SLC 500 Totalizers

I need to create code in RSlogix 500 that will track the product used per day. The vessel is a lme silo and we are measuring free space. The problem is this tank may be refilled a couple times a day. I need code that will compensate for the changing levels while still keeping track of the actual usage per day. Any help will be greatly appreciated

I believe we can help you but you need to help us help you.

How is the vessel filled?
Is the product in powder or liquid form?
How is the amount of product in the vessel measured?
Do you measure product outflow? inflow? or just vessel level?
Is product ever flowing out of and into the vessel at the same time?

The product is powder and is blown into the vessel from a tank truck.

We measure product outflow and the product will be flowing out of the vessel while being filled.

Thanks for your response

Richard

There is no need to used the silo level measurement, I suspect it will not give you the accuracy you may need, and the maths will be tricky, considering you will be adding and taking out at the same time. You could also be adding from tanker at the same time as your 24-hour period ends !

Since you are measuring the product outflow, then all you need to do is integrate the outflow rate to give product usage.
You could sample the outflow rate on a time basis, add the rate to a floating point data register, that gives you the total used over time. At the end of each day, divide the total used by the number of time intervals used to accumulate the total, and that will give you the total used per day.

Example:-

Accumulated flow-rates (kg/sec), sampled once per second = 28252400.0
Number of samples (seconds per day) = 86400.0

28252400.0 / 86400.0 326.9954 Kgs per day


If you start to get into problems with your accumulator losing accuracy (number of significant digits available in a floating point), then you can do the calculation per hour, store 24 results, then simply add them up at the end of the day.

I have used this technique on numerous occasions, mucj better than trying to track usage through silo levels.

This response may or may not help depending on your system setup.

We use our historian for such determination. We have a continuous process where we are generating product and pumping product at the same time. We do have extensive metering (and therefore historian logging) so we use SQL functions to determine our volume accumulated at any given time.

Okley, Thanks for the response. We also use a historian to sample the tank level every 24 hours and then subtract this reading from the previous days reading but when the vessel is filled from the tank truck during this time period causes this method a problem.

Daba, Thanks for the response. Your suggestion to measure ouflow rate sounds good. the problem I have is the lime feeder could be running and not delivering product(Clogged). Sorry if I lead you to believe we measure the lime feeder output. The only register I have to monitor is the vessel level.

Hope this helps and I do appreciate the help you two are offering on my situation.

Richard

How often do you trend the data to your historian? Does it show a level change when the product is being delivered?

If so, then you could determine how much was delivered, the beginning of the day accumulated value, and what the end of day accumulated value was.

By these three things, you should be able to determine how much was used during a given period.

Yes, I had assumed your feeder was monitoring the delivery rate, because without it you may be getting product quality problems.

None of the "vessel level" measurement methods will work very well if the vessel is being filled at the crucial (wrong) time. You may well have a way-bill stating how much is put into the silo at each "fill", but if you are filling and emptying at the same time as the day rolls-over, how do you apportion the respective amounts to your infeed or outfeed values.

You may be able to sort this by choosing your calculation time when the silo would definately not be being filled (say for example the delivery drivers never deliver during the samll hours), or by preventing them from starting to discharge their tankers into the silo in advance (you would have to determine how much in advance) of the "snapshot" time.

I'm guessing you don't want to spend any money on this, but if your product relies on reasonably consistent feeder rate, I would consider the ideal solution would be an in-line weigher (belt or tip-weigher) for your product feeder. You may be able to justify the cost with improved product quality.

You may be able to justify the cost with improved product quality.

Click to expand...

It's lime. Lime is lime. No improvement needed or wanted.

We also use a historian to sample the tank level every 24 hours and then subtract this reading from the previous days reading but when the vessel is filled from the tank truck during this time period causes this method a problem.

Click to expand...

It seems that to know the amount used, you are going to have to measure it as it is "used", or measure the amount added from the truck. Otherwise your tank-level measurement tells you nothing about how much you have used, only how much is available for use.

Does the truck bill of lading have an accurate weight amount? Then, Total Used for Day = Amount at Start + Amount Added from Truck - Amount at End of Day. Simply add a manual routine that allows typing in the amount delivered from the truck.

Thanks to all that helped me with this question.

I think the best solution is to actually weigh the product as it is being used. I was in hopes there might have been some magic way to compesate for the deliveries.

Thanks again
Richard

When totalizing with the SLC500 I recomend you use an STI subroutine. If you use a timer your elapsed time will alwasy be the timer preset plus the elapsed scan time, and over a day that can add up to significant timing, thus, totalzing errors.