## NSC Pressure Transducer - Full Scale Output

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I'm working on a circuit which uses a Honeywell NSC pressure sensor, uncompensated and unamplified.  Looking over the specs for this, I'm having a bit of difficulty understand full scale span (aka full scale output) that is listed for the sensor.

The typical value for full scale output in the datasheet is listed as 25.9 mV / V.  The sensor will operate at 5V.

My question is, does the sensor actually put out 0 to 25.9 mV / V, or is the range increased by 5 due to the excitation voltage?  Meaning, 0 to 129.5 mV / V output.

I'm trying to determine the minimum and maximum output voltage from the pressure sensor so that I can design an op-amp circuit which will increase the signal to be read by my AVR's ADC.

zipfactor wrote:
My question is, does the sensor actually put out 0 to 25.9 mV / V, or is the range increased by 5 due to the excitation voltage?

The spec "25.9 mV/V" implies "25.9 mV of output per volt of excitation" so, yes, the range is increased by a factor of 5.

Letting the smoke out since 1978

Thanks for the info.

Taking into account the offset voltage, which is listed at -7.0 mV / V, that would then make the range -35 mV to 129.5 mV? I apologize for the simplistic questions, just want to double check.

Thanks again.

It might be easier to use a sigma delta converter with differential input. You'll get better accuracy as you can use a ratiometric conversion and avoid having to trim analog circuits. Something like an Analog Devices AD7799. You could use an aducm360 and not need the AVR as this part has the converter and cortex m0 in the one chip.

Might also be easy to hook it up to an avr with a differential a/d. Gain of 100 would put the full scale out at 2.95V, which is in the 0 to 5V range of the a/d. Worth a try... all sw, no external components.

Imagecraft compiler user

Thanks for the input guys.

I didn't realize there was an all-in-one type solution as suggested by Kartman.  It's expensive, but it saves time and hassle of characterizing and calibrating the sensor.  In the long term sense, you more than likely avoid the problems with analog circuits, such as the need for recalibration due to drift, etc.

There's an IC for everything now it seems.

There's an IC for everything now it seems.

There is, as a young engineer I have loads of respect for the older time served guys like kartman bob et al, there are lots of things especially so with analogue that seem like cornerstones of electrical engineering, offset drfits, calibration and manual tuning of equipment must of been a big part of the job and designing to allow this

theres a lot of analogue stuff i have no experience in because there are so many other ways these days that offer benefits that can't be ignored and not just because its easier it is really better, as a young engineer I used to worry about not having experience in some of these areas but time has made me realise that I am living in a new age and I need to embrace all these new things rather than concentrating on the older technologies hence the older guys like Kartman et al will always be ahead as long as they stay current

Kudos to the experienced engineers

There are probably cheaper devices compared to the ones I've mentioned. LT, TI, Maxim and others should be visited to see what they've got. I mentioned the AD parts as i'd had experience with them. I used to do a lot of load cell work. LT have some 8 pin converters that might suffice.
Depending on the requirements, Bob's suggestion of using an AVR with differential inputs might suffice. At low signal levels, noise becomes an issue, so be wary.

Being lazy, the concept of tweaking gain and offset on analog devices on site in the middle east in 45+C temperatures loses it's appeal after the first one. Being able to do it digitally in the comfort of an air conditioned control room is much better.

Thanks for sharing your experience with everyone, it is very much appreciated, especially for all of us newbies.

Just a side note here that may or may not be of any use to the OP, but have you looked at Honeywells pressure transducers that have the analog stuff built in?  Measurement specialties as well.

I have used both and very happy with the results.  The end user has told me that the %TEB is less that they advertised.  Rock solid readings over temperature.

I have attached the datasheets for both of them.  Might make your life easier.

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jgmdesign wrote:

Just a side note here that may or may not be of any use to the OP, but have you looked at Honeywells pressure transducers that have the analog stuff built in?  Measurement specialties as well.

I have used both and very happy with the results.  The end user has told me that the %TEB is less that they advertised.  Rock solid readings over temperature.

I have attached the datasheets for both of them.  Might make your life easier.

Those look to be excellent solutions.  The only issue is that the pressure port needs to be able to measure the pressure of a liquid (which I neglected to mention initially), in this case distilled water.  I noticed on the measurement specialties option listed above that the factory had to be contacted for media compatibility.  Any experience with the pressure port be continuously exposed to water?

I also noticed the measurements specialties MS5803 series which comes protected with a stainless collar / gel coat assembly suitable for submersion in water.  The only issue is it seems no one stocks this as the distributors (digikey, newark, mouser) is backordered, however the price / configuration is very attractive.  Does anyone have any experience with this sensor?