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Which pressure sensor choose?

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Drake

Junior Member

Which pressure sensor choose?

Wednesday, May 6th 2015, 4:27pm

Hello everyone!

Someone knows the difference between the various pressure sensors in addition to the measurement range?
The Pressure sensor mps pressure Delta 1000 has the same cost of all the others in the catalog and the largest measuring range ... so why take the others?

Thanks in advance

Davide.

InfoSeeker

Senior Member

Thursday, May 7th 2015, 1:23am

I believe it is mostly an issue of resolution.

I choose the delta 40 because full scale is zero to 40 cm of head for two reasons:
1. My reservoir is about 20 cm tall
2. Minor variations over the smaller range range will be much more noticeable than the same variation over the the 10 meter range of the 1000 cm unit.

I mean, you could use a 50 hp pump for your loop, but there may be issues. A classic case of bigger is not always better. :)

This post has been edited 1 times, last edit by "InfoSeeker" (May 7th 2015, 1:24am)

sebastian

Administrator

Thursday, May 7th 2015, 7:06am

The resulution ist the same.
When you measure fill levels: with the Delta40 -> you have a resulting resulution of 0.5mm, total:400mm
with the Delta1000 -> resolution of 12.5mm, total:10000mm

InfoSeeker

Senior Member

Thursday, May 7th 2015, 5:30pm

Quoted from "sebastian"

The resulution ist the same.
When you measure fill levels: with the Delta40 -> you have a resulting resulution of 0.5mm, total:400mm
with the Delta1000 -> resolution of 12.5mm, total:10000mm

I am not sure I follow sebastian... if the Delta40 has a resolution of 0.5mm and the Delta1000 has a resolution of 12.5mm... does that not make the resolution of the Delta40 25 times finer than the Delta1000?

This post has been edited 1 times, last edit by "InfoSeeker" (May 7th 2015, 5:32pm)

sebastian

Administrator

Thursday, May 7th 2015, 6:12pm

Both sensors has the same electrical output range.
0mBar ... 40mBar ==> 0..3V
0mBar ... 1000mBar ==> 0..3V

Drake

Junior Member

Thursday, May 7th 2015, 8:40pm

Thanks a lot!

May I ask where you found these technical specifications?

InfoSeeker

Senior Member

Thursday, May 7th 2015, 8:45pm

sebastian is an aquacomputer rep & forum admin.

Shoggy

Sven - Admin

Thursday, May 7th 2015, 8:53pm

Quoted from "InfoSeeker"

Quoted from "sebastian"

The resulution ist the same.
When you measure fill levels: with the Delta40 -> you have a resulting resulution of 0.5mm, total:400mm
with the Delta1000 -> resolution of 12.5mm, total:10000mm

I am not sure I follow sebastian... if the Delta40 has a resolution of 0.5mm and the Delta1000 has a resolution of 12.5mm... does that not make the resolution of the Delta40 25 times finer than the Delta1000?

Yes, if you do the math the right way. The range for both sensors is about 800 steps from the lowest to the highest level.

10000 / 12.5 = 800
400 / 0.5 = 800

So if you use the mps 1000 and would start with an empty reservoir you would have to fill it up to 12.5 mm before the sensor will be able to detect a difference for the first time. In the same situation the mps 40 would have been already recognized 25 different levels. This example is not fully correct but will help to understand the difference.

So using a small reservoir with the mps 1000 is possible but the measurements will be imprecise because of the larger steps.

Drake

Junior Member

Thursday, May 7th 2015, 11:53pm

Right!
Resolution is 0.05 mmbar for Delta40... 0.125 mmbar for Delta100 and so on...
Can i have also the accuracy? :rolleyes:
Thanks again.

InfoSeeker

Senior Member

Friday, May 8th 2015, 3:19am

I believe the resolution IS the accuracy... 0.5 m for the delta40. The unit does not display mm of water column, but percent full.
To calibrate the sensor you provide the maximum fill level of the reservoir and the current fill level in the reservoir, from the bottom of the reservoir.

