Micro flow sensor


Thread Starter

Mark Ludlow

I am looking for a pulse-output flow sensor to work in the following scenario: I am injecting a 5% NaOH solution into a flow stream with a piston-type (HPLC) pump at high pressures and variable rates, with pH as a primary feedback variable. Flow rates range from about 20 to 100 ml/min. I
would like to have a totalizer as well as a time-integrated rate indication. I am considering a paddlewheel or similar sensor, but I am not certain of the applicability. First, the high pressures (30 bar) in the output stream eliminate most sensors I've seen. Would metering the pump feed work equally as well or pay I encounter excessive pressure drop to the pump inlet?
Second, because the pump output it periodic rather than continuous, I am wondering if a paddlewheel sensor would have the dynamic response to accurately account for everything going through it, at least to some nominal
accuracy of, say, 2%?

Any suggestions? What about other types of pumps that would survive the environment and produce relatively high pressures?

Mark Ludlow
Surf over to "http://www.coleparmer.com":http://www.coleparmer.com . They have an amazing array of pumps
designed for process automation. I think they have "intelligent" high pressure metering pumps.
I think I would use a metering pump that has a built in totalizer. The accuracy of this arrangement would be better than a paddlewheel sensor, i.e. Signet 2507, which is just fine for lower pressure systems. I've run them down to
I have some other ideas, just not enough time right now. Email me if you like.
Steve ([email protected])

david mertens

As you are working with a piston type pump (fixed displacement per stroke) the easiest solution would be to just measure the number of strokes the pump makes or the number of revolutions (the number of strokes per revolution should be fixed). Because the pump will displace the same amount of liquid at each stroke, this would easily be converted in an amount and by taking the time in account, the flow (volumetric, not massflow). The amount of liquid transferred per stroke should be in the technical specification of your pump. Kind regards.

Curt Wuollet

Why not simply keep track of piston displacement? Since it's a positive displacement pump, this should provide excellent accuracy with velocity
as flow and displacement as volume. At worst, you would have to account for a little lost motion, etc. Much easier than measuring the result.


First, try to use a pump or similar unit for which you can calculate the flow of additive, based on the number of strokes per minute. To measure the flow rate after a piston pump is a problem. One can install a dampener in the pipeline (ask mechanical engineers, but it is not the solution).

Usually with the dosing pump you can control the rate of strokes and the stroke length
Stroke length define the unit volume that is added each time, and the frequency the rate.

Practically by information about the stroke length - volume characteristics of the dosing pump you can calculate the adding rate.

Hope it helped.
This is, however, not the right answer.

Even piston metering pumps have problems with entrained air or gases, and can often be airlocked. Diaphragm metering pumps are of course, much worse.

The real answer is that there are any number of flow meters that will work, except that they are all usually too expensive to use, and they have to overcome the pulsation of the metering pump, the pressure, and often, the fluid itself in the case of corrosive or abrasive fluids.

Walt Boyes
Dear Mark,

Although we manufacture a flow meter called MicroFLOW, any time you have pulsing flow, metering accuracy is likely to be compromised. If
you were to use a true metering pump, the pump's accuracy may meet your requirements without the use of a flow meter.

We do have ways for our meter to work on such application if required. Let us know if we can help.


John Catch
You could try to use Quantim which is a flow meter/controller based on coriolis technology from Brooks instruments it measures and control's
very low flow contact them with your application
You can find information in there web site

I hope this helps you
Pedro Alexandre