Comparing Analog input in SLC504

Semi-newbie here but here goes:

SLC504 with 4-20 analog inputs from gas monitors... how do I set in my GTR and LES statements what to compare it to?? Not comparing from monitor to monitor, each monitor is independent and seperate in different parts of the plant. I need one output to turn on somewhere mid range (say 12ma) and then second to turn on at 20MA. What do I use as my source 2 for my compare statements without wasting two inputs with a fixed currents (12 and 20 MA) just for reference? Set some arbitrary binary value to compare to or....

Any Help ya'll could provide would be GREATLY appreciated!!!

Drew H. Carlton

I'm not sure if this is the right way to do this or not...

The book for your 4-20 mA input card should tell you what value 4 mA equals and what value 20 mA equals. You may have to hunt for it, but it's there. Say its 4000 for 4 and 30000 for 20. Do the math to find 12 mA (have way in between). That should be 17000 in this example. Then use those values to set up the LES/GRT instructions. i.e. When monitor 1 is greater than 17000 set state 1. When monitor 1 is greater 30000 set state 2. So on and so forth. I've done something similar before with 4-20 mA output to VFD's. It works pretty good. Your other option is to set up the input currents and read the value. Hope this helps. What kind of gas are you monitoring? Just wondering.

Sportster

First use the scale with parameters (SCP) to turn the analog input value into a meaningfull engineering value then use the comparison blocks GRT, LEQ etc to compare this value to a data table set value ie N7:0 or F8:0

If you are using an NI8 card then this can be configured in may ways for the data the plc reads

Drop Down the data format box to see diffent examples

To get there

Go IO Config > Double Click on your analogue card (ie NI8)> Then click the Configure button

See Pic

This should help you get started. (I have no idea why the colors on my PDF turned out so goofy!)

The alarm limit, N100:27 in my case, can be entered from an HMI or you can make it a programmed in constant. This is also true for the time delay.

Thanks a ton guys!!!

Wow!!! I will definatly be be back here... ya'll hooked my up like a tow truck with an answer...

Sportster: Anhydrous ammonia, we use it for refridgerant to bottle p_psi and D_P out here in west Texas. And Nitrogen for now but will be adding CO2 monitoring in the very near future. And you were correct, 3277 for 4ma (Input Min in SCP) and 16384 for 20 (input Max in SCP), had to pull those numbers out of another program but I confirmed them on some other topic on here.

Alan: I used the SCP but with a LIM to try and prevent an out of range condition... Do I need the LIM (see below)? I then scaled it to 0 - 250 (PPM NH3) in N:7.1-8 with warning condition set >50 and <250 then had alarm set at >250, might bump that down to 245 just for safety, or extend my SCP scaled factor to say 265, but sensor, I believe, is 250ppm max. For simplicity could I just use a LIM to get my warning between 50 and 250 and drop the GRT and LES?

Bloke: Didn't have that configure box, only an adv config with no where to format as such... using logix500 with a NI16I card... would have been nice though, is that a 5000 feature maybe?

Tom: Nice colors by the way Your ladder helped a bunch, is your GRT only there to filter lower level 'noise'? Like I was telling Alan, I used a LIM to possibly control an out of range condition:

[-LIM ----------------------------------------SCP ------------]
[ lower limit: 3277 ..........................input I:1.0 ]
[ value: I:1.0................................in min 3277 ]
[ upper limit: 16384..........................in max 16384 ]
[.............................................scale min 0 ]
[.............................................scale max 250 ]
[.............................................output n:7.0 ]
(spacing sucks...)

LIM Necessary???

Again Guys, thanks a ton!!! Understood the concepts for a while, but first time implementing them beyond a Moeller (Prefer the new Pico's now though ) I hope to someday be able to return the favor, but for now I will soak up all I can!

With your NI16I card you have it selected as a class 1 device. In a test project try reconfiguring it as a class 3 device. They are the same card, you can just get a lot more data back if you tell it that it is class 3. When you do that have a look at the tabs and there will be an advanced config, where you find all the nice features as shown on here.

regards Alan Case

I thought it would be ammonia, but I had to ask. It looks to me like you wouldn't use the Limit there. I would use it in regards to the output of the Scale. i.e. scaled output is greater than x but less than y, set condition 1. Are you doing this for alarming? If so; make sure the ppm is at the correct amount to alarm at. 50 and 250 sounds correct... but its late. You might not even need a limit at all; just use greater than. Hope this helps.

Sportster

ateav8gn said:

Bloke: Didn't have that configure box, only an adv config with no where to format as such... using logix500 with a NI16I card... would have been nice though, is that a 5000 feature maybe?

Click to expand...

Its definately a feature of Logix 500

As Alan States change your Card Configuration from a Class 1 Card to a Class 3 Card

Then See Pics

ateav8gn said:

Tom: Nice colors by the way Your ladder helped a bunch, is your GRT only there to filter lower level 'noise'?

Click to expand...

The first GRT is there to eliminate bogus readings if the input drops below 4 mA. I didn't show it, but other logic in my program sets the engineering units value, N100:35, to zero if the input data is LEQ 3200, and sets a "Signal Lost" alarm bit if it is.

argh!!

Dave:

I changed the NI16 to a class 3 (after 45 mins on phone with a*****'s at Rockwell) but I still don't get the configure button. Is this possibly because the software hsn't been updated in a year or two on the laptop I'm using, or (my guess) since I have already done 90% of my ladder logic and it will only let you do that with a blank pallate.... Dork at AB said to download the 1746-UM001 (120 page analog input card user manual) off AB.com and then bit by bit configue the input words..... I like your way much better. Didn't get time today to start the bit by bit but will read more into it tonight and se WTH is going on.

Thanks!

Drew

What version of Logix are you running ?

I would guess this may be your problem

I am on 6.2.00 build 14

Basically all logix does for the class 3 config is add a line of ladder to configure the NI16I

See my example which should be correct for your purpose on channel 1 slot 1

N100:0 is important and should be set to the value indicated

I think i am right in assuming from your above posts

NI16I Slot 1
4-20mA Input
required 0-250 scaled units

You must make sure that a class 3 device is selected or if this is not available then set your Module ID code for slot 1 to 10403

For Under/Over Range and errors see Input I:1.0 bits 13,14&15 (See Pic)

BTW You really should read the manual as it does help on this alot!

Pic1

Pic2