Hello everyone. I am having hard time trying to get measurements from sensor.
I have created thread here: http://forums.ni.com/t5/LabVIEW/steinhart-hart-with-vernier-thermistor/m-p/2811150
I think now formula is fine. So i realized it might be that i chose wrong node to work with thermistor based probe.
So now i picked NI WSN-3226 Voltage/Resistance Node. I don't know how to wire it correctly. EX0, AI0 and GND.
Any help would be so awesome. Thanks
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If possible, could you provide a basic schematic of your physical circuit? What node were you attempting to use before switching to the 3226? Are you using the EX0 to provide power to the thermistor, or an external power supply?
And most importantly: what type of thermistor are you using, and is it truly a thermistor, or an RTD? Do you have a conditioning circuit of some kind, or is it just a thermistor? It's very difficult to advise how to wire a sensor without information on the sensor used.
I was using WSN-3202 first. Since i can't connect sensor it self directly to WSN node, i have used ni-elvis board and BTA-ELV connector. So AI0 from node goes to connector where it says SIG1, AIGND goes to Ground, +5V from board to connector where it says 5V and Ground from board to connector GND. Hope you can emagine.
Connectro it self:
Now i am trying to get this working with WSN-3226 since it has not only voltage but resistance aswell.
Tryed a lot of different wiring with this one, none seems to work correctly.
Sensor i am trying to use: http://www.vernier.com/products/sensors/temperature-sensors/tmp-bta/
Thanks for the help.
With the signal conditioning board, you should only need to (and probably can only) acquire a voltage from this sensor. It doesn't appear that you'll be able to use the resistance-measuring capabilities of the node with this sensor.
One thing to be aware of is that the 3226 outputs 12V through the SEN PWR terminal, which you'll need to use. Refer to page 24 in the module's user guide. You'll likely need to bring that down to 10 or 5 V, whatever the sensor expects. Also note that the sensor power can only be turned on for 250 ms prior to taking a measurement, so if the conditioned thermocouple requires more time than that to settle or the thermistor calibration accounts for expected self-heating over time, you won't be able to get a clean signal.
That said, you can try connecting SEN PWR to the breadboard's 5V excitation pin (as noted, you'll need to bring down the voltage and will lose power in the process), short the grounds, and connect the signal out to the AI on the node. Also ensure that you have configured the SEN PWR in LabVIEW to power on 250 ms before acquisition. You should be able to do this via the node configuration window in your LabVIEW project.
I believe it should be possible, but the sensor you're using was designed for use exclusively with Vernier monitors. The adapter you have was intended as a very specific addon to allow use with NI-ELVIS academic hardware, which is very, very different from the WSN platform. Because of this, you will need to do additional work to get the sensor to work with the hardware you have.
The WSN node(s) you are using are certainly capable of acquiring a signal from the sensor, but it's not as straightforward as it would be with a more general sensor such as a three-wire RTD, which is what the 3226 is designed to do. Since the sensor you are using has a specialized interface, you'll need to break that out into something the WSN can work with.
I would also suggest contacting Vernier, as they likely have additional information on getting their sensors to work with other DAQs. It may also be possible to cut the cable and break out the RTD interface yourself since the ELVIS adapter you are using appears to do the same conditioning that the WSN 3226 would do in RTD mode, but I would strongly caution against attempting this until you've contacted the manufacturer and determined whether or not that would be a viable option. You should also be confident in your own abilities to do this operation and have several spare sensors on hand.
I also suspect that you'll need to recalibrate the thermocouple output once you've determined a hardware configuration that gives you reasonable results.
I hope that helps!
I am using board to supply power for sensor so i only use AI and COM pins of node to get data.
The thing is i can't understand how node knows if it's resistance or voltage i am measuring.
After data is processed through formula the result is 80-90 celsius which is insane, so i checked the AI signal coming to node before formula ant it says 2,81... i asked my self what that is, is it resistance? So i pluged 5V from board to AI on node and it says 4,92 so it's about 5volts, so i guess i am getting 2,81V from sensor not ohms that's why formula is not getting right results for me. What can i do? Apply ohms law or something to do with node?
Thanks for helping,Tom.
That's correct- you're getting a scaled voltage out, not a resistance value. The manufacturer has provided additional information on using their probes with different here:
Additionally, it appears that there are already example VIs provided that do this voltage-to-resistance-to-temperature conversion. I was able to find these by searching Vernier's website with terms like "ELVIS", "BTA-ELV", and "scaled voltage".
The "convert thermistor rdg" VI provided in that zip file appears to apply Ohm's Law to determine the resistance of the thermistor from the acquired voltage, as you noted.
As a note- all of this information was already available on NI and Vernier's website with minimal searching. It's probably a good thing to consolidate this information in one thread/place so that future users have access to it (which is why I'm linking everything), but doing some digging on your own or getting in touch with the manufacturer directly might have had you up and running last week! Additionally, you need to be sure you understand your sensor and conditioning circuit before attempting to use it- not understanding what's going on is a good way to end up with faulty measurements.
Also, are you planning on leaving the WSN node tethered to an ELVIS board for acquisition?
Looks like link are dead, could you upload it here please?
Yes i am planing to leave it to ELVIS (use elvis to supply power for sensor).
Unfortunately, I don't have the zip file that was linked on that page (I only ever retrieved it as a temporary file and didn't save a copy), although the zip was certainly still available on April 14th. I recommend contacting NI support to see if this is still available.
Have you considered using an alternate power supply for your sensor? WSN hardware is typically used in remote or inaccessable locations where their low power consumption and dynamic wireless mesh networking is advantageous, if you're planning on leaving the WSN tethered to a large ELVIS protoboard just for power then there is likely a different platform better suited to what you're trying to do.