Turning IEPE OFF (DC Coupling Mode)

[AT12]

Attached, is a picture of my old DAQ Assistant, as you can see DC Coupling, there is 2.2 V Offset.

The "Current" channel is Voltage I just re-named it to "Current". If I set-up a channel as Current it says that it doesn't support this kind of device. So the channel is the Voltage type.

Kind regards,

AT12

[ShalimarA]

Hi AT12,

I have some advice...

Instead of implementing the gain like you have done, I recommend that you use the custom scaling feature built in to the DAQ Assistant. This will cause your VI to be clearer and will give you your scaling in the manner that you would like it to be. 

The 4431 is not a device that supports current measurements, as you can see from the message given to you from the DAQ Assistant. You should be reading Voltage. But if what you want is to read a current signal, you should edit your DAQ Assistant so that it reads in voltage from AI0 and use the custom scaling tools. 

At the moment I still have not been able to replicate what you are seeing, as I do not have all your hardware. 

[ShalimarA]

Furthermore, it is disconcerting that you did not receive an error when you left your previous DAQmx functions unwired. You should rewire your error wires so that you start with an Error In control, instead of branching the signal error from the Obtain Queue VI. 

Also, have you looked at the Producer/Consumer design pattern? It seems you are using somewhat similar functionality and I'm interested to know whether this was based off of the design pattern, if not, I recommend you take a look at it. You can find it by going to Create New -> From Template -> Design Pattern -> Producer/Consumer Design Pattern (Data)

[AT12]

Hi Shalimar,

I am measuring Voltage as you can see by the subvi that I changed for the DAQ Assistant. The word "Current" in the old DAQ Assistant was simply a renaming of the channel that I did, but it is based on a Voltage channel (it wouldn't work otherwise!).

Instead of implementing the gain like you have done, I recommend that you use the custom scaling feature built in to the DAQ Assistant. This will cause your VI to be clearer and will give you your scaling in the manner that you would like it to be.

- Why is this? It works fine as it is - I need to manually change the gain for my experiments.

You can see from the image I sent that there is an actual 2.2 V offset.

This is a very frustrating issue for me as it limits what I can measure with the set-up, is there anything else I can do or if you could suggest someone that could fix this for me I'd be very grateful?

Kind regards,

AT12.

[AT12]

Hello again,

Furthermore, it is disconcerting that you did not receive an error when you left your previous DAQmx functions unwired. You should rewire your error wires so that you start with an Error In control, instead of branching the signal error from the Obtain Queue VI. 

Also, have you looked at the Producer/Consumer design pattern? It seems you are using somewhat similar functionality and I'm interested to know whether this was based off of the design pattern, if not, I recommend you take a look at it. You can find it by going to Create New -> From Template -> Design Pattern -> Producer/Consumer Design Pattern (Data)

The P/C design was built through advice from this forum.

I don't see how these issues are helping me in "Turning IEPE OFF (DC Coupling Mode)"?

Unfortunately, I don't have the time to look into things that are not causing me any problems, although I wish I could tidy things up nicely. There must be a way of turning the IEPE off so as the AI0 stops giving out 2.2 V DC?

Kind regards,

AT12

[AT12]

Furthermore, it is disconcerting that you did not receive an error when you left your previous DAQmx functions unwired. You should rewire your error wires so that you start with an Error In control, instead of branching the signal error from the Obtain Queue VI. 

Also, have you looked at the Producer/Consumer design pattern? It seems you are using somewhat similar functionality and I'm interested to know whether this was based off of the design pattern, if not, I recommend you take a look at it. You can find it by going to Create New -> From Template -> Design Pattern -> Producer/Consumer Design Pattern (Data)

The P/C design was built through advice from this forum.

I don't see how these issues are helping me in "Turning IEPE OFF (DC Coupling Mode)"?

Unfortunately, I don't have the time to look into things that are not causing me any problems, although I wish I could tidy things up nicely. There must be a way of turning the IEPE off so as the AI0 stops giving out 2.2 V DC?

Kind regards,

AT12

[ShalimarA]

Would you mind testing the channel in MAX? You can do test panels here as well as switching the IEPE off. If you could try this and let me know whether you still see the offset, that would be helpful. Could also let me know whether switching the IEPE off and on again in MAX causes any difference?

You can do this by going to the 4431 device in MAX under Devices and Interfaces and clicking 'Test Panels'. Then, select the channel in question and start the test. There is a tick box where you can enable and disable IEPE. 

[AT12]

Hi Shalimar,

Yes, no problem. I'll go and have a try at that for you.

I'll be in touch later,

AT12.

[AT12]

Hi,

Attached are images where the IEPE was off and then enabled in DC Coupling Mode.

I recorded the offset with the multimeter:

No tick = 2.28 V

Tick Enable = 23.35 V

I turned this back off and on again to the same result.

Thanks,

AT12

[ShalimarA]

Seeing as you're getting the same results in MAX as you were in your VI, it's clear that there isn't a problem with your VI, the issue is with the hardware. 

How have you connected your hardware? The 4431 uses differential connections and you need to ensure that your signal is properly grounded, as this may be causing the issue. 

[AT12]

Hi,

The USB is connected to a PC and the DAQ is grounded to a metal shield box. That's it. The input is connected to samples which are floating or a multimeter.

Thanks,

AT12.