1520 measure voltage normalized?

I'm using 1520's to replace some old signal conditioning amplifiers in a wind tunnel. Our sensors include pressure transducers and load cells on a force balance. They act like strain gages in that they require an excitation voltage, and produce a small return voltage that needs to be gained up to acheive good resolution for the old A/D converter.
I've been able to hook up and read a pressure transducer with the new system, but am confused by the reading that I receive. I'm using the DAQmx system to run everything, and when I set the AI.GAIN parameter to a valid gain setting, it doesn't seem to do much. If I set the gain to a high value, like 100, it clips the signal that I'm reading. It seems like the signal is normalized to someth
ing, but I made sure not to use the excitation for scaling.
Any ideas on what is happening? Is the hardware already doing what I'm trying to manually do?
Thanks for any help!
-Warren

Warren,
I am glad to see you using DAQmx and I also was impressed with the code you attached. One thing that has become a little different with DAQmx is how gain and scaling is applied. The AI Config.VI is the traditional way to set the gain on a DAQ board, with this setup a user would set the input limits and then LabVIEW calculated the gain. In the case where you set the input limits to 0.01. LabVIEW would calculate the largest gain possible. It is worth noting for input limits you need a reasonable minimum and maximum value. You are using a powerful feature of DAQmx with the property node to programmatically set the AI.Gain. This is a good way to do things, 1.) If the DAQ board supports the gains you are using, 2.) If
you are not in another place resetting those gains by also providing input limits.
I looked through you code and noticed you have a DAQmx Create Channels VI with a minimum and maximum input not connected inside the DAQ Create Channels.vi. I see you are doing this so you can have less code for creating multiple channels. Also on the VI above you are setting both the gain and the Input limits and dividing by 100. I wonder if you just set the input limits what the response would be.
I hope this all clarifies a little about what is happening. I recommend using LabVIEW to set the gains by specifying input limits. I also would refer to the following KBs to clarify more about available gains.
Linked KB about Gain Settings
P.S. Another interesting fact I saw was that you are setting a lowpass filter. I wonder how this affects the application.
Regards,
Robert Jackson

Similar Messages

Programmed vs measured voltage on Keithley 2400 and other things

Hello everyone,
I have two issues with our Keithley 2400, which we control through Labview, and I would be very grateful for some help/advice. The issues are listed below:
1) We use the 2400 for 4-point probe measurements, so we plot graphs of current vs voltage to get the resistance from the slope of the curve. However, when we look up the data generated during a measurement, the voltage sweep values that we program often, but not always, do not match the measured voltage values. For example, what was meant to be 1 V, might actually end up being 1.2 V or maybe 0.8 V, this can be both positive and negative with respect to the programmed values and is not constant. This also leads to the fact that our curves, although straight (so Ohmic conductor), do not go through the (0, 0) point on the graph.
2) Second problem is that we would like to determine what is the time between successive measurements in a voltage sweep. We have tried some example vi files that by default come with the Labview, e.g. Keithley 24XX Read Multiple - SW Trigger or Keithley 24XX Read Multiple. If someone knew how to find the time separation, then we would be grateful. We only have control over the number of invididual readings taken and the timeout, which we guess is the maximum time allowed for the measurement.
Many thanks!

Good Afternoon PiotrW,
1. Could you please provide the code you are using to program the voltage sweeps?
2. You could use the timestamp output of the Keithley 24XX.lvlib:Read (Multiple Points).vi to allow you to find the time difference between successive samples. It should be a simple case of subtracting succesive measurements from each other to find the time difference between data points.
Regards,
Al
Regards,
Al C
National Instruments,
Application Engineer

Can the USB-9211 Thermocouple Input device measure voltages ?

Can the USB-9211 be used to measure voltages ? It is designed for thermocouple measurements and its operating manual states there is a current source between its TC+ and TC- input terminals.
What amount of current is flowing ? Does it depend on the selected thermocouple type ? Can the current level be controlled by sotware ?
One application for me is to measure resistances of 1 ohm or less by measuring the voltage drop across the resistance induced by flowing a current through it. Might the 92111's current source be somehow used for this ?
What is its peak to peak input noise ? Its specs say 1 uV rms.
This is a delta-sigma converter. Is each successive measurement accurate or does some digital filtering have to be account for and thus it takes several readings for a signal change to become accurate ?

