Measuring current on a Voltage Rail 10V

I am attemting to measure the current and voltage on a 15V power rail. (Here is a copy of my circuit attatched) I am using a USB-6225 DAQ and Lab View,
I have my device under test connected to a power supply. I have connected two differential channels to the DAQ, one for the current and one for the voltage.
I understand that the DAQ can not handle more than 10V so I use a voltage divider to half the voltage. When I run the measurements, the current reported is incorrect. It shows 10A when it should be about 500mA.
When I reduce the voltage on the power supply to 10V, it all works fine, so I am guessing its got something to do with the 10V limit.
Please can you advise how I can connect this up correctly?
Solved!
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Attachments:
DAQ Set Up.jpg ‏29 KB

R(Sense) should be within 10 volts of the DAQ chassis. Thats all the common mode rejection you are likely to have on a DAQ device. (But check your device specification sheet ---- don't trust me RTFM!)
if you do not have a common "Ground" between the DAQ device and the supply you are monitoring you will need an opto-coupler (But any first year EE student could tell you that)
As an Asside.: Who the hell ever started the convention of stuffing R (sense) on the + side of a circuit anyhow? Use a regulated supply with "Remote sensing" if you really care about the DUT power consumption.
Jeff

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How to measure current and voltage and rpm with daq device

i am measuring current and voltage and am wondering should i use shunt resistors or current sensors hall effect sensors. i have a pci 6221 and a scc-68 breakout box. what specifications or size should the shunt resistor/current sensor be or should i use another device to measure the currrent and voltage. do i need any other safety device between the resistors, current sensors and the scc-68 breakout box when measuring the current and voltage. will the daq card pci 6221 pick up a signal from the resistor. what terminals should the wires from the resistors and current sensors be connected to in the scc-68. i am using a proximity switch to measure rpm of a motor. should the proximity switch be 2 or 3wire connection. should it have an analog or digital connection and is a power supply required to power the proximity switch and should it have an npn or pnp connection

hello,
i was going to use a 20amp 50mv, or a 20amp 100mv current shunt and connect wires directly into the AI input terminals of the scc-68 from the current shunt would these be suitable. would current shunts such as these be suitable to use http://uk.farnell.com/elc/sh10020/shunt-sh10020-20a-100mv-1-class/dp/1319576 or http://uk.farnell.com/datel/3020-01098-0/shunt-50mv-20a/dp/1339338
is it ok to use either a current shunt or should a hall effect sensor be used such as this http://ie.farnell.com/honeywell-s-c/csla2cd/sensor-hall-effect/dp/1082269 . which of them would be more accurate or are both of them fairly accurate.
when i am measuring voltage can i connect two resistors between the positive and negative of the wires going to the battery and connect two wires from either side of the resistor directly into the analog inputs of the scc-68 and measure the 12-15 volts directly would the pci6221 and scc-68 be able to measure the voltage drop across the resistor.
i wanted to measure rpm also does it matter whether the proximity switch has 2 or 3 wires and should it have an analog or digital/frequency output for cponnecting to the scc-68

Measure current and voltage in Elvis and labview

Hi! We're setting up a control system setup for class where we need to monitor the current and voltage that we are supplying/drawing from the ELVIS hardware within a LABVIEW setup. So far, we can accurately display voltage input and outputs from the AI and DAO terminals respectively. However, we can't seem to find a direct way measure current draw. I believe that we are supposed to be able to get DMM readings from the AI5 channel, but either we're not doing it correctly, or we still need to place a known resistance across it (which we cannot do, due to variable loads). Any advise please?
Cheers,
Gerald

Are you using Elvis I or II? From your post, I will assume it is Elvis I but please correct me if this is not the case. Page 38 of the manual shows that ACH5 is used for capacitor or diode measurements for the DMM. To measure current, use the connectors on the front of the Elvis unit and then route the current HI/LO on the protoboard to either the oscilloscope or an analog input channel. You can use the DMM Soft Front Panel to monitor current as well.
Message Edited by h_baker on 07-09-2009 04:54 PM
Regards,
h_baker
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Digital Multimeter Resources

