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Counting bubbles simultaneously on 96 inputs

Good morning,

We are working on a research project related to biomethanisation. We have 96 small digestors and we intend to measure the volume of biogas generated in each of them. The gas flows are very low so we intend to count gas bubbles in glass tubes filled with colored water.
We have one of these bubble counters (http://www.ncbe.reading.ac.uk/NCBE/MATERIALS/MICROBIOLOGY/bubblecounter.html) and we intend to fabric 96.
When a bubble pass in front of the sensor, the voltage pass from 2,25V to 0,83V and come back to 2,25V. The signal is detected by a LCD counter (LR 96702). It's an analogic signal, not a square signal and we know the puse length is above 50 microseconds (detection threshold of the lcd counter).

We need to regularly acquire (for example each hour) the number of bubbles generated by the 96 digesters so we want to connect the 96 bubble counters to a DAQ system.

I'd like you help us to choose the more adequate (and low cost) material for our application and I have several questions to ask :

- Can we use a board with numeric inputs? Are these inputs able to interpret a sine pulse as a square pulse? Or do we need to transform the signal?
- Do we need counter inputs? Or is it possible to count the pulses (detected by classical numeric inputs) in software with labview?
- If we need counters, is NI 7811R a good choice for our application?
- If it is possible to count the pulses in software, is NI 6509 a good choice?
- What cables and terminal blocks do we need? (shielded?)

Thank you in advance for your help.

Sébastien LEMAIGRE

CRP-Gabriel Lippmann
Département 'Environnement et Agro-biotechnologies'
BIOFAR-EVA
41, rue du Brill
L-4422 Belvaux
GD LUXEMBOURG

Tel:  +352-47.02.61.458
Fax: +352-47.02.64
e-mail: lemaigre@lippmann.lu

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Hi Sebastian,
 
Thank you for posting to the NI forums.  For your convenience and in the interest of completeness, let's keep this issue confined to one thread.  Please use the following link for all future postings.  Thanks!
 
Couting bubbles simultaneously on 96 inputs
 
Ed W.
Applications Engineer
National Instruments
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