Thermistor

I am struggling with what I think should be a relatively simple problem. I am trying to read a temperature with a 10K ohm Vishay thermistor. I picked this thermistor because there were sample VI codes and a link to the data sheet on the NI website. In the samples, the user utilized the DMM to take readings and apparently it worked fine. I am using a PCI 6259 card with a SCB-68 interface. I obtained the ABC values for the thermistor from the data sheet. When I use the Vex Thermistor DAQ my temperature values are not at all correct. I seems that I have a scaling factor issue but as I mentioned I obtained the values from the data sheet. I wired the R1 resistor as shown in the wiring diagram supplied by NI.
My Vex is 5 volts which I am tapping off of pins 8&9 from the SCB-68 interface and the R1 value that I was using ranged from 1K to 10K. I am confident that my wiring is correct because I am getting a signal.
Can anyone tell me If I am missing something or at least let me know what common mistakes are?
Thanks in advance.

Hi Boom,
The +5VDC provided on your SCB-68 is not a sufficient source of providing excitation voltage to your RTD. These voltages are to be used as references, not to source power.
For thermistor measurements, you'll need to provide an excitation voltage which would only be available with external circuitry such as the signal conditioning chassis (SCXI), or with our smaller signal conditioning platform: SCC.
The SCC-68 or SCC-2345 is a housing to plug in our premade circuit modules which then interface to your board. For thermistor, you'd use the SCC-RTD01 module, as long as you consider the options outline in Can I Make Thermistor Measurements with the SCC-RTD01?
I might also recommend you check out our Working with Thermistors and RTDs tutorial if you haven't already.
Regards,
Paul Davidson
Sound and Vibration Software Staff Product Support Engineer
National Instruments

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Has anyone any experience with a USB-6008 and reading a thermistor value

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I am using 'BC Components' NTC Thermistor. I used the express VI to create a Vex input and entered the A,B,& C values from the datasheet. The thermistor is the 10K version and I placed a 10K resistor in series with it. I wired it as is shown in the connection diagram, and applied 2.5 volts to it.
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Steve Lawson

I had a similar problem, had it working at one point then screwed it up.
try this:
Attachments:
Temp Pressure EXpress.vi ‏92 KB

How to interface multiple NTC Thermistors to a 8-1 multiplexer and then to myRIO .

I need to measure the temperature of 8 lithium ion battery cells in series individually for my battery management system . So I need to see how can I interface the 8 thermistors with 8 to 1 multiplexer and output to myRIO analog input.

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http://www.digikey.com/product-detail/en/HEF4051BP,652/568-1689-5-ND/763293
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to set it up to read thermistors. I'm using SignalExpress and keep
getting the message, "No supported devices found. Creating empty
SignalExpress block. Add channels to the block by clicking Add
Channels in the toolbar." whenever I try to Add A Step. Do I need to
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Hi- Since the 9219 doesn't support thermistor tasks, I believe you might be able to work around this by creating a 2 wire resistance measurement and applying a custom scale in your task. You'll need to multiply your resistance by your current excitation to get voltage. You'll then want to map your voltages to the temperatures specified by your thermistor. We don't have much documentation on doing this in Signal Express, however, there's a really good LabVIEW program on the NI Community, here. That example at least shows the program flow of what needs to happen. Additionally, this KB is helpful in understanding what has to be done to measure a thermistor with the 9219. Have a great day!
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Gorman,
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For example, I created a current excitation thermistor task in Measurement and Automation Explorer running into ai0 (channel 0) and I clicked on the connection diagram tab at the bottom. Here is the diagram that I got.
As you can see, you just need to connect to pins 68 and 34.
There is also an example program that you can download, which is in LabVIEW. Here it is.
Hope all this helps.
Regards,
Message Edited by Raajit L on 10-12-2007 06:05 PM
Raajit L
National Instruments
Attachments:
thermistor_current.png ‏23 KB

Thermistor measurement using NI PCI-6036E and CB-68LP

Hi everyone,
I am quite new to LabVIEW and DAQ and I am in an attempt of performing temperature measurement using the only existing hardware available which are NI PCI-6036E and CB-68LP. I was in the attempt of trying to perform the example of temperature measurement based on a book by Robert H. King "Introduction to Data Acquisition with LabVIEW", but as I go further I realized that the hardware I have is totally different that the one in the book, as the one in the book can perform direct resistance measurement from the thermistor.
I have learnt that there is a need of external excitation current needed but I am not sure of now to create one.
Is it true that I need to do a lot of external circuitry in order for me to realize the temperature measurement with only PCI-6036E and CB-68LP? I don't have a budget to buy SCXI or BNC-2120 accessory.
I bought a breadboard and a few resistors and connected to a voltage supply to build the external excitation but it failed miserably.
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Hi Lynn,
Thank you for your reply. I was just wondering at which terminal should I connect the AI0 of the DAQ card. I did the connection accordingly, by placing the external resistor in series with the thermistor. I connected the +5V source to one end of the external resistor and at the same point I place a connection to the AI0 and at the other end of the thermistor to the ground. The voltage seems to be a constant 5V.
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How to use labView to measure temperature using a thermistor

