Something to replace Integrals?

[Markoo]

Hi everyone!

New here with couple of questions for this great community from which I've already learned a lot:

I'm working with Unitronics US5-B10-RA28 which has so many possibilities and have encountered a problem - I have a slider set from 0-70 linked to analog output 0-10V. Units which it regulates are in l/h (liters per hour). What I need to do (among other things) is to calculate and display total consumption of fluid since startup. Also, consumption may change during operation of the machine. Normally I would use integrals, but here as I see this is not an option. Tried to get this number with dividing and so on, but i couldn't get results when I divide 1/3600 (for example). Is there any way to achieve this?

 

Thank you in advance and thanks for all the knowledge I've already gotten from this forum.

 

Marko

[Flex727]

Think about what an actual integral is. You take the curve and slice it up in small pieces and the area under the curve is the sum of the areas of the rectangles created as the widths approach zero. You can fairly accurately approximate this by determining the minimum time slice needed where you have little variation in the analog input (typically 100ms to 1 sec). I'll use 1 sec for this example. If you take your flow rate value (liters/hr) and divide by 3600, then you have the volume that flowed in 1 second. Sum that number every second to give a continuous volume.

One thing to be cautious of is that your initial flow rate number be large enough so that you don't lose resolution by dividing by 3600. To prevent that, do your linearization to about 3 decimal places (i.e. if your flow sensor were 0-100 liters/hr, then linearize to 0-100,000 instead of 0-100 - this provides an implied 3 decimals of precision that you can use if need be or drop off your final value by dividing the final number by 1000).

[Ausman]

Just to throw in my "two bobs worth" a left field alternative is related to how  you are getting the total figure.  It sounds like you are deriving it from what you are sending  to a flow controller.   If you want to be really, really accurate, then you should actually read  what the controller sends back, if this is possible.  Most analogue valves can take a little time to adjust to what you send, so in theory if you do accumulation maths on what you measure using an analogue position value from the valve, it will be more accurate.  Analogue valve actuators generally have mechanically linked analogue outputs that show the actual state of the valve, and in some ways this will do the job more easily as you would treat it as a totally separate thing.

And re my Aussie slang, .....one place that might help and will also give you a laugh at how we destroy language for a giggle http://www.wanowandthen.com/slang.html    Be prepared to lose quite a few (but very amusing) minutes reading it all. 

cheers,  Aus