RTD excitation current

Hi,
I have a question regarding the SCC-RTD01 temperature module. I connected a RTD to the module, ran the LabView example, and set the excitation current (external) to the recommended 1mA. I was happy to see a value of 25 deg C. I figured since I hadn't really calibrated anything being off by 2 degrees was no big deal. At one point I decided to try reducing the excitation current to 0.9mA and got a temperature reading of 56 deg C. Is this normal for the excitation current to change the measurement so drastically?
Thanks,
Mark

Yes that is normal
As already recommended, try to use the internal current source, than you can expect the given spec.
U=R*I and the R of your RTD is only small but well known changing with temperature.
If you need precision with low thermal masses or low thermal conduction you might look at self heating of you RTD.
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

Similar Messages

Can I measure dynamic strain with a SCXI-1531 and how steady is the excitation current?

I am looking at the possibility of using an SCXI-1531 module to take measurements from a single strain gauge. I am only interested in the dynamic content of the signal and so am considering using the constant current excitation method which does not require bridge completion. Is there anyone out there that has tried this or could advise me as to whether this module is suitable?
Having read the spec of the module, it looks promising except for the data on the excitation current which states:
"Accelerometer input excitation current: 4mA +/-10%, 24V compliant."
Now, does that mean that the current will be steady at a value in the range 3.6 - 4.4mA or that it may fluctuate within this range during measurement? The latter would not be acceptable for my application as this would be indistinguishable from a variation in strain.
Thanks for any help.
CAS

Hi CAS,
Essentially the excitation provided by the module will not allow you to acquire as you would like.
However, the good news is that you are able to disable the excitation provided by the module, and provide your own external excitation. You should then be able to acquire the signal using the SCXI-1531.
To disable the excitation in LabVIEW using DAQm, place down a DAQmx Create Channel.vi and then configure it for Strain measurements. Then you can create a control/constantto wire to the Bridge Information Terminal by right-clicking on the terminal and selecting control/constant. Within this cluster control/constant will be an enum element where you can specify the voltage excitation source to be external.
I have attached an example VI demonstrating this.
Hope this helps.
Steve
Attachments:
Excitation Example.vi ‏18 KB

Turning off excitation current out of SCC-RTD01

I have a strain gage which has four wires instead of two. The reason I have four wires is because at each pad, I have a chromel and an alumel wire to create a thermocouple. This way I can measure the temperature right at the gage (two TC per gage).
I need to measure the resistance of the gage as I change the temperature. I have a SCC-RTD01 module that I can use to measure the gage resistance (I've done this actually and it worked). But since this module puts out a 1mA excitation current, my thermocouple reading is wrong (because current flows through at least one of the wires creating a voltage that is not the pure thermocouple voltage).
Is there any way I can turn the excitation current off from LabVIEW? Or, does anyone have any other suggestion? Thanks.
Solved!
Go to Solution.

Hi JG001,
Thank you very much for clearing up the issue, I now understand your request fully. Really the fact of the matter is that the excitation is broken out to its own dedicated pins; it cannot be turned off, and this is found in the SCC-RTD01 manual. You can also verify this by inputting a 0 mA in your task for the excitation and you can find that it is not a supported value, only 1mA is a supported value, and it will throw an error as shown below. I have also included some screenshots from the manual that describe this. If the excitation could be turned off, 0mA would be a supported value for the current excitation level. I hope this clears up any confusion. A possible solution would be to use a relay to turn this off, perhaps the SCC-RLY01.
Adam
Academic Product Manager
National Intruments

Measuring resistance, changing excitation current

Hi, I am using a cDAQ-9172 and some 9219 modules to measure several resistances. The problem I have is that the resistances aren't entirely electrically isolated from each other, and I suspect the excitation current from measuring one resistance affects the value I record on another. For this reason I would like to sequentially switch off the excitation current on all but the channel which I'm measuring. (e.g. excite channel 1, record resistance, switch off excitation, excite channel 2, record resistance, switch off excitation and so on). Frankly I'm a little baffled on where to start with this. Until now I've been using the DAQ Assistant to set everything up, but I don't think I can achieve what I want with this, so I'm going to have to delve more deeply into communicating with the DAQ. Has anyone got any suggestions on where to start and where I can find some guides on changing the programming of the DAQ sub vi's?
Cheers

I'm getting somewhere with this, configuring one channel to read resistance and all the others to read voltage does work, but I can't get it to change which one is set to resistance. I modified the DAQ Assistant Express VI to accept channel inputs, and then I've set up for loops to generate channel numbers (of the form cDAQ1Modxaiy). The modified DAQ Assistant accepts these numbers and carries out the measurement, but then for subsequent iterations of the for loop, instead of accepting the new channel numbers it just carries out the same measurements on the same channels. Is there some way to force the DAQ to reset the channel allocations between iterations of the loop? I've attached VIs of the scanner VI and the modified DAQ assistant.
Cheers
Attachments:
Self sensing experimental-scanner2.vi ‏28 KB
TimsDAQ.vi ‏81 KB

Scxi 1520 excitation current specs?