Voltage sweep and measure current for Keithley 2400

Dear All
Hello,
anybody can help me?
In spite of nearlly10 days i am searchig to find any labview 2010 program for voltage sweep and measure current that works with RS-232, i has not able finde anything exept some exapmle that read single and multiple data. I has tried to learm labview and changed some prorgram from gpib to RS-232 but i couldn't.
In another attempt i find a good "votltage sweep and measure current" VI that work with RS-232 in labview 5.1.1. i converted it to 2008 but it need to old driver (ke24xx.dll) and dont work in my labview 2010 and I could't find old driver.
in these 10 days, my project on thesis has been stopped and i couldn't do anything for our keithley.
Please helpe...
in following i attached these files:
1-first it is voltage sweep that works with GPIB
2-Vi that i change gpib port to visa (rs232) that i don't know why it dosen't work.
3-it is Vi related to "votltage sweep and measure current" that works with RS-232 but need to old dirver so i can not use it.
4-SubVi needed to run program of 3 (but there is no driver for these subVIs) has been atached in reply post of this post
if any body has this program ("votltage sweep and measure current" that work rs-232) please send for me
thanks in advances.
Solved!
Go to Solution.
Attachments:
24xx Swp-V Meas-I gpib.llb ‏373 KB
modifi- arash-24xx Swp-V Meas-I - VISA oNLY.llb ‏172 KB
I V new2.vi ‏103 KB

The first time you asked this exact same question, you were given the way to get the driver and told that one of the examples does exactly what you want to do. You have chosen to disreregard this and pursue other options for these close to 10 days. If your thesis is stalled, that is really your own fault for not listening to the answers you were given. I have no idea why you would do this but I would suggest you go back to the original thread, reread it. and if you want further help, explain what the problem with the NI driver is.

How to measure current

Hi:
We have a DAQmx (6024E) and we want to measure the current from a
flowmeter. When I tried to use the example program of LabView, I found
that the measured current is much different from the current we got from a voltagemeter directly.
Please help me to figure out HOW TO MEASURE CURRENT with NIDAQmx and LabView. Thanks
Message Edited by kuroshio on 07-11-2005 10:49 AM
Message Edited by kuroshio on 07-11-2005 10:55 AM

Hello kuroshio,
Current measurements are really just a voltage measurement with V=I*R applied. Have you tried first measuring a voltage and comparing that to the voltage from your voltmeter? You could measure the voltage a couple of ways. I would suggest first using the Measurement & Automation Explorer (MAX) test panels. Make sure your signal is connected to the correct pins and choose differential as the terminal configuration. Once you have a correct voltage measurement, then you can use a LabVIEW example from the example finder (Help>>Find Examples) to get started with a current measurement. In the example finder, you can navigate to Hardware Input and Output>>DAQmx>>Analog Measurements>>Current. There are a couple examples there for current measurements. You will have to enter the value of the resistor you are measuring the current through. Be sure to re-post if you still have problems
-Alan A.

How to separate the source and the measured current

Hi Everybody,
I'd like to know if there is some way to separate the source and the measured current and just writte an mathematical expression to make a dependence between the source and the said parameter. Thanks in advance.

Sure,
Here is the deal:
I'd like to build a circuit with dependent sources, but instead of connecting the sense of current/voltage, I'd like to know if there is a way to writte a sentence for the source which is dependent of a parameter.
For example:
In this circuit I just wrote an expression for the source and its respective parameter. (8*Io).
Attachments:
images.jpg ‏7 KB

To measure current in DAQ should we use rms value or DC avereage value

to measure current in DAQ should we use rms value or DC avereage value

i am taking measurement for single phase or 3 phase voltage and current and display it on front panel voltage measurement is valid but doinh with current measurement i suffer some problem should i take dc avg value or rms value for measurement
when i take dc average value it give result as i want but doing with rms valur it give wrong result according to my circuit sitution. As, we know in ac case rms value is used for measurement but it give wrong result so guide me in this regard
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Attachments:
Final pp self.vi ‏156 KB
Untitled.png ‏46 KB

How to measure current on DC servo motor.

Need to measure current on DC servo motor. What is the best way to measure the current on the motor as it moves to position? Using PXI-7344 controller and MID-7654 drive unit.

