wiring pressure sensors on NI 9205

[chotzkon]

Hello, I would appreciate if anyone could help me on the following issue:

I need to use 2-4 pressure sensors (by SETRA, model 267) in order to sense differential pressure and converting it to bidirectional pressure range. I already have a NI 9205 module on a NIcDAQ 9172. The sensors are 3-wire circuit with four terminals available for wiring (-EXC, +24VAC/DC, -OUT and +SIG) with 0 to 10 VDC output. I have one 24VAC/DC power supply to use. My problem (as beginner to labview and NI products) on hardware is

- How to make the wiring connections to the 9205 module I already have??

- Is it appropriate to use this module for connecting 2-4 sensors like those (using the DIFF mode is up to 8 channels as I was reading on the manual)??

As for software, I am going to use Labview and NI MAX for configuring that. I have read that on DIFF mode there are less noise problems generally. Which one mode do I have to choose ??

Thank you all in advance!! I have read a lot on the forum regarding one single pressure sensor connected to module but not much for more than one. Any help on my matter is really appreciated!!

Cheers,

Kon

[edjones93]

Hello,

I am Ed at National Instruments Technical Support. Thank you for your query with us today, I have reviewed both manuals below:

1. http://www.setra.com/hubfs/Product_Operating_Instructions/Setra_Model_267_Operating_Instructions.pdf...

2. http://www.ni.com/pdf/manuals/374188d.pdf

Could you confirm that these are your devices, I ask in the case of the NI product as you have stated that it has 16 analog inputs, from the manual it is 32.

From what I have read in both manuals you should achieve your application by wiring the connections:

+SIG to AI0 and GND to AI8 for your first sensor in DIFF mode.

+SIG to AI1 and GND to AI9 for your second sensor in DIFF mode.

+SIG to AI2 and GND to AI10 for your third sensor in DIFF mode.

+SIG to AI3 and GND to AI11 for your fourth sensor in DIFF mode.

As given in Table 1 in the NI 9205 manual, I would follow this wiring for your setup. The methodology of choosing a mode is outlined in the article linked below, I do believe that in your case DIFF is appropriate and retains simplicity in the application in the extent that the more complex a system, the more complex it can be to setup, configure and if necessary, diagnose issues. This mode choice also corroborates with the sensor manual setup schematic.

http://www.ni.com/white-paper/3344/en/

I hope that this is helpful and you are successful in your application.

Best regards,

Ed

[Henrik_Volkers]

In addition to Eds answers:

I assume that the power supply is also near to the NiDaq and you are using a star topology for wirering...

I would use a shielded 2x2 twisted wire to connect the sensor(s) , shield only connected to ground  (PE, depending on your regulations, doesn't have to be the neg power supply sometimes called GND) and if possible connected only on one side of the cable.

One twisted pair for the power supply , and one twisted pair for the signal. that's 4 wire for your 3 wire connection, so you connect power GND and signal GND at the sensor connector.

Finally: Add a 10k resistor from the powersupply GND to the  NIDaq COM. (or a direct connection)  

to get a clean signal: sample ( with a samplerate beeing a multiple of your line frequency or say at least 10 time higher)  one or more periodes of the linefrequency and calcutate the mean.  and use the slow conversion ......

 To have a look at the noise: sample as fast as possible and have a look at the signal and its FFT

[chotzkon]

Hello Ed,

thank you for your reply. Yes, indeed, these two devices I am using. Sorry for writing 16 instead of 32 inputs -you are correct. As for the pressure sensor, because I have an older model than the one on the manual, there is a difference!! On my models there are 4 terminals available for wiring, as the -Exc and -Output are commoned on the circuit. Please check attached photo with the 4-terminal circuit.

So, in DIFF mode, for wiring I am going to have:

+24 VAC/DC connect to positive terminal of Power Supply

-EXC connect to negative terminal of Power Supply

-OUT connect to AI8 of 9205

+SIG connect to AI0 of 9205

Am I right??? Please confirm this wiring set up for the first sensor!!

If this is correct, following your previous reply, the other sensors will be wired as you suggested (+SIG of each sensor to AI1, AI2, AI3 respectively and -OUT of each sensor to AI9, AI10, AI11 respectively). BUT, what about the power supply of the other sensors?? Do I need one different power supply per sensor?? What would you suggest?? I currently use the DR-120-24 power supply model of the attached pdf file.

All the best,

Kon 

[chotzkon]

Hello Henrik,

thank you for your reply!! I will take into account your suggestions. Could you check my reply to Ed regarding the connections on my sensor?? Especially the power supply connections?? I have uploaded the datasheet of the power supply I currently use. Do I have to use one power supply per sensor?? Or could I use one PSU per 2 sensors?? Sorry for the inconvenience, but I was never good with electrical circuits (I still cannot understand how I passed the exams on that courses... hahahah) 

Thank you in advance.

Best regards from Northern Ireland,

Kon

[edjones93]

Hello Chotzkon,

With regards to OUT, this does not correlate with the manual I have found, if this is the ground (GND) then yes this would be connected to AI8.

The best next step you can do is call the company who you acquired the sensors from and confirm with them whether OUT also refers to GND.

For the question regarding the power supply. This should be fine to daisy chain however you will be limited. While the 24 Volts will remain constant the current will be divided per device, you will need to ensure that you are providing the minimum current the devices require. For example: the maximum current supply of your power unit is 5 Amps, if your pressure sensors require 1 Amp then you could potentially daisy chain a maximum 5 sensors to the power supply. However since the minimum current nor wattage are given in the manual for the sensor you will need to contact the provider of the sensor to acquire this information.

I hope that this is helpful and you are successful in your application.

Best regards,

Ed

[chotzkon]

Hello,

continuing my previous posts, I have been using two of the SETRA sensors finally with labview but I have some issues regarding the results I get. So, finally I use two sensors, both connected on a NI-9205 module on a cDaq-9172 chassis by National Instrunments. In another slot of cDaq I have a NI9211 module (a few thermocouples). A Differential connection is used for the sensors on the NI-9205 module (see attached .jpg file) using the first two physical channels (AI0/AI8 and AI1/AI9). 

On Labview, I have set up differential measurements with 0-10V range of output voltage for each sensor (as the sensors work on this range) converting this output linearly to Pressure (in Pascals). 

As for powering up the pressure sensors, I use one power supply unit (see attached .pdf file for specifications- see: Model DR-120-24), having 24V output and 5A current. Asking SETRA, I was told that every sensor needs 7-11mA current (although this value is applyied on the new models and not on the older one I use-they had no info to provide for the old one). So, I assumed that I am able to use 2 sensors on one power unit (right?) 

All the connections I have made are shown in the attached .jpg. Please take a look. 

I have finally written a program on labview for aquiring and saving the signals.

The problem is on my results I have attained so far. Please check the attached excel file. I have copied the signals (in Pascals) of one experiment. There are two signals -one for the upper and the second for the lower pressure sensor. The lines are not -close to- straight and the signal jumps all the time. Because I measure pressure difference in a compartment I would expect having trends closer to straight lines.

Do you have any advice?? I would assume noise but still I am not so knowledged on electrical circuits. 

All the best,

Chotzkon