1762-if2of2 output wired to input different value

[DwightA]

I was trying to use a Micrologix 1100 and a 1762-if2of2 Analog IO card to demonstrate A/D and D/A conversion.

Simple ladder logic
Enter a value into one of the N7 (integer locations)
Move the value entered to the output
Output is hardwired back to input
Move from input into the next N7 location

I assumed (probably where the problem is) that the input would equal the output, but is doesn't?

Why is the input, not the same as the output?

Thanks

 

[Bit_Bucket_07]

Perhaps the Input and Output are scaled differently?

http://www.plctalk.net/qanda/showthread.php?t=107154

 

[geniusintraining]

Why move it to a N? just move the input word to the output word

 

[rdrast]

How far off are the values?
Are you using Current or Voltage?
Post a screenshot of the module configuration dialog?

 

[OkiePC]

Looking at a program I have with that card, it appears that the scaling inputs and outputs should be the same when the inputs and outputs are set for Raw/Proportional data format and current signals. Then:
4mA = 6240
20mA = 31207

But I also believe that the default configuration for that card when you add one to your RSLogix 500 file will be to select 0 to +10vdc.

The 1762-IF4 has some switches on the card used to select voltage or current, the default being current. I am pretty sure those switches have to exist on the combo card as well. Are you using voltage or current signals?

 

[geniusintraining]

The 1762-IF4 has some switches on the card used to select voltage or current, the default being current. I am pretty sure those switches have to exist on the combo card as well. Are you using voltage or current signals?

Yes the combo has the on/off switches as well

 

[DwightA]

As far as I can tell, Input and output are scaled the same.

I wanted to move a value from an N value, out the output, back in the input, and moved to the next N value to demonstrate the entire process digital to analog and back to digital

Both Input and Output set for voltage
output 8 get 8 back, output 15000 get back 14520, output 30000 get back 29016

 

[Mickey]

Post your .RSS file if you can. Zip it first. Someone may spot something.

 

[drbitboy]

Both Input and Output set for voltage
output 8 get 8 back, output 15000 get back 14520, output 30000 get back 29016

Is 3% accuracy between two devices (DAC and ADC) totally unexpected?


"Typical Overall Accuracy" is 0.55% -20 to 65C; 0.3% at 25C, so those results are perhaps higher than advertised by a third to two-thirds of an order of magnitude.

 

[OkiePC]

If the dipswitches on your card are also set for voltage, and the results are 97% accurate, I'd say you have successfully demonstrated D/A and A/D conversion as well as one of the pitfalls.

Using voltage mode, how long are the wires and are they terminated well? Do you have a calibrator you can use to figure out whether it is the output or the input that is "off"?

Try your test with current signals and see if it is better.

Those cards I believe are 12 bit resolution and bit shifted left, so what you are seeing might be quite normal.

 

[DwightA]

Spec says .3% accuracy, 3% seems large to me?

 

[DwightA]

No real field wiring, just a short (<6in) jumper.
Measuring out with voltmeter. Output seems to be a little low.
I was assuming if the reference was off, Input and Output would have same error?

 

[OkiePC]

Note that your voltmeter will add a microscopic load, so don't leave it connected all the time.

Confirm that the dipswitches inside the card are set for voltage (this is not the default).

 

[geniusintraining]

What I would do.... just to narrow down the issue

Put your voltage on your input, 0-10 and just move the input word to your output word and check with a meter that they are the same, if they are off then its your card if they are the same you have another issue

We make a lot of trainers and some have the IF2OF2 and the sample program we load to them to verify the I/O is just that, we have a 0-10vdc potentiometer and the output goes to a 0-10vdc meter, if everything is working correctly you can turn the pot to 1 and the meter is 1