Precise DC voltage measurement using NI9219

While measuring dc voltage across a resistor using NI9219 , the 3rd and 4th digit after decimal point of the result continuously fluctuates .
To measure voltage coefficient of a resistor using either Elvis ii or ni9219, what method should be used?
Thanks in advance.
Smita Bannapure

You have posted to a board for an obsolete product called "Measure". It is not a board to dump generic questions. The Multifunction DAQ board would be more appropriate though I don't see where you have a problem at all.

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Why differnent channel can affect each other in voltage measurement using 2532

I use PXI 2535 to measure lots of channels (connected with electrodes) voltages using the sample vi: niswitch DMM swtich synchronous scanning.vi. Among these channels, one channel was -0.6V and other channels were about -1.0V. But after running the vi, the -0.6V turned into about -0.9~-1.0V. It is very strange. I connected another electrode (-0.6V) to a channel (all other electrodes still connected), whether I used the soft front panel or the sample vi its voltage all turned into about -1.0 V. I didn't find this phenomenon when I used 2532 finished the above measurement. I suspect there was current flew between channels with high and low voltages.
The red line (HI) was connected to r0, and the black line (LO) was connected to a reference electrode. The V diffence between different channel vs the reference V were recorded.
When I measure voltages with low difference (lower than 100-200mV), each voltage can be measured correctly (using 2535).
thanks advance
小木虫
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I used a setup shown in Fig. 1 to measure potentials of 121 electrodes (120 zinc wire and 1 iron wire, 1mm in diameter, embedded in epoxy resin, each electrode allowed one surface exposed) in NaCl solution against a reference electrode (with a constant potential). The HI line of DMM was connected to r0 and the LO line was connected to the reference electrode.
Fig.1
These 121 electrodes were connected to the terminal of 2535 with 5 pin Ribbon cables, each of which has 25 lines.Generally, the potential of Zn is about -1.1V and -0.5-0.6V of Fe in NaCl solution. I used the niswitch DMM switch synchronous scanning.vi, sample of LV8.5 to measure these potentials. But I found that the potential of Fe was about -1V, which was similar to that of Zn. This did not occur when PXI 2532 was used. I used a portable DMM to measure the potential of Fe in the 121 electrodes and the results was -0.56V whether I run the sample vi or not. Then I suspected that the switch bring some effects on the measurement.To clarify this problem, I connected a Fe wire to c135 channel (as shown in Fig.1) and measure the influence of other 121 electrodes on the potential measurement of the c135. 1. I did not connect pin Ribbon cables to the switch and used the DMM waveform demo to express the potential of the c135 channel evolution. I opened the soft front panel of the switch and made the c135 connect to r0, which was connected to the HI line of the 4071. When the demo was run, the potential was constant and about -0.56V, as shown in Fig. 2.
Fig.2
2. I connected one pin Ribbon cable (25 zinc wire connected to switch terminal). When the demo was run, I found that the potential was constant and about -0.56V, as shown in Fig.3.
Fig.3
3. When two pin Ribbon cables (50 zinc wire connected to switch terminal) were connected to the switch, similar result was obtained, which was shown in Fig 4.
Fig.4
4. When three pin Ribbon cables were connected to the switch, the potential of c135 fluctuated, which were shown in Fig 5 a-c.
Fig.5 (a)
Fig.5 (b)
Fig.5 (c)
We conclude that the number of the Zn wires have an effect on the Fe potential measurement using PX I 2535. But why not using PXI 2532 ?We also found other interesting phenomenon: when one or two pin Ribbon cables were connected to the switch (25 or 50 wire electrodes connected to the 2535), the waveform of the potential of c135 (Fe wire) can be affected by the nearby body action, e.g. stand up and sit down, go by the test table. The waveform changes were similar to the Fig.5. I’d like to know the reason for this phenomenon and how to prevent it? Thanks advance.
Attachments:
problem about measurement.pdf ‏113 KB

Recording Temperature and Voltage measurements using Keithley 2182 Nanovoltmeter

Hello all,
I am relatively new to LabView and looking to extend a vi I am currently using.
I am trying to record voltage and temperature measurements from a Keithley 2182 nano voltmeter using a GPIB cable. I have a vi that can do this for either voltage or temperature not both. At the moment I only record what is shown on the display of the nano voltmeter.
Could somebody explain how I could get labview either to change between voltage and temperature on the nano voltmeter or whether it is possible to have two simultaneous measurements of temperature and voltage and how I would achieve this.
Thanks
Mike