In p. A-3 of the scxi 1520 manual, for the excitation specs there, it says:
"Max. operating current in all ranges - 29 mA"
Is this for the whole SCXI 1520 or just for each channel? Because I need for each channel 5V with 1.6 mA supply. That means for all channels, about 12.8 mA.
Can the SCXI 1520 support this?
Please help me on this. Thanks!

Dear cb34,
Thank you for choosing National Instruments Support!
The SCXI 1520 Module has the operating current range of 29 mA per CHANNEL and not for the whole board. So, You are in good shape to use the system that you have because 1.6 mA per channel is well below the limits that you would need.
Thanks and Regards
Shekhar S
National Instruments

I am trying to use a SC-2024-RTD DAQ board to do 3 things (monitor two sensors (input) and control a small motor (output)) simultaneously. I have not been successful using labview for output. I can't even get it to show a voltage at the output pins.

I have it configured for voltage modulation, channel 0, and I am testing Ix0+ and Ix0-. To run it, I am right-clicking on the function and clicking "test". What's wrong?
thanks, Alex Millie
[email protected]

Ix0(+/-) are make the excitation current. You can see this in figure 4-1 in the user manual. You can see the output voltage from the MIO card by looking at the voltage from terminal 23 to terminal 20 (channel 0) and terminal 23 to terminal 21 (channel 1). You can see this pinout on page 3-5 of the SC-2042-RTD user manual.

Thermocouple Measurements using an RTD for CJC

I am using an SCXI 1001 chassis with SCXI 1102 cards attached to TBX 1303 units and also SCXI 1121 cards attached to TBX 1328 units. I need to measure a number of K and T typre thermocouples in this system (using 1102 cards), and was hoping to use a PT100 RTD for my Cold Junction Compensation. Is it possible to achieve this by using the excitation current from an 1121 card and measuring the RTD value with the 1102 cards. It seems that when trying to select the CJC source in Max in the 1102 setup screen, there is no capacity for reading values from cards other than 1102 cards i.e I can't read the 1121 values.
What is the best way to achieve this using the setup I have?

James,
On the virtual channels of SCXI 1102 MAX configuration if you have not set-up any additional channels at this point then the CJC selection will only offer the internal Thermistor for it's CJC reference or a user value defined one. If you wish to use a PT100 you will need to set this up in MAX first using the Virtual Channels. Once you have that working go back to the SCXI 1102 and configure the CJC reference as User Defined, you should then be able to use the PT100 channel that you have just created.
Side note: The 1102 has been designed to thermocouple measurements and the internal CJC should be accurate enough for general measurements.
Kind regards
Joe
NI-UK

RTD SENSOR

I have a RTD type temperature sensor and NI 6024E DAQ card. I need to know how to connection 3-wire rtd sensor to my scb-68 box ,and how to give the excitation current to RTD sensor.
Thanks.

The NI 6024E by itself does not have current excitation available. We do provide signal conditioning hardware that you can use in conjunction with the 6024E to integrate with the RTD. For instance, the SCC series signal conditioning hardware provides for channel-to-channel conditioning. There is an SCC RTD module(SCC-RTD01) that provides current excitation as well as other signal conditioning (filtering, amplification) that will optimize your RTD reading. You can use this module with 2,3, or 4-wire RTDs.
The SC-2345 is the carrier for SCC modules. Both the RTD module and carrier are linked below for your reference.
NI SCC-RTD01 -- RTD Input
http://sine.ni.com/apps/we/nioc.vp?cid=12311〈=US
SC-2345
http://sine.ni.com/apps/we/nioc.vp?cid=10778〈=US
Regards,
Todd D.
NI Applications Engineer

Measuring temperature with RTDs over a long distance

I have created an application using the FP-RTD-122 to take RTD mearurements from multiple locations in a plant. The measurments are correct when the RTD leads are connected directly to the module (about 6ft). However when we wire the RTDs in the plant to the module, the measuremtns are incorrect. For instance the temerature is 79C at one location, but shows as between -193C and 19C in Measurment and Automation Explorer. The distance is about 150 ft. I have found a reference in the internet that suggests using a temperature transmitter that converts the RTD signal to a 4 to 20 mA signal. Does anyone have any experience with measuring RTD over long distances? Do I really need a temperature transitter? If so, do I need to use the FP-AI-111 module instead?

