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MPX2100d + MCU with water level measuring project

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micropad

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Dear All,
I suppose to order from ebay MPX2100d Pressure Sensors to measure water level of my house water tank

I suppose to display result on LCD connected to MCU

Water tank 500L
Water tank fixed on roof top 4m from ground
Suppose to display 5L resolution

Please see the attached datasheet and advice me that , can I success this project using this MPX 2100 sensor

Please advice
Thanks in advance
 
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At what height from the ground are you proposing to mount the pressure sensor? i.e. does it have to withstand a 4m head of water or just the head due to the depth of the tank?
 
So you will have a 2-3m head of water acting on the sensor. Its full-scale range, as per the datasheet, corresponds to ~10m head (100kPa) and outputs 0-40mV over that range. Your tank head varies by only 1m, giving only a 4mV total output variation and you want a resolution of 1% of that, i.e. 40uV. That's going to take some sophisticated instrumentation-grade (i.e. expensive) amplification to process the sensor signal :(
 
IMHO the simplest solution would be to use something like a car fuel gauge sender, i.e. a float varying a resistance. The micro could do any necessary calibration to allow for non-linear effects.
 
Dear alec_t,

Thank you so much out of the box solutions.
Dear alec_t please look in to the attached application pdf from preescale.com. what do you think about this amplification cct.

Its full-scale range, as per the datasheet, corresponds to ~10m
Can you please tell me where did you get this ~10m ( from your post #4)

Please advice
Thanks in advance
View attachment 68754
 
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Its full-scale range, as per the datasheet, corresponds to ~10m
Can you please tell me where did you get this ~10m
MPXM2102GS
Range 0 to 100 kPa
Appcn Sensitivity ± 0.1 kPa (10 mm H2O)
 
Dear alec_t,

How about the amplification cct that I attached in my post #7. Can I use this cct to amplify signals out from MPX2100d

Please advice
 
I couldn't find the datasheet online for the amp IC in your attachment. It may be obsolete. It would probably be expensive even if obtainable.
 
I think it showing op amp
It certainly is showing an opamp, but a 741 is unlikely to give you the precision and stability you need to resolve down to 40uV. Google for 'instrumentation opamp'.
 
Using this pressure sensor
https://www.newark.com/freescale-se...o-250kpa/dp/07F9899?in_merch=Popular Products

It has a resolution of 20mV per kPa. Your tank is 1M tall @ 500L therefore 5L = a 5cm delta in the level.

A 5cm delta is about .5 kPa change (https://www.convertunits.com/from/meter+of+head/to/Kpa)

Thus a 10mV change in your sampled signal.
Assuming a 5V supply is also the Vref for the ADC and you have 10bit sampling => 5cm is equivalent to 2 out of 1024. Thus it is barely doable ( with simple sampling) without any differential amplification.
If you use oversampling I feel you can do it adequately without any instrumentation amps.

Now this sensor is from near vacuum to > 2 atmospheres, therefore your sampling range is sitting between about 1.9V to 2.6 v (full range of 4.8V @ 250kPA). Thus if u supply the ADC with a precision Vref of perhaps 3 V you can improve the accuracy significantly:
https://www.newark.com/texas-instruments/lm4040d30ilp/ic-shunt-v-ref-3v-1-to-92/dp/33M9287

A 10mV delta now delivers over 3 out of 1024 (10bit sample), thus a 50% improvement. You can use this directly with minor oversampling. :D
 
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