Measuring low current on myDAQ

The NI ELVISmx digital multimeter used with myDAQ only displays currents in the low milliamp range. Is there any way to measure lower currents (micoamp range)?
Thanks!

I will guess so. You should study how current measurement is done.
http://focus.ti.com/analog/docs/microsite.tsp?sectionId=560&tabId=2180&micrositeId=7&familyId=57
Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)

Similar Messages

Triggerring PXI-4110 to measure 1 current value while HSDIO PXI-6552 generating waveform

Hi,
Some question about PXI-4110 to measure current while PXI-6552 is generating the waveform.
1. Let say, I need to measure 3 points of current values, i.e. while PXI-6552 is generating sample-1000, 2000 and 3500. On the edge of sample 1000,2000 and 3500, the PXI-6552 will send a pulse via PFI line or via PXI backplane trigger line. My question is, is it possible to trigger PXI-4110 (hardware trigger or software trigger) to measure current values at these points ?
2. Let say I need to measure the current on 0ms (start of waveform generation by PXI-6552) , 1ms, 2ms, 3ms, 4ms... and so on for 1000 points of measurement, code diagram as shown at the figure below. It is possible for the VI "niDCPower Measure Multiple" to measure exactly at 1ms, 2ms, 3ms .. ? How much time will have to spend to complete acquire 1 point of measurement by "niDCPower Measure Multiple" ?
Thanks for viewing this post. Your advice on hardware used or software method is much appreciated. Thanks in advance.
Message Edited by engwei on 02-02-2009 04:24 AM
Attachments:
[email protected] ‏46 KB

Hi engwei,
1. Unfortunately, the 4110 does not support hardware triggering. Therefore you cannot implement direct triggering through the backplane or anything like that. However, there are a couple of possible workarounds you can try:
a) Use software triggering: Say your 6552 is generating in one while loop, and your 4110 is to measure in another while loop. You can use a software syncrhonization method like notifiers to send a notification to your 4110 loop when your 6552 has generated the desired sample. This method, however, will not be very deterministic because the delay between the trigger and the response depends on your processor speed and load. Therefore, if you have other applications running in the background (like antivirus) it will increase the delay.
b) Use hardware triggering on another device: If you have another device that supports hardware triggering (like maybe an M-series multifunction DAQ module), you can configure this device to be triggered by a signal from the 6552, perform a very quick task (like a very short finite acquisition) then immediately execute the DCPower VI to perform the measurement. The trigger can be configured to be re-triggerable for multiple usage. This will most likely have a smaller time delay then the first option, but there will still be a delay (the time it takes to perform the short finite acquisiton on the M-series). Please refer to the attached screenshot for an idea of how to implement this.
2. To make your 4110 measure at specific time intervals, you can use one of the methods discussed above. As for how long it will take to acquire 1 measurement point, you may find this link helpful: http://zone.ni.com/devzone/cda/tut/p/id/7034
This article is meant for the PXI-4130 but the 4110 has the same maximum sampling rate (3 kHz) and so the section discussing the speed should apply for both devices.
Under the Software Measurement Rate section, it is stated that the default behavior of the VI is to take an average of 10 samples. This corresponds to a maximum sampling rate of 300 samples/second. However, if you configure it to not do averaging (take only 1 sample) then the maximum rate of 3000 samples/second can be achieved.
It is also important to note that your program can only achieve this maximum sampling rate if your software loop takes less time to execute than the actual physical sampling. For example, if you want to sample at 3000 samples/second, that means that taking one sample takes 1/3000 seconds or 333 microseconds. If you software execution time is less than 333 microseconds, then you can achieve this maximum rate (because the speed is limited by the hardware, not the software). However, if your software takes more than 333 microseconds to execute, then the software loop time will define the maximum sampling rate you can get, which will be lower than 3000 samples/second.
I hope this answers your question.
Best regards,
Vern Yew
Applications Engineer, NI ASEAN
Best regards,
Vern Yew
Applications Engineer
Attachments:
untitled.JPG ‏18 KB

How does MID-7604 measure peak current?

