Problem with Honeywell ASDX Analog pressure sensor

Question

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. 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. 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: honeywell-sensing-asdx-series-analog-pressure-sensors-product sheet-008090-12-EN.pdf

e14 Contributor · Accepted Answer

Dear Friends

thanks for your helps, your answer inspired me to solving this problem.

i use a 4.7Kohm with 1% accuracy resistor but my problem not solved, so i decide to connect the tubes to sensor directly (I used to use Pneumatic connector for connecting tubes to sensor) and after that i saw it's worked. all the sensor shows same pressure.)

i think because these sensors are ultra-Low pressure sensors (-1250/+1250 Pa) using usual pneumatic connection is not a good Idea.

I learn a lot of your answers and thanks so Much for your answers and your time

Best Regards

michaelkellett · Answer

The way I read the data sheet is that the load resistance should not be less than 5k - so no load resistor should be OK. @ Ashkan - are your sensors the 5V type (what's the part number written on them ). MK

dougw · Answer

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.

dougw · Answer

Just to confirm, I asked Honeywell - Here is their answer: " In regards to the Minimum load resistance of 5.0 kOhm, that is the absolute Minimum; therefore, the load resistance would be any number equal to or greater than 5.0 kOhm. " You already have this situation, so load resistance is not the problem...