Hi,
For each read, no matter Temperature or Voltage there is a certain command that is send to the voltmeter.
I don't think (actually I'm pretty sure) you cannot read it in parallel but you can do it successively: One read Voltage, one read Temperature and so on.
There should be something like:
while not STOP do
1. send GPIB command for changing Keithley to Voltage Measurement
2. send GPIB command for Voltage Read
3. read GPIB -> Voltage
4. send GPIB command for changing Keithley to Temperature Measurement
5. send GPIB command for Temperature Read
6. read GPIB -> Temperature
end
You can take a look in VI to see which are the commands send for Voltage and Temperature reads and to mixed them like I described it above.
If you don't manage it share your VIs (for temp and volt.) maybe it will be easier for me (or something else) to give you some additional advices.
Paul

Voltage measurement using SCXI 1302

I am trying to measure voltages using SCXI 1302

Great! Are you having any problems?
The SCXI-1302 is just a terminal block. If you have a specific question, you might want to post some more information. Like:
1) What SCXI module are you using (the one connected to the 1302).
2) What SCXI chassis are you using?
3) What DAQ device are you cabling to?
4) What version of NI-DAQ do you have?
5) Are you getting any particular errors?
6) Are you testing in Measurement & Automation Explorer?
7) What programming language are you using, and what version? LabVIEW, CVI/LabWindows, C++, etc.
-Alan A.

How to measure voltage changes using a NI-9219 with strain gauges and use the data in labview

I am updating an old LabView/Data Acquisition system that uses strain gauges to measure two forces (normal and axial) as well as two moments (Pitch and Roll). I am having trouble reading the voltage changes over my strain gauges using my NI-9219 as well as filtering the data with both a lowpass and smoothing filter. The program attached has the project and should have all the sub-vi's used in the program. This program was written on LabView version 8.5 and is being updated to a 2013 version of LabView. Also, the hardware previously used was a combination of a NI SCB-68 and NI USB-6251. If anyone could help me it would be greatly appreciated!
Attachments:
New SSWT.zip ‏751 KB

Hi Coffeyfj,
Did you ever had this set up working? The first thing that I would do as I mentioned in the previous comment would be to use one of the LabVIEW examples. I recommended to you using the (strain - Continuous Input.vi). If you can read any voltage changes with the example vi, then we will know the problem we are having is in your code. If you cannot read any voltage changes using the example I mentioned, we can start trouble shooting the hardware connections. Are you connecting the excitation voltage? If yes, Are you making the right connections. Please refer to page 19 of the following document (half and full bridge modes)
NI 9219 Operating Instructions and Specifications - February 2009
http://digital.ni.com/manuals.nsf/websearch/4197ED4BD126E0B486257546005851CA
Regards,
William Fernandez
Applications Engineer
National Instruments

Low frequency Voltage measurement

Hi,
I am using PCI 6025E to control load bank and to measure voltage, current and frequency of a generator.
While current and frequency measurement is not a problem, voltage measurement is toublesome.
Since on test bench already there are few PCI boards and huge number of sensors, I do not want to add NI 9205 or any other additional boards and clutter the area (other people are also working there).
The problem with voltage measurement is that out of three generators two run from 400 RPM to 1600 RPM i.e.. somewhat 15-55 Hz.
I had two solutions for this:
1, Putting a step down transformer (230 Vac / 5 Vac) and then measure the voltage. But when testing at somthing like 15 Hz I have to deal with magnetic saturation with commercially available transformer. I do not want to take pain to go on built my own transformer.
2, Using high precision voltage Divider. The problem is that what should be the galvanic isolation? Isolation transformer, but then again low frequency problem.
Hence could someone suggest me since there is a bit confusion in my head.
Thanks.
Solved!
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If you have a sine generator (15Hz migth be hard for the soundcard ) you can do a calibration of your transformer.
(If only the voltage amplitude is of interest , use a isolated DMM as reference and run your generators)
Or you buy a isolation voltage sense amplifier. (weidmueller, phoenix, wago, ...)
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'

Examples of Transducer Impedance measurements using NI 4552.

Are there any examples available for Impedance Calculations from Voltage and Current Data taken from NI 4552 acquisitions?

Hello,
I would recommend taking a look at the LabVIEW shipping example for NI-DSA called "Frequency Response Example.VI" You could measure the voltage across the circuit using channel 0, and then use a current transducer (probably just a precision resistor) to measure current on channel 1. The results of this calculation would give you the impedence at various frequencies. By switching between magnitude and phase views, you can examine the resistive and reactive components of the impedance.
Good luck!