Drake

Junior Member

Friday, May 8th 2015, 8:21am

From Wikipedia :)

Resolution is the smallest change in the underlying physical quantity that produces a response in the measurement.

Accuracy is the measurement tolerance, or transmission of the instrument and defines the limits of the errors made when the instrument is used in normal operating conditions.

If you use this sensor to estimate the pressure drop across the loop or across a component? Can you post please what is the SW representation?

Thanks again.

Jakusonfire

Full Member

Saturday, May 9th 2015, 6:22pm

The Accuracy rating of the all the sensors used is + or - 2.5% of the full scale span maximum error. So plus or minus 2.5% of 1000 is much larger than the same percentage of 40.

These are only pressure sensors of course so accurate measurements of fill level or any other application depends on the accuracy of your calibration. For our purposes the sensitivity and resolution are far more interesting than accuracy.

This post has been edited 1 times, last edit by "Jakusonfire" (May 9th 2015, 6:27pm)

Drake

Junior Member

Saturday, May 9th 2015, 10:31pm

If I can take advantage again of your patience and experience...
If I want to monitor the pressure drop of the entire loop (2 rad 360, 1 cpu and 2 vga) witch sensor will do the best think?

There is data loggin?
There is the possibility to extract the data?

Jakusonfire

Full Member

Sunday, May 10th 2015, 3:43pm

That would depend on the total resistance, pump pressure and flow rate used. A common loop like that might be say 4 PSI at 4L/m or about 30kPa.
The sensors are approx 4kPa , 10kPa, 50kPa and 100kPa

If you use more pump power then pressure differential will be higher. With less flow rate it will be lower. Overall, measuring the entire loop pressure drop requires a sensor that cannot be very sensitive so small changes would be difficult to read and I can't personally see a use for it.
Monitoring the pressure drop across a single component with a sensitive device like the 4kPa model will easily show small changes in flow rate that would be caused by clogging or whatever.
The 4kPa model can effectively be the only zero resistance flow meter because it can measure pressure drop across a component that is included in the loop already. It would just require custom calibration to convert that to flow rate.

Drake

Junior Member

Monday, May 11th 2015, 11:18pm

Ok I will go for the delta 500!

range: 0-500 mbar,
resolution: 0.625 mbar (500/800)
accuracy: + or - 12.5 mbar

One other thing that is not clear to me is, how to measure the liquid pressure without let the liquid entering in to the sensor... perhaps i need that thing called pressure equalisation membrane?

http://shop.aquacomputer.de/product_info…550k8nun8jmd39d

Jakusonfire

Full Member

Tuesday, May 12th 2015, 9:13pm

If the fluid could not get to the sensor then it would not be able to measure anything.

Those membranes are really only useful for fill level meters as if pressure builds internally the fill level shown will change. They won't do anything for measuring differential across a whole loop.

Drake

Junior Member

Wednesday, May 13th 2015, 10:12am

I belive it's only a junction. :)

I found i guide on the net about the installation of the delta 100 as a filling sensor... "this tube is then connected to the “LOW” marked port of the sensor…. THIS TUBE MUST NOT CONTAIN ANY FLUID IT MUST JUST BE FILLED WITH AIR!!!!...."
And an istallation of a delta 500 as a sensor of pressur drop measure and probably i misinterpreted the image.
Drake has attached the following image:
  • membrane.jpg

This post has been edited 1 times, last edit by "Drake" (May 13th 2015, 10:16am)

InfoSeeker

Senior Member

Wednesday, May 13th 2015, 12:46pm

The Pressure Equalization Membrane is a replacement for the low pressure tube by using atmosphere as the tube.

A good explanation can be found in section 6.3 and 6.4 of the MPS manual.

This post has been edited 1 times, last edit by "InfoSeeker" (May 13th 2015, 12:48pm)

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