The 9211 measures voltages between 0 and 80 mV only. The current source is only use to force a full scale input if an open thermocouple is connected and cannot be controlled by software. The input impedance of each channel between TC- and TC+ is 20M Ohm. However, the current that flows in the amplifier is very small, 50 nA.
The main problem here is the fact that the current source is not controlled by the user. This means that connecting a resistor of 1 Ohm between TC- and TC+ would not just produce a voltage that maybe due to external exitation, but the internal source should also be taken into account. Since the user has control over it, it would be a guess work to try to make sense of any voltage value read in.
its peak to peak input noise is 1 uV rms as indicated in the specs.
So as long as the measurements allow for enough settling time (12S/s), each one is accurate.

Trying to measure voltage through 1 wire connection

Hai ,
I am trying to measure voltage through 1 wire connection using NI hardwares like 1)chasis SCXI-1000 2) DMM PCI- 4060, 3) MUX SCXI-1127 and 4) Terminal Block SCXI-1331. Please see a attached picture of my set up.
I am unable to establish my connection through 1_WIRE_LO_REF .I want to use it as my reference point (GND) through which I can measure the voltage .I think there may be problem in my design or in the labview code.Could u please verify and suggest the appropriate one.
Can I use 1_wire_Lo_ref is so which port to be used, actually i have six ports for this point (or) is there any altenative
I hope u respond soon and in the affirmative
with regards
madhava
Attachments:
Scanning_of_SCXI-1127_48_write.vi ‏144 KB
IM0000041[1].jpg ‏722 KB
IM0000041[1]1.jpg ‏722 KB

Hi Madhava,
Are you unable to get the example program to work? Are you using an Aux cable to connect the switch to the DMM or are you triggering from the connector block of the switch?
One good resource is to open the NI-Switches Help from Start >> Programs >> National Instruments >> NI-Switch >> Documentation >> NI-Switches Help. Go to the Search tab and search for Single Module Scanning - Handshaking. There are sections for SCXI or PXI depending on which form factor you are using. This will explain which triggers to use and how to connect the DMM and Switch together.
In the same help file, if you search for Scan Lists, this will show you the proper syntax for the scan lists. The scan list can all be listed in one text box and does not have to be an array of strings.
I think the best way to proceed is to take the example that I showed you save it as a new program so you can go back to the original if you need, make it work and then modify it to do what you need. Add the write to file for example. If you have any questions about specific issues, I can help you with those.
Thank You,
Nick F.
Applications Engineer

Measuring voltage from thermocouples

How do i measure voltage from a thermocouple which is joined to another one. Meaning that they have a common point. I have tried reading in a voltage from 1 point and then subtracting it with the other but it does not give me the reading the multimeter is showing

Hello,
For troubleshooting bad readings, probably the first thing to do would be to check the board's configuration.
Is it configured in differential mode? Differential mode is the most recommended mode for thermocouple readings. When using differential mode, just make sure to connect the positive lead of the thermocouple to ACH0 (for example), and the negative to ACH8.
Once you have all the signals connected to your DAQ board, try running a MAX Test Panel. I usually run it using Continuous Mode. Before starting the acquisition, check the input limits in MAX, adjust them according to the input signal so that the board applies the appropriate gain.
Finally, create a Virtual Channel (by taking into consideration the thermocouple type). Are you re
ading the correct temperature? Is the CJC in your terminal block enabled? It's always easier to compare the temperature than the millivolts readings.
I hope these tips help. Good luck with your application!

How can i synchronize analog output and analog input timings to generate and measure voltage at the same time.

how can i synchronize analog output and analog input timings to generate and measure voltage at the same time.

