Need 20 Foot Probe with multiple temperature sensors

TheWaterboy · Mar 3, 2014

I need to measure temperature stratification in a large tank. I'm looking for a sensor ~20 feet long that can measure temperature at points every few feet?

Anyone used anything like this?

Mickey · Mar 3, 2014

Sounds like something that may need to be custom built. See link below.

http://www.thermometricscorp.com/index.html

Albert LaFrance · Mar 3, 2014

Maybe use a drop pipe with arms attached at various levels, each holding an individual sensor?

Tom Jenkins · Mar 3, 2014

I've never seen such a critter. I'd suggest taking a 20' length of reasonable diameter pipe, weld nipples at the required increments, and thread thermowells with RTDs onto each. You could then run the wiring up through the pipe. The thermowells would permit acces to the RTDS for replacement, testing, etc.

Make sure you put wire numbers on each lead before you install the RTDs - otherwise you have a lot of ringing out to do!

TheWaterboy · Mar 3, 2014

I figured I probably had to build one, but it was worth asking. Thanks guys.

danw · Mar 3, 2014

Google 'multi point RTD'

Burns Engineering makes them, as do others. They're used for exactly what you're doing, temp gradients in tanks.

http://www.burnsengineering.com/document/pdf/Averaging-Multipoint_Measurement_Compendium.pdf

daba · Mar 3, 2014

danw said:
Google 'multi point RTD'

Burns Engineering makes them, as do others. They're used for exactly what you're doing, temp gradients in tanks.

http://www.burnsengineering.com/document/pdf/Averaging-Multipoint_Measurement_Compendium.pdf

Good info - often come across needs for something like this.

Upsides : Most people just put multiple stabbings in the side of the vessel for thermowells. But that can be a PITA if the vessel has heating/cooling jackets / insulation etc.

Downsides : if one of the sensors fails, you have to replace the whole shebang, which would obviously be higher cost. It might also need a roof removal or "maintenance aperture" - getting a 20+ foot probe out of the top of a 20+ foot tank would need a lot of room "up there".

Generally, I would say that if a temperature gradient in your vessel is a problem, rather than a process requirement, then it's time to install a mixer, or a rousing loop.

danw · Mar 3, 2014

Multipoint sensors are used extensively in the refined petrochemical markets because the storage tanks are huge, the gradients exist and the density/temperature relationship contributes significantly to the (in)accuracy of the tank volume calculation.

daba · Mar 3, 2014

danw said:
Multipoint sensors are used extensively in the refined petrochemical markets because the storage tanks are huge, the gradients exist and the density/temperature relationship contributes significantly to the (in)accuracy of the tank volume calculation.

Mostly "outside", I guess...

But as I said, good info, and nice to know they can be made to order

TheWaterboy · Mar 5, 2014

Thanks DanW. That's a good start.

shooter · Mar 6, 2014

several options here, put them on the outside, simple under a bolt on each height.

another one use a big pipe, and a smaller hose, mount the sensors on the smaller one, with centre rings to keep it in place.

cabling should be taken care off, with Pt100 best use 4 wires/sensor, 3 is also possible, even 2 is possible with a gnd wire going to each sensor.
as speed is very low you can use a switcher.
another one could be together with the level sensor on a float that sinks (used in marine to see the temperatures in the big ocean)

still another one is optical fibre, it is more expensive as a simple sensor but the results are very good.

TheWaterboy · Mar 6, 2014

Since this answer was so easy for y'all, perhaps you all know where to find an inexpensive MUX for all the RTD's?
I ran across one that cycles through 4 channels and provides 4-20 output. 2 digital outputs provide the PLC feedbacl on which channel is being read.
Thats a good solution but I need at least 6 channels.
Since these are so expensive, I want to build the first one of these as a proof of concept so I'll grab a bunch of RTD's but I still need a mux. Ideas?

JeffKiper · Mar 7, 2014

What plc? I would look at a remote rack or a small brick plc.
I an an AB guy so I would use a small MicroLogix1400 with 3 Spectrum controls 1762sc-IF8u. 8 thermocouples or 4 RTD. I think they are $400 a card so under 2k you have the PLC ready.

TheWaterboy · Mar 10, 2015

(Wow, its been a year ? )
This has been put back on radar to do before summer starts. I like the modules from Spectrum. That looks like a good direction to go.

Need 20 Foot Probe with multiple temperature sensors

TheWaterboy

Lifetime Supporting Member + Moderator

Mickey

Lifetime Supporting Member

Albert LaFrance

Lifetime Supporting Member

Tom Jenkins

Lifetime Supporting Member

TheWaterboy

Lifetime Supporting Member + Moderator

danw

Lifetime Supporting Member

daba

Lifetime Supporting Member

danw

Lifetime Supporting Member

daba

Lifetime Supporting Member

TheWaterboy

Lifetime Supporting Member + Moderator

shooter

Member

TheWaterboy

Lifetime Supporting Member + Moderator

JeffKiper

Lifetime Supporting Member + Moderator

TheWaterboy

Lifetime Supporting Member + Moderator

Similar Topics