Test and Measurement Forum

Hi,

For some time I have been manually logging various parameters associated with my aquarium; pH, temperature and CO2 flow-rate. I have become very bored with the daily grind and wish to automate the whole process. The DrDAQ looks like a very good step in the right direction, but I have problem with how to log the CO2 flow-rate.

Currently, there is a "bubble-counter" fitted in the CO2 line. It lets me see, and sometimes hear, bubbles of CO2 as they are forced through a small, water filled bottle. I simply measure the period between these bubbles to obtain an uncalibrated flow-rate.

Do you have any ideas about how I might make a similar measurement using Pico technology?

Cheers

This is an intersting application.

The pH is obviously taken care of via the DrDaq's pH input. However flow is a little more complicated. You will need to source a suitable flow sensor with a voltage output. The sensor should give a voltage out proportional to the flow rate. The DrDaq's voltage input could then take care of the flow measurement.

Unfortunatley, we do not stock any flow sensors. A good place to source a suitable sensor would be http://www.sensorland.com

Best Regards

Mark,

I hunted around for applicable flow sensors. Unfortunately, my requirements are rather awkward - the basic problem being a very small flow rate.

At some point I gave up the search and decided to make one myself. If I may say so myself, I am quite pleased with the results. It uses an IR detector and emitter to spot gas bubbles in a small water-filled container, and an Atmel microcontroller to do the measurements and a degree of signal filtering. Finally it uses a DAC and op-amp to provide the voltage required by the DrDAQ. Because of the resultant high current requirements, a mains adapter provides a parallel power supply.

Having got this far, I finally commited myself to buying the DrDAQ itself. It's an excellent piece of kit and does everything I want, except I cannot get it to recognise my sensor.

Last night I tried a using simple dummy sensor built from a 2K2 resistor and a 100K pot. Even this didn't seem to be recognised by PicoScope (5.08). The calibration file (bubbpers.dds) looks something like this:

[Scale50]
Resistor=2.2
LongName=Bubble Period
ShortName=BperS
Units=secs
MinValue=0
MaxValue=40
OutOfRange=0
Places=0
Method=0
Fast=No
NoOfPoints=11
Raw1=0
Scaled1=0
Raw2=0.2
Scaled2=4
...
Raw11=2
Scaled11=40

When I try to use either my bubble sensor or the dummy, the Y-axis of the scope appears without the correct label and a simple 0 to 100 range. Can you help?

Thanks,
'Nic

Hi,

I tried the following File which is very similar to yours but more suitable for my equipment:

[Scale50]
Resistor=2.2
LongName=Bubble Period
ShortName=BperS
Units=secs
MinValue=0
MaxValue=40
OutOfRange=0
Places=0
Method=0
Fast=No
NoOfPoints=2
Raw1=0
Scaled1=0
Raw2=2.5
Scaled2=40

This worked fine on Ext1 so we know there's no problem with the software. Perhaps your sensing resistor is the wrong value? ... it should be connect between pins 2 and 3.

The voltage input should be between pins 1(+ve) and 2(ground).

Kind Regards,