MicroLogix 1100 SCP instruction Raw data not matching scaled data

[Kidblue]

Those aren't for the base input

So what are they for? I've always used 0-1023 [0-10V] as the raw data in when using both the ML1100 + ML1400 base units.

As Mickey commented, it may not be your problem, but i'm curious why you are using 0-5V (or 1-5V) as your raw data scaling?

Rob

 

[James Mcquade]

The micrologix 1100 analog input resolution is 10 bits.
Also the resistor The resistance is 250 ohms +/- 0.25 ohms for a 1-5 volt signal or 500 +/- 0.25 ohms for a 2 to 10 volt signal.

regards,
james

 

[Brad Frayo]

yes as James says we are using a 250 ohm resistor across the analog input

 

[harryse7en]

yes as James says we are using a 250 ohm resistor across the analog input

I hate to state obvious things, but could it be a faulty resistor? Although I would still expect the raw to match the scaled more closely

 

[Brad Frayo]

Resistor is not issue

The discrepancy is not in the raw data input. There is a discrepancy between the raw input and the scaled output. I have a feeling it has to do with the horsepower of 0-1023 resolution to go in reverse direction.

 

[bernie_carlton]

I'm curious about the numbers on the left side of your trend. Your SCP seems to imply 0-500 as input and 0-200 as output. Are you actually plotting the results of other calculations which take place after the SCP?

The scaled number should be the ((input - 100)/2). Can we see just those numbers in a trend?

 

[Brad Frayo]

the scale on the left only refelct the scaled output for a 0-40 foot reservoir. The 20.0 foot scaling output is incorrectly shown from another program. Everything else is the same. The other trending is on a different scale. 0-500, but shown proportionally correct. The top has been chopped off as the trend was a screen shot takin from a water district computer via a VPN connection.

 

[bernie_carlton]

OK, I understand.

 

[ianingram]

I am clutching at straws to help...

For the File that the SCP instruction is in (LAD 3), the JSR is unconditional, I assume...

 

[widelto]

hey Brad, have you actually measured voltage on your analog input.

 

[bernie_carlton]

As a test, create a rung just after the SCP which does this:

Moves the input value to an N register
Moves the output of the SCP to the very next register.
Do a reverse SCP (swap the inputs and outputs) on the first two and put its results in the next register.
Subtract the input and the output of the reversed SCP. Put that in the fourth register.

Watch them. If they change too quickly then condition the rung. The registers will hold the result of the last scan while the condition was true.

The third register should track the input (+/- 1 , this depends on the rounding done by the SCP instructions). The fourth register should be zero, 1 or -1.

If this is satisfactory then point the trend to the first two registers. See what you get.