6115 analog input

[hibeyzil]

Hi all,

i m trying to create a vi for getting voltage data  from a micro edm machine.I implemented that both with oscilloscop and PCI 6115  and the results were completely different.My question is why couldnt i get the same signal from labview?

I have some other questions.

can it be due to anti aliasing filter?i havent disabled it.Actually i dont know whether as default its true or false

Can it be a grounding problem i use TB2708 and i did not ground any input channel.

I use AC coupling but according to results there is no AC coupling used.It seems like the offset is 90V.

Here is the files which includes my vi and  chart from oscillscop and lab view 

regards,

Nazli

[kikiduu]

Nazli,

The range that you set for the card in +-40V . The voltage that you are applying (as shown in the oscillope readings) varies from +/- 130V. So the readings from your 6115 indicates that the device is saturated. Try giving a voltage within +/- 40V.

Message Edited by kikiduu on 12-24-2008 12:49 PM

[kikiduu]

Also you should not apply more than 60VDC to TB-2708. It can damage the card.

[hibeyzil]

during the measurement  used 1x 10 probes.

Dont u think that its a kind of grounding problem because if we look at labview results they are swing around 90 so there is no AC coupling?

am i wrong?

Nazli

[kikiduu]

Ok.

What type of signal source are you using? Is it floating or ground refernced? Refer to page 6 TB-2708 Installation Guide for connecting these types of signals. You need to set a switch on the TB for each channel based on the signal type.

[hibeyzil]

Actually the system , i get my data is micro edm machine i put the probes where the arc occurs so i have (+),(-) terminals but indeed i m not sure wheter this kind of machines have a reference ground  i assumed that it was a ground referenced signal.

Could you please make it clear which switch i should set i ve already had a look this reference TB-2708 file but  got confused:(

[hibeyzil]

i suppose i should  do this setting  from the part 1 on the figure 1(switch configuration part)  in the TB-2708 file right?

Another point what about the ground pins  on the I/O pins part? am i supposed to ground this pins?

Greetings

NAzli

[kikiduu]

Yes, you have to open the Access Door to Configuration Switches and set the switches.

The I/O pins are for accessing the DIO lines. Leave them as it is. They are not required in your case. If you are not sure ablout your signal source, try both the recommended options listed in Table 2 and see if it works.

[hibeyzil]

Thanks alot.i ll try both ,for grounded and floated signal source BTW :i contacted someone from NI technical support and they meant that it could be a filter problem(anti aliasing).and they sent me the edited version of the vi.I havent done any new implementation  with it but as soon as i do some i ll let you know about the results.If you dont mind i have another question is the filter by default off or on?

in case you would like to see the new Vi, i ve attached it.

Greetings ,

Nazli

[kikiduu]

Nazli,

What you are setting is the low pass filter. Normally cutoff of antialias filter is set automatically based on sampling rate. I am not sure whether the low pass filter is enabled by default. I have a strong feeling that it is not enabled by default. 

Also in the program you have used an enum for the filter cutoff. This is incorrect as when you select 50000 the value passed is 1 and for 500K the value passed is 2. So try to use a DBL instead of enum.