What are the details about how the MID-7604 measures and regulates motor winding current?
We manufacture motion systems incorporating small step motors. One of our customers has ordered a motion system with the MID-7604. This is our first experience with the MID-7604.
When duplicating motor performance comparable to our other Step-motor Controllers, we must set the MID-7604 to 3X the motor's traditional rated peak current. For example, for a super-small MicroMo/Arsape Step motor, we traditionally limit the current to 250mA (RMS). However, with the MID-7604, we must raise the current limit to 700mA (peak) to achieve the same performance.
While we're not sure about the current regulation philosophy of our other Step-motor Controllers, the Step-motor Manufacturer's Specification Sheet limits the current to 250mA per phase with both phases energized to prevent overheating. Pumping in 700mA from the MID-7604 to achieve comparable performance just seems excessive. However, we're just playing with numbers here and not knowing what they mean. In the end, we're ignoring the numbers and instead, measuring motor torque and winding temperature in order to set the peak current switches on the MID-7604.
* How can we think of the current setting for the MID-7604?
* Is it not a PWM device that using width of voltage pulses to produce the current?
* What does "PEAK CURRENT" and "RMS CURRENT" mean?

Hey JThomas,
I'm sorry to hear that you smoked a stepper motor.There are a couple of reasons that your MID-7604 drive could appear to be operating strange.
There is a series of DIP switches on the front of the MID drive that allow you to set various things. One of those DIP switches is the current reduction switch. This switch is default in the ON position from the factory I believe so if it has never been turned off, chances are it's ON. When the Current Reduction switch is active, the stepper drive drops the current energizing the coils by 50% if there hasn't been a step in the last 500 ms. If you were gauging the strength of the drive based off of holding torque, then this could be the reason you were raising the current to a higher rating than you thought was neccesary. This settings is for customers who have an application with stepper motors that focus more on moving torque instead of holding torque.
Another possible reason for the increased current to match performance of your drives is if the bus voltage of your drives is some voltage other than 24 VDC. If your drives that you are used to using are say 36V drives, then at a lower current setting, they would provide greater torque at higher speeds because of the higher voltage being able to energize the coils faster.
Also, the KILL feature releases the axis from being actively driven. The HALT command simply locks the motor while leaving the coils energized to hold the position that it is currently in.
I hope some of this has helped you out. Let me know if I can elaborate on anything.
Thanks,
Evan D.
IMAQ/Vision R&D
National Instruments

How to measure a current signal with NI 6211?

How to measure a current signal with NI 6211?

Hi Clecio,
This is a charge accelerometer. It is different from the IEPE accelerometers that outputs a voltage signal.
You need a charge amplifier. Then according to the charge amplifier output we can select an appropriate module to measure the signal.
It is not possible to measure charge accelerometers with NI 9234 directly.
Best Regards,
Rodrigo Schneiater
Application Engineering
National Instruments Brazil
If this information was useful, please click in the 'KUDOS!' beside.

OBIEE Error[14041] Nested Aggregation measure are currently not supported

Hi,
Please provide workaround for the OBIEE Error[14041] Error in measure definiion. Nested aggregation measures are currently not supported.
I have two logical columns - Current YTD Invoice Quantity and Prior YTD Invoice Price. I want to create a column which is -
(Current YTD Invoice Quantity * Prior YTD Invoice Price)/ sum(Current YTD Invoice Quantity * Prior YTD Invoice Price)
sum in the denominator should be the sum of all rows returned by the report. So level based measures cannot be used as there are multiple report and dimension used may vary.
Columns Current YTD Invoice Quantity and Prior YTD Invoice Price are already aggregated to Sum.
If I try to do the sum on the physical column while creating logical column, the query is running for 6-7 hours and not giving any result. Both the columns belong to different alias table in physical layer.
Please let me know if you guys know any work around for this issue. Also let me know whether this type of nested aggregation are supported in 11g or not?
Thanks.

