Differential Measurement Of My UUT

Hi,
I having problem using PCI-6025E for differential measurement on my UUT (an audio product, BTL output).
I had switch to differential mode in MAX. Measurement connection positive (ACH0), negative (ACH8).
I able to get the RMS value and freq of the measurement however the waveform is not uniform (unable to get beautiful sinewave).
When I use Scope to measure the UUT output, I able to get uniform sinewave.
I also tried to replaced the DAQ board however in vain.
May I know what can be wrong in my measurement?
Thank you in advance.........
Best Regards,
Norman

You might get better answeres in the Multifunction DAQ forum . The feedback forum is for site issues. Good luck!
LabVIEW Champion . Do more with less code and in less time .

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Problem with Non Reference Single ended and Differential measurements

The following was misposted at the Real-Time DAQ category and should appear in this Multifunction DAQ category:
I am doing a differential measurement and then a non referenced single ended AI measurement using the same PCI 6025E card. Most of the time I get good measurements however a small percentage of the time I get very strange measurements.

Make sure that you have set up each of your channels for the appropriate mode of measurement. By default, Measurement & Automation Explorer (MAX) has a property set for your card, either differential, nonreferenced singled ended, or referenced single ended. If all your channels are in one mode, then you can just left those defaults stay. Otherwise, as in your case, you would need to programmatically set each channel for the right mode.
For instance, in LabVIEW, the AI Configure.vi has an input parameter for "coupling and input config". This is an array of data that includes the measurement mode. Each element of the array corresponds to the element in the channels array, so you can configure each channel appropriately. Make sure that you have this set up in yo
ur program, and you should get the correct measurements.
Finally, double-check your physical connections to see that they match the measurement mode you chose. You can find this in the 6023E/6024E/6025E User Manual or the PCI E Series User Manual at the http://www.ni.com/manuals website.
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Geneva L.
Applications Engineer
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http://www.ni.com/ask

Differential measurements with a DAQ-500 card

I can't put the differential measurement mode in the Measurement & Automation Explorer. I'm using a DAQ-500 card of NI. Is this because my card doesn't support such measurement mode? There are no jumpers on the card for such a configuration...
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Hello Nicolas,
Thank you for your question regarding a DAQ-500 card. It sounds like you're having problems getting the card to operate in differential mode. Is your device perhaps a PCMCIA DAQCard-500? If so you should be able to use four analog differential inputs. Where is the problem occurring in MAX? Can you right click on the DAQCard-500 in Traditional DAQ Devices >> properties >> AI and then go to mode and select Differential there? If the device is indeed the DAQCard-500 shown here and the problem hasn�t been solved you may want to try to reinstall the card.
Other resources can be found on the ni.com website by clicking the support tab at the top of the home page. Then search from Technical
Resources at the top of the page for your topic. I hope these resources help! Let me know if you need any other support with this issue.
Shea C.
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CRIO NI9205 current shunt differential measurement

Trying to make differential measurement of the voltage drop of a low side current shunt to monitor battery current.
The battery is isolated from the cRIO NI9205 measurement common. Is it necessary to add a 100k resistor to common to ensure that my common mode is within spec's.
What measurement accuracy would you expect if a 0.2% shunt resistor was used ?
Attachments:
currentShunt_a.jpg ‏14 KB

Some remarks to the accuracy:
Tempco of the shunt? The current will heat up the resistor and the value will change ....
The absolute value of your shunt can measured by a calibration...
I hope you use 4 wire technique
If you are not only measuring a DC current the impedance of the shunt is important. ( inductivity and capacity ... yes even a shunt can have a resonant frequency )
Usually the datasheet of the shunt will give you an answer.
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'

Differential Measurements with AI-10X

Is it possible to make measurement in differential mode on FP-A10X, using two channels to achieve this (like on E series Cards)? I saw that it's possible with dualchannel modules, but I need to measure [0-40V] signals...and dual chanels module can't...

The only way to get differential measurments on non-differential FieldPoint modules is to use a single channel per module.
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Which terminals of PCI-6221 (68-PIN) to connect for DIFFERENTIAL measurements?

