Flowmeter and Hall output question

cdm13

Hi Everyone,

I have a need to take the output from a paddle wheel flowmeter
and get voltage out of it to interface to a portable USB type datalogger.
Data logger input is 0 - 30 vdc.

The flowmeter has a "current sinking Hall effect output signal".· Can anyone
help with a general direction how I might use a bs2 in combination with
a D to A chip to make this work?· Or are there other avenues to get this to work?

Previous projects of mine have incorporated the melexis sensor to read
rpm on the 2x16 LCD,so I have a littel familiarity with the code and hardware
of the hall effects in that sense.

Thanks for the help...

Curtis

FerretMK4

In that type of flow meter there is a Hall effect sensor that outputs a pulse every time one of the paddles passes the sensor and this represents some quantity of fluid. A Hall effect sensor detects the presence of magnetic material such as steel so when the paddle passes it creates a spike in the sensor signal wire. In your case the signal wire would be connected to a counter with a pullup resistor and when a paddle goes by the voltage in the signal wire will drop momentarily as the sensor sinks current to ground, and this should result in one count. To calculate flow you need to record the number of counts per some time interval so you need a time base. Whatever the calibration is, it will be in terms of counts per unit volume. Take your flow rate in counts per second and divide by the calibration factor and you get volume per second. If you're relating flow to events, you could use the event to capture the counter value and reset it.

Your data will be in the form of the pin output of the counter so you need to use the Stamp's digital lines for input into your data storage. You need to figure out how many counts you're going to get during each sample period and that will determine how many bits the data word will have in it. You may need to put a buffer between the counter and the Stamp in order to save and freeze the count in the buffer and reset the counter then let the Stamp take whatever time it needs to read the digital lines and store the data. You don't want the digital lines changing or being invalid while the Stamp is trying to read the lines.

You could use a D to A after the buffer and use an instrumentation amplifier to get to 30 volts for max flow, then have the USB datalogger convert back to digital again, but this is the long hard way to do it. USB digital dataloggers are cheap, cheaper than analog because they don't have any converters in them; they're just a terminal with isolation buffers and simple stuff like that.

There will be a wide range over which the meter calibration is linear. If the flow is very slow the leakage around the paddles becomes more significant and the meter will read low. There will be some upper speed limit as well. This type of meter is meant for clean liquids.

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