Voltage measurement error

Hello,
I am using a PXI system (PXIe-1073 chassis, PXIe-6363 DAQ card, PXI-2567 relay driver card) connected to my custom PCB.
My PCB has a 2.5V output precision reference IC whose output is connected to an analog input of PXIe-6363 DAQ card through the 68-pin connector and DAQ cable (SHC68-68).
When I measure the 2.5V output at the 68-pin connector (Analog input pin of the connector) using an external DMM (with High Z input impedance), I measure exactly 2.5003V, which is what I expect. However, LabVIEW reports back 2.4987V with an error of 1.6mV.
So, I disconnect my PXI system from my PCB and connect the DAQ card cable to the SCB-68 connector block and supply 2.5V external supply to the analog input and GND through the connector block. Now, both external DMM and LabVIEW report exactly 2.5V. This suggests that the DAQ card and software (voltage measurement VI) are working fine.
Then why do I have an error of 1.6mV when the PXI system is connected to my PCB ? If the problem is in my PCB, then why does the external DMM measure accurately right at the DAQ 68-pin connector ? What could be going on ?
Thanks
Jeet

Hello,
Yes, the PXI chassis is still connected to the PCB when I measured with an external DMM.
Upon further investigation, I found that my switched mode power supply was injecting 240 mV-pp noise on the Ground. This Ground noise was getting filtered down to 60 mV-pp through a choke but it still wasn't good enough. So I used another RF bead (with 1K impedance @ 100 MHz) to further suppress the ground noise and that did the trick. Now my voltage measurements are right on.
Thanks
Jeet.

How to take voltage measurements every minute

Hi all,
I am currently new to labview and i am trying to take timed voltage measurements. Here is what i am trying to do;
I am using labview 2010 and I am trying to take temperature and humidity readings in sync with each other. To measure the temperature i am using a cDaq and mudule 9213, for humiduty i am using the voltage from module 9234 and converting it using the ambient temperature and voltage from my humidity sensor.
Now what i want to do is take voltage and temperature measurements say every minute or 30 seconds, but my buffer fills from the voltage readings and gives me an error or the table takes values from what im assuming is the buffer, one by one, instead of grabbing the current data from the module.
My real question here is how do i take current voltage measurements every 30 seconds?
Thank you for any advice.
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Did you stop your VI when changing voltages? It would make since if you did since the chart will retain its memory while the table's Express VI is reset with each run.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
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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.

Slow AC voltage measurement readings with hp34401a

Hi,
I am currently using the hp34401a to record an input and output signal voltage (this is then converted programmatically to frequency response). This measurement however I consider to take exceptionally long for what it is (approx 3 seconds per measurement). I am using Configure measurement.vi (set to AC voltage on auto range) and Read(single point).vi. If anyone can give me some ideas how to speed up these readings that would be appreciated.
I have had a look at a similar test done with Labview 6.2.1, where the testing is much faster. The same instrument is being used but with Traditional NI-DAQ.
Thanks
Tania
Note: Labview 8.6

TanWal wrote:
I have tried all the possible/ suggested ways I can think of to improve the reading. There seems to be little that can be done in AC. Even applying the fast filter did nothing to improve the time. I tried to do DC voltage measurement, then take a multipt read and use the Basic rms.vi to obtain an AC value but this is very inaccurate. It seems that this DMM is very limited in its speed for this type of measurment.
I took a look in the spec. Forget the DC way if you have frequencies higher 80Hz....however if you have sampled waveforms do a tone detection (FFT based) or better a SAM (sinus approximation via min MSE) to get the best out of your data ( For FRF with sinus excitation). With RMS measurements you will measure hum and noise too, however you didn't tell us the uncertainty goal nor your DUT.
I don't use this instrument but from the spec and my experience with HPs(agilent) you should be able to get 10 reading/s in AC mode BUT still have to wait for the settling of the AC filter after switching (I assume you use the front and rear input)
I would encourage you to write a small state machine for the task and post it here.
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'

Temperature Measurement using Iex Thermistor with PCI 6259

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.
Your help is greatly appreciated!
Bryan
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.
Bryan

SCXI AC Voltage Measurement

Hi,
I am attempting to measure a shunt voltage (AC) using an SCXI 1001 / 1102 / 1300 set up. Data transfer is via SCXI 1600 USB using windows XP. I've installed the XP hotfix associated with data corruption issues.
I've been attempting to collect at 100k and get total nonsense when viewing the waveform in MAX. I've checked the channel with a DC voltage and it appears correct and the AC signal is correct when measured with a multi meter at the terminal block and with a scope.
This is a differential measurement 0-100mV AC @ 60Hz. Task settings: continuous / 200k buffer size / 100k rate
Any suggestions?
Thanks in advance!
Jon