Hi!
I would like to do some differential measurements with a PCI 6221
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Hello surfaces:
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AI0+ pin68
AI0- pin34
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AI3+ pin30
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AI4- pin61
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MAX differential measurement does not match DAQ Assistant output

I am using a USB Compact DAQ AI 9205 and have a differential input running into AI23 and AI31.The signal is run to the AI module with a shielded twisted pair cable.
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When measured using DAQ Assistant in the VI, the output shows -.5 volts.
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Metzler:
If only one channel is returning erroneous values, it may be possible that there is a malfunction in hardware. In order to confirm/eliminate the possibility, could you test the suspect input with one of the shipping DAQmx examples?
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Question in reading differential measurement

Hi,
I am a new user in Labview and DAQ. I am trying to read pressure data from a Dynisco PT160 pressure transducer (Output vdc: 0 - 10V, 16-32 vdc excitation) via a USB6009. I tried to connect the positive and negative output from the transducer to AI 0+ and AI 0- of the USB6009 (Differential mode), respectively. I set up AI 0+ as differential input in labview. However, the reading of AI 0+ in labview is incorrect even after I did proper scaling and connected a pair of resistors to ground for bias currents. Then, I tried to connect the positive and negative output to AI 0 and GND, respectively (Single-Ended Mode) and the reading in labview is correct. However, the reading is noisy, which I somewhat expected after reading the "Field Wiring and Noise Considerations for Analog Signals" document. I want to know if I have done something incorrectly when I was using the differential/RSE mode? Also, any other advice in pressure reading will be greatly appreciated.
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Regards,
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Help, I need to measure from multiple UUT with independent timers.

Hello, I want to set up 20 independent test all controlled from one VI. I want to have the information feed back to the main VI in real time. I also want to have each test on its own timer with separate start and stop.
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Attachments:
Discharge Test.vi ‏16 KB
Discharge SubVI.vi ‏67 KB

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Can I measure 2 differential channels on a single SCC-SG24?

I am trying to use a single SCC-SG24 module to excite and measure the
output of 2 pressure transducers. The module is installed in the
ACh2 position of an SC-2345 carrier. When I configure the module
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configure the SCC-SG24 to measure 2 differential channels on a single
SCC-SG24? Thanks.

Hi,
I did a little looking into the DataSheet
for SCC Modules, and I found the following schematic.
As you can see there 2 instrumentation amplifiers that make it to where your measurements
are really differential, and then mapped to the NRSE lines in the
SC-2345. If you were to set up the DAQ board for differential it would
simply read the difference between one pressure transducer and the next.
Long story short, you set up the DAQ board for NRSE for all of the channels,
the SCC-SG24 makes it to where you are really taking a differential
measurement. Everything works quite simply in the end.
Regards,
Message Edited by Otis on 10-11-2005 12:56 PM
Otis
Training and Certification
Product Support Engineer
National Instruments
Attachments:
728815-SCC-SG24_Channels.GIF ‏10 KB

Parallel and Synchronized Multi UUT's Test

Hi,
We have more than 150 tests should be applied to verify our product and we have big quantity to be tested in short period.
For this purpose I decided to test 4 UUT's at a time using suitable configuration. I have heart that Test Stand can meet the requirements and I have red TS help (batch & parallel test) but I get confused since I'm not expert in TS.
To make it clear I have:
*4 DMMs
* 4 set of switches and relays to apply 4 tests at a time.
* shared sources (AC PSU, DC PSU, FGen) that can feed 4 UUT at time.
What I'm looking for is:
Is it possible to apply 4 tests at a time using TS? (I think yes)
Since I have shared power sources, can I synchronize all the UUT's to be at the same step? (I mean all 4 UUT's should start step1 and wait till all finishes step 1 to start step 2.)
When any UUT3 fail, UUT3 test stops and other tests should complete the whole sequence.
I have already developed TS sequence that call group of sub-vi's to test single UUT at time.
Knowing the previous points what is the right way to apply my test?
Help me please.
Thanks