Hi Adil,
Yes, I did create a hierarchy for the time dimesion.
No, I was not able to specify the aggregate rule since the source of the logical column is another logical column
But the time hierarchy works for rows that is not based upon the SUM aggregate at the answers level.
Say I have 3 columns: Income,Expense, Bottom Line (formula : Income- Expense)
Income is created based upon a case statement in the Logical Column and
Expense is also created based upon a case statement in the Logical Column.
Income 1000 Rupees
Expense -300 Rupees
Bottom Line 700 Rupees (where the Bottom line is a row based upon the Answers aggregate formula
which is SUM(Income+Expense))
When I add a column year, I get the following output
Income 2009 500 Rs
Income 2008 500 Rs
Expense 2009 -150 Rs
Expense 2008 -150 Rs
Bottom Line 2009 700 Rs
Bottom Line 2008 700 Rs
The Bottom Line doesn't spread across the Year
Hope this helps you to understand what my problems is.
Thank you!

How to measure the current/power running through iMac

Hi
After I moved from my old house to my new appartment, my 24" late 2006 iMac instantly started making this annoying high pitch noise.
I've tracked it to coming from the area around the hard drive fan.
I believe there might be a problem with the ground connection in the electricity system in the building.
Is there a way to measure the current running through my dear iMac?
Thank you very much.
//Spaceranger
ps.: also see my previous post where I tried to figure out what might be the problem.

See here for the full tech specs of your machine:
http://support.apple.com/kb/SP28
You could connect a Volt/ Amp meter to the power outlet which will tell you what voltage/ current is being supplied, but you have to ensure the meter is set correctly or it could damage the meter being used.
I'd ask an electrician to come in and have a look at the supply. They're qualified and know what they're talking about and may be able to shed some light on the problem.

How can I measure a current continually after switching it to a DMM?

Whether a current could be measured continually after switching it to a DMM? How to write the scan list?
I tried many times and failed.
Thanks advance
小木虫

Hi 小木虫,
Ignore my first reply. I misunderstood your question and provided an example of how to create a "make before break" scan list entry. You do not need this for your application. I think "break before make" will suffice.
I now understand that you want to make multiple current measurements after creating a switch connection. The scan list entry you provided: r2->c0 & r3->c1; will create the connection required for the DMM to measure the current flowing between c0 and c1. However, the DMM will send a trigger back to the switch after making its first measurement.
One way to make multiple measurements is to create multiple connection entries in the scan list. Each scan list entry triggers the DMM to make one measurement. I don't like this idea much, as it will actuate the relay many times (once for each measurement).
Is hardware-timed operation necessary? If you used a switch software trigger, you could make the scan list connection (r2->c0 & r3->c1; ) and then begin a DMM multi-point acquisition. Once you've collected all the required current measurement samples, you could send another switch software trigger to continue with the next scan list entry.
Will this work?
Chad Erickson
Switch Product Support Engineer
NI - USA
Message Edited by Chad PSE on 02-20-2009 01:51 PM

How to measure high currents accurately (upto 24A) using FPGA

I need to measure high currents accurately. I have only a FPGA board and TBX 68 terminal block. Do I need any other NI hardware?

The answer will depend on your specific situation, such as the voltage levels you are working with, the source of the current, the influence some additional components such as a shunt resistor may have, etc. Can you provide more details about the application, the source of the current, the voltage levels, how quickly the current will change, the stimulus for a current change, etc.
The most common method to measure a current is to add a shunt resistor in the current loop and measure the voltage across the shunt to calculate the current based on the voltage and resistance. You would need to make sure the absolute voltage levels (relative to the ground of the FPGA board) do not exceed its specifications (+-10V). The value of the shunt will depend on the current and the accuracy you need in the measurement.
If you use a 5 milliohm shunt, then you will have a 0.12V drop across the shunt resistor at 24A. The 7831R has a relative accuracy of about 300uV, this would translate into a relative accuracy of about 61mA for a 5 milliohm shunt (absolute accuracy will be less). If you cannot tolerate a 0.12V drop at 24A, then you will have to use a smaller shunt resistor which will give youless accuracy in the current measurement.
The shunt resistor value will have to be precisely measured ahead of time using a good DMM and a 4-wire resistance measurement. There will be some error associated with this measurement. The resistance will also change due to self-heating as the current through it changes (0.12V * 24A = 2.88W) adding some non-linearity to the measurement.
This is probably the simplest approach. If this setup is not feasible (e.g. the voltage in not within the 7831R input range) then you will need some additional signal conditioning. There are some off-the-shelf components for measuring larger currents that would translate the current into a voltage that you can measure with the FPGA board. Look at the following component as a place to get started.
A closed loop current sensor like the following may work. It runs off a 5 V supply, and is relatively easy to wire up:
http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=102&M=SCD20PUN
Christian L
NI Consulting Services
Christian Loew, CLA
Principal Systems Engineer, National Instruments
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Measure ai (current) and ci (puls width) with NI6023 and DAQMX

