SLC 5 analog input problem

I have a SLC5/05 with a 1746-NI16V. I am trying to configure it for single ended inputs. Please notice in the screenshot the upper SCP is outputing 18 to N10:6, but the lower one with the same parameters is outputting 4825 to N10:5, which is correct. What is wrong with the top one?

We can't see the input on the top rung, but I'm guessing it is false so the top SCP isn't executing.

It is also possible that the destination of the top one is being used elsewhere. If you right-click on a blank part of the ladder and select properties you will see a window pop up. I don't remember the tab it is on, but it is at the bottom of one of the tabs. Look for two options that say Cross-Reference. One is cross-refencing the outputs and the other is cross-refencing the inputs. You want to cross-reference the outputs. Select that and then apply the changes. You'll see numbers appear in yellow below some output instructions. That will tell you a file and rung number where that address is being used elsewhere in your logic. We DON'T want to see that below your SCP.

On another note, The input Min and max should be the values you are seeing from your analog input when they are at its lowest and highest. This is commonly 0 and 32767.

The Scaled min and max would be what you want your value scaled to. For example 0-1800rpm.

OG

It looks to me like there is a logic instruction (XIC or XIO or summat else?) on feeding the SCP on Rung 001; if the output run of that logic instruction evaluates to false, then the SCP on Rung 0001 will not execute, and the value of N19:6 will not change.


Whoops, this is the same thing that OG wrote.

Normally the SLC500's Input card's range is 3277 (4mA) for Input Min and 16384 (20mA) for Input Max.

in a SCP you'd use the following in the Scale Min/Max.
Outputs tend to run 6242 (4mA) to 31208 (20mA).
Full band is 0 (0mA) to 32764 (21mA).

Nova5 said:

Normally the SLC500's Input card's range is 3277 (4mA) for Input Min and 16384 (20mA) for Input Max.

in a SCP you'd use the following in the Scale Min/Max.
Outputs tend to run 6242 (4mA) to 31208 (20mA).
Full band is 0 (0mA) to 32764 (21mA).

Click to expand...

Data values depends on how the OP configured the card. See PDF

Thanks everyone for your comments.
OG, my scaling was just something simple to determine if it works. I actually have 0-10 Vdc input and need to display the value as 0-10.0.

Included is the rest of the ladder diagram, showing rung 0000. I am working from home today (without the PLC), so the diagram will not run.

The XIC in rung 0001 is my input, at 18 (.018Vdc) when off, 4825 when on.

OG I assume the crossover list shows any other use of the input (this will be helpful for my real program, this is just my analog input test program).

The issue that I saw (reference first picture) that while I had 4.825 Vdc on the input at I:4.8, I only had 18 written to N:10.6
To determine what the problem was, I created the second SCP referencing the same input, and used N10:1-4 to scale it. I would think copying the scaling from the top SCP to the bottom would give me the same output, but it didn't.

My question is why don't the outputs match?

AS others have said get rid of the XIC on rung 001.

Why do you have it there?

So I think everyone is right that getting rid of the XIC in run 0001 will fix it (but don't have the PLC until Monday to try).

Thanks everyone, that was a real duh.

I think what I was getting stuck on was looking at the values in the SCP block. Please clarify: The input value in the block will stay the same, regardless of if the block is running, but the output value is real time?
Put another way, the input shows the last enabled reading, but the N10:6 output reads the present output?

Mickey,
I was advised not to change the Analog input ranges so the module can be replaced without re-configuring, so they are still set at -10 to +10 volt input.
So for 0-10 vdc input I would configure the analog input for 0 - 10250 (equal to 0 - 10250 milli volts, correct?

mtech2766 said:

Please clarify: The input value in the block will stay the same, regardless of if the block is running, but the output value is real time?
Put another way, the input shows the last enabled reading, but the N10:6 output reads the present output?

Click to expand...

All values will *display* as their current state, regardless of whether the block is running. The output value will not be *updated* unless the block is running/enabled.

The input value will reflect the voltage present at the input card at any given moment.

When the block is enabled, the math instruction will perform its calculations and place the resulting value in the output.

When the block is not enabled, the output will continue to hold whatever the last value placed in it was, regardless of how the input changes.

thanks, that explains my confusion

The values displayed are the current values in real-time. The value for the input will update all the time whether the SCP is true or false.

In the bottom SCP, you are using addresses for the min/max fields so those will also update dynamically if those values change. You can click on them and change the scaling settings on the fly. Very useful! The top SCP is using fixed values for the min/max settings, so the only way to change them is by editing the logic.

Now, the output...If the SCP instruction is true then it will show you the current value being sent to your output device. If the SCP is false, then it is not affecting the output address, but you are still seeing the current value for that address.

When the SCP is false, something else in your logic COULD write to that address, and you would see it changing here on this SCP. That's where that cross-reference comes in handy. It would show you if something else were writing to that address. That is usually not desirable!

OG

EDIT: plvlce was faster than me!

OG Thanks for the additional explanation.

I also have an input that will be between 0 and 1 vdc.
When it is said the input max value of SCP is the input value, it means the digital input value the Ain module sees, correct?
So in my 0 to 1 vdc input (channel configured for -10 to +10 V), would my max input value would be 1638?

mtech2766 said:

OG Thanks for the additional explanation.

I also have an input that will be between 0 and 1 vdc.
When it is said the input max value of SCP is the input value, it means the digital input value the Ain module sees, correct?
So in my 0 to 1 vdc input (channel configured for -10 to +10 V), would my max input value would be 1638?

Click to expand...

Raw data values will depend on how you have the card configured.

-10 to +10 volts range and the data format range you selected ( engineering units, scaled for PID, proportional counts or NI4 data format) see my pdf in post #5

if you can post your .RSS file and someone can see how it is configured, zip it first.

If your card is set for +/-10V using the RAW Proportional setting, then the unscaled data would range from -32768 (-10V) to +32767(+10V).

So 0 - 1 volt would be 0 for the minimum and 3276.7 for the maximum.

Alternatively, if you are able to do so, crank up the input to its max signal (1 volt) and note the data value for the input. Crank it down to its minimum and that value would be your minimum value. Then you can set your scaled min and max to the values you want to use.

OG