This is not an easy task. Here are some ideas:
Direct current measurement:
Add shunt resistors into the motor cabling and measure the voltage over the resistors. As the 7654 doesn't provide DC current but PWM current (32 kHz) you will have to acquire the data pretty fast (at least with 200 kHz). This could be done with a DAQ-board like the PCI-6220. Additionally you will have to do some math to calculate the RMS value of the current.
Control voltage measurement:
You could measure the output voltage of the 7344 as it is proportional to the duty cycle of the PWM current signal of the 7654. You will also need some additional measurement hardware but you wouldn't have to use shunt resistors and RMS calculations. The major disadvantage of this option is cabling as there is a single cable connection between the controller and the drive and you would have to use e. g. two external connector blocks and an additional cable in order to be able to connect your measurement hardware to the voltage output of the 7344.
Torque measurement:
Torque is also proportional to motor current so you could add a torque sensor to your motor and measure the output signal with e. g. a PCI-6220. Depending on your hardware setup this might be the best option.
I hope that helps,
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I want to do a remote lab for basic electronic lab. One of the task is to measure current and resistance. How to do it if I only have DAQ card and using Visual Basic 6 and Measurement Studio. Can anyone give me a clue.

If your DAQ device is supported by DAQmx, you can use it with VB6. Here's how: NI-DAQmx Support in Visual Basic 6.0.
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Keithley 2636 measures current and 2400 offers a 3 volt pulse synchronized in a labview program

Hello,
I am not very familiar with labview and I neet a program to realize keithley 2636 measuring current and 2400 offering a 3 volt pulse synchronized.
It means that when 2636 measure one times, 2400 give a pulse. When 2636 measure 100 times, 2400 offers 100 pulses synchronized.
The Channel A of 2636 is used for measuring and Channel B is used for another works.
The attatchment is the labview program I created and it can not be run synchronized.
Thanks for your help!
email:[email protected]
Attachments:
repeat04.vi ‏38 KB

Hi Lin,
I did not talk about a GPIB (or similar) cable to connect both devices with a PC, I did talk about the special cable for synchronizing both devices with each other called TriggerLink!
Please read the user manual of your K2400, (chapter 11 on triggers, or figure 1-2 for a view of the rear panel). It describes the TriggerLink capabilities of Keithley devices!
RTFM!
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
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Using 6052E card to measure current

Hi,
I am very new to implementing hardware with basic measurement in labview.
I have a PXI6052E card.
I believe it has AO of -+10 V.
Does anyone know where or how I can find examples of how to make a basic multimeter with the card?
I want to provide -10V and +10V with 0.04A to a circuit and the read the current for that circuit.
Is it possible?
Thanks
Best regards,
Krispiekream

Krispiekream,
Do you understand basic circuit theory?
The AO is a (weak) approximation to a voltage source. That means that it tries to produce the specified output voltage, regardless of the current bing drawn by the external circuit. The actual circuit cannot produce more than 5 mA without either deviating from the specified output voltage or possibly being damaged. The actual amount of current drawn is determined by Ohm's law and the external resistance. If the output is 10 V and the external resistance is 500000 ohms, then the current will be 10 uA.
However, as has been pointed out, the device has no method to measure its output current. One way you could measure the current through the external device would be to connect a resistor in series between the AO pin and the external device. Using an input of the AI part of the device, measure the voltage at the junction of the series resistor and the external device. The difference between the voltage programmed at the AO and the voltage measured divided by the resistance of the series resistor is the current flowing. From Ohm's law you can then determine the resistance of your external device. Make the series resistor larger than 2000 ohms and you cna be sure that a short circuit in the external device will not draw more than the speicified 5 mA from the AO.
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Analogue input voltages railing to +/-32768

Adam
Hi,
I recently bought a RIO-7833R PCI card and am having weird problems with it.
I would like to use it to measure analogue voltages. However, even when nothing is connected to the card, the analogue input channels are railing to +/- 32768. I've written a very simple program to measure these voltages and it’s hard to see how there could be a bug in this code (see attached image). So, I'm thinking it has to be something with the driver of the card or some other bug in LabVIEW, or perhaps a setting on the card that needs to be changed.
Complicating things is that I actually had another card that was doing the same thing that I returned. When they sent me this brand new card it also gave the same values, so I do not think it is a hardware problem with the card. In addition, I've also changed the computer the card was installed in, and again, I get the same values.
Has anybody seen this before? Could there be a bug in the labview driver? I've tried changing the setup of the card in MAX so that the measurements are "differential” or “single ended,” but this does not appear to solve the problem.
Thanks,
Attachments:
FPGA problem.jpg ‏170 KB

