# Possible to reconfigure Pressure Sensor output from 3-4v to 0-5v??

Hello,

I am working on a water level measurement system that measures the level of water in overhead tank that i have on the roof. Now to measure the level i have the MPX5100 from Freescale hooked-up to the water supply coming from the tank in our house.

The problem is that due to the change in height the sensor reads around 70kPa when the tank is almost empty and around 82kPa when almost full, however, the sensor is rated from 0-100kPa. So that means i am using almost just 10% of the measurable scale. Right now, according to my calculation, the output changes for every +/- 11cm change in the level. Would love to reduce this as much as possible.

As a result the output varies from 3.2v to 4.0v. Is it possible to convert this into 0-5v (OPAMP??) before it reaches the ADC so that i get a better resolution.

Please do point me in the right direction....

Thanks

since you did not state which model you have, I have to assume you have a differential pressure one. Using an absolute sensor would require zeroing before using so that your zero is the tank zero.

The location of the sensor is important. assuming a DP model, it sounds like you have a 1 meter tall tank and your sensor is located in piping that is 9 meters lower than that. like your tank is on the roof and the sensor is in the basement ?

if you placed your sensor at the bottom of the actual tank, it would be closer to 0 when the tank is empty. if my guess is correct, then you are actually measuring the weight of the liquid in the tube and then also the tank. a sketch of your installation would help.

of course if you have an absolute sensor, setting the zero would eliminate the problem with the reading.

properly locating the sensor will offer the best overall results. multiplying the output will multiply any errors at the same time.

if you went to a more sensitive ADC, you can get better resolution of the raw sensor.
if you add a quad op-amp and connect it as an instrument op-amp, you will add stages that will allow you to zero and span the output to your desired values.

a combination of both, sensor location and output correction will give you the best overall results. with the op-amp, you can also add a filter to remove some of the unwanted noise without loosing too much accuracy.

as for an op-amp circuit, this might help.

dave-in-nj:
since you did not state which model you have, I have to assume you have a differential pressure one. Using an absolute sensor would require zeroing before using so that your zero is the tank zero.

The location of the sensor is important. assuming a DP model, it sounds like you have a 1 meter tall tank and your sensor is located in piping that is 9 meters lower than that. like your tank is on the roof and the sensor is in the basement ?

if you went to a more sensitive ADC, you can get better resolution of the raw sensor.
if you add a quad op-amp and connect it as an instrument op-amp, you will add stages that will allow you to zero and span the output to your desired values.

a combination of both, sensor location and output correction will give you the best overall results. with the op-amp, you can also add a filter to remove some of the unwanted noise without loosing too much accuracy.

as for an op-amp circuit, this might help.

NXP® Semiconductors Official Site | Home

Apologies for the delayed reply. Yes you are right I have the differential version dual port MPX5100DP.

I don't really care about the "zeroing" of the sensor as ill be processing the values later anyways ( need the output in %). Yes you are bang on, the tank is on the roof, two floor above the sensor. I wish i could mount it next to the tank but there are a lot of practical issues so it has to be mounted inside the house. I am using the house plumbing to access the water pressure.

The only thing i need is a low noise method of converting out of 3-4v to 0-5v. I have INA326EA ( http://www.ti.com.cn/cn/lit/ds/symlink/ina326.pdf ) lying around which i can use as an instrument op-amp. Do you thing it will work? Will it help reduce the noise and increase eventual resolution?

Also i have never used amps before. Guess its time to learn ;D

Thanks for the link to op-amp circuit.

I have tried goggling for examples of sensor output conditioned with instrument op-amp but am not getting much.

Would be great if you could point me in the right direction.

Thanks everyone..

A much simpler and less troublesome approach is to use an external, higher resolution ADC, which divides the 3-4 V interval into much finer steps.

In my water system, which has a sensor located at the house, for a tank located about 30 meters higher in elevation, I use an MCP3202 12 bit ADC, multiple sampling and averaging to get 13 bit resolution. Works great.

Adafruit sells an Arduino-compatible breakout board for a 12 bit ADC which will work.

Your instr.amp will do just fine.

Connect output from pressure sensor (3V--4V) to pin 3
Make a voltage divider to connect near 3V to pin 2
Set gain (2 resistors) to approx. 5

i interest to what you have done so much, will you share about that in a video please
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this is similar :http://forum.arduino.cc/index.php?topic=311413.msg2159205#msg2159205