Nate,
RTDs allow temperature measurement by reading the resistance of a sensor. This is normally done by exciting the sensor with a known current and measuring the resulting voltage. There are three general types of RTDs; two-wire, three-wire, and four-wire. Two wire RTDs are less accurate because the wire resistance is indistinguishable from the sensor resistance. Three wire RTDs use two wires on one leg (one to carry the known current and one to measure the voltage) allowing one portion of the wire resistance to be nullified. 4 Wire RTDs use two wires on each leg (one for the excitation current) to nullify the wire resistance. As a result, 4 Wire RTDs are the best ones to use for high precision or long distance measurements. To measure 4 Wire RTDs with FieldPoint, you will need to use the [c]FP-RTD-124 module instead of the [c]FP-RTD-122. With that said, I do not know how well 4 wire RTDs will do at 150 feet. 4-20 mA transmitters will easily handle 150 feet so they will probably be your best option. To measure the 4-20 mA signal, you can use the [c]FP-AI-100, [c]FP-AI-110, [c]FP-AI-111, [c]FP-AIO-600, or [c]FP-AIO-610 modules.
Regards,
Aaron

Need help for a post-processing "trigger"

Dear all,
Without getting into much detail, I have a system that is simultaneously introducing a sinusoidal Force (F) and measuring the sinusoidal response (X) of a structure under resonance. I need to acquire the whole time signal, including the free decay response in the end (please find attached a sample picture of the time signal and the corresponding data file), so I cannot use a trigger during the measurement. During the stationary response it may be seen that the signal has a slight negative slope: that is due to a phenomenon of dilatation of my structure that is dissipating heat at the same time.
My problem is how to know exactly when my NI-USB 6216 DAQ has stopped the excitation force, which, in my sample waveform would be around 0.025s (I require an automatic process of identifying it).
Is there any VI, filter or trigger function that might provide me that information?
Thank you in advance for your help.
Kind regards,
Diogo Montalvão
Attachments:
R50_18um_controlo_40_60_temp_24_1_12_v0_time_16.txt ‏373 KB

The brute force method:
Can't you use another analog input channel and capture the excitation voltage?
Or if you have a shaker with an amplifier that provide a current monitor output you can capture the excitation current and might find that due to the voltage control some amount of force is still introduced after setting the control voltage to zero and you might have to implement a system model that include the shaker and the output impedance of your amplifier :0
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

Need help getting DPX101 pressure transducers to read correctly in labview

hello, i previously posted about some resource errors i was getting,
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correct through labview.
basically i have no experience with labview, and for this project one
of my professors handed me a box with stuff in it and said here you go
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the way the system is laid out is I have an SCC2345 (tan box) with i
believe a PWR02 in it.
There are 4 modules, 2xSCCTC02 and 1 SCCAI01 and 1 SCCAI02. I have
familarized myself with the specs of these modules, and the SCCTC02 is
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SCC-AI01
Input Range: +/- 42V
Output Range: +/- 8.4V
Gain: 0.2
SCC-AI02
Input Range: +/- 20V
Output Range: +/- 10V
Gain: 0.5
There are 3 pressure transducers, all Omega DPX101, of the following
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own Omega ACC-PS1 power supply.
The ACC-PS1 has the following specs:
ACC-PS1
Excitation Voltage: 18V
Excitation Current: 2mA
Voltage Gain: 1 +/- 2%
Output Signal FS Peak: 10V
Input Power: 2 9V Battery
The system is laid out as exactly shown here:
http://hilltop.bradley.edu/~award/SP/gts.PNG
Using a DAQ assistant, i have it acquire all 5 values at 1000 times
per second and then it updates it to a text file every 100ms.
The pressure sensors each came with calibration sheets and these had a
sensitivity value, and i thought the sensitivity was the "scaling"
value used in the DAQ Assist (5000psi = 1.1mv/psi, 500psi = 10.30 mv/
psi, 250psi = 19.90mv/psi). I entered in these values and i ran some
tests and i was getting a value of 18.6 from labview when a pressure
of 1000psi was applied to the 5000psi sensor. how do i get this to
output 1000 for when 1000psi is applied?
Also, the pressure transducers have a "bias voltage" listed on the
calibration sheets, 8.2 V. Would this have an impact also?
any ideas on what i should do?
is my problem clear enough?
Thanks
-AJ-