Read this Tutorial
http://zone.ni.com/devzone/cda/tut/p/id/3615#toc3
And also refer to this link where You have repeated this question.
PS: Please stick to one thread. That way, its easier to keep track of your query and answers

Measuring voltage and temperature

Hallo,
I've got the problem of measuring voltage and temperature simultaneously, with diferent numbers of samples. I want to use two of the "DAQmx write", but then the error "The ressource is reserved" appears.
Software: Labview 8.2.
Hardware: NI cDAQ - 9172
NI 9211 (Temperaturecard)
NI 9201 (Voltagecard)
How can i fix it?
Attachments:
Fehler.JPG ‏89 KB
Fehlerbeispiel.vi ‏27 KB

Hello LochiMD,
there are sereral things you have to care about.
The best would be, you have a look on the following link:
Synchronize continuous Acquisition of Multiple Analog Input Devices
https://decibel.ni.com/content/docs/DOC-12182 (Have a look on the picture, especially left side)
You should use the VI DAQmx Timing (Sample Clock), samples per chanel and sample mode is necessary.
If you do this, your program should work.
Best Regards,
Nina

How to measure voltage?

Equipment used:
- Connector Block CB-68LPR
- DAQ Board NI6013
- VI Logger
- Pressure tranducer (runs on 5V)
What am I trying to do:
- Connect pressure tranducer to connector block, so I can display measured voltage in VI Logger.
What I have done:
- Pressure tranducer has got -Vin +Vin +Vout. I have connected +Vout to AI ch0 and -Vin to AI ch8 (differential).
- In VI Logger, I have created virtual channel that is reading Voltage (max 50V, min -50V).
The problem I have got:
- VI Logger is reading 5V all the time. The voltage should increase/decrease lineary as the pressure is increased/decreased
but it doesn't. It is always 5V that is not true. I have tested the device in the test panel and Vout (ch0.) is always 5V exact.
How
to solve this problem? What and how should I check, have I connected everything properly?
Thank you.
Regards Slav.

I had a similar problem. I changed the input from differential to single ended and it works. You need to connect your V- to Agnd. Unless there is a reason you need to read differential...thermocouples that I set up work fine in differential but there is no common ground to a voltage source.
Make sure you have set up the Virtual Instrument in MAX properly. Good luck.

Recording measured voltage and current values from LCR 4284A

Hello,
I want to use the labview VI to record the measured voltage and current values from LCR 4284A. These are shown as Vm and Im on the instrument screen. Is it possible to record these values using a VI?
I have looked through the drivers that are available through the "Instrument driver network" (Link) for 4284A but none of the VIs give any option to monitor Vm and Im. If you know how this can be done then I would really appreciate a reply.
Thanks
Mansoor

I haven't used the instrument but there are functions to enable/read voltage level and current level monitors. Are those different than what you are asking for? What does the manual say about Vm and Im and programatically getting them? If you can find the command in the manual, you can just open the VI Tree and do a text search for the command.

RSE mode measuring voltage

To whom it may concern:
I would like to post this question here so that it is easy to understand.
I would like to ask how 6250 measure the voltage using AI+ and AIGND. One of your collegue told me there is no current flowing to Rin if AIGND = Vs(0). I am trying to measure 100ohm resistor using AI+ and AIGND. I used DMM to measure from the top the resistor to AI+, the current was 0A and measure the current from the bottom of the resistor to AIGND. The current is 0A.
In fact, how 6250 measure voltage . If you put DMM instead of 6250, there is current going through DMM and you can show voltage. How about 6250. Could you please tell me?
I have attached a picture to let you understand what I mean. and where I got the information.
Here is the link
http://zone.ni.com/devzone/conceptd.nsf/webmain/D59654FA44D2F9FA86256F4A006064F3
Attachments:
First%20Picture.jpg ‏33 KB

Hello LochiMD,
there are sereral things you have to care about.
The best would be, you have a look on the following link:
Synchronize continuous Acquisition of Multiple Analog Input Devices
https://decibel.ni.com/content/docs/DOC-12182 (Have a look on the picture, especially left side)
You should use the VI DAQmx Timing (Sample Clock), samples per chanel and sample mode is necessary.
If you do this, your program should work.
Best Regards,
Nina

Measuring voltage with gpib board

I am using a NI AT-GPIB/TNT PnP board !! I am trying to use it to measure
voltage levels. Can i do this with out using an external instrument ??