Thank you very much Andy for you supports.
Your information is very helpful and it encourages me to deeply go through Test Stand.
I would like to clarify the image here.
·         4 UUT to be tested at the same time.
·         The test contains many main steps which include group of measuring points.
·         Every main step consist of Two stages:
o        1st: setup and powering stage. (Shared for all 4 UUT)
o        2nd: Measurements stage. (each UUT has its own DMM and group of switches)
·         The powering stage should be implemented at the beginning of each main step ones for all UUT.
·         The measuring stage will be implemented for each UUT and for each measuring point till main stage terminate.
·         When all UUT terminate the First main step, new main step starts with new setup and powering stage.
  Could you please advice me what to do?
Thanks & Regards

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.
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Modular Instruments Product Marketing Engineer
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9205 differential voltage wiring

I am using a NI 9205 to measure differential Voltage.
I am a bit confused on the wiring. It appears that the wiring diagram shows that all low side signals ( -) should be tied to common which is tied to ground.
It seems if I do this, then I am not truly measuring a differential voltage, but RSE voltage.
I have read the manual and the NI field wiring tutorials, so please don't point me there, or post a picture, I am fully aware of what they look like, and still don't understand
them as well as I want.
Thanks for any help.

Where COM should be tied depends on the voltages that you plan on measuring.
There are several relevant voltage limits for the NI 9205 to consider:
Measurement Range:±10V max
The module can only measure a signal that is a maximum of 10V between the negative terminal and the positive terminal. The negative terminal in this case is either AI - for differential measurements, AI Sense for NRSE measurements or COM for RSE measurements. This is the range that the device can actually measure signals
Maximum Channel to Channel Voltage±30V max between any channel and COM
No channel (AI, DI, or PFI) should be more than 30V from the COM terminal. Any more than this and the module may be damaged.
Maximum Channel-to-earth Voltage±60VDC (±250Vrms for the Spring Terminal version)
This is the maximum potential that can be sustained between the COM terminal (or any other terminal) and chassis ground before the isolation barrier is damaged. The isolation barrier can withstand higher for short periods of time, but nothing over this value should be sustained.
So, the answer to your question depends on the voltages you are measuring. If all of the signals that you are measuring will be withing ±10V of earth ground, the easiest solution is just to tie COM to the chassis ground lug. If the voltages need to be between 10V and 30V from earth ground, you are certain they won't float out of this range, and you are measuring differentially then you can again tie COM to chassis ground as well. If the voltages must exceed 30V from ground, you'll need to tie COM to something that ensures that all of the three above conditions are met.
For example, if you are measuring signals that vary from 40V to 60V, you'd tie COM to a 30V power supply to ensure that it stays withing 60V of earth ground and within 30V of the highest signal (if you are measuring differentially or NRSE). If you were measuring in RSE mode, you'd tie COM to a 50V power supply to keep it within 10V of each AI measurement.
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Seth B.
Staff Test Engineer | National Instruments
Certified LabVIEW Developer
Certified TestStand Developer
“Engineers like to solve problems. If there are no problems handily available, they will create their own problems.”- Scott Adams

SMU as Ammeter to Measure Current

I would like to do something similar to what is discussed in the following thread using multiple channels of a PXI-4141 4-channel SMU:
http://forums.ni.com/t5/Digital-Multimeters-DMMs-and/SMU-used-for-current-measurement/td-p/1297856
I would like to understand the statement in the final post of that thread regarding burden voltage/shunt resistance. In my application, it is critical that I compensate for the presence of a shunt resistor when I take a current measurement. How do I determine what the effective shunt resistance or the effective burden voltage might be when using the current-measurement capabilities of the SMU?
Thanks!
Jeff
Jeffrey Zola

