Pressure Sensor with current source of 1.5mA?

[nick703]

Hello Friends ,
I have a Pressure sensor of MEMS 5PSI. below is the datasheet link.
https://www.te.com/commerce/Documen...6CA6pdfEnglishENG_DS_86C_A6.pdf86-005A-C

So my first question is can i provide 5 voltage input throw 3.3Kohm resistor to get 1.5mA curretn source in pin 3 and 2.
or other solution required.
and second question is datasheet mention 100mV output at full span of pin no. 1 and 4. but when i measure i got atmosphere pressure level give me 168mV output.
please give me guide regarding output span.
i have also make circuit using lm324 quad op-amp but circuit didn't give me 3.012V span?
so please help me.

 

[FvM]

LM324 noise isn't the problem, it can be filtered for pressure sensor applications. But offset and drift is several orders of magnitude to high. 30 years ago, we designed pressure sensor amps with OP07, these days there are many suitable OPs with 100 µV and below offset/drift spec.

 

[danadakk]

The reasons designers use IAs from vendors (that laser trim them in production)
rather than roll their own differential amps -

Excellent reference handbook -

https://www.analog.com/media/en/training-seminars/design-handbooks/designers-guide-instrument-amps-complete.pdf

Regards, Dana.

 

[nick703]

ok after testing with above my circuit and check in real machine with actual data and calculated data below is the result. i think this is good but i need more improvement in circuit to adjust output error with some trim pot and some circuit.

because every sensor is calibrated with manufacture in range like 95.5mV , 94.2mV etc.

now i have amplify this to 0-5v or 0-10v using opamp. and other option is directly fed this signal to ADC and take measurement. like i have ad7193, ad1115s module.

please suggest best opamp- who worked in pressure sensor to remove the opamp offset and noise.

i have also find below signal conditioner circuit. try in next 2 day to arrange component.

 

[KlausST]

Hi,

because every sensor is calibrated with manufacture in range like 95.5mV , 94.2mV etc.

No, they are not caibrated to this value.
For calibration they have the "gain set resistor", so you can replace the sensor without new adjustment.

Btw: I avoid pots. I rather do this with simple "add" and "multiply" in software.

Opamps: There are a lot of parameters of your application that we don´t know. Thus I recommend to go to a distributor´s internet site and use the OPAMP selectionn guide.
Don´t be afraid when there are many matching OPAMP. Just choose the one that suits you best.

You may give us a couple of types and we can have a look at them.

Btw: I don´t like the idea of suing a signal from 0 to 5V. Neither OPAMPs nor ADCs are good close to the supply rails. Leave at least a 50mV headroom (for rail to rail devices).

I don´t know what cable lenth you have from sensor to amplifier. To improve stability and noise you could use a fixed gain instrumentation amplifier (not using the gain set resistor the usual way).
Then use DC to measure the gain set resistor value and do the multiplication in software. This increases stability and reduces noise.
No need to continously measure the resistor value. So when you connect both sides of the resistor with GND you have an aditional low ohmic path to reduce noise in the cable.

Klaus

 

[danadakk]

Just as an aside there are processors out there that have DeSig on them that can
essentially perform all the signal path onchip and do it with very high accuracy
and resolution.

Measuring Weight Using a Load Cell and PSoC

This project demonstrates how to measure weight using a load cell (strain gauge) interfaced with Cypress’s PSoC Analog Coprocessor. By Arvind Krishnan and Rajiv Badiger.

www.hackster.io

The above a single chip design.

There is also the correlated double sampling approach -

https://www.infineon.com/dgdl/Infineon-AN66444_PSoC_3_and_PSoC_5LP_Correlated_Double_Sampling_to_Reduce_Offset_Drift_and_Low_Frequency_Noise-ApplicationNotes-v05_00-EN.pdf?fileId=8ac78c8c7cdc391c017d073054915445

 

[robert574]

I've been reading this thread and I sense patience here so I'd like to ask a question.
Can you give an example of a few instrumentation amplifiers for use with strain gauge bridges (4) that you like? Oh yea, it's the 3.3/5V ESP/UNO thing.

 

[danadakk]

A good ref book -

https://www.analog.com/media/en/training-seminars/design-handbooks/designers-guide-instrument-amps-complete.pdf

Regards, Dana.