Author Topic: Flow Meter Integration  (Read 51453 times)

Fitzsimmons Hydraulics

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Re: Flow Meter Integration
« Reply #15 on: November 05, 2014, 11:06:05 PM »
Still working on this circuit. I've been waiting to test if this low flow error exists in our glycol loop as well, considering the oil meter I've been working with so far is very old and perhaps unreliable. Turns out the glycol loop behaves in the same way.

The period signal grows larger as the pump flows less, until around 17-18 GPM. Here is where I see the signal drop off. I've logged this data by tenths of a second and found that as the flow approaches 17-18 gallons, the signal begins reading very large, intermittent values. As the flow reaches these values, the period signal seems to latch to 10,000,000. I believe this is the same as 1Hz, or the lowest frequency that the controller can register. To me it seems that the turbine blades are being "missed" by the pulse pickup, since the absence of a signal would generate a period value of infinity.

Due to this, I went and looked at the specs for our meters. Our Blancett 1100 series model B111-115 for glycol is rated for 15-180 GPM, so I think the easy answer here is that we need a smaller meter. However, this is not conclusive to me because the oil flowmeter is a Flow Tech LT750 rated for 5-172 GPM, yet behaves in the same way.

I have attached a screenshot of the flowmeter page as well as some test data from a logfile generated with the oil flowmeter. Any thoughts, suggestions, or speculations are very welcome - it almost works but I'm a bit stumped! Sorry for so much data - the strange readings begin around time stamp #46000. The data out represents GPM times 10.

Offline oiltronic

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Re: Flow Meter Integration
« Reply #16 on: November 21, 2014, 04:32:02 AM »
Executive summary:
  • Yes, 10,000,000 is a .Per input value limit.
  • Checked sensor input with oscilloscope?
  • Correct input range and voltage thresholds?
  • Digital output option for sensors?
  • Tried sensors on main controller?
Long-Winded version:
I believe the 10,000,000 value is a limit within the IX024 module for a .Per input which I've ran into before (on an MC050).  So I just used the period measurement component instead.  I've considered using multiple measurement methods before (.Freq input, .Per input, period components, etc.) , each with a different span, then selecting the appropriate one according to the current rate.   Thankfully I never had to go that far.

Considering the inertia of hydraulic fluid and glycol, the numeric jumps & hiccups in your spreadsheet data really seem like missed pulses.  But if those are analog-output mag-pickup sensors, then the peak-to-peak voltage of the sensor might decrease with flow.

Try an oscilloscope on the meter output, both when connected to the input and when disconnected, so you can see what the pin is seeing and maybe adjust the input pull-up, voltage span, and threshold voltages on that pin.  Maybe there is a digital output option for those meters.

I would also try to hook up any high-speed inputs like that to the main controller, and leave the IX module for slow analog or digital inputs.  This would also let you try using the period component.

« Last Edit: November 21, 2014, 06:13:17 AM by oiltronic »