Hi cosgrove,
How do you display the data collected? Is it in a log file or a graph/chart? Have you tried a different channel on the module or a different chassis? What is the signal source and how is it connected to the SCXI system? You could try grounding the signal by adding large (100k or more) resistors that lead from the positive input to ground and the negative input to ground. Have you tried varying the sample rate? A 60Hz waveform would be perfectly defined at far less than a 100 kHz sampling rate.
Let me know if any of this improves the problem and we can work from there.
Ben R.
Modular Instruments Product Marketing Engineer
National Instruments

Keithley 2000 voltage measurement

Hi,
I want to write a code to display the voltage measured from a keithley 2000 meter using RS232 serial port and display it on a graph using Labview 8.5 on Windows Vista based Laptop
. I guess the first step is to download the driver for keithley2000 http://sine.ni.com/apps/utf8/niid_web_display.model_page?p_model_id=248. I want to go step by step. Please give me the main key steps on how to proceed on this problem and i will then work in detail based on your directions.
How do i know that laptop is recognizing the meter and RS232 connection is sound? What are the next key steps i need to work on? Please give the directions.
Thanks

For fast reading, it is important not to use the MEAS? command, but READ followed by FETCH? (if I remember correctly). Normally these DMMs operate at 1 PLC (power line cycle -> 50/60 Hz), so you need to adjust the NPLC (number of power line cycles).
There is to options to work with the Keithley DMMs inside LabVIEW. You could use the LabVIEW drivers for the Keithley 2000, those can be found on ni.com and on the keithey homepage. Propably they only implement GPIB, the you need to make some modifications on them for RS232. The other option is to send the commands as found in the DMM manual via VISA.
Felix
www.aescusoft.de
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Acquiring AC voltage signal using NI 9206 9205 and cRIO

Hello. I am having difficulty accurately acquiring an AC voltage signal using a NI 9206 and cRIO. I'm attempting to acquire voltage signals from two types of Magnelab Current Transformers: split core and rope. In Labview, I first populate an array of size 2,500 with the sensor signal (DIFF mode), then compute the RMS of the array. For the split core CTs, I am able to accurately acquire the correct voltage reading (verified by measuring the corresponding amp on the line using a Fluke 434 Power Analyzer. For the rope CT, however, using the same array/RMS method, I am unable to accurately acquire the correct voltage reading. Measuring the amp on the line using the Fluke 434 PA, the correct voltage from the rope CT should be 0.05v. Using the 9206 (DIFF mode), the RMS from the array gives a voltage reading of 0.071. Now the interesting part is when I measure the line voltage using two different True RMS DMMs, I get two different readings. One multi-meter, a Klein CL2000, reads the correct voltage at 0.05v. Another multi-meter, a Fluke 189, reads incorrectly at 0.071, the same as I get using LabView and the NI 9206. I suppose the question is how is the Klein interpreting the signal differently than the Fluke 189 and the NI 9206 via LabView. One difference between the split-core and rope CTs is that the rope CTs require an external power supply 12-30v AC or DC. I am providing them with 12v DC. I have tried multiple voltages in both AC and DC and still get the same incorrect reading. I'm quite certain it is not a power supply issue, although perhaps the integrator in the rope is creating a unique signal. Any ideas? I appreciate any input.
Thanks,
J.Grant
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AK2DM:
Update - solution found
While the Butterworth low-pass filter sort of worked, it was NOT the solution. I spent some time analyzing the rope CT signals by sampling at a very high rate. The AC signal coming off the rope CTs is triangular NOT sinusoidal. The RMS function in LabView assumes a sinusoidal waveform and essentially calculates the RMS as the average of voltage peaks (for each cycle) / sq.rt (2). Since the AC voltage single emanating from a regular split-core CT is basically sinusoidal, the LabView RMS of the signal gives an accurate reading of the voltage signal. Unable to find a RMS function in LabView for a triangular AC voltage signal, I ended up developing my own custom triangular RMS function in LabView. My function analyzes the signal by finding the peak of every cycle within the signal, takes the average of these peaks, then divides this average peak by sq.rt (3). see this link for formulas:
http://www.optics.arizona.edu/nofziger/OPTI%20380B/Lab%201/AVG%20and%20RMS%20Values%20of%20Periodic%...
Using the triangular method, I am able to accurately acquire the signal off the rope CTs.
Thanks for your help!

Precise DC voltage measurement using NI9219

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