Hi Daemon
GPIB boards are just for instrument communication only!!! They are certianly
in no way designed to measure voltages.
Tim
daemon wrote:
> I am using a NI AT-GPIB/TNT PnP board !! I am trying to use it to measure
> voltage levels. Can i do this with out using an external instrument ??

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

Trying to measure voltage through SCXI-1127/1331 1-wire connection

We have NI hardwares like: 1) Chasis SCXI-1000, 2) DMM PCI- 4060, 3) MUX SCXI-1127 and 4) Terminal Block SCXI-1331
We have a system with two large glass plates standing vertically and placed parallel to each other each having 24 electrodes on them. Distance between them is 4-5 inches. The plates are places in such a way that the electrodes are on the outer side and accessible to the user. We are trying to flow different liquids of different density through the channel in between. Please find attached a picture of it.
So a total of 48 electrodes and hence, wires are connected, 24 on both sides. On each side there are 3 rows with 8 electrodes/row, making a total of 24 wires. Wire#1-24 are on side A (say) and wire# 25-48 are on side B (the other side). The medium between the two sides will be salted water (say for now).
We want to measure potential/voltage in such a manner so that we can calculate the voltage difference between all possible electrode combinations between side A and side B. Like V1-25, V1-26, V1-27,...,V1-48,V2-25,V2-26,........,V24-48, all 24 X 24 possible combinations. We are connecting two end of a power source to side A and side B so that there is some current flowing in the water.
I have connected wire# 1-48 to 1-48 in SCXI 1331 (left out the zero to avoid confusion). Now that I'm measuring values through the program attached ("Scanning_....vi"), I can see that the first 16 values are showing some values of standards E-2. But from 17-48 are showing values of standard 5E-3 and I guess they are not taking any values at all. Can you tell me why this might be happenning?
Can 1-wire measurement be applied for this scenario. If not then let me know how to achieve our goal. I can manually take a Multimeter and measure all the combinations one by one, but measuring all the values at the same instance would be better and that only can be done by automation and I hope that the NI hardwares I have, should be sufficient to do that. Please let me know if it is otherwise.
Another thing, in one of my previous contact with NI someone mentioned connecting 1_WIRE_LO_REF. Is it needed in this case? If yes, then if I connect one end to 1_WIRE_LO_REF, where should I put the other end?
In case the program is wrong or more than 16 values can not be taken please let me know alternate path or show me how to make changes in the program. I would appreciate your help in this issue. Thank you.
Message Edited by ERT_LSU on 09-17-2007 12:16 PM
Attachments:
Scanning_of_SCXI-1127_48_write.vi ‏144 KB
IM0000021.jpg ‏767 KB
IM0000041.jpg ‏722 KB

I connected the COM of my power source to the 1_WIRE_LO_REF. There are 4-5 points to connect. I choose the middle slot. Is there any significance of assigning so many slots to 1_WIRE_LO_REF?
No change in result. Can you please test run the program I attached and see whether it's correct or not. You'll see 48 segments getting the output. First 16 of them are showing some seemingly proper values. rset are either too small or as big as 5 V.
I'm providing 5Vs from the power source. You might have seen the old analog ones. I'm using one of them. there are different Voltgae option. I'm using the 5V and so I've connected a wire from the 5V connection to one of the electrodes on B side (28th electrode) and the COM ports goes to the A side (4th electrode) and also to 1_WIRE_LO_REF.
Now I'm thinking if the program if not working. Because it seems that we are getting (seemingly) proper values for the first sixteen and something's messing up the values for the the rest of the electrodes.
Do I have to use two 24X1 MUXs i.e, use physically different boards and also two different programs to measure them? Or I can just use 1-24 as 24X1 and 25-48 as another 24X1 in the same board and measure them through the same program? Thanks in advance.
Message Edited by ERT_LSU on 09-17-2007 04:00 PM

Trying to measure voltage through SCXI-1127/1331 2-wire connection [ Edited ]

