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Problem with Honeywell ASDX Analog pressure sensor

Former Member

Dear friends

Few months ago I decide to built a multi channel pressure box, so I bought 16 Honeywell ASDX differential analog pressure sensor (Model: ASDX RRX005NDAA5). the datasheet of this type of sensor attached.

Base on datasheet, this sensor has 3 active pin, pin No.1 is for voltage supply, Pin No. 2 is Analog output and Pin No. 3 is GND.

image

I design a PCB board to mount all 16 sensors on a single board. I use a 5Vdc power supply device for PCB board, now when I TURN ON the device and there is no applied pressure on sensors (just ambient pressure), the output voltages are almost 2.47 - 2.49 Volt (I checked Pin 1 voltage for each sensors and all of them is same 5Vdc). the problems are here:

 

Problems:

1. I expect when there is no applied pressure, the output voltage be 2.5V but as i mentioned above it is a little less, what is the reason?  

2. when I applied an specific pressure (for example 300Pa) most sensors shows different voltage in their output and so it is impossible to calculate the Pressures. the datasheet said i can calculate pressure by below Eq.

 

image

 

3. by the changing of the pressure, change in output voltage of sensors are not equal. for example if I increase the Pressure 500Pa, the voltage change for one sensor is almost 1.5V but the voltage change for another sensor is 0.7V!!

I will be so appreciate if help me

Attachments:
imagehoneywell-sensing-asdx-series-analog-pressure-sensors-product sheet-008090-12-EN.pdf
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  • 0

    Dear John, Michael and Douglas

    thanks for your quick reply

     

    the below picture shows my device, sensors and board

    image

    let me answer your question one by one:

    1) are you using the correct voltage for the sensor (they do 5V and 3.3V parts)

         I use adjustable -+5 Vdc and set this power supply on 4.99V

    2) is the load > 5k

        dear Michael and Douglas, I don't use any resistance on pin 2

    3) have some been damaged - the damage pressure for a 5"H2O device is only 15" which is  a very low pressure.

        I use this sensor in a low speed wind tunnel (the MAX speed is around 45 m/s and it is equal to  1113.7 Pa), so I don't think sensors damaged

    4) Capacitor

         I use one 100nF before any Vss pin of each sensor

     

    do you think the problem may be caused for the way i connect sensor to pneumatic connector? (see below picture)

    actually I am a mechanical engineering graduate and not very familiar with electronic details, can i use a 10 Kohm resistor? and do I use this resistor on output (Pin 2)

      imageimageimageimage

  • 0 in reply to Former Member

    That "Minimum load resistance" spec is definitely ambiguous.

    Normally an output would be specified to to drive a maximum load, where a smaller resistance is a bigger load, so you would want a larger resistance than what was specified.

    Here it seems they are saying the output needs a minimum load of 5K, which, if taken strictly, means the resistance from output to ground should be less than 5K. (because a smaller resistance is a bigger load)

    So if minimum refers to the output load it means one thing, if minimum refers to resistance it could mean the opposite.

    You may need to get clarification from Honeywell.

    I would try a 4.7K resistor to see if it helps. (you have already tried a much higher resistance)

    As to why the device would need a heavy load, it is not clear, maybe the output is unstable without a load, or maybe it gets quite non-linear without a heavy load.

  • 0 in reply to dougw

    I'm sure the correct interpretation is that the load needs to be between 5k and infinity. If the opposite were correct, then direct short from output to ground would be OK according to datasheet, which is nonsense. So the problem is in something else.

  • 0 in reply to kulky64

    Hi kulky64,

     

    I stand corrected and agree with your interpretation of what " minimum load resistance" means in this case. I also see that I misinterpreted what   originally posted. Seems I am off my game today. I have added the phrase "minimum load resistance" to my list of things to be careful of, in the future,  right below the listing "Free Lunch".

     

    John

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