Hey Jeff,
Thanks for sharing the diagram with us. I think I understand this much better now. The pinouts for the front-end connector do have separate paths for each Lo but the 414x SMUs have these all these connected together internally. The Sense LO leads however are separated out per channel allowing for differential measurement remotely thru the sense leads.
Regarding the voltage drop when using the SMU, there are a combination of factors (some already discussed) that will affect how much voltage drop will be seen in the system overall, including:
1. Thermal EMF
The thermal EMF for the 2530 is spec'd at < 50 uV in 1-wire mode, however this should be less in 2-wire mode as the much of the EMF from one wire is cancelled out by the other wire. Did you have a chance to look at the thermal EMFs in the matrix configuration yet? I would expect this to be much smaller than 50 uV but if you have some measurements, please feel free to share them with us.
2. I*R drops in cabling and switches
The resistance from channel to column is spec'd at <2 ohms. Since the SMU would be taking up two columns, I would double the resistance to 4 and then conservatively estimate the total wire resistance to be 6 ohms, giving us a total of 10 ohms, conservatively. At 10 uA, we have the potential of 100 uV of voltage drop.
3. Offset output/measurement accuracy of SMU itself
For the 4141, this is spec'd at +/- 600 uV when self-cal has been performed in the last 24 hours, and the temperature hasn't changed more than +/- 5 C from self-cal; the 4140 is spec'd at +/- 5 mV when using the same time and temperature conditions. The 4141 only, has a +/- 1 degree spec of +/-150 uV, which is the offset accuracy I mentioned in my previous post. You can look at the section titled, Voltage Programming and Measurements Accuracy/Resolution in the spec for more information there.
4, SMU voltage load regulation
Voltage load regulation tells us how much the output voltage will change based on the output current of the SMU when in local sense. The spec for the 4140/4141 is 10 uV per mA of output current, so therefore, this is negligible when we're talking 10 uA or less (< ~100 nV)
Based on these numbers I provided above, we're looking at a conservative estimated system burden voltage upward of +/-300uV for the 4141 and +/- 5.15 mV for the 4140 when sourcing 10 uA. I'd expect these numbers to be much less but this is just a first-pass estimate.
Keep in mind that the offset voltage (#3) will be the smallest right after performing self-cal, so a smaller offset error can be assumed if performing self-cal more frequently than 24 hours.
To reduce the voltage drop created by #2 and #4, you can use remote sense to compensate out the voltage drop in your wires, switches and the resistance internal to the SMU itself. This of course would require 2 extra columns and 2x number of rows to route the extra signal paths. What is the expected voltage across your DUT? Sometimes it's useful to look at the ratio of the burden voltage to the DUT voltage so see how great of an impact the burden voltage will have on the overall performance.
Do you have a target for the overall burden voltage you would like to hit? Is 300 uV or 5.15 mV too large for your application? Generally, burden voltages on DMMs will be on the order of 100 mV to 1 V, so an SMU will definitely give you an advantage in that regard. Also, another feature on the 4141 only that may be useful for your application, is that you can have a programmable output resistance. I'm not sure if this would work for your application, but I saw that you were using dummy resistors to simulate the shunt and the 4141 may be able to simplify this for you. Perhaps you could cut your column count in half by reprogramming the output resistance from 0 ohms to x ohms? Just a thought but, wanted to share with you just in case.
Let us know what you find and we'd be happy to help.
Thanks!
Brandon G
National Instruments
Precision DC Hardware Engineer

PXIe-6363 Voltage Measurements

Hi Guys,
First post here. I tried to search the documentation first but came up empty.
I'm using the analog inputs on the 6363 card to make some voltage measurements. I have 2 questions:
I know the channels are limited to +/- 10 volts for the inputs. I have a 25 volt line with a series current sense resistor (50mOhm). I want to make a differential measurement across the resistor using 2 of the analog channels. The actual voltage across the two points will be in the mV range but the single ended voltageon each will be ~25 V. Will this work?
In a similar setup but on a 5 volt line can I make a differential measurement across a current sense resistor using 2 of the channels and then turn around and use one of those same channels to make a single ended measurement wrt gnd?
Thanks for your help!
Solved!
Go to Solution.

There is a line in the data sheet that states
Maximum working voltage for analog inputs (signal + common mode)
±11 V of AI GND
So with a common mode voltage of 25V, you will hurt your card. The 5V line should be fine.
If you look at Digikey, there are chips specifically made to sense a current shunt. The amplifiers will turn the differential voltage into a single ended relative to ground.
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Differential Measurement Of My UUT

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