Conductivity Probe via CompactDAQ

[amd15@uakron.edu]

Good afternoon all,

  I'd like to use the CompactDAQ setup to operate a conductivity probe, but I'm not sure which modules I need.  The probe I'm interested in is available at http://www.vernier.com/probes/probes.html?con-bta&template=standard.html .  This probe uses a BTA connector (which I'm willing to remove to bare wires) and is designed be used with Vernier's own SensorDAQ (http://www.vernier.com/mbl/sensordaq.html) , which supposedly interfaces and was designed in collaboration with LabVIEW.  Any answers to the following questions would be incredibly helpful:

1.  Do conductivity probes require voltage or current for measurement?

2.  Provided the answer to Question 1 is "voltage" or "current", do I need an Input or Output DAQ module?

3.  What sort of setup might be required to perform the same function as the SensorDAQ as offered by Vernier?

4.  Are there any examples of running a conductivity probe using only NI hardware/software, save for a third party probe?

5.  Is this topic in the right thread?

Thanks to anyone who can shed some light on my project.

[Seth_B.]

Greetings,

You are indeed in the right thread.

I've been reading through the specifications for that probe that Vernier lists on their website and it doesn't look like Vernier has enough information listed to determine what DAQ device would work best with this probe.  This is likely because they do not intend their sensors for use in research, only in education.

That being said, I can recommend some questions you could ask of Vernier to determine what DAQ device you should choose:

1. Does the sensor convert conductivity to voltage, current, or resistance?
2. What are the min/max values for the above readings?
3. What is the sensitivity of the device (how small of a change in voltage/current/resistance do we need to try and read?)
4. Does the sensor require excitation? (It most likely will)
5. If so, current excitation or voltage excitation and what levels?
6. Does it need any kind of AC or DC coupling?

These questions are usually answered by a sensor's specifications page, so we will need this information to determine what module or modules we will need.  Good luck!

[DAQjr]

I believe I can answer a few of your questions...

1. The Vernier probes output a voltage signal. I believe it has a range of 0V to 5V.
2. You would need an input DAQ module. The sensor will output the voltage and you need a module to read (input) it.
3. A basic analog input module like an NI-9201 should be able to read from the sensor. The primary feature that would not be available to you (that the SensorDAQ does provide) is the ability auto-identify the sensor. It seems like that is not much of a shortcoming, since you are only talking about using one type of sensor. You would either need to cut off the BTA connector or get a female BTA adapter like those available for NI-Elvis.

Cheers!

[DAQjr]

Seth,

1.  Voltage... must be stable for 1 second before measurements are available.

2.  0V to 5V...

3.  The sensor seems to have 3 different ranges available.  I'm not sure how that works.  Is there a switch on the sensor or do you have to buy the sensor with the range you want or what?  Don't know.

4 & 5.  The sensor requires a 5V power source, per the BTA pin out.

6.  DC coupling is used in the SensorDAQ.

JR

Message Edited by DAQjr on 12-16-2008 08:50 PM

[amd15@uakron.edu]

Good afternoon,

  First, thank you all for your consideration.  Between your suggestions of setups and explanations of how things fit together, I think I've learned enough to try out a setup using a 5V output module (to the probe) and a +/10V input module (from the probe).  I talked with Vernier regarding their pin setup and the output signal from the conductivity probe is 0-5V; the +/10V pin on their pinout diagram isn't used for this probe.

  DAQjr, the various ranges are conductivity ranges based on a cell constant, which is just a geometric ratio of sensor surface area to distance between sensor plates.  The larger the cell constant, the smaller and further apart the sensor plates are.  Strong electrolytes require a larger cell constant (and hence smaller, more distant plates) to compensate for the increased current flow in the solution.  The different ranges are selected when ordering the part; most simple conductivity probes do not have interchangeable sensors, although some do have multiple sensors that can be chosen per application.

  Again, thanks to everyone for their help.