Pressure.VI help

[JohnS (STUDENT)]

HI

Im a student who is working on pressure testing with the polymer PDMS. I am hoping you can help me with a slight problem I've encountered. I am using a Honeywell P40 series pressure sensor connected in a NI USB 6218. It is a program to measure the pressure through an average 1.2mm pipe inner diameter,  included is the  user manual for the honeywell 40PC series:

http://docs.google.com/viewer?a=v&q=cache:rLeZ4BjNn6EJ:content.honeywell.com/sensing/prodinfo/pressu...

I have connected pin 1 pin 2 on the pressure sensor to pin 19 and pin 20 respectively on the NI USB 6218. i have not connected pin 3 of the pressure sensor to any pin of the NI usb 6218 will this have an effect?Should i connect it to a ground pin and if so does it matter which one?

I have the VI program in labview 9 but am unable to become accustomed to it as i am used to Labview 7. I will include the program in the email and would appreciate if you took a quick look and could inform me how i would use it and/or if the program is complete.
Much thanks
John Stewart 3rd Year Mechanical Engineering.

[Ben.h]

Dear John

I have found the spec sheetshowing the screw terminal for the usb 6218

http://www.ni.com/pdf/manuals/371931f.pdf

appendix A-19

and from it I can see that pin 19 and 20 are analogue inputs (AI). So your system is currently connected up incorrectly.

Solution

From the link of the pressure sensor you posted, pin 1 is the supply voltage (which needs to be connected to positive dc voltage) and pin 2 should be grounded i.e. to zero or a ground pin on the 6218. Pin 3 is the output voltage (i.e the voltage generated from a change in pressure) and does need to be connected to an AI pin on the 6218.

Regards

Ben

[JohnS (STUDENT)]

Thanks Ben.

In regards to the program i started again for a more simplier VI program. The initial, and constant unless applied pressure, value of the graph is around 0.5 (I used an aquire Input voltage on the Measurement and Automations program through DAQ assist). To convert the readings to the approciate pressue values (initial reading/no pressure101KP atmospheric pressue) do i need to contact Honeywell and find out their voltage/pressure formula to acquire the correct readings?

Much Appreciation for your time

John.

[Ben.h · Accepted solution]

Hiya John,

From the link you sent me on the pressure sensor, in "General Information", it says;

'The 0.5v to 4.5v analogue output is linearly proportional to input pressure'

In other words if the measured voltage at the output you are reading is 0.5V at atmospheric pressure (101KPa), the maximum measurable pressure at the output will relate to a pressure of 909KPa, for example if the amplification K value equals 1. (unless it is inversely proportional, where as the pressure decreases the voltage increases). But you will have to calibrate your sensor to find out the amplification K value.

For calibration see what the measured voltage at the ouptut is for a proven known input pressure and then you could use some simple maths find out the amplification K value.

i.e (0.5V / (101KPa)) = K (Vout / (Known Pressure))

But if you have any further doubts on this I'm sure a call to Honeywell specialists wouldn't go a miss...

Regards

Ben Hartrick

[JohnS (STUDENT)]

That makes perfect sense! Thanks for making it so clear and taking your time explaining to me what I assume is common knowledge for labview! Thanks a lot! Much appreciated Ben Hartrick!