and backfeed power into your PLC output. RC cars use speed controllers with circuits that are designed to deal with this. PLC analog outputs are not.

Maybe I'm overreacting or not understanding your plan, but this sounds to me like a recipe for burned out analog output cards (and those are pretty expensive).

Thomas Sullens
March 21st, 2005, 08:38 PM
analog signal controlling an analog output signal in RSLogix 500? How do you adress the bit inputs and outputs?
If your card was in slot 2 it would be I:2.0 I:2.1 the output word would be O:2.0 O:2.1. If the card was in slot 3 it would be
I:3.0 I:3.1 and O:3.0 and O:3.1.
This may help
I`m like jimbo3123 i don`t understand what your trying to do either, but what ever it is this will help on the addressing????


March 21st, 2005, 09:02 PM
I am just learning about this myself at class. What he is doing sounds similar.

I think his question is this

IR output is say 4 to 20 mA.
This correspond to bit values 0 to 1600. I picked these numbers out of the air, 1600 is evenly divided by 4, 20 and 10.
the bit values would correspond to a voltage output range of 0 to 10 VDC.
SO (if I understand correctly)
4 mA = bit value 0 = 0 VDC output
12 mA = bit value 800 = 5 VDC output.
20 mA = bit value 1600 = 10 VDC output.

Have I got the picture OK ??
Feedback more than welcome

Dan Bentler

Thomas Sullens
March 21st, 2005, 09:41 PM
IR output is say 4 to 20 mA.
This correspond to bit values 0 to 1600. Have I got the picture OK ??

Dan if 20 ma equaled 1600 then 4 ma would equal 320.
1600/20*4 . Now if you scaled this into 0 to 10. 320 would be your input low 1600 the Hi. 0 would be output low and 10 would be the output Hi. I sure hope this is right! :banghead:


panic mode
March 21st, 2005, 09:56 PM
there is another thing with the little sensors you want to use.
they are not intended for 24VDC operation and the output is not linear.

Ken Moore
March 22nd, 2005, 05:02 AM
Don't understand your application but:

If you want to have your output follow your input,say when the input is at 50% of full range, the output will be at 50%, just use two SCP's. Scale the input using the raw counts of the input card to what ever range you want, lets say 0-100%. Then the second SCP would have 0-100 as the input min and max, the output min and max would be the raw count values of the output card, the destination would be the output address O:1.0 or such.