I'm trying to create a labView that will give a temperature reading based on a circuit using a thermistor. Any ideas on the VI or how to construct the circuit would be helpful!

Well, you need to generate a voltage. You also need a way to read that voltage. Do you have a meter, or a DAQ device?
Temperature Measurements with Thermistors: How-To Guide
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http://www.discovercircuits.com/T/therm.htm
http://www.facstaff.bucknell.edu/mastascu/elessonsHTML/Sensors/TempR.html
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Hello All,
I am having some difficulty measuring temperature using MAX with Iex Thermistor setup, and would like to know if I have missed any thing important. I am using external current excited thermistor with 2 wire configuration and PCI 6259 card with MAX.
This is a channel that was originally configured to Voltage measurement and MAX measures about 900mV from this channel OK, the voltage converts to Temperature to be around 30C. Then I added a new channel and configured it to measure temperature directly using MAX default Iex Thermistor setup. This is when the problem show up: I will get a constant -273C instead of 30C as expected when run the channel in MAX. I must have been doing something wrong here.
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Solved!
Go to Solution.

Hi Ravens, thank you for taking the time on this problem. I am sure the issue was not caused by the A, B, C parameters being wrong, as when I ran the channel in MAX, I am getting a constant -273.15 value, and it was not updated as a real measurement.
To your 2nd question, this is a case of measuring 1 thermistor value using the Iex Thermistor method vs. Voltage measurement. If I set it up to measure Voltage directly, I can see the realtime updates of the measurement values of voltage, which converted to Temperature in my VI to be reasonable values of temperature.
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NI 9219 and 22k Ohm Thermistors

Hi all,
Is there any chance to read thermistors more than 10K ?
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Pets

Hi Pets,
Unfortunately the maximum resistance the NI 9219 can measure is 10.5 KΩ. Other posts are related to the same issue. If you need to measure temperatures below 0°C you will still need external signal conditioning (such as a shunt resistor in parallel with the thermistor): see: thermistor data acquisition using cDAQ-9172 You can even measure the thermistor with a 9215 but using this module would require external excitation current and signal conditioning too.
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Wie schliesse ich ein Thermistor an?

Wie muss ich einen Thermistor anschliessen, und was hat es mit dieser Iex-source auf sich?

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Dear Customer,
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Thermistor reading clamped at -17 deg C

Hi signal conditioning experts.
I am measuring several thermistor temperature channels using an SCXI-1503 connected to a PCI-6221.
The thermistors when open circuit (i.e. not connected) read approximately -17.7 deg C, but when the thermistor is connected the temperature reading is correct.
All was well, I thought, until I tried to measure a temperature below -17.7 deg C, and then the reading stayed clamped at this temperature of -17.7 deg C.
The task is set up in MAX, and the minimum range is set to well below -17 deg C so this is not it. Any ideas what may be the problem?
nrp
CLA

Hi again NRP
Thank you for your patience. I have now two options for you in regards to solving this problem.
1. The SCXI-1503 as we know can only handle a thermistor up to 100 k ohms, this is why your thermistor was saturating at -17.7 deg, as although your thermistor can produce 600 k ohms (temp of -50 deg C), saturation occurs at 100 k ohms; at -17.7 Deg C. So one solution is to change your value of thermistor to one with a low recording working temperature range but no more than 100 k ohms. I have found an external pdf doc for you to see the types of thermistors that are calibrated with low temps involved. One such resistor can record temperatures to -44 Deg C with a resistance of 99.26 k ohms. (Within 100k ohm range of SCXI module) and will allow you to record the low temperatures you require. I have included a link to this thermistor below. (Model Number 44004 - first column)
http://www.omega.com/temperature/Z/pdf/z256-257.pdf
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http://www.ni.com/pdf/manuals/374271a.pdf
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Many thanks for using the NI forums and I look forward to your reply.
Kind regards
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National Instruments UK

Write 32 channels thermistor data (temp in degree vs date/time) into xls file for all channels continuously.

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