Totalizer In Micro850 PLC

[JackSigma]

In my control panel I'm using omega engineering fpb151 paddlewheels. I was told by the manufacturer that the paddlewheels i have only have 4-20ma output

 

[TimD]

Yeah, that FM is either/or for analog/digital. Bummer.

I've done interrupt programming on a ML1400 for improved accuracy, but in the end, I have to tell clients that don't have dual output flowmeters... "use the totalizer as a best assumption"

I interrupted the CPU every 1,000ms (1sec) to take a reading, and totalized it over 60sec, then added the 1min totalized value to the 'master' retentive totalizer after each elapsed 60seconds.

I'm not familiar with the newer Micros yet, using CCW, so bear with me here. In Logix 500, I use the "STI" Function File under Controller Properties. PFN is the ladder section for the per-second totalizers, UIE, AS and TIE are set to "1" and SPM is set to "1000" (1000 msec)

Below is code, very similar to your own code at the top of this thread. The main difference is I use the Interrupt capability of the CPU.

 

[TimD]

Here are some snippets to help you understand the Interrupt code.

Hope this is helpful.

Cheers,

Tim

 

[drbitboy]

CCW/Micro8xx does have the equivalent of RSLogix 500 STI routines, but that has nothing to do with OP's problem.

OP (@JackSigma): the problem is either in your AI configuration or scaling or possibly the AI hardware has an accuracy problem.


Do one or both:


1) Describe the scaling, connections, flowmeter configuration, plc configuration for both MicroLogix and Micro8xx setups.



2) Put your code into .ZIP (ZIP-archive the .RSS; ZIP-archive the CCW directory and descendants), also putting both into .PDF form would be useful.

 

[JackSigma]

I don't have any micrologix code, i was just saying that i programmed my totalizers in CCW the same way i always do in RS500.
My project file is too large to post here, so here is my scaling setup for my analogs

 

[JackSigma]

The flow meter is scaled 0-700gpm and verified to be set up correctly by the manufacturer

 

[drbitboy]

The obvious questions first:

1) Are you sure 4000-20000 is the correct raw range that corresponds to 4-20mA on analog input channel _IO_X4_AI_00?

1.1) Are you sure that P1FLOWMIN is the correct flow in GPM for a 4mA signal?

1.2) Are you sure that P1FLOWMAX is the correct flow in GPM for a 20mA signal?

1.3) Have you checked the 4-20mA analog input channel with a calibrator or signal generator?

1.4) Have you checked the current with a multimeter against the _IO_X4_AI_00?

1.5) Have you checked the value of P1_FLOW against an independent flow measurement? E.g.

1.5.1) An indicator on the flow meter, if such exists?

1.5.2) Tank surface area times tank level change over a known time, with no other inflows to, or outflows from, a tank?

I would assume the answers to all of those are yes, but we should confirm they are before going forward.

2) Side query: what is the purpose of the [NXB LES AIO 4000.0 MOV 4000.0 AIO NXB GRT AIO 20000.0 MOV 20000.0 AIO BND] branches? Unless you are using AIO somewhere else in the program, that will not affect anything.

 

[drbitboy]

The flow meter is scaled 0-700gpm and verified to be set up correctly by the manufacturer

Have you personally verified the manufacturer's verification?

20k gallons per day is ~14gpm (1440min = 1d; √2 ~ 1.4), so a bucket check with a 5gal pail would take about 20s, if the needed piping exists and is safe.

 

[drbitboy]

700gpm at 20mA which is 20ft/s (FPB151 data sheet), and suggests a 4" Sched. 80 pipe (~3.8" ID).

20kgal/d is 14gpm, which is 2% of 700gpm range.

Strike 1.

14gpm in a 3.8" ID pipe is ~0.4ft/s, and the minimum velocity for that flowmeter is 0.3ft/s (FPB151 data sheet).

Strike 2.

14gpm water at 10°C in a 3.8" ID pipe has a Reynolds Number of ~8769 (cf. https://www.omnicalculator.com/physics/reynolds-number), minimum Reynolds Number is 4500 (FPB100 series user manual)

Meh; fouled it off.

If nothing else, with a max flow of around 2-3% of range, there could be a measurement resolution problem, especially at lower flow rates, so accuracy may be a pipe dream.

Bottom line: that meter might have been sized improperly for that application (flow rate and pipe diameter).

Caveats - a lot of assumptions in there e.g.

• 4" Sched. 80 pipe
• Relatively constant flow second to second over a day

 

[drbitboy]

Accuracy can also be affected by the installation. E.g. the installation should have anywhere from ~5' to 16' of uninterrupted straight pipe upstream of the flow meter, and 1.5+' downstream.

​

 

[johnd_125]

I assume you have checked connections, scaling, AI configuration etc. Your programming worked in RS500 and you got accurate totals. So similar programming concepts should work in CCW.

The difference is the hardware (Micro versus SLC, Micrologix).

1. I don't know the actual modules you are using but the Micro plug in AI module is not as accurate as lets say a SLC module. 12 bit versus 16 bit and ±1% full scale accuracy versus ±.365% full scale.

2. Perhaps the flow signal being read by the Micro hardware is just off by a certain amount. If its a consistent amount you could bias the actual flow reading.

3. In my experience paddle wheel flow meters are notoriously inaccurate but here again if they worked for you before, they should work, now.

4. Dumb question maybe but flow into a well could be less than flow out if water is coming in from some other source?

Good luck and post back when you figure it out.

 

[OkiePC]

...
I'm using omega engineering fpb151 paddlewheels.
...

That looks like a rebranded GF Signet. Ensure that the correct K-Factor is programmed into your flow meters. There's a chart in the signet literature that has K-Factors for all the common pipe types and installation saddles. I would bet that the Omega literature is identical with a logo swap.

 

[JackSigma]

I was emailing the omega tech support about this issue because i found that if the paddlewheels are mounted vertically(which they are) they must be filled with water at all times, which is not the case. which could explain the high reading but im not accumulating unless a pump is running, but at this point I don't know.

 

[drbitboy]

by mounted vertically do you mean the fpb151 is on top of a horizontal pipe?

 

[JackSigma]

No like the flow is vertical,