PX26 PRESSURE SENSOR AND AD620aN AMPLIFICATION PROBLEMS

[jpanhalt]

The 001 version is a very sensitive differential pressure gauge with a 1 psig range. Like the previous person asked, which of the specifications do you not understand? A 1 psig pressure differential is on the order of what you might see with a party balloon. It is not a lot of pressure.

John

 

[Reloadron]

I gave you a procedure and method to calibrate 0 to 1 PSI back in one of the other threads you had. 1.0 PSI = 27.7 inches of water column. I showed how to accurately set this up. I also covered the inaccuracies of the Arduino analog input A/D conversion and how to compensate for that in your code.

Ron

 

[Reloadron]

This was all covered in any of the several threads you have on this subject. You have the 0 to 1 PSID sensor. With 10 volt excitation and 1 PSI applied your sensor output is 16.7 mV. I also strongly suggested you use a good stable 10 Volt reference for the excitation, especially considering the sensor sensitivity and range. I gave you links to suggested references. All of this is why it is not wise to start multiple threads on the same subject. Currently you have 4 or maybe 5 threads on all of this. People trying to help have no idea what you are doing or what has or has not been covered. Now on top of the other threads you have two new additional threads. Here is one of the threads for the curious.

Ron

 

[krishnachaitanya]

oops, i thought i should post al my new questions separately, instead of posting everything in one, Sorry


I was wondering what zero balance is +-1.5mV?
and span tolerance +-3mV?

So, lik you know from my other posts I got it amplified the Vout using Ad620aN, so now im trying to relate the pressure with voltages so i know what voltage indicates what pressure I dunno where to start from.

 

[krishnachaitanya]

thanks ron

 

[krishnachaitanya]

Should I need a known pressure source, is there any way to test without a know pressure source, how are sensors generally calibrated relating the physical pressure value to an electrical voltage, are the outputs linear? can i assume that since 16mV for a full excited for 1psi,and relate them that way, is there any offset, what does 0psi relate to this, is it 0mv? so whats my range can i relate directly . these are few questions i'm trying to understand . I have never done this before so its taking me time to understand these.

 

[KeepItSimpleStupid]

I was wondering what zero balance is +-1.5mV?

OP amps and sensors will have a zero point that isn't zero. For a differential sensor, zero can easily be calibrated out. e.g. OFFSET

and span tolerance +-3mV?

The GAIN also has some slop. You can turn that into a +-percentage and see if it really matters. Fixing this one requires a better calibration source appropriate for the sensor.

You may also find temperature effects etc.

==

It's some of the inputs into what's called an "error budget analysis".

 

[DerStrom8]

Hi everyone,

I have merged all related threads into this one. It will be easier to follow now that it's all consolidated

Regards,
Matt

 

[Reloadron]

Hi everyone,

I have merged all related threads into this one. It will be easier to follow now that it's all consolidated

Regards,
Matt

Thanks Matt, all in all there are about 5 or 6 threads. You and Tesla are my heros.

Ron

 

[Reloadron]

oops, i thought i should post al my new questions separately, instead of posting everything in one, Sorry


I was wondering what zero balance is +-1.5mV?
and span tolerance +-3mV?

So, lik you know from my other posts I got it amplified the Vout using Ad620aN, so now im trying to relate the pressure with voltages so i know what voltage indicates what pressure I dunno where to start from.

This evening or tomorrow morning I will cover all of this again including how to accurately calibrate this. Currently ripping a room out of my house.

Ron

 

[DerStrom8]

Thanks Matt, all in all there are about 5 or 6 threads.

I only found three or four. I think we can carry on the conversation here though, no need to bring in the older ones (unless someone specifically requests we do).

Always glad to help!

Cheers,
Matt

 

[krishnachaitanya]

ok thanks , havent really used forums before, so did not know about it, sorry and thanks
If the older threads are causing toruble delete them maybe, i dunno.

Ron, thanks i'm trying to look for some stuff too. I'l be waiting for it!

 

[DerStrom8]

ok thanks , havent really used forums before, so did not know about it, sorry and thanks
If the older threads are causing toruble delete them maybe, i dunno.

Ron, thanks i'm trying to look for some stuff too. I'l be waiting for it!

No worries, you're all set

 

[KeepItSimpleStupid]

FWIW: Your merge did not result in notifications for me, but I knew to look here.

 

[Reloadron]

OK, one more time from the beginning starting with the sensor. I will explain how I would go about this using what you have. You have a PX26-001 DV 0-1 PSID which is a 0 to 1 PSID differential pressure sensor. For your particular sensor the sensitivity or output is (16.7mV, 1.67mV/V for 1 PSI range) meaning the sensor full scale output (Full Scale = 1 PSI) will be 16.7 mV when 10 Volt excitation is applied. Earlier I mentioned and covered (as other forum members did also) the importance of stable excitation. I strongly suggested using a 10 Volt Reference for the excitation. Using a stable excitation is the only way to assure your sensor will provide a stable and accurate output and remain stable in use.

Your goal is to run your sensor signal to an Arduino Mega analog input channel. Therefore you want to amplify the signal from the sensor (0 to 17.7 mV) to something useable like 0 to 5 volts. Therefore you need a Gain of about 282.5. You have an Analog Devices AD620 IA (Instrumentation Amplifier). I provided a drawing as to how I would go about doing this. There are several ways to go about it. I would use a dual power supply I would use a +15 and -15 Volt supply. One reason for choosing 15 Volts is because using the +15 Volt supply you can power the 10 Volt reference I mentioned earlier. While the AD 620 can be used with a single supply there are drawbacks to doing so. Should you wish to use single supply I suggest you configure exactly as shown in the data sheet: Figure 38. A Pressure Monitor Circuit that Operates on a 5 V Single Supply. Personally I would do as mentioned and use a dual supply, we also covered this in detail in another thread.

When all is said and done at this point you have 0 to 1 PSID = 0 to 17.7 mV = 0 to 1 PSID = 0 to 5 V. I suggested you use a 10 turn potentiometer for Rgain with the AD620. So how to calibrate at this point? Unless you have a precision pressure calibration system you need to find an alternative means to achieve a 0 to 1 PSI pressure. I explained this in detail in another thread. 0 to 1.0 PSI = 0 to 27.670 inches of water column. I explained how to use a simple aquarium air pump to get accurate pressure readings. I suggest you read this and modify the concept to get an accurate 0 to 1 PSI reference for calibration. For example if 27.7 inches of water column = 1.0 PSI then each 6.92 inches of water = 0.250 PSI. There are many ways to derive accurate pressure using a plastic tube, a ruler and some water.

As to the 0 to 5 Volts going to the Arduino that becomes 0 to 5 volts 0 0 to 1023 bits, I gave you example code samples to convert all of that to PSID. I also pointed out that the Arduino is only a 10 bit (0 to 1023) A to D system. I showed how using my Arduino Mega with 2.5 Volts applied read 524 bits and not the expected 512 or so. I showed in a code sample how to calibrate that.

Finally I will point out that when using delta pressure to measure flow the results are not a linear function, I assume you know that? This is a square law response. That means for a given pipe diameter, a known fluid temperature and density that if 1.0 PSID = for example 10.0 GPM of flow that 0.5 PSID will not be equal to 5.0 GPM of flow. It is not a linear curve.

Ron

 

[krishnachaitanya]

This sums up all my problems in one single post with answers to all my questions. Thanks ron for taking the time to sumit up for me. If someone has a problem like this i hope this one post is a perfect solution Manuel for them.

 

[Reloadron]

If there is anything you don't understand just ask.

Ron