Hai ,
     this is madhava from LSU,I am working on ERT with NI hardwares like 1)chasis 1000 2) DMM PCI-4060 3) SCXI -1331(2 in number)
I have a system with two large glass plates standing vertically and placed parallel to the user.I am trying to flow different liquids of density through the channel in between.Please see a attached picture of it.
    There are total of 48 electrodes 24 on each side to which wires are connected. On each side there are 3 rows with 8 electrodes/row, say 1-24 on side A and 24-48 on side B. The medium between the two sides is salt water.
     I want to measure the potential in such a manner that I can calculate the voltage difference between all possible electrode combinations between side A and side B.I have connected a two end power source to side A and side B, i.e. +ve to side A and -Ve to side B , so   the electrode on the A side acts as the "source" and the electrode on the B side acts as "sink".
    I want to use 2 SCXI- 1331 's for this experiment.
    I tried it with 1 SCXI - 1331, but did not get proper values.So what do you suggest shall I continue this with the 1 wire or could you please help me with the two wire experiment, so that I can get more combinations.
           I hope you respond soon and in the affirmative.
With regards
Madhava
Attachments:
Scanning_of_SCXI-1331_48_write.vi ‏144 KB

Welcome to the discussion forums, Madhava!
The optimal solution is to have a 2x48 (or more) matrix so
that you could easily choose one point on either plate (column) connected to
one lead of the DMM (row0) and another point on the other DMM lead (row1).
Since the SCXI-1127 doesn’t support this configuration, you’ll have to try
something else with your existing hardware.
Because you can only use a multiplexer setup instead of a
matrix for your number of signals, the closest you can get to the above
suggestion is to measure one electrode to ground and then read the next
electrode to ground and include logic to find the difference between the two voltages.
I suggest you start with a LabVIEW shipping example (Help » Find Examples) such as niSwitch
DMM Switch Synchronous Scanning.vi or niSwitch
DMM Switch Handshaking.vi (found under Hardware
Input and Output » Modular Instruments » NI-SWITCH). You will have to modify
it to include another SCXI-1127 and set them both up in a 1-wire 64x1 multiplexer
topology. Take measurements as quickly to each other as possible on both
switches. Again, this is a workaround to what you really should be doing for
optimal performance (and the easiest setup).
The last option is to limit your measurements to electrodes
directly across from each other (or any other fixed mapping setup) and use a
2-wire 32x1 multiplexer topology. By nature, this is taking a differential
signal measurement between two constant points. This would allow you to easily
use LabVIEW’s shipping examples without modification.
I hope this helps you get a feel for your options and the
consequences of each.
Mark E.
Precision DC Product Support Engineer
National Instruments
Digital Multimeters (DMMs) and LCR Meters
Programmable Power Supplies and Source Measure Units

Best structure to measure voltage across 8 resistors in parallel via 8 separate analog channels

Im setting up a simple circuit w/ 8 resistors in parallel. It will be connected to a PCI 6036E DAQ. I need to measure the voltage across each resistor, take x amount of samples, and then automatically move on to the next resistor and so on and also save the values to a file. Im going to connect each resistor to a separate analog channel. I have already setup a vi to read the voltage across one resistor and take X amount of samples, display the waveform, and also save the data to a file.
What would the best structure be to run this test? I am thinking a Sequence structure, but it seems like people tend to avoid using that. Or would a case/while loop be better?
From my understanding, the data will not pass out of a sequence structure until it is finished. this doesnt seem to be that big of a problem for me, as I only want the data at the end....
thanks for the help!

Use a for loop. Put your code inside the loop, but delete the analog channel number. Make an array constant and poplulate the array with each analog channel number. If you wire the array to the loop (left side), you will see the terminal is a hollow box. This means indexing. The loop will operate on the first array element, then repeat with the second array element, and so on until all array elements have been processed. Wire the hollow box to the point in your code where the analog channel number was deleted. Now the loop will execute the same code using a different channel each time. If you wire the output to the right edge of the for loop, you will again see the hollow box. All of your measurements will be contained in an array at that hollow box. Process the outputs as you like, maybe display the entire array, or index the array to get the individual elements, whatever. The advantage of the for loop is that you have to write your code only once. Everything is seen on one screen making it easier to read. Sequence structures are not good programming practice because a lot of the code is hidden, and you have to go to different sequence frames to see the hidden code. Also, why duplicate the code in each frame when the loop will do it all. Good luck.
- tbob
Inventor of the WORM Global

1520 measure voltage normalized?

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