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Author Topic: Scx30anc pressure sensor  (Read 2425 times)
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Poty
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« on: March 13, 2021, 11:09:33 23:09 »

IŽm about to start using a pressure sensor (absolute) from Honeywell, the Scx30anc, up to 30psi. In Datasheet, it specifies Vs=20VDC max, but donŽt specifies minimum Vs. As you may infer, it will be connected to a PIC, which uses 5VDC. Does anyone have an idea about if this value as Vs for this sensor will be enough? I think (reading datasheet which IŽll add to this post), that using 5VDC will reduce the full scale span in a undeterminate value (datasheet indicates 90mv of span for Vs=12VDC), which makes me think that a lower value may induce wrong values. Any suggestion? I choosed this one (not bought yet) because its price in my country.
Regards,
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Sideshow Bob
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« Reply #1 on: March 14, 2021, 07:57:24 07:57 »

From what I can see the output is "ratiometric"
https://www.sensorsone.com/ratiometric/#:~:text=Ratiometric%20is%20used%20to%20describe,output%20and%20input%20supply%20voltage.

So if has sensitivity of 3mV/psi at 12 volt. It will have a sensitivity (5V/12V)*3mV/psi at 5 volt. Also do yoy know how to work with pressure sensors? It is many potholes using these sensors. Like if you are measuring relative to atmospheric pressure. atmospheric pressure is never static. And also how do plan to connect it to your electronics in order to amplify the output before the ADC
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Poty
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« Reply #2 on: March 14, 2021, 07:53:00 19:53 »

Hi, Sideshow Bob! I was planning 3 alteratives, since sensor will be pretty close to the uC.
1st one, direct to the uC ADC port, which in this case is a 10 bit one
2nd one through a specific ADC, which is a 24 bit one, and communicates with SPI to the uC
3rd one, can be an OPAMP and then the uC.
I think the first one will be the worst, but will be enough to the purpose that I`m looking for.
I agree with your mention about ratiometric, and this is another worrying subject... as the calculation, sensitivity will reduce to 1.25mV/psi and full span will be 50mv, im a range from 2.5 to 3VDC
So, IŽll have to use 3VDC as Vref (at least) and in 10bits, means that uC will have to read 50mV/1023 = 49uV... and at this point, is definitely a bad idea to use this sensor in a direct connection, with a 5VDC source.
It is not specified on Dtsh, but ANC defines an absolute pressure sensor.
So, alternatives are ADC and opamp, or buy another expensive kind of sensor.
I have seen a few more, but almost 4x the price of this one... Remember, this is Argentina, the 4th world....

Posted on: 14 March 2021, 16:10:50 - Automerged

As a reference, SCX30ANC price is U$S15 and MXP10DP is U$S31 (2x) (Mercado Libre Argentina)
In ebay, SCX30ANC price is U$S 75(??) and MXP10DP is U$S8.09 (Ebay USA)
Seems that vendor wants to release the last ones sensors, or maybe all of them are failed.... Last option is not common, since there are some warranties.
Anyway, buying from Ebay or Amazon from here, maybe duplicates the original value.... which in case of MXP10 isnŽt so bad...
But as a reference, my income at this moment, is around U$S500/month...
I was checking an alternative, an arduino ready module... U$S 19 here.... maybe I can use this one. Seems a good option.

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« Reply #3 on: March 15, 2021, 09:10:46 09:10 »

As a tip. A pressure sensor pretty much a Wheatstone bridge. So you will need a differential reading to read it in a proper way. The best way of doing this is using a true instrumentational amplifier. This is quite important so please do not brush it of. People are willing to help a lot in this forum if you put in some effort by self. If you do not know what a  instrumentational) amplifier is. Read about it and come back (putting in some effort you know Wink )
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« Reply #4 on: March 17, 2021, 04:35:53 04:35 »

I did, and I`ll do some tests, and return with answers. Great suggestions. IŽll be in touch.
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« Reply #5 on: March 17, 2021, 07:23:55 07:23 »

I did, and I`ll do some tests, and return with answers. Great suggestions. IŽll be in touch.
Just saying that for the sake of doing experiments. You can build a instrumentational amplifier. Out of 3 operational amplifiers Like shown here  https://en.wikipedia.org/wiki/Instrumentation_amplifier. If you are using only 10 bit ADC, it may work good enough
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« Reply #6 on: March 17, 2021, 11:11:42 11:11 »

You can build a instrumentational amplifier. Out of 3 operational amplifiers Like shown here  https://en.wikipedia.org/wiki/Instrumentation_amplifier. If you are using only 10 bit ADC, it may work good enough
That circuit was put up as an option in a project barnstorming meeting, the engineer who was doing the work, did not research into it.
He thought he just needed to use 3 opamps, his solution was to invert the signal then invert it back,
the funny thing was due to all the tweaking he got the panel reading the unit under test within specs. 
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« Reply #7 on: March 17, 2021, 12:28:07 12:28 »

That circuit was put up as an option in a project barnstorming meeting, the engineer who was doing the work, did not research into it.
He thought he just needed to use 3 opamps, his solution was to invert the signal then invert it back,
the funny thing was due to all the tweaking he got the panel reading the unit under test within specs. 
Among other things it will depend on how the pair of R2+R3 are matched and the R1 pair. It is not that circuit do not work. But if accuracy is needed the latter circuit is far from optional on many levels. But if it work for a one off circuit. It will do no harm trying it out
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« Reply #8 on: March 29, 2021, 10:01:54 22:01 »

A new stage and simplification.
An arduino module with a 40kPa pressure sensor, and an analog to digital module, from a load cell (which is almost the same that the pressure sensor has).
Ready to start checking.
Regards!
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« Reply #9 on: March 30, 2021, 01:46:51 13:46 »

A new stage and simplification.
An arduino module with a 40kPa pressure sensor, and an analog to digital module, from a load cell (which is almost the same that the pressure sensor has).
Ready to start checking.
Regards!
The little red PCB with the sensor on, from what I see. Do have an ADC IC. The green board made for a load cell. Do as far as I can see. have a better solution with a stabilized reference for load cell/pressure sensor excitation. Built into the ADC
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« Reply #10 on: March 30, 2021, 04:38:56 16:38 »

Both pcbs have SX family ADCs, and youŽre right, load cellŽs one, has an SX711, which has an internal regulator for sensor supply. IŽll perform a few tests, to check which is the incidence of that difference in readings. But seems a better solution to use SX711 as the main ADC component. Anyways, my VDD source will be regulated, because IŽll use 220VAC as power source. Maybe it wonŽt give me too many problems.
IŽll let you know what I get.
Regards.
PD: I have datasheets of both circuits, if anyone is interested.
« Last Edit: March 30, 2021, 04:41:21 16:41 by Poty » Logged

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