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!

Similar Messages

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.

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.
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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.

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.

Some wire connection problem for SCB-68 usage in measuring voltage

I am using FPGA 7831R along with SCB-68 to measure some voltage from my monitor terminal from my motor. When I measure the voltage between the monotor output and GND using a multi-meter the measurement is very reasonable and it can be changed when motor speed is changed. However, When I use FPGA input function to measure the monitor output(corresponding AI0 on SCB-68), the number displayed on the scope is always 10. The displayed value from GND is also 10(corresponding AI1 on SCB-68), so when I substract AI0 from AI1 the value is zero. Did I do something wrong in wire connection.
Should I connect the AIGND terminal to somewhere or leaving it floating.

Hi shuishen1983,
What are the connections that you have made for this measurement? What kind of signal is it? Are you trying to do a differential or single-ended measurement? In either case, you should have a look at this wiring guide.
Jared S.
Applications Engineering
National Instruments

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

Bad readback voltage from SCXI 1331 / 1127 /1000

I am using SCXI 1000 with 1127 with1331 in our application with the 2 wire configuration. My application is to read and log all the cell voltages(31 cells) and during the application i am not able to get the correct read back voltages for the cells between cell 17 to cell 31. When i did the root cause analysis i found grounding any polarity of any cells which results me to get the bad read back voltage from cell 17 to cell 31 and all the cells were around 2.3 V.
-Karthick

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 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

Problems on measuring temperature using thermocouples connected to SCB-68 terminal block

I have problems on measuring temperature using thermocouples connected to SCB-68 terminal block.The thermocouples were connected to the differential channel 1 and a return path for the instrumentation amplifier bias currents and a 4 Hz low pass filter were both developed. But the readings were floating and jumped randomly between 0 and 200 Deg Cel abnormally.The CJC on the terminal block was disabled and a new one was developed by myself. However, the readings for the CJC were accurate and quite stable. So what is the reason for the floating of thermocouple readings? Did I miss anything that I need to do? Thanks.

Are your TCs floating or grounded? Basically, if your TCs are mounted to a metal test article and the object is grounded to earth, then, the TCs are grounded -- and very likely contaminated with ground loops. You will need to reference the TC inputs accordingly. These ground loops will cause the TC data readings to float - recall that TC readings are in the millivolt level. It does not take much of a ground loop to ruin a TC measurement.
Also, try this... first, set the filter to 10KHz and sample for a few seconds at 20 KHz (take 32768 data points). Now subtract the mean value from the trace and perform an FFT on the data. Look for the dominant frequency. Is it 60 Hz or some multiple? If yes, the likely cause is a ground reference problem.

I'm reading a negative voltage from an analyzer and it should be positive.

I have a carbon dioxide analyzer connected to a SCB 36 board. I'm reading a negative voltage in the Measurement and Automation Wizard that I can't seem to troubleshoot. THe wires from the analyzer are connected in ACH2 and ACH10 with resistors bridging ACH2 and ACH10, as well as ACH10 and AIGND. This is a differential mode set up, right? I can't figure out what could be causing this problem.
Also, the negative reading does not scale when I change the reading on the analyzer. Our oxygen analyzer connected to the same board (ACH1 and ACH9) is set up exactly the same way and it's working fine. I'm thinking its a hardware problem but could be the DAQ channel, the analyzer, or the DAQ card (PCMCIA 6024E).
I'm planning on obtaining a voltmeter so that I can test the voltage from the analyzer but beyond that, could anyone give some troubleshooting tips?
Thank You,
Seung Yoo

Try measuring a truly floating source such as a 1.5V battery.
Is the analyzer's output floating or ground referenced? Is the polarity of the wires correct.
Try connecting the oxygen to the channel in question and see if results are as expected.
Good luck
~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~

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.
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Best Regards,
Nina

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Looks like this is a bit of an issue for some other users of your RAM and not necessarily a MSI thing! This user has a ASUS board! Good luck and hope you get it sorted out.
Backround:
I bought some DDR3-1333 ram that was advertised as 6-6-6-20 @ 1.8v and, as expected, running on my board's default 1.5v it was only getting like 9-9-9-24. In fact, @ stock voltage the best I could boot up with (unknown stability) was 9-7-7. In an attempt to get the best (advertised?) performance I went ahead and manually set the timings to 6-6-6-20, left all other timings on auto, and upped the voltage to 1.8v
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Is running at 1.8v going to hurt something? (See my setup MB, and CPU stats)
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Edited by: Legionarius on Sep 15, 2011 3:56 PM
Edited by: Legionarius on Sep 15, 2011 3:57 PM

Measuring voltage from thermocouples

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