Hi I need to measure ai (current) and ci (puls width) with NI6023 and DAQMX.
My problem is that I can measure the two by them selves.
But I need to measure both at the same time!
Is it possible?
How does the code look?
J;-)

Hello
DAQmx support multitasking operations and you are therefore able to execute multiple tasks at the same time.
I do not know what software you are writing your code in, but if you are using LabVIEW you should just place the two tasks in parrallel loops and execute them or have both VI's runninng at the same time that are performing the tasks!
Regards
Mohadjer

Measuring harmonic current

hi all
i'm currently working on my honours project and uni, and im starting to go round in circles, was hoping i could get pointed in the right direction.
i want to measure the harmonic currents and sub harmonic currents of an induction motor, using labview, via a DAQ. i can get the input current in numerical and graphical form, but im having problems with the distortion measurement block. i can get the THD as a numeric output, but not graphical, the same for when i set the block to output a specific harmonic. is it just not possible??? do i just have to go with the numbers??
i also used the harmonic analyser block, but it doesn't appear to be doing much at all!!!
my other ideas involve the spectral measurement block or using an fft block, from which i was gettting numerical outputs once again, but no graph.
if anyone has any suggestions as to what i should maybe look into it would be much appreciated!!!
thank you, louise

ive attached my project for you too lok at. it's not that i dont have a graph, i just that its not showing anything!!! i can get a dot when i go in and change the settings, but i would prefer a line. this may not be possible however.
thnk you , louise
Attachments:
splitsignal1.vi ‏263 KB

Method for measuring low value of RPM using counters

I need to measure frequency of low values,which is the best for obtaining a low value of RPM,the hardware used is NI-PXI 6602 card.

There are examples written for measuring the frequency of TTL signals. If you are using LabVIEW, you can search the data acquisition examples and you will find a separate folder for counters (...Program Files\National Instruments\LabVIEW\examples). There will be a NI-TIO.llb which will contain all examples you can use with the NI 6602. There is a Measure Frequency VI that will work for you. For text-based programming environments, there will be examples installed within the ...\Program Files\National Instruments\NI-DAQ\Examples directory. I hope this helps.
Regards,
Todd D.
Applications Engineer
National Instruments

What example would I use to measure emission current and leakage current (voltage vs. current)?

I need help on measuring current @ anode (emission) and leakage current @ (gate voltage).
Using gpib config.

I don't think you'll find any examples that suit, but that's life. It's rare
to find someone doing the same work with the same kit when more than one
instrument is involved.
Keithley should have examples for the electrometer that show you how to set
it up and take readings via the GPIB- that's the harder of the two
instruments because it does more. If they're not shipped, look on
www.keithley.com, since they have a large selection of example Labview
programs for their hardware- though I know nothing about that particular
instrument.
The power supply should be trivial; it should just have commands to set the
voltage (and current limit perhaps) and switch the output on and off. This
may be a good thing to learn to do GPIB programming on since there's
very
little involved. Check out the example
examples\Instr\smplgpib.llb\LabVIEW<->GPIB.vi to see how to send commands
and receive responses. Once you have a program that provides a sequence of
power supply voltages to your device, then start playing with the
electrometer examples and making something to read the current. Then put
them together and write a top level that builds a current/voltage plot for
the device.
I assume there's no problem with the physical connections and how to wire
the test device up to the instruments? That's out of the scope of this group
in any case.
m wrote in message
news:[email protected]..
> I am using the kiethly 619 electrometer and a bertan power supply.