Hi,
For your convenience and the consistency of our forums, please use the following thread for all further posts. Thanks!
http://forums.ni.com/ni/board/message?board.id=170&message.id=243262&jump=true
Best regards,
Ed W.
Applications Engineer
National Instruments

NI-DAQmx: Impact Test real-imagine plot

Hello.
I am a student of mechanical engineering and I am not familiar with signal proccessing. I have to use LABView for a measurement experiment. In that project I have to use an impact hammer and an accelerometer to test surfaces of some specific meterials. My teacher tell me that I have to take the real-imagine plot of undamaged pieces as a model so I can use them at future for model. My problem is that the code I had write or the one that I use form NI example (NI-DAQmx: Impact Test) returns me a messy plot no matter how many hits I made. My teacher said me that as many hits I do the plot will be more clear but he cannot figure out what goes wrong either cause he is not familiar with labview neiher.
I wrote two different codes one using ready VI's and one that made the mathematic as my theory book say.
Please help me cause I am in a dead-end and can't move on with that.
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Thank you!

Hi Albert,
An accelerometer is a type of sensor that is used to measure acceleration and output a corresponding voltage. Using Data Acquisition (DAQ) hardware, you can acquire the voltage from the accelerometer. However, most accelerometers will need some form of current excitation, typically IEPE Excitation which is a widely used standard. You can view these sites for a discussion of Accelerometer Principles and Types of Accelerometers.
Some DAQ cards are custom built to not only acquire the voltage but to supply the excitation current at the same time, specifically Dynamic Signal Acquisition (DSA) cards. An acceleration task is an instance of a DAQmx input task specially created for measuring accelerometers. You can programmatically configure the task in the LabVIEW or create the task in Measurement and Automation Explorer (MAX), as seen in this Knowledge Base. You will notice in the screenshot below, when configuring an acceleration task in MAX, you can supply values for the accelerometer's sensitivity, units, and the amount of current needed by the accelerometer. All of these values can be found in an accelerometer's specifications document. By entering these values, an acceleration task will allow you take the voltage measurements and scale them into g's or whatever unit your accelerometer measures. This way you do not have to create a custom scale yourself.
Hope this explanation helps.
Regards,
Mallori M.
Mallori M
National Instruments
Global Customer Education Program Mananger
Calculate the time you will save with NI Training
Attachments:
ScreenHunter_01 Dec. 02 21.42.PNG ‏39 KB

Hello, i am trying to take the measure of a temperatura but i couldn´t do it.

can u tell me how can i make a continuas thermistor measured? i need to take a real time temperature on a motor.
thanks

I agree with the above comments.
We would need to know more about:
1. which DAQ card you are using
2. what type of signal conditioning (if any) is implemented
3. the interconnection / circuit relation between the motor and the thermistor
4. are you providing proper excitation current (if thermistor)
To learn more about LabVIEW, I suggest you try looking at some of these tutorials.

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.
I am using Windows XP PC running LabVIEW 2011.

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.
I wanted to monitor the change in temperature of the thermistor by monitoring the voltage variation. When I measure the voltage with an external multimeter there seems to be some changes in the voltage, from 4.51V to 4.54V when I place my thumb on the thermistor to give some heat. However, I couldn't monitor any variation with the VI on LabVIEW. Did I misconnected everything?
I build the VI solely using DAQ Assistant to measure voltage.

Is there any process of identifying

hi,
sap gurus,
good morning
my client wants to capture the gross weight and net weight of the truck thru weigh bridge which is
located inside of the company premises.
i came to know that it is possible only thru transportion module
but
we can capture frieght cost into sales order or billing documents
but
what about the weight from weigh bridge.
do i need to ask an ABAPER to write any coding........?
plz help me on this
id is timmampalliattherateofgmaildotcom
regards,
balaji.t
09990019711

The brute force method:
Can't you use another analog input channel and capture the excitation voltage?
Or if you have a shaker with an amplifier that provide a current monitor output you can capture the excitation current and might find that due to the voltage control some amount of force is still introduced after setting the control voltage to zero and you might have to implement a system model that include the shaker and the output impedance of your amplifier :0
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

RTD excitation current

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