Hi Adam,
I understand you are getting some strange readings from the analogue inputs on your NI PCI-7833R.
From what you say I agree that it is unlikely to be a problem with your specific piece of hardware. I have had a search to see if there are any known hardware faults for this device fitting your description and didn't get any results.
I don't believe the driver will be creating a problem for such a simple task as long as you have the correct one for your hardware and OS installed. You can check that it shows up in the software section in MAX.
I would suggest then that you try using the known working analogue input project for your device in the LabVIEW example finder which can be found on the start up screen.
In the example finder Select the Browse tab>>>Open the hardware folder>>>R Series>>> Basic IO>>>Analogue Input - R Series.lvproj. This has the FPGA VI to deploy to your hardware and a test Host VI. See if you can then get the expected 0 input when unconnected and test with a signal input on the graph.
Hope this helps
Jack. W
Applications Engineer
National Instruments

6036e Daqcad AI voltage rails until device reset.

Hi,
I'm running a daq program (attached) which has some DIO, AI and AO in loop and readings on 2 of the Analog channels (#1&5) that are connected to load
cells, rail at one end of the range set.
A DMM attached reads the correct voltage of 2V. The strange thing is Max reads the right voltage only when the device has been reset after running the VI.
AI channels (#0&4) connect to a Force sensor that requires excitation turned on by digital writes. AI channel #1&5 are connected to the load cell in question.
I have tried 2 laptops, 2 daqcard-6036e on XP and driver 7.2 & 7.3 , same results. VI always rails. MAX rails only after VI is run and works fine.
I have decreased the sample rate to 1s hardware ti
med no effect. This programm is similar to the DAQmx example of Multi-channel PID control with some additinal digital-O & analog-I's added.
I looked at the KB's on AI Rails but they refer to the range and gain. I have tried a range of +-10V and still see railing.
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/6bcac575d4f3c98386256e8e0025d0c5?OpenDocument
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/d797b39b1088df2886256dd30058d9bf?OpenDocument
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Attachments:
tuned_pid.vi ‏336 KB

I think we can limit this to just your analog inputs.
First, do you know what mode your DAQ card is in for your analog inputs (differential, referenced single ended, nonreferenced single ended)?
Second, exactly how do you have your analog inputs wired (to what pins of your DAQ board)?
Here's why I ask. If you're using your DAQ board in differential mode, then for your first analog input, your positive goes to AI0 and negative goes to AI8. For the second analog input, it's AI1 (+) and AI9 (-), and so on.
If you have your (+) inputs going to AI0, AI1, etc but your (-)s going to AIGND, then you're set up for single ended mode, not differential, and your signals will probably rail.
It just might be that NI-DAQ is setting up your card for one typ
e of input, while your program is resetting it for a different type of input.
Mark

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

How to measure CompactRIO system input voltage

Hello,
I would like to measure the voltage of the two 9-35V DC inputs going to the CompactRIO RT controller. I am using the 4-slot chassis due to space considerations and do not have a 24V analog input module on-board to be able to do this via a module. On the 9205 analog input module there is a hook for "chassis temperature" that works perfectly. I am trying to find a similar hook to read the voltage that the CompactRIO is running on.
I will be running this CompactRIO on two 24V batteries and wanted to be able to detect when the battery levels were too low to continue operation. When this state is reached, or hopefully prior to, I want to offload the data I have collected before running out of power to do so.
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www.cimit.org

Hi Eric,
I am not an electrical engineer, so trying to figure out a clever way to split the voltage and measure it on three different inputs would be a job for one of the other researchers here. This seems like a straightforward feature though. We are using the CompactRIO as an onboard controller for a robot, but I would imagine that other more "mission-critical" applications would benefit from knowing the voltage that is powering the C-RIO. Much like the on-board chassis temperature reading, it seems like an important piece that is missing from the basic feature list. I don't know if we even have the 3 inputs free on the AI module as they are used to control everything else.
Hmm.
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Cambridge, MA
www.cimit.org

Measuring current on a Voltage Rail 10V

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