I've just come across a puff for this device. There's a 66-page data sheet
It's a Maxim part, so it probably doesn't really exist. Has anybody actually got their hands on one? Or know what real parts sell for?
It looks cute - as much of Maxim's puffery does - and accurate time of flight measurements have other applications (as John Larkin tells us from time to time).
-- Bill Sloman, Sydney
140 in stock at DK. ~$16
Just order a life time supply. George H.
eet
ually got their hands on one? Or know what real parts sell for?
flight measurements have other applications (as John Larkin tells us from t ime to time).
Thanks. I should have looked there. I've got no idea what I might use it fo r, but if Digikey has stocks it's probably worth reading all 66 pages of th e data sheet.
And interesting theoretical question with time-of-flight flow meters is how they cope with the transition from laminar to turbulent flow.
In the laminar flow region, the velocity profile across the pipe is stable and parabolic. The time-of-flight pulse takes a sample of the flow velocity along a straight line from one side of the pipe to the other, which overwe ighs the velocity at the centre of the pipe (which has very little cross-se ctional area) and underweighs the contributions from the outer regions (whi ch are moving more slowly but represent larger cross-sectional areas as you move away from the middle).
In the turbulent flow region, you get "plug flow" with laminar flow in a "b oundary layer" close to the pipe wall, and a more or less uniform velocity across the bulk of the pipe. My guess is that central - turbulent - region of flow is actually a series of vortices managing the transfer of energy fr om the centre of the pipe to the outer surface of the plug, but I don't kno w enough about hydrodynamics to have a clear picture of what might be going on.
What is obvious is that the time of flight flow meter will give a different average flow velocity as it moves from one type of flow to the other.
Presumably the electronics could compensate for it if it knew the Reynolds number for the flow regime. Maxim might be clever enough to build some of t hat into the electronics, but the Reynolds number depends on the kinematic viscosity of the fluid, which is going to be temperature dependent
If you've got a compressible fluid, life gets even more complicated.
-- Bill Sloman, Sydney
So much for it not existing.
sheet
ctually got their hands on one? Or know what real parts sell for?
f flight measurements have other applications (as John Larkin tells us from time to time).
for, but if Digikey has stocks it's probably worth reading all 66 pages of the data sheet.
ow they cope with the transition from laminar to turbulent flow.
e and parabolic. The time-of-flight pulse takes a sample of the flow veloci ty along a straight line from one side of the pipe to the other, which over weighs the velocity at the centre of the pipe (which has very little cross- sectional area) and underweighs the contributions from the outer regions (w hich are moving more slowly but represent larger cross-sectional areas as y ou move away from the middle).
"boundary layer" close to the pipe wall, and a more or less uniform velocit y across the bulk of the pipe. My guess is that central - turbulent - regio n of flow is actually a series of vortices managing the transfer of energy from the centre of the pipe to the outer surface of the plug, but I don't k now enough about hydrodynamics to have a clear picture of what might be goi ng on.
nt average flow velocity as it moves from one type of flow to the other.
s number for the flow regime. Maxim might be clever enough to build some of that into the electronics, but the Reynolds number depends on the kinemati c viscosity of the fluid, which is going to be temperature dependent
No time to elaborate, but they either shoot at two angles in each direction or shoot both ways, so the turbular flow is averaged out
Cheers
Klaus
a
of > > > >flight measurements have other applications (as John Larkin tell s us
t for, but if Digikey has stocks it's probably worth reading all 66 pages o f the data sheet.
how they cope with the transition from laminar to turbulent flow.
ble and parabolic. The time-of-flight pulse takes a sample of the flow velo city along a straight line from one side of the pipe to the other, which ov erweighs the velocity at the centre of the pipe (which has very little cros s-sectional area) and underweighs the contributions from the outer regions (which are moving more slowly but represent larger cross-sectional areas as you move away from the middle).
a "boundary layer" close to the pipe wall, and a more or less uniform veloc ity across the bulk of the pipe. My guess is that central - turbulent - reg ion of flow is actually a series of vortices managing the transfer of energ y from the centre of the pipe to the outer surface of the plug, but I don't know enough about hydrodynamics to have a clear picture of what might be g oing on.
rent average flow velocity as it moves from one type of flow to the other.
lds number for the flow regime. Maxim might be clever enough to build some of that into the electronics, but the Reynolds number depends on the kinema tic viscosity of the fluid, which is going to be temperature dependent
on or shoot both ways, so the turbulent flow is averaged out
That isn't the point. The measurement is an integral along a single line, w hich necessarily puts more weight on the flow rate along the axis of the pi pe - where it's going to be fastest - though the bulk of the flow moves alo ng the pipe parallel to the axis and is consequently undersampled.
This isn't a problem which is hard to fix with laminar flow, where the velo city profile is predictably parabolic, but presents more of a problem with turbulent flow, where the velocity profile has a steeper gradient in the bo undary layer at the walls of the pipe, and transitions to a more or less co nstant (averaged over turbulent excursions) "plug flow" rate in the turbule nt centre of the pipe.
-- Bill Sloman, Sydney
It seems to exist at the moment, but Maxim has a bad reputation for not making all that many of a particular part, and stopping making them with very little warning.
-- Bill Sloman, Sydney
VTC shut down a fab and there was no replacement process, hence a number of products were orphaned. If I were running the show, I would have never made the contract with VTC in the first place because you are bound to get f***ed over. That is the risk you take by not owning the fab.
Now fabless semiconductor companies can do fine in digital products. The lifetime of a digital chip is a few years. But analog chips are sell-able for decades. Some companies have long term support contracts with TSMC, so those products may be safe in the short term, but I don't know about decades.
This particular product is CMOS, of which Maxim has a few fabs, so it is not likely to be discontinued.
If you were around in the 1980s, there was a switch from negative to positive photo resist, and all sorts of chips got orphaned.
At some point you just can't fab legacy products in a manner where the customer will be willing to pay for the product. One semi I worked for had a chip that was just a pain in the ass to produce. Rather than kill it, they kept jacking up the price. Unfortunately the demand increased, but at least it became worthwhile to work on the yield issues due to the new ridiculous margin.
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