Low velocity flow meter for fluids


Thread Starter



I am looking for a flow meter that is capable of monitoring fluids at velocities of > 0.003 m/sec inside an 47cm dia bore. The bore will at times have metal tubes passed through it of up 30cm dia.

Any suggestions appreciated,
If the fluid doesn't have a large percentage of suspended solids, an ultrasonic transit time clamp-on flow meter might see that low a flow. It won't be 'accurate', but it might well see it.

Copied exactly from the catalog page for Siemens FUS1010 clamp-on flow meter:

Siemens FUS1010
± 0.5 % ... 1.0 % of flow,
for velocities greater than 0.3 m/s
(1 ft/s)
± 0.0015 ... 0.003 m/s
(± 0.005 ... 0.01 ft/s),
for velocities less than 0.3 m/s
(1 ft/s)

the "± 0.0015 ... 0.003 m/s" statement has to be a misprint. I know that the ~1% accuracy low limit is 0.3m/sec velocity. So, I'm not sure what that spec is trying to say.

But I can say that I've been amazed at how sensitive ultrasonic clamp-on transit time has been at low flows. Not that it's 'accurate' (compared to Mr. NIST's reading) at low flows, but it can see very low flows (like a 2am in morning, single urinal flush off a 4" water line supplying a multistory commercial building).

Thermal dispersion is very sensitive for low flow gases. I've never used it on liquids, but vendors like Sierra or Kurz should be able to tell you if thermal can see and report low flows in that range.