Low current charge

My MacBook Air 1.1 will not charge at full power.
At the same time the hinges broke on my A1237 MBA the ability to charge went away. The MBA was sent in for repair og the hinges and to checked for the charging issue. Hinges was pepaired under the Apple policy at no charge, thanks. The battery and the MagSafe DC-In Board was replaced with no change as a result.
The next suggestion was to replace the Logic Board, here I said stop and asked for the battery and the DC-In to be put back into the computer and returned to me. To my luck the battery had already been returned to Apple and the DC-In could not be found. So I ended up with having the hinges repaired, the battery and the DC-In changed at zero cost.
So far so good.
But the charging problem is still the same. The computer sees if the charger is attached or not, changing from running on battery to no charge, there is no light on the connector, just a very fake green light, barely visible. In system information I can see that there is small charge of 90 mA.
The computer is running, no discharge if adaptor is connected (90 mA charge), the computer can charge an attached IPhone.
I have tried all the known reset options a number of times.
Is seems to me that charging circuit is playing tricks and have come into a sustain mode from where it will not go into full charge mode. There must be an alternative to having the logic board replaced at $4-600?
Any suggestions?

gpotts,
Thanks again, here's my battery profile: (keep in mind this is the 2nd hand battery I am profiling) BTW, something happened when I was doing this message, I left the notebook on for about 20 minutes, it dropped from +90% to 48%, macbook prompted me that the battery is running low. I plugged the adaptor and it went back to +95% within minutes...
Good thing is, I haven't seen the sudden drop to 0% ever since I removed Vista, and also I am able to charge my battery everytime I try now, no more "NOT CHARGING" or "X" indication.
Any clues??? Thanks in advance.
Battery Information:
Model Information:
Serial Number: DP-ASMB013-34cf-** <Edited by Moderator>
Manufacturer: DP
Device name: ASMB013
Pack Lot Code: 0001
PCB Lot Code: 0000
Firmware Version: 0102
Hardware Revision: 0300
Cell Revision: 0100
Charge Information:
Charge remaining (mAh): 1533
Fully charged: No
Charging: Yes
Full charge capacity (mAh): 1597
Health Information:
Cycle count: 349
Condition: Good
Battery Installed: Yes
Amperage (mA): 466
Voltage (mV): 12597
System Power Settings:
AC Power:
System Sleep Timer (Minutes): 60
Disk Sleep Timer (Minutes): 10
Display Sleep Timer (Minutes): 60
Automatic Restart On Power Loss: No
Wake On AC Change: No
Wake On Clamshell Open: Yes
Wake On LAN: Yes
Display Sleep Uses Dim: Yes
Battery Power:
System Sleep Timer (Minutes): 10
Disk Sleep Timer (Minutes): 10
Display Sleep Timer (Minutes): 2
Wake On AC Change: No
Wake On Clamshell Open: Yes
Display Sleep Uses Dim: Yes
Reduce Brightness: Yes
Hardware Configuration:
UPS Installed: No
AC Charger Information:
Connected: Yes
Charging: Yes

Measuring Low Frequencies with LabVIEW and FieldPoint Using [c]FP-CTR-500/502

I am trying to use this example in a LabView 8.0 and a Field Point FP-CTR-502 module but without any sensor I get frequency and period values.
Is that possible to use this example with LabView 8.0 or not?
I am trying to use an anemometer Campbel Scientific A100R.
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B45EACE3ED7556A4E034080020E74861&p_node=174404&p_source=External
Attachments:
Low_Frequency_Measurement_CTR_LV71.vi ‏193 KB

You can launch MAX from start\programs\National Instruments\Measurement & automation.
Concerning source signal wiring, you can have a look to the following link : http://zone.ni.com/devzone/conceptd.nsf/webmain/01F147E156A1BE15862568650057DF15?opendocument
Hope this helps,
Manuel R
AE dans une autre vie

Measure power/current being delivered by PXI-4110 on a specific channel?

I have a PXI-1033 chassi and inside it there's a PXI-4110. How do I use LabVIEW 8.2.1 to determine the power/current consumption on a specific output channel?

I have a PXI-1033 chassi and inside it there's a PXI-4110. How do I use LabVIEW 8.2.1 to determine the power/current consumption on a specific output channel?

Measuring low current on myDAQ

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