adccommunitymod (AutomationDirect) asked a question.
Flow sensor application
Created Date: March 27,2000
Created By: fj1200
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I am considering using paddlewheel type flow meters for measuring water flow rates in my next application. Since I 've never used these before, I am not sure how they will interface with my PLC. The flow meter outputs can be either a square wave or sine wave at somewhere between 0 and 100 Hz. First, does this require a high speed counter card? And second, would the HSC and a sine wave signal be compatible? Any advice would be appreciated.
Created Date: March 27,2000
Created by: fj1200
I am considering using paddlewheel type flow meters for measuring water flow rates in my next application. Since I 've never used these before, I am not sure how they will interface with my PLC. The flow meter outputs can be either a square wave or sine wave at somewhere between 0 and 100 Hz. First, does this require a high speed counter card? And second, would the HSC and a sine wave signal be compatible? Any advice would be appreciated.
Created Date: March 27,2000
Created by: Russ
Hi,
The square wave output I would think is the best for hooking up to a counter. You didn't mention what PLC model you want to use, but the 100 Hz frequency of the pulses shouldn't be a problem as the DL05, 105 and 205's high speed counters all go up to several kHz. The 405 has a co-processor module ( F4-08MPI ) that is designed to accept pulse inputs from Hall effect magnetic pick-ups like those found on turbine meters. Whatever module you decide to use, pay close attention to the voltage and timing specs of the inputs. Specifically, make sure your meter can supply enough current and voltage ( typically 12 - 24 VDC on the 05/105/205 counters ) to drive the PLC's HSC inputs. Also check the timing characteristics of the meter and make sure it produces a signal long enough ( on/off, off/on response time ) to be captured by the PLC. After you are sure the hardware will work, it's also worth considering your programming requirements - make sure the PLC has the speed,memory and calculation capabilities you will need to implement your measurement and control system. Hope this helped and good luck with your project!
Created Date: March 28,2000
Created by: bob whalen
Data Industrial (1800 338 0312) has paddle wheel sensor - 220B. It provides pulse output that I have used with counter. A solution I like better is to also use their 4/20ma converter - model 310. It is programmable and you can set 4/20ma for the flow span that you want.
Created Date: March 29,2000
Created by: Tom Jenkins
We usually use 4-20 mA transmitters, but we have had good luck with the pulse type of signals as well. There are advantages to using a 24 VDC square wave pulse signal:
1) lower cost for both the meter and the PLC
2) by counting the pulses over a time delay you are inherrently filtering or averaging the signal, so if you have a "noisy " signal or fluctuating process value it is not bothersome
3) since each pulse is essentially a fixed volume you can totalize the flow by simply counting pulses and multiplying by the correct scale factor
Created Date: April 13,2000
Created by: Mike McClanahan
If you have to have accuracy then forget the paddle wheel. We tried them but they could not maintain accuracy over a varying flow rate. Would have been nice to since the output worked well with the PLC
Created Date: March 27,2000
Created by: loveplc
Want to save yourself a lot of time and trouble? Get the right controller for the paddlewheel. It'll allow you to do the scaling and most likely offer output options like BCD or 0-10V FS output. Then all you have to do is convert to engineering units. Of course, if money is a constraint, then I like the second posters idea of using a square wave type. It really is a hall effect of magnetic pickup type sensor that just swithes on and off.